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   11881篇
  免费   24篇
  国内免费   43篇
系统科学   35篇
丛书文集   80篇
教育与普及   32篇
理论与方法论   42篇
现状及发展   5134篇
研究方法   568篇
综合类   5901篇
自然研究   156篇
  2013年   97篇
  2012年   193篇
  2011年   333篇
  2010年   85篇
  2009年   59篇
  2008年   191篇
  2007年   226篇
  2006年   204篇
  2005年   228篇
  2004年   209篇
  2003年   211篇
  2002年   201篇
  2001年   381篇
  2000年   365篇
  1999年   264篇
  1992年   233篇
  1991年   180篇
  1990年   204篇
  1989年   190篇
  1988年   201篇
  1987年   205篇
  1986年   160篇
  1985年   248篇
  1984年   170篇
  1983年   149篇
  1982年   166篇
  1981年   136篇
  1980年   170篇
  1979年   385篇
  1978年   292篇
  1977年   289篇
  1976年   249篇
  1975年   287篇
  1974年   309篇
  1973年   308篇
  1972年   344篇
  1971年   344篇
  1970年   428篇
  1969年   361篇
  1968年   383篇
  1967年   351篇
  1966年   319篇
  1965年   203篇
  1959年   108篇
  1958年   204篇
  1957年   137篇
  1956年   123篇
  1955年   105篇
  1954年   81篇
  1948年   83篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
912.
913.
The somatostatin content in pancreatic islets of obese-hyperglycemic mice was much lower than in the islets of normal mice. Also the release of somatostatin was decreased from the islets obtained from the obese-hyperglycemic mice. Tissue culture for 1 week changed neither the content of, nor the amount of somatostatin released from, the pancreatic islets.  相似文献   
914.
A Sodhi  S B Prasad 《Experientia》1985,41(1):93-95
It is reported that concanavalin A (conA) and wheat germ agglutinin (WGA) have a differential binding pattern on normal mouse spleen lymphocytes and the surface of Dalton's lymphoma cells. It is suggested that sialic acid on the cell surface controls the expression of lectin binding sites. Further, it has been observed that the increased release of sialic acid from cell surfaces after cis-dichlorodiammine platinum (II) (cis-Platin) treatment is due to the increased activity of sialidase.  相似文献   
915.
A protein with many functions?   总被引:2,自引:0,他引:2  
R B Freedman 《Nature》1989,337(6206):407-408
  相似文献   
916.
917.
Coexistence of A- and B-form DNA in a single crystal lattice   总被引:5,自引:0,他引:5  
J Doucet  J P Benoit  W B Cruse  T Prange  O Kennard 《Nature》1989,337(6203):190-192
It is well known that DNA can exist in a variety of conformations which can be interconverted by relatively mild changes in conditions. The in vivo conformation of DNA is usually thought to be the B form, but there is recent evidence that other conformations may be important in DNA-protein recognition. Different fragments of DNA crystallized under virtually identical conditions can form A, B or Z helices. A fragment that adopted an A conformation in a crystal was found in the B conformation in solution, whereas NMR spectroscopy of A-DNA films revealed the presence of a substantial amount of disordered B-DNA. Until now, however, a DNA fragment of a given sequence has not been crystallized in more than one global conformation. We report here an X-ray diffraction study of crystals of the DNA octamer dGGBrUABrUACC. In addition to a 'framework' of A-DNA, which gives discrete X-ray reflections, there are partially disordered B-DNA helices, recognized by their diffuse scattering features.  相似文献   
918.
There are many practical decision problems where decision makers' preferences may be inconsistent and contradictory. In this paper, new methods for ordering and classifying multi-attribute objects by discordant collective preferences are suggested. These methods are based on the theory of multiset metric spaces. The proposed techniques are applied to ranking companies and a competitive selection of projects, which are estimated by several experts upon multiple qualitative criteria.  相似文献   
919.
Cooperative tandem binding of met repressor of Escherichia coli   总被引:10,自引:0,他引:10  
We present biochemical and genetic data to support the hypothesis that the Escherichia coli met repressor, MetJ, binds to synthetic and natural operator sequences in tandem arrays such that repression depends not only on the affinity of the DNA-protein interaction, but also on protein-protein contacts along the tandem array. This represents a novel form of regulatory switch. Furthermore, there seems to be homology between the organization of the met and trp operators.  相似文献   
920.
Summary Supernumerary chromosomes have been detected in the karyotype ofD.n. albomicana. Their number varies from one to three. They are the smallest elements in the karyotype. Karyotypes ofD.n. albomicana with and without supernumerary chromosomes have been presented.  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