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   2808篇
  免费   155篇
  2023年   33篇
  2022年   13篇
  2021年   14篇
  2020年   65篇
  2019年   89篇
  2018年   169篇
  2017年   165篇
  2016年   149篇
  2015年   115篇
  2014年   103篇
  2013年   686篇
  2012年   95篇
  2011年   100篇
  2010年   92篇
  2009年   81篇
  2008年   79篇
  2007年   64篇
  2006年   58篇
  2005年   44篇
  2004年   43篇
  2003年   40篇
  2002年   52篇
  2001年   43篇
  2000年   41篇
  1999年   29篇
  1998年   35篇
  1997年   31篇
  1996年   27篇
  1995年   24篇
  1994年   20篇
  1993年   17篇
  1992年   18篇
  1991年   11篇
  1990年   11篇
  1989年   19篇
  1988年   10篇
  1987年   12篇
  1986年   13篇
  1985年   17篇
  1984年   23篇
  1983年   22篇
  1982年   22篇
  1981年   14篇
  1980年   19篇
  1979年   18篇
  1978年   18篇
  1977年   12篇
  1976年   14篇
  1975年   13篇
  1971年   9篇
排序方式: 共有2963条查询结果,搜索用时 15 毫秒
171.
172.
173.
Welfare policy is multidimensional because of the political compromises, competing goals, and federalist structure underpinning it. This complexity has hindered measurement and, therefore, the comparability of research on race and welfare policy. This paper describes a measurement strategy that is transparent, replicable, and attuned to matching the assumptions of statistical models to the policy process. We demonstrate that this strategy leads to more nuanced conclusions regarding the relationship between minority caseloads and the flexibility of state welfare policies. The strategy and recommendations are adaptable to research agendas that scholars bring to the comparative study of welfare in the U.S. states, countries, or other units—and to other complex policies enacted in federal systems.  相似文献   
174.
175.
176.
177.
178.
179.
We have investigated the survival of PCR-amplifiable mitochondrial and nuclear DNA in a small number of modern and medieval bovine leather samples. The results of this preliminary investigation demonstrate that, while no nuclear DNA can be PCR-amplified from any of the specimens, mitochondrial DNA can be amplified from all samples. To investigate this contrasting pattern of DNA survival further, we have vegetable-tanned cow skin in our own laboratory, and directly assayed the survival of PCR-amplifiable mitochondrial and nuclear DNA at each step of the process. The results indicate that nuclear DNA is reduced to sub-amplifiable levels as a result of the tanning baths, whereas amplifiable mitochondrial DNA survives the complete process. Our results suggest that old and archaeological bovine leather may represent a useful source of genetic information, although this information will most likely be limited to that which can be gained from mitochondrial DNA.  相似文献   
180.
It is important to determine the geological sources of Palaeolithic ambers in the south of Europe in order to understand the mobility and interchanges of prehistoric societies. Fourier transform infrared (FTIR) spectroscopy analysis carried out on Upper Palaeolithic ambers from La Garma A cave (Cantabria, Northern Spain) allowed us to identify their source area. Their diagnostic features were found to be similar to the amber obtained in the Lower Cretaceous outcrops close to this archaeological site, and to differ clearly from Baltic amber, which has been generally suggested as the amber found in European prehistoric sites. These results show that the origin of the Gravettian amber found in La Garma A is local and, consequently, a hypothetical contact route is not required to be able to account for the presence of this material in the Iberian Palaeolithic context studied here. For the first time it has been demonstrated that the provenance of an archaeological amber in the Iberian Peninsula is local, with both geographical and spectroscopical evidences. Our study also concludes that the archaeological amber of La Garma A possibly belongs to an araucariacean resin that originated from the coniferous forests which grew in the northeast portion of the Iberian Plate c.110-million years ago.  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