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   6980篇
  免费   28篇
  国内免费   34篇
系统科学   78篇
丛书文集   57篇
教育与普及   4篇
理论与方法论   41篇
现状及发展   3673篇
研究方法   333篇
综合类   2715篇
自然研究   141篇
  2018年   58篇
  2017年   61篇
  2016年   60篇
  2015年   56篇
  2012年   130篇
  2011年   234篇
  2008年   148篇
  2007年   167篇
  2006年   169篇
  2005年   158篇
  2004年   152篇
  2003年   135篇
  2002年   155篇
  2001年   182篇
  2000年   187篇
  1999年   122篇
  1992年   107篇
  1991年   87篇
  1990年   77篇
  1989年   70篇
  1987年   75篇
  1986年   77篇
  1985年   140篇
  1984年   93篇
  1983年   82篇
  1982年   71篇
  1981年   79篇
  1980年   76篇
  1979年   164篇
  1978年   152篇
  1977年   166篇
  1976年   151篇
  1975年   162篇
  1974年   178篇
  1973年   153篇
  1972年   138篇
  1971年   179篇
  1970年   280篇
  1969年   204篇
  1968年   210篇
  1967年   221篇
  1966年   167篇
  1965年   120篇
  1964年   86篇
  1959年   77篇
  1958年   91篇
  1957年   91篇
  1956年   61篇
  1955年   54篇
  1954年   57篇
排序方式: 共有7042条查询结果,搜索用时 0 毫秒
21.
Summary The results described here demonstrate that THC-induced catalepsy in mice can be substantially inhibited by the prior administration of 1-THC-7-oic acid, the major metabolite of THC in most species including humans. This raises the possibility that the intensity and duration of action of THC may depend to a large degree on the levels of this metabolite at the sites of action.We thank the National Institute on Drug Abuse for supporting this project by grants DA-02043 and DA-02052 and for supplying all of the cannabinoids. One of us (S.B.) is also the recipient of a Research Scientist Award from NIDA. We are grateful to Kristen Carlson and Thomas Honeyman for helpful suggestions in preparing this report.  相似文献   
22.
S M Stack  W V Brown 《Nature》1969,222(5200):1275-1276
  相似文献   
23.
24.
Mean plasma insulin concentration was reduced and mean plasma glucose concentration increased following the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mol kg–1 i.a.) in conscious calves given continuous infusions of exogenous glucose (30–60 mol min–1 kg–1 i.v.). It is concluded that the rise in plasma insulin concentration which occurs in these animals in response to glucose is mediated, at least in part, by a nitric oxide-related factor (NOx).  相似文献   
25.
26.
The isolation of N-quinaldyl-L-arginine·HCl (1) from the CoccinellidaeSubcoccinella-24-punctata is reported. The structure, first established on the basis of the analysis of the spectral properties of1, has been confirmed by synthesis. The alkaloid is of endogenous origin and markedly deterrent to ants.  相似文献   
27.
The splenomegaly and the appearance of a significant number of CFU-E (erythroid colony-forming units) and BFU-E1 (erythroid burst-forming units) in the Belgrade laboratory rat (b/b) spleen prompted us to analyse further the molecular evidence for increased hematopoietic proliferation in the b/b spleen. Messenger RNAs (mRNAs) specific for globins, proteins for iron transport and deposition and the band 3 protein were used in rat erythropoietic tissues as markers for proliferation and erythroid differentiation. In the b/b spleen, all mRNAs analysed display an erythroid-specific pattern of expression. This analysis also revealed an enhanced level of mRNA for ferritin in the +/b spleen, whereas erythrocyte-specific mRNA production was normal.  相似文献   
28.
The immunization of biungulate animals with killed foot-and-mouth disease virus (FMDV) requires periodic vaccinations due to a low vaccine immunogenicity. Therefore, FMDV antigens need to be combined with adjuvants such as aluminum hydroxide, saponin or oil emulsions. Animal handling for periodic inoculations, and the repeated doses of vaccines that have to be administered increase the commercialization costs. Moreover, the use of adjuvants may induce adverse effects.In the present work we show that it is possible to increase the life span of neutralizing antibodies in serum when a single dose of cyclophosphamide (Cy) is administered four days before vaccination with aluminum hydroxidesaponin FMDV vaccine.  相似文献   
29.
Summary The article surveys our knowledge of the normalizing factor, gained from its discovery a quarter of a century ago up to the present time, under the following headings: Discovery; Physiological properties; Isolation and characterization; Structure determination (Identity of the normalizing factor with nicotianamine); Chemical properties; Analysis; Synthesis; Occurrence and physiological role; Related compounds; Prospects.  相似文献   
30.
Summary Resting oxygen consumption of the vascularly isolated gracilis anticus muscle of the rat perfused by natural circulation via the femoral artery with diluted or undiluted blood depends on oxygen delivery (the product of flow rate and arterial oxygen concentration-DO2) only when DO2 falls below 16 l/min/g.  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