全文获取类型
收费全文 | 23027篇 |
免费 | 213篇 |
专业分类
管理学 | 3158篇 |
民族学 | 147篇 |
人才学 | 1篇 |
人口学 | 3444篇 |
丛书文集 | 78篇 |
教育普及 | 2篇 |
理论方法论 | 1639篇 |
综合类 | 624篇 |
社会学 | 10683篇 |
统计学 | 3464篇 |
出版年
2021年 | 67篇 |
2020年 | 189篇 |
2019年 | 223篇 |
2018年 | 1882篇 |
2017年 | 1989篇 |
2016年 | 1334篇 |
2015年 | 264篇 |
2014年 | 286篇 |
2013年 | 2081篇 |
2012年 | 717篇 |
2011年 | 1444篇 |
2010年 | 1252篇 |
2009年 | 1009篇 |
2008年 | 1074篇 |
2007年 | 1257篇 |
2006年 | 216篇 |
2005年 | 571篇 |
2004年 | 540篇 |
2003年 | 473篇 |
2002年 | 351篇 |
2001年 | 319篇 |
2000年 | 308篇 |
1999年 | 314篇 |
1998年 | 209篇 |
1997年 | 205篇 |
1996年 | 242篇 |
1995年 | 188篇 |
1994年 | 204篇 |
1993年 | 177篇 |
1992年 | 236篇 |
1991年 | 232篇 |
1990年 | 211篇 |
1989年 | 219篇 |
1988年 | 205篇 |
1987年 | 185篇 |
1986年 | 190篇 |
1985年 | 174篇 |
1984年 | 207篇 |
1983年 | 200篇 |
1982年 | 165篇 |
1981年 | 137篇 |
1980年 | 139篇 |
1979年 | 166篇 |
1978年 | 136篇 |
1977年 | 119篇 |
1976年 | 102篇 |
1975年 | 101篇 |
1974年 | 95篇 |
1973年 | 93篇 |
1971年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Pieper R 《Work (Reading, Mass.)》2012,41(Z1):3321-3324
Work equipment and installations with a high risk for health and safety of employees should be paid a special attention. The German Product Safety Act, which is aimed to manufacturers or distributors in order to protect consumers, maintains a conclusive catalogue of these so-called "installations in need of monitoring" fixing the work equipment and installations for which such special inspections can be demanded. This catalogue has remained unchanged for decades and has been transformed nearly unmodified into the Plant Safety Ordinance. Currently, there is a discussion about this catalogue in Germany. A major point of concern is the definition and the significance of "especially" dangerous work equipment and installations. Two recent research projects are dealing with the problem how to define "especially". 相似文献
992.
The purpose of this study was to develop a regression equation that, incorporating the potential energy of the load in the hands, was capable of improved predictions of spinal compression forces. A stepwise polynomial equation was developed from EMG profiles of 15 muscles, and its spinal joint loading predictions at L4/L5 were compared to current methods of calculating spinal compression. Absolute muscle activation was shown to increase with increased loading height, indicating that the central nervous system responds to changes in spinal stability. The inclusion of potential energy into the calculation of spinal disc compression at L4/L5 improved estimates of the compressive forces acting on the spine. This is the first model to incorporate potential energy into a predictive model for lumbar spine compression without the use of electromyography. It was concluded that potential energy plays a vital role in dictating the recruitment patterns of the trunk. 相似文献
993.
Almeida e Silva CM Okimoto ML Albertazzi D Calixto C Costa H 《Work (Reading, Mass.)》2012,41(Z1):1094-1099
This paper explores the importance of researching the intuitiveness in the product use. It approaches the intuitiveness influence for users that already had a visual experience of the product. Finally, it is suggested the use of a table that relates the tasks performed while using a product, the features for an intuitive use and the performance metric "task success". 相似文献
994.
