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   29931篇
  免费   72篇
  国内免费   74篇
系统科学   142篇
丛书文集   363篇
教育与普及   58篇
理论与方法论   121篇
现状及发展   12833篇
研究方法   1185篇
综合类   14920篇
自然研究   455篇
  2013年   249篇
  2012年   369篇
  2011年   837篇
  2010年   158篇
  2008年   429篇
  2007年   511篇
  2006年   540篇
  2005年   515篇
  2004年   603篇
  2003年   502篇
  2002年   494篇
  2001年   1003篇
  2000年   959篇
  1999年   584篇
  1992年   540篇
  1991年   433篇
  1990年   461篇
  1989年   489篇
  1988年   434篇
  1987年   434篇
  1986年   491篇
  1985年   580篇
  1984年   440篇
  1983年   426篇
  1982年   363篇
  1981年   363篇
  1980年   398篇
  1979年   970篇
  1978年   782篇
  1977年   739篇
  1976年   574篇
  1975年   696篇
  1974年   967篇
  1973年   767篇
  1972年   803篇
  1971年   961篇
  1970年   1209篇
  1969年   883篇
  1968年   911篇
  1967年   852篇
  1966年   765篇
  1965年   593篇
  1964年   157篇
  1959年   313篇
  1958年   523篇
  1957年   380篇
  1956年   293篇
  1955年   295篇
  1954年   282篇
  1948年   207篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
61.
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   
62.
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   
63.
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   
64.
A new microscopic principle   总被引:2,自引:0,他引:2  
GABOR D 《Nature》1948,161(4098):777
  相似文献   
65.
Summary An alcaloid C16H19NO3 has been isolated fromErythrina tholloniana; the iodohydrate of this erythroidine has a melting point of 225°C and 239°C for its chlorhydrate. It has a powerful curare-like action on the frog or on its isolated sciatic-sartorius preparation; at a concentration of less than 1/1,000,000, a complete neuromuscular block is produced: the electrical stimulation of the motor nerve does not produce any contraction, but the muscle reacts by an end-plate potential having the same characteristics (shape, duration, possibility of summation) as the electrical waves produced in the same preparation curarized by ordinary curare or by quaternary ammonium derivatives. Decurarization by veratrine 1/200,000 is accompanied by the same electrical reactions as those which have been described in preparations treated by curare.On mammals, the alcaloid has little curariform activity; on the isolated phrenic-diaphragm preparation of the rat, incomplete block was produced at a concentration of 1/5000.  相似文献   
66.
1 Results In addition to single wall and multiwall carbon nanotubes[1], several structures,which are more or less related to fullerenes,including carbon nanohorns[2a], carbon nanospheres[2b] and onion like carbon structures[2c] have been reported.A new simple straight forward method to access some of these structures is the solid-state pyrolysis of different organometallic complexes in a sealed vessel,which led so far to carbon nanotubes[3a,b], carbon nanocables[3c] and onions[3d].  相似文献   
67.
68.
69.
70.
The evolution of the universe   总被引:1,自引:0,他引:1  
GAMOW G 《Nature》1948,162(4122):680-682
  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