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   42027篇
  免费   1631篇
  2020年   537篇
  2019年   827篇
  2018年   933篇
  2017年   1134篇
  2016年   1226篇
  2015年   935篇
  2014年   912篇
  2013年   14107篇
  2012年   1054篇
  2011年   1089篇
  2010年   1090篇
  2009年   1073篇
  2008年   1014篇
  2007年   923篇
  2006年   823篇
  2005年   582篇
  2004年   575篇
  2003年   540篇
  2002年   515篇
  2001年   533篇
  2000年   471篇
  1999年   543篇
  1998年   468篇
  1997年   420篇
  1996年   409篇
  1995年   421篇
  1994年   366篇
  1993年   418篇
  1992年   395篇
  1991年   297篇
  1990年   293篇
  1989年   315篇
  1988年   311篇
  1987年   335篇
  1986年   312篇
  1985年   428篇
  1984年   458篇
  1983年   465篇
  1982年   400篇
  1981年   394篇
  1980年   431篇
  1979年   425篇
  1978年   411篇
  1977年   432篇
  1976年   380篇
  1975年   384篇
  1974年   295篇
  1973年   269篇
  1972年   250篇
  1970年   226篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
The issue of fairness often is central within environmental policy debates. The recent proliferation of state and local comparative risk projects for informing the selection of environmental policy priorities offers an appropriate setting to explore the issue of procedural fairness in risk-based decisionmaking. This paper describes and evaluates the process by which one of the initial state comparative risk projects, Washington's “Environment 2010,” attempted to include a broader range of participants in identifying, assessing, and generating preferred management strategies for a wide range of environmental hazards. The Washington case study suggests that comparative risk projects can be fairer procedurally, but that significant barriers remain. Noting that greater procedural fairness does not necessarily produce greater substantive fairness, the paper concludes that more attention needs to be directed at the process by which comparative risk projects translate their consensus upon risk priorities into subsequent actions.  相似文献   
862.
Why Protest?     
This study examines both behavioral and attitudinal dimensions of public opposition to the siting of a recycling center using inperson surveys and observed measures of behavior. This is a perfect NIMBY (not-in-my-backyard) case, as the underlying activity is widely supported while the facility to do it is opposed locally. One finding is that attitudes may differ significantly from behavior. Levels of behavioral opposition are not only lower than attitudinal opposition, but they decline more quickly with distance. A second finding is that behavioral opposition is motivated not only by perceived costs from a facility, but also by perceptions of the fairness of the siting process.  相似文献   
863.
864.
865.
An important line of research concerning historical fertility patterns in currently developed countries of Europe has concluded that, prior to the fertility transition, marital fertility was essentially constant over time, and deliberate fertility control was virtually unknown. It has been argued that variations over time in overall fertility were largely the consequence of variations in nuptiality. Other researchers have challenged these views and present evidence for the existence of a significant minority of fertility controllers in pretransition populations. In this article, we find support for this second view and argue that (1) there was significant, non-random variation in marital fertility over time, prior to the transition; (2) in many cases, this variation in marital fertility was large relative to contemporaneous variations in nuptiality; and (3) in a substantial minority of the cases, the variation over time in pretransition marital fertility was so large that it is suggestive of deliberate fertility control. Thus, our findings question the view of fertility transition as an innovation in deliberate marital fertility control. While most of our evidence is based on data from England and Wales, we find corroboration of our key results in other European data.  相似文献   
866.
867.
Several samples of geological stones from statuary pedestals found in various archaeological sites in Cyprus have been characterized using non-contact laser infrared photothermal radiometry. Thermal diffusivities and effective optical absorption coefficients were calculated using a one-dimensional thermal-wave model. The mean values and standard deviations were tabulated and comparisons were made with lithographic and petrographic studies of the samples. Good correlations were found, thus demonstrating that laser photothermal archaeometry is a promising methodology for the accurate, potentially non-destructive and convenient characterization of the origins of ancient stones in Cyprus and other geological and archaeological sites.  相似文献   
868.
The study addresses the chemical variations for Roman Samian wares manufactured during various periods at different workshops within the Lezoux production centre. Instrumental neutron activation analysis and inductively coupled plasma spectrometry were used to determine the chemical constituents of the pottery. The two techniques were evaluated based on the capacity of each to identify the same compositional groups for Lezoux Samian with the use of multivariate statistics. The compositional analysis redefines and clarifies how potters used the clay sources at the site to produce fine wares. The results indicate that the majority of potters from different workshops at Lezoux shared the same clay source during the second century AD.  相似文献   
869.
Blue glass trade beads from well-dated late seventeenth- to early twentieth-century sites and collections have been analysed non-destructively by instrumental neutron activation analysis. The beads display enough variations in their elemental contents to allow us to characterize the different chemistries. The implication of these results is that similar chemical analyses of blue beads from undated archaeological sites may be used to help date the sites, since each bead chemistry has a specific earliest period.  相似文献   
870.
Fifty-three copper-based metal fragments, recovered from the Robitaille site in southcentral Ontario, were analysed by neutron activation to establish their chemical make-up and to sort them by their trace elemental chemistries. Three different European copper samples, one brassy copper and 48 brass samples with five different chemistries were found. As few as eight trading actions may account for all of the recovered European metal fragments.  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