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   45956篇
  免费   172篇
  国内免费   231篇
系统科学   395篇
丛书文集   931篇
教育与普及   88篇
理论与方法论   154篇
现状及发展   20929篇
研究方法   1698篇
综合类   21451篇
自然研究   713篇
  2013年   393篇
  2012年   624篇
  2011年   1353篇
  2010年   305篇
  2008年   778篇
  2007年   858篇
  2006年   880篇
  2005年   852篇
  2004年   833篇
  2003年   832篇
  2002年   837篇
  2001年   1412篇
  2000年   1323篇
  1999年   854篇
  1992年   812篇
  1991年   643篇
  1990年   723篇
  1989年   696篇
  1988年   683篇
  1987年   756篇
  1986年   697篇
  1985年   905篇
  1984年   709篇
  1983年   589篇
  1982年   510篇
  1981年   553篇
  1980年   703篇
  1979年   1394篇
  1978年   1184篇
  1977年   1182篇
  1976年   951篇
  1975年   1007篇
  1974年   1356篇
  1973年   1193篇
  1972年   1246篇
  1971年   1409篇
  1970年   1802篇
  1969年   1368篇
  1968年   1350篇
  1967年   1317篇
  1966年   1155篇
  1965年   827篇
  1964年   267篇
  1959年   471篇
  1958年   770篇
  1957年   553篇
  1956年   496篇
  1955年   443篇
  1954年   474篇
  1948年   321篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
J M Nunnari  D L Zimmerman  S C Ogg  P Walter 《Nature》1991,352(6336):638-640
The rough endoplasmic reticulum membranes of mammalian cells contain specific ribosome-binding sites. A purification to apparent homogeneity of a negatively charged protein (ERp180) of relative molecular mass 180,000 (180 K) was reported which was proposed to function as a rough endoplasmic reticulum ribosome receptor. We report here that ribosome-binding site activity quantitatively solubilized from rough endoplasmic reticulum membranes does not cofractionate with ERp180. By contrast, ribosome-binding site activity fractionates as a much smaller, positively charged protein.  相似文献   
102.
There is considerable debate among scholars over whether Descartes allowed for genuine body–body interaction. I begin by considering Michael Della Rocca’s recent claim that Descartes accepted such interaction, and that his doctrine of the creation of the eternal truths indicates how this interaction could be acceptable to him. Though I agree that Descartes was inclined to accept real bodily causes of motion, I differ from Della Rocca in emphasizing that his ontology ultimately does not allow for them. This is not the end of the story however, since two of Descartes’s successors offered incompatible ways of developing his conflicted account of motion. I contrast the occasionalist view of Nicolas Malebranche that changes in motion derive directly from divine volitions with the non-occasionalist claim of Pierre-Sylvain Regis that such changes derive from a nature distinct from God. In light of Della Rocca’s interpretation, it is noteworthy that the issue of eternal truths is relevant to both alternative accounts. Indeed, Regis took the doctrine that such truths are created to provide crucial support for his alternative to an occasionalist account of body–body interaction. What does not help Della Rocca, however, is that Regis’s view of motion requires a fundamental revision of Descartes’s ontology.  相似文献   
103.
Summary (1) Doubly refracting lipoid droplets can be demonstrated in normal and pathological sera by means of alcohol ether extraction. This is not possible with ether extraction alone.(2) These lipoid droplets can be demonstrated only, or almost only, when they are precipitated out of alcohol or ether alcohol  相似文献   
104.
105.
106.
107.
108.
109.
110.
Summary The preceding empirical relation was found between the surface tension of liquids, the specific weight of liquids, and the velocity of sound:=6.3 · 10–4 3/2. In place of the vèocity of sound can be used, with suitable changes in the equation, the compressibility or, in the case of solid substances, the elasticity of the material in question. The range of validity of this relation is so large that it is possible by means of it to calculate the surface tension of solid substances and of gases.  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