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   648670篇
  免费   77370篇
  国内免费   439篇
  726479篇
  2018年   5456篇
  2016年   7268篇
  2015年   10333篇
  2014年   11776篇
  2013年   17395篇
  2012年   19061篇
  2011年   19528篇
  2010年   13101篇
  2009年   12212篇
  2008年   17455篇
  2007年   18019篇
  2006年   16921篇
  2005年   16255篇
  2004年   15813篇
  2003年   15568篇
  2002年   15070篇
  2001年   28726篇
  2000年   28958篇
  1999年   22960篇
  1998年   8337篇
  1997年   9015篇
  1996年   8597篇
  1995年   7900篇
  1994年   7844篇
  1993年   7897篇
  1992年   19497篇
  1991年   19336篇
  1990年   18454篇
  1989年   18266篇
  1988年   16820篇
  1987年   16229篇
  1986年   15014篇
  1985年   15173篇
  1984年   12682篇
  1983年   10940篇
  1982年   8476篇
  1981年   7702篇
  1980年   7331篇
  1979年   12115篇
  1978年   9636篇
  1977年   8960篇
  1976年   8402篇
  1975年   9209篇
  1974年   9838篇
  1973年   9620篇
  1972年   8700篇
  1971年   8065篇
  1970年   6949篇
  1969年   6684篇
  1968年   6061篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
42.
Transcriptive expression during sea urchin embryogenesis   总被引:2,自引:0,他引:2  
  相似文献   
43.
44.
Subsequent to observations that pulmonary responses to antigen challenge are of different magnitudes in sensitized rats that are anesthetized with different drugs, we conducted studies to test whether the alterations in responses were due to changes in airway responsiveness to cholinergic or serotonergic challenge, opioid-receptor mediated events, or changes in mast cell mediator release. Immunoglobulin E-sensitized rats anesthetized with ketamine/urethan had larger changes in lung resistance and plasma histamine after pulmonary antigen challenge compared with rats anesthetized with fentanyl-droperidol. Blockade of opioid receptors with naloxone did not affect the responses. In unsensitized rats, airway responses to aerosolized methacholine were similar for the two anesthetics, indicating unchanged smooth muscle responsiveness; however, airway responses to intravenous serotonin were enhanced by ketamine and ablated by droperidol. We conclude that ketamine- and droperidol-induced alterations of pulmonary allergic responses are due to changes in sensitivity to serotonin and in mast cell mediator release. We speculate that mast cell mediator release may be modulated by a serotonin receptor-linked mechanism.  相似文献   
45.
A finite element based method to determine the incremental elastic material properties of planar membranes was developed and evaluated. The method is applicable to tissues that exhibit inhomogeneity, geometric and material nonlinearity, and anisotropy. Markers are placed on the tissue to form a four-node quadrilateral element. The specimen is loaded to an initial reference state, then three incremental loading sets are applied and the nodal displacements recorded. One of these loadings must include shear. These data are used to solve an over-determined system of equations for the tangent stiffness matrix. The method was first verified using analytical data. Next, data obtained from a latex rubber sheet were used to evaluate experimental procedures. Finally, experiments conducted on preconditioned rat skin revealed nonlinear orthotropic behavior. The vector norm comparing the applied and calculated nodal force vectors was used to evaluate the accuracy of the solutions.  相似文献   
46.
47.
48.
49.
50.
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   
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