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   649618篇
  免费   72100篇
  国内免费   407篇
  2016年   7784篇
  2015年   10423篇
  2014年   12075篇
  2013年   17262篇
  2012年   19256篇
  2011年   19896篇
  2010年   13564篇
  2009年   12548篇
  2008年   18204篇
  2007年   18796篇
  2006年   17757篇
  2005年   16986篇
  2004年   16923篇
  2003年   16079篇
  2002年   15768篇
  2001年   26509篇
  2000年   26511篇
  1999年   21222篇
  1998年   7831篇
  1997年   8213篇
  1996年   7786篇
  1995年   7166篇
  1994年   7011篇
  1993年   7116篇
  1992年   17881篇
  1991年   17798篇
  1990年   17386篇
  1989年   16917篇
  1988年   16021篇
  1987年   15390篇
  1986年   14240篇
  1985年   14275篇
  1984年   11962篇
  1983年   10272篇
  1982年   7989篇
  1981年   7275篇
  1980年   6944篇
  1979年   11516篇
  1978年   9062篇
  1977年   8541篇
  1976年   8091篇
  1975年   8812篇
  1974年   9771篇
  1973年   9566篇
  1972年   8804篇
  1971年   8080篇
  1970年   7206篇
  1969年   7074篇
  1968年   6720篇
  1967年   5717篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.  相似文献   
63.
64.
Reconstruction of bony structures of the face is always a problem as big as the defect and the function that must be replaced. Everything from simple grafts to sophisticated distant bone flaps has been used. Based on the studies of Cutting et al., Psillakis et al., and Casanova et al., we have developed the full-thickness galeoparietal bone flap, initially for mandibular reconstruction, but of great use for all maxillofacial reconstructions. From July of 1987 to December of 1988, 14 patients have been operated on. The experience with this flap is shown in four patients as follows: primary reconstruction of a mandible as a result of ameloblastoma, secondary reconstruction of a mandible with associated old fractures and malalignment of segments, bilateral malar reconstruction in a patient with Treacher Collins syndrome, and severe sequelae of an already treated Romberg case. Small variations could be made to best accommodate the technique used to the defect we were treating. Some technical details, the experience, the results, and possible sequelae or complications are also discussed.  相似文献   
65.
66.
67.
68.
Isopropanol administered in a large (6 g/kg, orally) as well as in a lower dose (1 g/kg, I.P.) is slowly oxidized into acetone by the intact rat. Using two inhibitors, 3 amino-1,2,4-triazole and pyrazole, investigations on the hepatic enzymatic system involved in the oxidation of isopropanol show that catalase does not play an important part in this pathway, contrary to alcohol dehydrogenase which is the major enzyme responsible for this oxidation. Although isopropanol oxidation is mainly catalysed in the liver through alcohol dehydrogenase, no alteration of the hepatic extramitochondrial redox state occurs after the administration of a large as well as of a lower dose of isopropanol. From these experiments it may be concluded that alterations of the liver NAD+/NADH ratio, which seem to play an important part in the ethanol induced fatty liver, are not involved in the isopropanol induced one.  相似文献   
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