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   27764篇
  免费   140篇
  国内免费   295篇
系统科学   440篇
丛书文集   409篇
教育与普及   89篇
理论与方法论   90篇
现状及发展   11109篇
研究方法   1121篇
综合类   14304篇
自然研究   637篇
  2013年   307篇
  2012年   625篇
  2011年   1242篇
  2010年   425篇
  2009年   401篇
  2008年   683篇
  2007年   806篇
  2006年   804篇
  2005年   721篇
  2004年   548篇
  2003年   470篇
  2002年   513篇
  2001年   824篇
  2000年   852篇
  1999年   595篇
  1992年   470篇
  1991年   402篇
  1990年   423篇
  1989年   386篇
  1988年   376篇
  1987年   406篇
  1986年   372篇
  1985年   460篇
  1984年   430篇
  1983年   303篇
  1982年   321篇
  1981年   313篇
  1980年   342篇
  1979年   804篇
  1978年   648篇
  1977年   590篇
  1976年   521篇
  1975年   557篇
  1974年   682篇
  1973年   572篇
  1972年   570篇
  1971年   685篇
  1970年   814篇
  1969年   640篇
  1968年   682篇
  1967年   695篇
  1966年   612篇
  1965年   462篇
  1964年   200篇
  1959年   238篇
  1958年   387篇
  1957年   272篇
  1956年   220篇
  1955年   231篇
  1954年   204篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Summary Silver-staining has been used to identify the nucleolus organizer regions (NORs) in the bharal. These show homology with sheep, goat, cattle and aoudad. The association of the NORs on both telomeres of chromosome 3 results in a ring chromosome.  相似文献   
102.
Summary The hemolymph volume ofHeliothis zea larvae was determined by the amaranth dye method and found to vary from 28 to 288 l. It averaged 30.6% of b.wt, a value comparable to that obtained with C14 inulin. Amaranth became evenly distributed in the hemocoele in 3–5 min.  相似文献   
103.
Summary A statistically significant decrease of prealbumin and statistically significant increases of alpha2-macroglobulin and IgA were found in blood plasma of patients with Down's syndrome using quantitative crossed immunoelectrophoresis.We are indebted to Prof. T.C. Bøg-Hansen, University of Copenhagen, for the helpful discussion of our results.  相似文献   
104.
Summary In the sandal plant affected by spike disease, caused by mycoplasma-like organisms, the changes occurring in the 5-and 3-nucleotidase activities were studied and their possible significance discussed.  相似文献   
105.
Summary A novel sesquiterpene lactone, 9--hydroxyparthenolide (1) was isolated from a chloroform extract ofAnvillea garcini that was collected in Iran. The structure of1 was assigned on the basis of high field NMR decoupling experiments and other spectroscopic evidence. This -methylene lactone has shown significant activity in both the 9KB cell culture and P388 mouse leukemia test systems.The authors acknowledge the support of contract No. N01-CM-97296 from the National Cancer Institute and the use of the Purdue University Biochemical Magnetic Resonance Laboratory (NIH grant No. RR01077). This is paper 16 in the series Potential Antitumor Agents.  相似文献   
106.
107.
108.
For the identification of a peptidyl principle inducing sexual agglutination in the yeast, 2 supposed hexapeptides (1a, b) were synthesized by the conventional method. The 1a (H-Arg-Gly-Pro-Phe-Pro-Ile-OH) revealed complete identity with the natural peptide in TLC, MS and biological property on agglutination. The 1b showed the sexual agglutinability in the same degree as 1a, though distinct differences were observed in the chemical data. Both 1a and 1b had a strong bitter taste.  相似文献   
109.
D S McDevitt  S K Brahma 《Experientia》1977,33(8):1087-1089
The ontogeny and localization of the gamma crystallins in Discoglossus pictus lens development has been determined. Using antibody specific for amphibian gamma crystallins in the immunofluorescence technique, it was found that gamma crystallins first appear in primary lens fibre cells in the lens rudiment, and continue to be restricted to the fibre area as lens development progresses. Thus the role of gamma crystallins as indicators of a differentiated state remains constant in amphibian evolution, having been demonstrated in the most archaic anuran superfamily, as well as in others more recently evolved.  相似文献   
110.
Summary Pronase and -chymotrypsin digested the major glycoprotein in the human and mouse red cell membranes and in SDS gel electrophoresis the glycoprotein disappeared accompanied by the appearance of a new band of lower mol.wt. However in the membranes of sheep, rat and rabbit, no digestion was demonstrated. The effects of pronase on anion permeability were almost identical for human and animal erythrocytes.  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