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   59256篇
  免费   262篇
  国内免费   552篇
系统科学   1259篇
丛书文集   375篇
教育与普及   291篇
理论与方法论   518篇
现状及发展   33233篇
研究方法   1049篇
综合类   21153篇
自然研究   2192篇
  2013年   806篇
  2012年   690篇
  2011年   2734篇
  2009年   629篇
  2008年   857篇
  2007年   991篇
  2006年   1086篇
  2005年   1241篇
  2004年   2359篇
  2003年   1945篇
  2002年   1661篇
  2001年   1566篇
  2000年   1034篇
  1999年   1048篇
  1998年   644篇
  1997年   777篇
  1996年   538篇
  1994年   688篇
  1993年   689篇
  1992年   984篇
  1991年   822篇
  1990年   895篇
  1989年   710篇
  1988年   676篇
  1987年   715篇
  1986年   767篇
  1985年   919篇
  1984年   824篇
  1983年   706篇
  1982年   807篇
  1981年   850篇
  1980年   964篇
  1979年   1524篇
  1978年   1364篇
  1977年   1342篇
  1976年   1151篇
  1975年   1150篇
  1974年   1122篇
  1973年   1313篇
  1972年   1385篇
  1971年   1458篇
  1970年   1607篇
  1969年   1359篇
  1968年   1266篇
  1967年   1206篇
  1966年   1022篇
  1965年   804篇
  1964年   494篇
  1958年   621篇
  1957年   519篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
D C Gautam  L Kapoor 《Experientia》1991,47(3):280-282
Genotoxic effects of dithane M-45 were studied on the bone marrow cells of male albino mice (Lacca strain) in vivo. Different doses (30 mg, 40 mg and 300 mg/kg b.wt) of dithane M-45 were injected intraperitoneally and their effects were investigated after time intervals of 1, 2, 5 and 10 days. The chromosomal aberrations observed in the bone marrow cells of male mice after treatment with dithane M-45 were fragments, rings, dicentric chromosomes, terminal chromatid deletions, chromatid gaps and breaks. In addition to these chromosomal aberrations, physiological effects such as uneven stretching of chromatin material, end-to-end chromosomal associations, exchange configurations, clumping, stickiness and centromeric associations were also observed.  相似文献   
182.
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   
183.
基于Windows NT的HRPS-Ⅱ设备的控制系统设计   总被引:1,自引:0,他引:1  
介绍了华中科技大学开发的HRPS-Ⅱ型选择性激光烧结设备的体系结构,根据选择性激光烧结的工作原理并结合该系统的硬件结构开发了基于NT操作系统下的控制软件.该控制软件是一种分层的结构,各个不同优先级的任务在不同的层面上运行,实时性强的部分运行在硬件中断级别上,对控制软件的关键性技术进行了描述.通过试验运行,该设备成功地加工出了复杂的原型件,证明控制系统开发是成功的.  相似文献   
184.
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   
185.
186.
187.
Progress on nuclear liquid gas phase transition (LGPT) or critical behavior has been simply reviewed and some signals of LGPT in heavy ion collisions, especially in NIMROD data, are focused. These signals include the power-law charge distribution, the largest fluctuation of the fragment observables, the nuclear Zipf law, caloric curve and critical exponent analysis etc.  相似文献   
188.
189.
Summary By means of intratracheal injection, particles of metalloid silicium about five microns in size are introduced into the lungs of guinea pigs, and the secondary parenchymatous reactions are studied from 10 minutes to 105 days. In the dust cells, the silicium is progressively broken up into very small particles of less than 1 micron in size. The cells do not show degeneration or mummification as the ordinary silica cells (Mavrogordato) do.  相似文献   
190.
人类发现自身陷入一种境地,在那里似乎没有真正意义的途径使我们从围绕自身的技术型企业中解脱出来,所以我们需要创造一个走向生态纪元的社会。很多社团近期已经热心于进入一个生态社会并在一些领域采取行动,这些领域便是新故事、生物区域主义以及生态特征。  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