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   31756篇
  免费   130篇
  国内免费   263篇
系统科学   451篇
丛书文集   624篇
教育与普及   94篇
理论与方法论   124篇
现状及发展   13027篇
研究方法   1195篇
综合类   15973篇
自然研究   661篇
  2013年   342篇
  2012年   606篇
  2011年   1288篇
  2010年   412篇
  2009年   393篇
  2008年   685篇
  2007年   796篇
  2006年   814篇
  2005年   749篇
  2004年   683篇
  2003年   514篇
  2002年   513篇
  2001年   840篇
  2000年   873篇
  1999年   625篇
  1992年   504篇
  1991年   425篇
  1990年   437篇
  1989年   420篇
  1988年   378篇
  1987年   398篇
  1986年   417篇
  1985年   524篇
  1984年   409篇
  1983年   350篇
  1982年   330篇
  1981年   340篇
  1980年   377篇
  1979年   930篇
  1978年   739篇
  1977年   725篇
  1976年   553篇
  1975年   666篇
  1974年   926篇
  1973年   755篇
  1972年   770篇
  1971年   906篇
  1970年   1093篇
  1969年   891篇
  1968年   864篇
  1967年   899篇
  1966年   747篇
  1965年   613篇
  1964年   200篇
  1959年   325篇
  1958年   522篇
  1957年   392篇
  1956年   312篇
  1955年   325篇
  1954年   303篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
研究了Al3+离子的固溶对C-S-H表面吸附Na+离子量的影响.实验结果表明,Al3+离子固溶于C-S-H结构中将使C-S-H表面所带的负电量增大,因而也就增大了C-S-H表面对Na+离子的吸附能力.  相似文献   
24.
1 Results Pyrimidinones (PMs) are a class of important heterocycles which have been well documented throughout the literature due to their biological importance. They exhibit a wide range of pharmaceutical and therapeutic properties[1].A rapid and efficient one-pot method for the synthesis of 4,6-diarylpyrimidin-2(1H)- ones and related heterocycles is described.The condensation of acetophenone derivatives,aldehydes and urea in the presence of sulfamic acid was employed to synthesize a variety of pyrimid...  相似文献   
25.
26.
中国共产党始终代表中国先进生产力的发展要求的论断,是站在历史唯物主义的角度,揭示出我们党兴旺发达的根本动力.  相似文献   
27.
The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) is a widespread receptor-coupled signalling system at the plasma membrane of most eukaryotic cells. The existence of an entirely separate nuclear phosphoinositide signalling system is suggested from evidence that purified nuclei synthesize PtdInsP2 and phosphatidylinositol 4-phosphate (PtdInsP) in vitro and that a transient decrease in the mass of these lipids occurs when Swiss 3T3 cells are cultured in the presence of insulin-like growth factor-1 (IGF-1). These IGF-1-dependent changes in inositol lipids coincide with an increase in nuclear diacyglycerol and precede translocation to the nucleus and activation of protein kinase C (refs 5, 6). Circumstantial evidence that links these changes with mitosis comes from the isolation of a 3T3 clone that expresses the type-1 IGF receptor and binds IGF-1 peptide but does not respond mitogenically or show transient mass changes in nuclear inositol lipids. A key question is how IGF-1 initiates the rapid breakdown of PtdInsP and PtdInsP2 in the nucleus. Here we present evidence that nuclei of 3T3 cells contain the beta-isozyme of phosphoinositidase C, whereas the gamma-isozyme is confined to the cytoplasm and that IGF-1 treatment stimulates exclusively the activity of nuclear phosphoinositidase C.  相似文献   
28.
DNA fingerprinting transforms the art of cell authentication.   总被引:4,自引:0,他引:4  
G N Stacey  B J Bolton  A Doyle 《Nature》1992,357(6375):261-262
The increasing diversity of new cell cultures is seriously stretching the capabilities of traditional methods of identification. DNA fingerprinting is set to play an important role in increasing confidence in the authenticity of cultures in research and industry.  相似文献   
29.
We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition.  相似文献   
30.
B L Stoddard  D E Koshland 《Nature》1992,358(6389):774-776
To validate procedures of rational drug design, it is important to develop computational methods that predict binding sites between a protein and a ligand molecule. Many small molecules have been tested using such programs, but examination of protein-protein and peptide-protein interactions has been sparse. We were able to test such applications once the structures of both the maltose-binding protein (MBP) and the ligand-binding domain of the aspartate receptor, which binds MBP, became available. Here we predict the binding site of MBP to its receptor using a 'binary docking' technique in which two MBP octapeptide sequences containing mutations that eliminate maltose chemotaxis are independently docked to the receptor. The peptides in the docked solutions superimpose on their original positions in the structure of MBP and allow the formation of an MBP-receptor complex. The consistency of the computational and biological results supports this approach for predicting protein-protein and peptide-protein interactions.  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