首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5734篇
  免费   39篇
管理学   588篇
民族学   72篇
人口学   1119篇
丛书文集   9篇
理论方法论   345篇
综合类   133篇
社会学   2569篇
统计学   938篇
  2021年   16篇
  2020年   23篇
  2019年   48篇
  2018年   595篇
  2017年   592篇
  2016年   446篇
  2015年   47篇
  2014年   53篇
  2013年   363篇
  2012年   173篇
  2011年   526篇
  2010年   423篇
  2009年   353篇
  2008年   346篇
  2007年   432篇
  2006年   46篇
  2005年   105篇
  2004年   122篇
  2003年   122篇
  2002年   55篇
  2001年   49篇
  2000年   57篇
  1999年   61篇
  1998年   43篇
  1997年   33篇
  1996年   35篇
  1995年   35篇
  1994年   33篇
  1993年   31篇
  1992年   29篇
  1991年   28篇
  1990年   28篇
  1989年   20篇
  1988年   31篇
  1987年   33篇
  1986年   25篇
  1985年   29篇
  1984年   34篇
  1983年   22篇
  1982年   24篇
  1981年   20篇
  1980年   18篇
  1979年   16篇
  1978年   17篇
  1977年   15篇
  1976年   15篇
  1975年   12篇
  1974年   12篇
  1973年   13篇
  1972年   11篇
排序方式: 共有5773条查询结果,搜索用时 562 毫秒
191.
Despite high rates of comorbidity between problem gambling and mental health disorders, few studies have examined barriers or facilitators to the implementation of screening for problem gambling in mental health services. This exploratory qualitative study identified key themes associated with screening in mental health services. Semi-structured interviews were undertaken with 30 clinicians and managers from 11 mental health services in Victoria, Australia. Major themes and subthemes were identified using qualitative content analysis. Six themes emerged including competing priorities, importance of routine screening, access to appropriate screening tools, resources, patient responsiveness and workforce development. Barriers to screening included a focus on immediate risk as well as gambling being often considered as a longer-term concern. Clinicians perceived problem gambling as a relatively rare condition, but did acknowledge the need for brief screening. Facilitators to screening were changes to system processes, such as identification of an appropriate brief screening instrument, mandating its use as part of routine screening, as well as funded workforce development activities in the identification and management of problem gambling.  相似文献   
192.
The UK Lotto game was introduced in November 1994 with a standard 6/49 format and an entry fee of £1 per ticket. After several years, revenue began to fall despite extensive publicity and a variety of inducements. By 2013, nominal weekly revenue was less than half the 1995 level. In October 2013, the operator doubled the price of a ticket to £2 and made a number of changes to the pay-out structure of smaller prizes. The intent of the changes was to reverse the long downward trend in game revenue by encouraging higher jackpots and offering more pay-out opportunities for each ticket. We use draw by draw revenue and other data to evaluate how players responded to these changes and find that, while ticket sales fell dramatically, total revenue rose following the changes. Primarily this appears to have been the consequence of increased frequency of rollovers (and therefore of more frequent high jackpot draws) rather than ticket price inelasticity. However, although there was a short-term gain in revenue, the changes did not arrest, and indeed seem to have accentuated, the long-run trend decrease in the revenue generated by the game.  相似文献   
193.
Growing human populations make it imperative for ecologists to identify strategies to conserve biodiversity in human-dominated landscapes, such as cities. Effects of urbanization on birds are particularly well-studied, but questions remain regarding the best conservation approaches. Debate about the relative utility of focusing conservation efforts on nature reserves versus developed lands has focused largely on comparing species abundance or presence, with few studies addressing underlying behavioral or demographic mechanisms. Here we evaluated differences in avian reproductive success in nature reserves and matrix habitats to test the assumption that nest predation is lower within areas protected from development. Specifically, we investigated 1) whether nest survival differed in replicated pairs of forest parks and residential neighborhoods and 2) whether differences in nest survival were associated with changes in which species most frequently depredated nests. From April–August 2007–2014, we monitored nests of two native birds, American robin (Turdus migratorius) and northern cardinal (Cardinalis cardinalis), and video-documented nest predators in paired forest-matrix habitats in the Columbus, Ohio metropolitan area. We found similar rates of nest survival in the two habitats for both robins (Χ21?=?0.715, p?=?0.398, n?=?741 nests) and cardinals (Χ21?=?0.926, p?=?0.336, n?=?1156 nests), but interactions between predators and prey differed. In particular, domestic cats (Felis catus) were over five times as likely to depredate cardinal nests in matrix habitats versus forest parks (Χ21?=?7.24, simulated p?=?0.010; nforest?=?3, nmatrix?=?7). Our results suggest that at least in some circumstances, nest success of native birds may be equivalent between nature reserves and adjacent residential matrix habitats, and thus residential neighborhoods may contribute positively to bird conservation in urban landscapes.  相似文献   
194.
