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   17594篇
  免费   44篇
  国内免费   71篇
系统科学   91篇
丛书文集   265篇
教育与普及   33篇
理论与方法论   83篇
现状及发展   8164篇
研究方法   786篇
综合类   8101篇
自然研究   186篇
  2013年   94篇
  2012年   236篇
  2011年   446篇
  2010年   105篇
  2008年   268篇
  2007年   304篇
  2006年   325篇
  2005年   326篇
  2004年   411篇
  2003年   313篇
  2002年   299篇
  2001年   504篇
  2000年   475篇
  1999年   339篇
  1992年   294篇
  1991年   225篇
  1990年   241篇
  1989年   242篇
  1988年   207篇
  1987年   240篇
  1986年   282篇
  1985年   340篇
  1984年   232篇
  1983年   229篇
  1982年   209篇
  1981年   220篇
  1980年   231篇
  1979年   566篇
  1978年   481篇
  1977年   443篇
  1976年   343篇
  1975年   412篇
  1974年   568篇
  1973年   459篇
  1972年   475篇
  1971年   560篇
  1970年   702篇
  1969年   545篇
  1968年   544篇
  1967年   543篇
  1966年   435篇
  1965年   376篇
  1964年   121篇
  1959年   193篇
  1958年   330篇
  1957年   247篇
  1956年   190篇
  1955年   192篇
  1954年   190篇
  1948年   127篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
101.
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   
102.
Summary -Terthienyl and 5 polyacetylenes were examined for chromosome damaging activity using Syrian hamster cells. None of these naturally occurring compounds induced sister chromatid exchanges and neither -terthienyl nor phenylheptatriyne induced chromosome aberrations.The authors wish to thank the National Science and Engineering Research Council for financial support of this research.  相似文献   
103.
Summary Direct incorporation and cold trap experiments suggest that cholest-4-en-3-one is an intermediate in the conversion of cholesterol into 3-hydroxymethyl-A-nor-cholestane in the marine spongeAxinella verrucosa. Cholest-4-en-3-one is further transformed by the sponge into cholest-4-en-3-ol, 5-cholestan-3-one and 5-cholestan-3-ol; these compounds arise from side reactions, which are not part of the major metabolic route leading to 3-hydroxymethyl-A-norsteranes.  相似文献   
104.
Summary Rats given aluminium hydroxide after cold-restraint stress but before the post-stress delay period, ulcerated significantly less severely and less frequently than rats given the drug before cold-restraint stress or those given water at either time period. Both aluminium hydroxide treated groups exhibited less ulceration than non-drug groups. These data suggest profound parasympathetic and hence, gastric acid, involvement in restraint delay-induced ulceration in rats.  相似文献   
105.
106.
Summary A needle type of colloid osmometer has been devised with special attachments which made it useable with 3-l samples. It has been used in oncometry of fresh water teleosts to give the following results: 5.1±1.0 mm Hg for goldfish, 5.2±0.71 mm Hg for carp, and 14.3±0.75 mm Hg for eel.This study was supported in part by Research Grant 387036 from the Ministry of Education of Japan.invited to National Institute of Physiological Sciences, Okazaki, Japan.  相似文献   
107.
108.
109.
Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner.  相似文献   
110.
Summary Thymidylate synthetase (methylenetetrahydrofolate: 2-deoxyuridine-5-monophosphate C-methyltransferase; EC 2.1.1.45) from neonatal mouse liver has been purified 714-fold by affinity chromatography on aminohexylsepharose bound 10-methyl-5,8-dideazafolate.Supported by grant CA22754, awarded by the National Cancer Institute, DHEW.  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