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   26451篇
  免费   394篇
  国内免费   511篇
系统科学   467篇
丛书文集   388篇
教育与普及   266篇
理论与方法论   88篇
现状及发展   6401篇
研究方法   829篇
综合类   18575篇
自然研究   342篇
  2021年   229篇
  2015年   237篇
  2014年   338篇
  2013年   436篇
  2012年   577篇
  2011年   950篇
  2010年   486篇
  2009年   491篇
  2008年   707篇
  2007年   773篇
  2006年   721篇
  2005年   661篇
  2004年   619篇
  2003年   539篇
  2002年   580篇
  2001年   1060篇
  2000年   980篇
  1999年   903篇
  1998年   492篇
  1997年   481篇
  1996年   453篇
  1995年   426篇
  1994年   366篇
  1993年   293篇
  1992年   601篇
  1991年   497篇
  1990年   492篇
  1989年   470篇
  1988年   449篇
  1987年   367篇
  1986年   344篇
  1985年   350篇
  1984年   287篇
  1983年   254篇
  1979年   529篇
  1978年   409篇
  1977年   382篇
  1976年   324篇
  1975年   379篇
  1974年   511篇
  1973年   402篇
  1972年   400篇
  1971年   533篇
  1970年   640篇
  1969年   444篇
  1968年   482篇
  1967年   410篇
  1966年   416篇
  1965年   279篇
  1958年   248篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
E Littler  A D Stuart  M S Chee 《Nature》1992,358(6382):160-162
Human cytomegalovirus (HCMV, a betaherpes virus) is the cause of serious disease in immunologically compromised individuals, including those with acquired immunodeficiency syndrome. One of the compounds used in the chemotherapy of HCMV infections is the nucleoside analogue 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (ganciclovir). The mechanism of action of this drug is dependent on the formation of the nucleoside triphosphate, which is a strong inhibitor of the viral DNA polymerase. Thymidine kinase, which is encoded by many of the herpesviruses, catalyses the initial phosphorylation of ganciclovir. But there is no evidence for the coding of this enzyme by HCMV, and DNA sequence analysis of the HCMV genome has shown that there is no open reading frame characteristic of a herpesvirus thymidine kinase. Here we present biochemical and immunological evidence that the HCMV UL97 open reading frame codes for a protein capable of phosphorylating ganciclovir. This protein seems to be responsible for the selectivity of ganciclovir and will be useful tool in the understanding and refinement of the antiviral activity of new selective anti-HCMV compounds.  相似文献   
42.
The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding.  相似文献   
43.
全国学生体质、健康调研工作所涉及的指标多、数据量大、计算内容多,因此,有必要研制一套功能较齐全完备、便于使用的微机统计计算系统.该文介绍了该系统的设计思想、特点、结构、功能以及使用效果,该系统适用于全国各地及各高等院校,可处理以前的体质调研数据或其他有关数据,通用性与实用性较强.  相似文献   
44.
本文介绍利用信号流图及梅森公式分析设计负反馈电桥电路,以及在电阻传感器测量线性化中的应用。  相似文献   
45.
46.
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   
47.
Thyroid cancer after Chernobyl.   总被引:17,自引:0,他引:17  
  相似文献   
48.
49.
50.
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