Recent concern over increasing loss of biodiversity has prompted considerable interest in the role of urban green spaces as reservoirs of local biodiversity. This study assessed the diversity of three indicator taxa - plants, ants and birds - on golf courses spanning a wide range of environmental variation in terms of climate, elevation, course age, size and connectivity to native woodland. Species richness and community composition was further compared between contrasting on-course habitat types that reflect different management intensities. We identified a set of taxon-specific environmental correlates indicating an intricate interplay of landscape- and local-scale variables that affect local species diversity. Our results show that floristic diversity is positively associated with the amount of rainfall, whereas ant and bird diversity are related to local-scale factors, particularly the number of trees and the size of water features on a site. The amount of on-course native habitat was a strong predictor of plant and ant diversity and was also associated with the number of unique species at the site level; this reinforces the value of remnant habitat patches as local biodiversity reservoirs that represent mini hot-spots in an otherwise species-poor urban landscape. Community composition for all three taxa differed markedly between non-playing and playing areas, with boundary and remnant habitats generally having more diverse, species-rich communities. Our results suggest that local floral and faunal biodiversity on urban golf courses can be enhanced by creating woody non-playing areas and, especially, by preserving, restoring or expanding remnant habitats.  相似文献   
195.
Time of peak bat activity during the night differs among bat species due to temperature, prey availability, habitat availability, and/or interactions between species. Habitat availability is altered in urban areas, which may affect insect prey availability and interspecies interactions. Our objectives were to use mobile acoustic monitoring to determine when bat species were active in a single night in urban and nonurban sites and if nightly bat activity patterns differed in urban versus nonurban sites. Bat echolocation call sequences were recorded using Anabat acoustic detectors while driving transects through the night at five sites (three “urban” and two “nonurban”) located in the Piedmont region of north-central North Carolina from May through August 2016. Transects were driven three times per night starting 45 min, 180 min, and 300 min after sunset. Recorded echolocation call sequences were analyzed manually using AnalookW and automatically using Bat Call Identification and Echoclass software. Total bat activity was not different between urban and nonurban sites. However, total bat activity was lower later in the night in urban sites, but stayed the same in nonurban sites. Species specifically, there were more Eptesicus fuscus, Lasionycteris noctivagans, and Tadarida brasiliensis call sequences and fewer Lasiurus borealis, Nycticeius humeralis, and Perimyotis subflavus call sequences in urban sites than nonurban sites. There were also fewer E. fuscus, L. noctivagans, and N. humeralis call sequences later in the night in both urban and nonurban sites. Only Lasiurus borealis activity in urban sites later in the night reduced and L. borealis activity in nonurban sites remained at the same. These results suggest that bats in urban areas partition time differently, which is important to consider for urban conservation efforts and planning.  相似文献   
196.
Urbanization is a process that heavily alters marine and terrestrial environments, though terrestrial urban ecosystems have been studied far more intensively. Terrestrial studies suggest that urbanization can facilitate mesopredators by enhancing food and shelter resources and reducing predation pressure from apex consumers. This in turn has considerable consequences for ecological communities. We evaluated spatial distribution patterns and habitat-use of the marine mesopredator, giant Pacific octopus (Enteroctopus dofleini), relative to terrestrial urbanization intensity in Puget Sound, Washington, USA. Using field surveys and citizen-contributed data for E. dofleini, we examined whether: (1) Distribution was related to urbanization, (2) Abundance was related to the extent of benthic anthropogenic debris, and (3) Diet differed as a function of urbanization and den cover. Our results suggest that urbanization impacts may differ with depth. Mixed-effects logistic regression model estimates for the probability of occurrence increased with urbanization in deep-water (> 24 m), and decreased with urbanization in shallow water (< 18 m). Accompanying field surveys indicated that E. dofleini abundance was correlated with the number of benthic anthropogenic debris items, and that E. dofleini diets were not affected by urbanization intensity or den cover. Though E. dofleini may be synanthropic within certain urban environments, the mechanisms driving this pattern likely differ from those affecting common urban mesopredators on land, with den provisioning from man-made structures being more important than altered food resources.  相似文献   
197.
