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   89763篇
  免费   3416篇
  国内免费   3篇
管理学   11542篇
民族学   540篇
人才学   24篇
人口学   6906篇
丛书文集   517篇
教育普及   3篇
理论方法论   9779篇
综合类   2107篇
社会学   42908篇
统计学   18856篇
  2023年   509篇
  2021年   587篇
  2020年   1585篇
  2019年   2405篇
  2018年   2145篇
  2017年   3265篇
  2016年   2514篇
  2015年   2209篇
  2014年   2781篇
  2013年   19047篇
  2012年   2421篇
  2011年   2234篇
  2010年   2038篇
  2009年   2256篇
  2008年   2100篇
  2007年   1854篇
  2006年   2129篇
  2005年   2301篇
  2004年   2176篇
  2003年   1903篇
  2002年   1977篇
  2001年   2020篇
  2000年   1803篇
  1999年   1698篇
  1998年   1486篇
  1997年   1339篇
  1996年   1318篇
  1995年   1266篇
  1994年   1245篇
  1993年   1209篇
  1992年   1170篇
  1991年   1119篇
  1990年   1122篇
  1989年   968篇
  1988年   1054篇
  1987年   955篇
  1986年   844篇
  1985年   1027篇
  1984年   1088篇
  1983年   954篇
  1982年   876篇
  1981年   804篇
  1980年   782篇
  1979年   835篇
  1978年   712篇
  1977年   642篇
  1976年   586篇
  1975年   572篇
  1974年   458篇
  1973年   388篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
992.
993.
994.
Tree health is a critical parameter for evaluating urban ecosystem health and sustainability. Traditionally, this parameter has been derived from field surveys. We used multispectral remote sensing data and GIS techniques to determine tree health at the University of California, Davis. The study area (363 ha) contained 8,962 trees of 215 species. Tree health conditions were mapped for each physiognomic type at two scales: pixel and whole tree. At the pixel scale, each tree pixel within the tree crown was classified as either healthy or unhealthy based on vegetation index values. At the whole tree scale, raster based statistical analysis was used to calculate tree health index which is the ratio of healthy pixels to entire tree pixels within the tree crown. The tree was classified as healthy if the index was greater than 70%. Accuracy was checked against a random sample of 1,186 trees. At the whole tree level, 86% of campus trees were classified as healthy with 88% mapping accuracy. At the pixel level, 86% of the campus tree cover was classified as healthy. This tree health evaluation approach allows managers to identify the location of unhealthy trees for further diagnosis and treatment. It can be used to track the spread of disease and monitor seasonal or annual changes in tree health. Also, it provides tree health information that is fundamental to modeling and analysis of the environmental, social, and economic services produced by urban forests.  相似文献   
995.
996.
Summary.  To help to design vaccines for acquired immune deficiency syndrome that protect broadly against many genetic variants of the human immunodeficiency virus, the mutation rates at 118 positions in HIV amino-acid sequences of subtype C versus those of subtype B were compared. The false discovery rate (FDR) multiple-comparisons procedure can be used to determine statistical significance. When the test statistics have discrete distributions, the FDR procedure can be made more powerful by a simple modification. The paper develops a modified FDR procedure for discrete data and applies it to the human immunodeficiency virus data. The new procedure detects 15 positions with significantly different mutation rates compared with 11 that are detected by the original FDR method. Simulations delineate conditions under which the modified FDR procedure confers large gains in power over the original technique. In general FDR adjustment methods can be improved for discrete data by incorporating the modification proposed.  相似文献   
997.
Each individual wage rate set by Davis-Bacon or by any similar state or local prevailing wage determination petrifies the outcome of competing views of how construction work should be staffed and paid on public works projects. Although presented with great precision (to tenths of a cent for both wages and fringe benefits), the level of wages themselves are of surprisingly little consequence: Those set at union levels soon rise, being automatically updated to new contracts and conditions; the rest fast become obsolete in any rising market, because surveys to update them are rare. But in addition to setting wage levels, determinations also delineate which jobs get to have rates set for them, and perhaps most critically, whether those delineated are identified as union or notunion. Whatever pattern is found may remain in effect for years or even decades, influencing which journeymen and laborers own what job tasks and who may perform what. Also, if a particular job happens to be set as union, it may bring with it dozens or even hundreds of related special job categories, grades of sub-groups, fine distinctions of fringe benefits, and complex divisions of geographic applicability based on local union jurisdictional areas. This study uses determinations recently made in Pennsylvania as an example to examine the mechanics of the wage-setting process. I find that, in addition to the endemic problems one might expect associated with a complex and partly judgmental process, every step of finding and setting prevailing rates includes overwhelming deference on the part of government towards union views and methods. It shows why unions representing less than 20 percent of the private construction work force consistently set the parameters controlling most of public construction. It ends with some suggestions on how better surveys and determinations could be made.  相似文献   
998.
This paper develops a likelihood‐based method for fitting additive models in the presence of measurement error. It formulates the additive model using the linear mixed model representation of penalized splines. In the presence of a structural measurement error model, the resulting likelihood involves intractable integrals, and a Monte Carlo expectation maximization strategy is developed for obtaining estimates. The method's performance is illustrated with a simulation study.  相似文献   
999.
Despite sociopolitical controversy surrounding the solid waste crisis, little sociological attention has focused on this crucial environmental issue. Drawing on research from the technological controversies, environmental concern, and solid waste literatures, this study examines the pre-implementation anxieties of a Louisiana community faced with a proposal to build an incinerator in its backyard. Utilizing survey data, a causal path model is developed in which the perceived advantages of the technology, general environmental concern, and support for recycling initiatives are identified as explanatory variables of incinerator opposition. Implications of these findings for the study of technical controversies and the larger solid waste crisis also are suggested.  相似文献   
1000.
Childhood parental loss and adult depression   总被引:2,自引:0,他引:2  
Previous research demonstrates convincingly that childhood parental deaths and parental divorces have implications for adult well-being as defined by levels of depression, educational attainment, early age at marriage, and risk of divorce. What this research has failed to examine are the interconnections among these outcomes. Specifically, are the socioeconomic and marital outcomes of parental loss implicated in the observed higher levels of depression? This analysis takes a first step in answering this question. Using data from a sample of 1,755 married men and women, I estimated regression models which examine the extent to which adult socioeconomic status and current marital quality mediate and/or modify the loss-depression relationship. Parental divorce was strongly related to socioeconomic and marital outcomes. Furthermore, current marital quality contributed importantly to understanding the higher levels of depressed mood observed among persons from divorced homes. Parental death was much more weakly related to socioeconomic and marital outcomes, and these outcomes played little role in explaining its relationship to depression. Finally, all of these relationships were stronger among women than men. These findings support the utility of life-course approaches to understanding adult mental health.  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