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   27882篇
  免费   138篇
  国内免费   295篇
系统科学   441篇
丛书文集   409篇
教育与普及   89篇
理论与方法论   92篇
现状及发展   11132篇
研究方法   1129篇
综合类   14388篇
自然研究   635篇
  2013年   309篇
  2012年   629篇
  2011年   1244篇
  2010年   424篇
  2009年   401篇
  2008年   693篇
  2007年   813篇
  2006年   810篇
  2005年   727篇
  2004年   558篇
  2003年   471篇
  2002年   516篇
  2001年   827篇
  2000年   854篇
  1999年   595篇
  1992年   471篇
  1991年   401篇
  1990年   423篇
  1989年   391篇
  1988年   374篇
  1987年   405篇
  1986年   373篇
  1985年   460篇
  1984年   433篇
  1983年   305篇
  1982年   322篇
  1981年   313篇
  1980年   343篇
  1979年   805篇
  1978年   650篇
  1977年   592篇
  1976年   522篇
  1975年   560篇
  1974年   685篇
  1973年   574篇
  1972年   573篇
  1971年   690篇
  1970年   819篇
  1969年   642篇
  1968年   686篇
  1967年   697篇
  1966年   616篇
  1965年   464篇
  1964年   200篇
  1959年   238篇
  1958年   389篇
  1957年   272篇
  1956年   220篇
  1955年   231篇
  1954年   205篇
排序方式: 共有10000条查询结果,搜索用时 15 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