Urbanization causes species loss around the world, but its effects on phylogenetic diversity are poorly known in tropical forests. Using a patch-landscape approach in an urbanizing region of the Brazilian Atlantic Forest, we tested whether the increase in landscape urbanization reduces plant species density, phylogenetic richness and divergence, and increases the relatedness among co-occurring individuals and species. We assessed plant responses to urbanization in adult (diameter at breast height?>?10 cm) and sapling communities (2.5–10 cm diameter) separately, as saplings are proxies of the future flora. We sampled 2860 woody plants belonging to 155 species in nine circular landscapes with urbanization level varying from 0% to 45%, and estimated the relatedness among the species that have increased and decreased in relative abundance in more urbanized landscapes (winner and losers, respectively). As expected, species density and phylogenetic richness decreased with the increase in urbanization. These responses were consistent for adult and sapling communities, suggesting a persistent loss of species and lineages in more urbanized landscapes. Contrary to our expectations, phylogenetic divergence and structure did not respond to urbanization, indicating that the more urbanized landscapes still retain much evolutionary history. However, because the relatedness among winners was greater than among losers, it is likely that the phylogenetic divergence gradually reduces and the relatedness increases, resulting in impoverished forests with uncertain ability to provide ecosystem services such as carbon storage and pest control. This environmental cost should be taken into account to align urban sprawl with biodiversity conservation.  相似文献   
198.
Urban environments are often associated with reduced biodiversity, presumably because they are typically more fragmented, warmer, and drier than nearby non-urban environments. However, urban landscapes offer significant complexity that have allowed some taxonomic groups to flourish. Understanding how urban-exploiting animals navigate this spatiotemporal heterogeneity is important given the continued global urban land expansion. Here, we examined the factors influencing resource-use in an urban community of ants, which represent a widespread and important taxon in urban ecosystems. In particular, we sought to integrate ants’ nutritional, thermal, and spatial niches to better understand how urban animals successfully access critical resources throughout their active season. Meteorological season (spring, summer, and fall) and/or species (n?=?9) influenced ants’ preferences for nutrition (ratio of ingested protein-to-carbohydrate ratio), as well as the temperature, type (impervious vs. non-impervious), and shade status (shaded vs. non-shaded) of surfaces used during activity. Our data also indicate links among habitat variables, as well as between nutritional preferences and habitat use. Together, our results suggest that species and seasonality influence ecological (combined nutritional, thermal, and spatial) niches in an urban community. We encourage future work in urban ecosystems that continues to integrate more features of the ecological niche, and to examine the outcomes of variation in niches (e.g., non-overlapping niches may explain both the persistence of some native animals and the success of invaders).  相似文献   
199.
This study explored the experiences of mothers in college using a qualitative design. Results showed that a lack of financial resources was the chief barrier for student mothers in their educational pursuits while social/emotional support was the most important contributor to student mothers’ success in college. Participants relied heavily on student loans to cover costs of childcare or family to help watch their children. Role conflict experienced by student mothers has implications on family and college retention. Implications of this study included the adaptation and revisions of policies at the state and federal levels in addition to implications at the university level. Limitations of the study included a lack of racial and ethnic diversity and only including student mothers currently enrolled in college. Several recommendations for future research are described.  相似文献   
200.
A broad empirical literature asks if social policies designed to provide benefits to low-income families also affect family formation patterns. While most of the evidence suggests that family formation effects are small at best, and often nonexistent, recent research argues that policies that alter budget constraints considerably should have greater family formation impacts. We tested this hypothesis by investigating the Social Security Student Benefit Program (SSSBP), a program designed to provide large higher education subsidies for the children of disabled, retired, or deceased parents. Conditions for receipt of SSSBP created strong incentives to delay marriage. Utilizing data from the National Longitudinal Survey of Youth, 1979, and a difference-in-differences model, we found that women potentially qualifying for the SSSBP were much less likely to marry before age 22 and were older when they had children, while the program did not influence the probability of women ever marrying or having children. Impacts on men, however, were negligible.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号