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   1177篇
  免费   53篇
管理学   165篇
民族学   5篇
人口学   89篇
丛书文集   6篇
理论方法论   165篇
综合类   7篇
社会学   697篇
统计学   96篇
  2023年   6篇
  2022年   9篇
  2021年   8篇
  2020年   25篇
  2019年   27篇
  2018年   44篇
  2017年   53篇
  2016年   44篇
  2015年   31篇
  2014年   40篇
  2013年   206篇
  2012年   38篇
  2011年   42篇
  2010年   47篇
  2009年   35篇
  2008年   43篇
  2007年   55篇
  2006年   40篇
  2005年   41篇
  2004年   34篇
  2003年   34篇
  2002年   40篇
  2001年   21篇
  2000年   22篇
  1999年   21篇
  1998年   16篇
  1997年   10篇
  1996年   13篇
  1995年   11篇
  1994年   14篇
  1993年   8篇
  1992年   9篇
  1991年   8篇
  1990年   10篇
  1989年   5篇
  1988年   8篇
  1987年   11篇
  1986年   9篇
  1985年   14篇
  1984年   7篇
  1983年   13篇
  1982年   9篇
  1981年   10篇
  1980年   8篇
  1979年   7篇
  1978年   5篇
  1977年   3篇
  1976年   2篇
  1975年   5篇
  1974年   6篇
排序方式: 共有1230条查询结果,搜索用时 70 毫秒
551.
552.
553.
An urban population of Endangered San Joaquin kit foxes (Vulpes macrotis mutica) has persisted in the city of Bakersfield, (Kern County, California), for several decades. Urban kit foxes may play an important role in future range wide recovery efforts for the species. As such, a comprehensive understanding of the issues that can influence the long-term survival of this population is essential for the development of effective management strategies. Although urban kit foxes have been studied extensively in Bakersfield, interactions between kit foxes and other urban carnivore species are poorly understood. Urban environments can provide a number of opportunities for species to interact in ways not usually observed in natural habitats. Interactions between urban populations of striped skunks (Mephitis mephitis) and kit foxes were investigated at denning locations and cat feeding stations on the California State University-Bakersfield campus, California, USA. A total of 130 individual denning sites were identified, of which 39 (30%) were used by both species. Simultaneous den use by foxes and skunks was recorded on four occasions. Inter and intra-specific aggression was recorded at cat feeding stations on ten separate occasions including three incidences of aggression towards kit foxes by skunks and feral cats (Felis catus). Telemetry data and cat feeding station observations clearly show that interspecific contact does occur in urban environments.  相似文献   
554.
This study investigated the impacts of urban wetlands and their adjacent residential environments on the transmission dynamics of West Nile virus (WNV) within the state of New Jersey (USA). A working hypothesis was that urban wetlands decrease the local prevalence of WNV through the dilution effect from increased bird diversity, and through relative reductions in the numbers of competent avian host and mosquito species commonly associated with WNV. Surveys of mosquito and bird communities were undertaken at six urban wetlands and their adjacent residential environments over two seasons (2009, 2010). The community compositions of both avian and mosquito species differed significantly across habitats, and over relatively short geographical distances. Residential areas contained significantly higher proportions of WNV-competent mosquito species (31.25?±?5.3?%; e.g. Culex pipiens and Culex restuans), and WNV-competent avian host species (62.8?±?2.3?%, e.g. House Sparrow and American Robin) when compared to adjacent urban wetlands (13.5?±?2.1?%; 35.4?±?2.1?% respectively). Correspondingly, WNV infection rates within local Culex spp. populations indicate that WNV was more prevalent within residential areas (28.53/1000) compared to wetlands (16.77/1000). Large urban wetlands (>100?ha) produced significantly lower weekly WNV infection rates in local Culex spp. (6.67?±?2.84/1000) compared to small (<15?ha) wetlands (22.57?±?6.23/1000). Avian species richness was also influenced by patch size. Large urban wetlands contained significantly more species than small wetland patches. These results confirm that the community compositions of mosquito and avian hosts are important drivers in WNV infections, and that the ecological conditions that favor transmission are more strongly associated with urban residential environments than with adjacent urban wetlands.  相似文献   
555.
