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   43343篇
  免费   1659篇
  2020年   546篇
  2019年   838篇
  2018年   989篇
  2017年   1186篇
  2016年   1270篇
  2015年   948篇
  2014年   931篇
  2013年   14212篇
  2012年   1091篇
  2011年   1141篇
  2010年   1122篇
  2009年   1096篇
  2008年   1053篇
  2007年   970篇
  2006年   846篇
  2005年   616篇
  2004年   581篇
  2003年   549篇
  2002年   539篇
  2001年   560篇
  2000年   503篇
  1999年   576篇
  1998年   478篇
  1997年   438篇
  1996年   415篇
  1995年   427篇
  1994年   378篇
  1993年   432篇
  1992年   407篇
  1991年   308篇
  1990年   314篇
  1989年   340篇
  1988年   327篇
  1987年   367篇
  1986年   338篇
  1985年   447篇
  1984年   478篇
  1983年   506篇
  1982年   430篇
  1981年   421篇
  1980年   451篇
  1979年   440篇
  1978年   428篇
  1977年   432篇
  1976年   399篇
  1975年   397篇
  1974年   306篇
  1973年   287篇
  1972年   263篇
  1970年   233篇
排序方式: 共有10000条查询结果,搜索用时 78 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.
67.
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   
68.
69.
70.
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