This paper presents the Ergonomic Work Analysis method in a Brazilian Dentist's office. Through the study, the constraints and the strategies in avoiding them were identified. It was found that dentists hardly use the position most indicated by the International Organization for Standardization (ISO) and the Federation Dentaire Internacionale (FDI) for both the patient and the dentist, which is respectively supine and 9 o'clock, due to the limited space and layout. Five types of treatments performed by the professional have been studied. The frequency and duration of actions in these treatments were accounted for and the standard positions adopted were identified. The AET was found to be a very suitable method to grasp the dentist's activity and build a point of view of the profession, which is characterized as: stressful, perfectionist and restrictive. Time management is presented as an important strategy to control the tension arising from performing the treatments. 相似文献
995.
996.
Neeta S. Bijoor Heather R. McCarthy Dachun Zhang Diane E. Pataki 《Urban Ecosystems》2012,15(1):195-214
In semi-arid cities, urban trees are often irrigated, but may also utilize natural water sources such as groundwater. Consequently,
the sources of water for urban tree transpiration may be uncertain, complicating efforts to efficiently manage water resources.
We used a novel approach based on stable isotopes to determine tree water sources in the Los Angeles basin, where we hypothesized
that trees would rely on irrigation water in the soil rather than develop deep roots to tap into groundwater. We evaluated
the oxygen (δ18O) and hydrogen (δD) isotope ratios of xylem water, irrigation water, soil water, and groundwater in a study of temporal patterns
in water sources at two urban sites, and a study of spatial patterns at nine urban sites and one “natural” riparian forest.
Contrary to our hypothesis, we found that despite frequent irrigation, some trees tap into groundwater, although in most species
this was a small water source. Some trees appeared to be using very shallow soil water at <30 cm depth, suggesting that these
mature urban trees were quite shallowly rooted. In the natural site, trees appeared to be using urban runoff in addition to
shallow soil water. We were able to identify tree uptake of precipitation at only 3 sites. The results show that some irrigated
trees utilize groundwater and do not rely solely on irrigation water, which may make them able to withstand drought and/or
water conservation measures. However, some irrigated trees may develop very shallow root systems, which may make them more
susceptible. 相似文献
997.
Urbanization is a pervasive and growing threat to amphibian populations globally. Although the number of studies is increasing,
many aspects of basic amphibian biology have not been investigated in urban settings. We reviewed 32 urban studies from North
America and quantified the number of species studied and their response to urbanization. We examined existing research on
breeding habitats, life-history stages, movement patterns, and habitat use relative to urbanization. We found amphibians as
a whole respond negatively to urbanization (69 reported responses were negative, 6 were positive and 35 showed no effect).
We caution, however, that many North American species still lack or are associated with conflicting information regarding
species-specific responses (e.g., 89 potential responses were unknown). Approximately 40% of all anuran and 14% of caudate
species in North America were investigated in the literature; however, the most diverse genera (e.g., Plethodon and Eurycea) were the most understudied likely due to their cryptic terrestrial lifestyles and biases in sampling protocols that assess
wetland habitats via call surveys. Research on movement and small scale habitat use was deficient. Adult, juvenile, tadpole,
and egg mass life-history stages commonly served as direct measures of species presence and abundance; however, such data
do not accurately reflect recruitment into subsequent age classes and population persistence. The lack of data on many North
American species may be contributing to poor management of urban amphibian populations and their habitats. 相似文献
998.
999.
1000.
The relationship between social insurance, which provides families protection against certain risks, and child economic security is understudied. Using the 2004 Survey of Income and Program Participation (SIPP) matched to Social Security Administration benefit records, this article investigates the economic welfare effects of the child component of the US Social Security program. We examine how the poverty rate of child beneficiaries would change, absent Social Security income, and how heavily the family incomes of these children rely on it, by family characteristics. Our findings reveal that Social Security plays an important role in mitigating economic insecurity among children deprived of a wage-earning parent through disability, death, or retirement. Family structure, earnings, and employment status are identified as key factors moderating the effect of Social Security on child recipients’ financial circumstance. 相似文献