Hurricane track and intensity can change rapidly in unexpected ways, thus making predictions of hurricanes and related hazards uncertain. This inherent uncertainty often translates into suboptimal decision-making outcomes, such as unnecessary evacuation. Representing this uncertainty is thus critical in evacuation planning and related activities. We describe a physics-based hazard modeling approach that (1) dynamically accounts for the physical interactions among hazard components and (2) captures hurricane evolution uncertainty using an ensemble method. This loosely coupled model system provides a framework for probabilistic water inundation and wind speed levels for a new, risk-based approach to evacuation modeling, described in a companion article in this issue. It combines the Weather Research and Forecasting (WRF) meteorological model, the Coupled Routing and Excess STorage (CREST) hydrologic model, and the ADvanced CIRCulation (ADCIRC) storm surge, tide, and wind-wave model to compute inundation levels and wind speeds for an ensemble of hurricane predictions. Perturbations to WRF's initial and boundary conditions and different model physics/parameterizations generate an ensemble of storm solutions, which are then used to drive the coupled hydrologic + hydrodynamic models. Hurricane Isabel (2003) is used as a case study to illustrate the ensemble-based approach. The inundation, river runoff, and wind hazard results are strongly dependent on the accuracy of the mesoscale meteorological simulations, which improves with decreasing lead time to hurricane landfall. The ensemble envelope brackets the observed behavior while providing “best-case” and “worst-case” scenarios for the subsequent risk-based evacuation model.  相似文献   
556.
557.
Brian Gran 《Sociology Compass》2008,2(5):1462-1490
Across the world, political leaders and policy experts frequently use the labels ‘public’ and ‘private’ to organize social policies. A line seemingly separates public from private efforts, with social policies publicly organized in some countries and privately organized in others. According to this perspective, a public social policy is undertaken by government or deals with a public matter. When a social policy is private, non‐public actors and institutions, like employers, undertake it or it deals with a private matter, like body control. This article examines whether public or private approaches to managing social policies are currently emphasized in European countries. I begin by defining social policy and then provide an overview of the public–private dichotomy in managing social policy. I review predominant typological frameworks of public–private organization of social policies and examine three welfare social policies and three social policies dealing with body control by comparing public–private organization of these six policy areas across 21 European countries. I conclude by discussing the limited diversity of public–private organizations of social policies in Europe.  相似文献   
558.
Abstract

Objective: The Training Interventions and Genetics of Exercise Response (TIGER) study is an exercise program designed to introduce sedentary college students to regular physical activity and to identify genetic factors that influence response to exercise. Participants: A multiracial/ethnic cohort (N = 1,567; 39% male), age 18 to 35 years, participated in the study. Methods: Subjects underwent 30 weeks of exercise training, 3 days/week, for 40 minutes at 65% to 85% of age- and gender-predicted maximum heart rate reserve. Multiple measures of body size/composition, heart rate, and blood pressure were obtained. Results: A total of 1,567 participants, (39% male), age 18 to 35 years, participated in the TIGER study. The prevalence of overweight/obesity in participants was 48.0%/19.3% in non-Hispanic Whites, 55.3%/24.2% in Hispanic Whites, 54.9%/25.4% in African Americans, and 38.3%/11.3% in Asians. Average within-semester retention was 68%, but overall retention (30 weeks, 2 semesters) was 20%. Conclusions: The TIGER study represents an efficacious strategy for introducing college-aged individuals to regular aerobic exercise.  相似文献   
559.
Does immigration hamper union organizing in the United States? The prevailing literature strongly suggests that it does and for two reasons: first, immigrants increase the labor pool and diminish union influence over the labor market. And second, immigrants may be harder to organize than native workers. In this dominant view, unions are well served to restrict immigration and have always done so. But how, then, to explain the fact that American labor has long been deeply divided over the response to immigration? Drawing on new archival research and interviews, this paper uncovers a neglected side of American labor history in which many union leaders have extended solidarity to immigrants and sought to organize them. Moreover, analysis of time series data on immigration and union density corroborates the implicit theory of this alternate account of labor history: immigration has, in fact, no statistically significant effect – either positive or negative – on union density over time. Depending on specific conditions and strategies, unions can and have been successful in organizing during periods of high immigration.  相似文献   
560.
The design of large‐scale field trials where the residuals are correlated has been of recent interest, in large part because of advances in statistical and computational methods of analysis. The construction of designs for correlated data has typically used A‐optimality and is computationally intensive. This involves calculating the inverse of the information matrix for treatments under the supervision of an optimization strategy that explores the design space. We propose an approximation to A‐optimality, using nearest‐neighbour balance, that is less computationally demanding and can achieve at least 95% efficiency relative to A‐optimality in many practical situations.  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