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   41271篇
  免费   1625篇
  2020年   522篇
  2019年   816篇
  2018年   917篇
  2017年   1114篇
  2016年   1216篇
  2015年   929篇
  2014年   905篇
  2013年   14066篇
  2012年   1055篇
  2011年   1078篇
  2010年   1067篇
  2009年   1067篇
  2008年   1013篇
  2007年   933篇
  2006年   819篇
  2005年   568篇
  2004年   567篇
  2003年   524篇
  2002年   502篇
  2001年   482篇
  2000年   422篇
  1999年   491篇
  1998年   454篇
  1997年   413篇
  1996年   393篇
  1995年   406篇
  1994年   356篇
  1993年   403篇
  1992年   387篇
  1991年   290篇
  1990年   283篇
  1989年   302篇
  1988年   298篇
  1987年   325篇
  1986年   285篇
  1985年   402篇
  1984年   434篇
  1983年   444篇
  1982年   385篇
  1981年   382篇
  1980年   420篇
  1979年   408篇
  1978年   396篇
  1977年   420篇
  1976年   376篇
  1975年   381篇
  1974年   288篇
  1973年   260篇
  1972年   242篇
  1970年   219篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The concentrations of two major elements and thirteen trace elements in 73 selected sherds of fine grey ware from the Iron Age and Roman period, excavated at Conimbriga, Santa Olaia and Tavarede, Portugal, were determined by instrumental neutron activation analysis. These concentrations were used to calculate distance matrices which were then subjected to cluster analysis employing SAHN and k-means methods, as well as to principal components analysis, to group the sherds according to the overall similarity of their compositional characteristics. The results showed that equivalent groupings appeared regardless of the taxonomic method used. Two major clusters were recognized corresponding to two different sites, namely Conimbriga and Santa Olaia, suggesting that the ceramics from these sites were made locally. No significant differences in compositional patterns were observed between iron age and roman sherds from Conimbriga.  相似文献   
62.
This study explores the spatial structure of retailing in Milwaukee, Wisconsin, in the era before the introduction of the electric streetcar in 1890. It uses city directory listings to chart changes in the numbers and types of retail outlets, their degree of nucleation and the functional complexity of such nucleations. The evidence suggests the early appearance of non-central retailing, the rapid dispersal of high as well as low order goods to non-central sites and the early emergence initially of a three-level and then, by 1870, a four-level hierarchy of shopping clusters. The pattern of retail clustering varied with the class and ethnic character of neighbourhoods, and clusters gravitated toward major arterial routes even in the pre-mass transit ear. Urban retailing in the second half of the nineteenth century was neither randomly dispersed nor over-whelmingly concentrated in a single central retail district, but developed a spatial hierarchy that clearly anticipated modern patterns.  相似文献   
63.
64.
65.
66.
A problem which has arisen in discussions of an elm-disease explanation for the Neolithic elm decline has been the lack of fossil records of Scolytus scolytus (F.) (elm bark beetle), which is the main carrier of the fungus which causes the present epidemic of Dutch Elm Disease. Now, the discovery of wing cases of two individuals from elm decline deposits at Hampstead Heath, London, proves that the beetle was present in Britain during this episode. The deposits in which it occurs are described, and the various implications for elm disease causing, aiding or at least occurring during this stage of the early Neolithic are discussed.  相似文献   
67.
68.
69.
70.
The pro‐life movement regularly employs tactics of political harassment in its campaign against abortion. As the murder of the controversial abortion doctor George Tiller in Wichita, Kansas, demonstrated last year, such tactics often betray a potential for violence. This paper explores how the militant tactics of the pro‐life movement in the 1990s have contributed to the formation of a ‘new’ political identity in Kansas politics: that of the moderate Republican. But for those that seek to counter‐mobilize against the Christian right, the political stakes remain high.  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