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   529166篇
  免费   62746篇
  国内免费   327篇
  592239篇
  2021年   4516篇
  2018年   5091篇
  2017年   4678篇
  2016年   7331篇
  2015年   11357篇
  2014年   12816篇
  2013年   17251篇
  2012年   20628篇
  2011年   20564篇
  2010年   13470篇
  2009年   12588篇
  2008年   17917篇
  2007年   18429篇
  2006年   16826篇
  2005年   16530篇
  2004年   16157篇
  2003年   15407篇
  2002年   14702篇
  2001年   22459篇
  2000年   22375篇
  1999年   18238篇
  1998年   7322篇
  1997年   7245篇
  1996年   6994篇
  1995年   6363篇
  1994年   6314篇
  1993年   6220篇
  1992年   14217篇
  1991年   13430篇
  1990年   13122篇
  1989年   12953篇
  1988年   11599篇
  1987年   11187篇
  1986年   10249篇
  1985年   10178篇
  1984年   8789篇
  1983年   7606篇
  1982年   6164篇
  1981年   5592篇
  1980年   5231篇
  1979年   8029篇
  1978年   6320篇
  1977年   5769篇
  1976年   5413篇
  1975年   5631篇
  1974年   6111篇
  1973年   5967篇
  1972年   5284篇
  1971年   4884篇
  1970年   4069篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Book review     
  相似文献   
992.
993.
994.
995.
Transcranial Doppler ultrasonographic recordings of the middle cerebral arteries were performed on eight children with autistic behavior compared to eight controls. Blood flow measurements were assessed at rest and during auditory and visual stimulations. The main result was obtained during the auditory stimulations and concerned the left artery blood flow which is lower in autistics than in controls in these conditions (p less than .02). This result confirms the possibility of a left hemisphere dysfunctioning in autistics and may be related to clinical features as language disabilities and paradoxical reactivity to auditory stimuli.  相似文献   
996.
A generalized Morse index theory is used to study travelling waves in a natural selection-migration model for a diploid organism when the selective strength is weak.  相似文献   
997.
Shell shape and growth of two unionacean species, Villosa villosaand Elliptio icterina, are analyzed with univariate and multivariatetechniques. The relationship of shape variables to size variablesis examined. Under the lognormal assumption, parametric testsof these allometric relationships are valid. Variables describingthe ventro-posterior region of the shell are shown to be thebest of those tested for discriminating between the sexes ofboth species regardless of statistical method. Neither speciesexhibits size sexual dimorphism. Shape sexual dimorphism ofV. villosa is constant during adult growth, but the more subtledimorphism of E. icterina changes as adults continue to grow. (Received 20 January 1986;  相似文献   
998.
Certain features of the Olduvai clavicular fragment have been examined in the light of data already existing on the form of the clavicle in primates. Although similar to that of modern man, the fragment exhibits features which suggest that its function may have differed somewhat from that of the clavicle in man. The new information correlates well with that obtained from the fragmentary Sterkfontein scapula.  相似文献   
999.
QSAR studies have been performed on the homologues of 3-triazines, using molecular connectivity index and van der Waal volume as structural parameters. The regression analysis has shown good correlation between antitumour activity and the two structural parameters.  相似文献   
1000.
Possible interactions between calpain II and phospholipids such as phosphatidylinositol, phosphatidylserine and phosphatidylcholine were studied using fluorescence and gel filtration techniques. Changes in fluorescence intensity of purified calpain II show that the enzyme strongly interacts with phosphatidylinositol and phosphatidylserine and to a lesser extent with phosphatidylcholine. These results are corroborated by the gel filtration technique which permits the isolation of the enzyme phospholipid complex. Association between calpain II and various phospholipid vesicles can occur in the absence of calcium. Such binding occurs without any observable change of the molecular mass of the two subunits on SDS-polyacrylamide gel electrophoresis.  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