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   40610篇
  免费   102篇
  国内免费   214篇
系统科学   182篇
丛书文集   647篇
教育与普及   100篇
理论与方法论   146篇
现状及发展   19160篇
研究方法   1536篇
综合类   18622篇
自然研究   533篇
  2013年   330篇
  2012年   514篇
  2011年   1024篇
  2008年   671篇
  2007年   735篇
  2006年   719篇
  2005年   706篇
  2004年   753篇
  2003年   687篇
  2002年   681篇
  2001年   1183篇
  2000年   1122篇
  1999年   780篇
  1994年   385篇
  1992年   742篇
  1991年   551篇
  1990年   646篇
  1989年   622篇
  1988年   608篇
  1987年   700篇
  1986年   651篇
  1985年   816篇
  1984年   632篇
  1983年   552篇
  1982年   483篇
  1981年   508篇
  1980年   634篇
  1979年   1247篇
  1978年   1070篇
  1977年   1021篇
  1976年   842篇
  1975年   914篇
  1974年   1184篇
  1973年   1067篇
  1972年   1103篇
  1971年   1271篇
  1970年   1541篇
  1969年   1233篇
  1968年   1214篇
  1967年   1156篇
  1966年   1014篇
  1965年   706篇
  1964年   263篇
  1959年   388篇
  1958年   697篇
  1957年   507篇
  1956年   439篇
  1955年   411篇
  1954年   404篇
  1948年   308篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
291.
Summary Growth-promoting alpha-globulin (GPAG), a specific serum protein complex which induces mitotic activity in continually replicating metazoan cells in vitro, was shown in this study to support growth of astrocytes and mesenchymal cells as well as process formation of nerve cells isolated from cerebral hemispheres of chick embryos.  相似文献   
292.
Summary The conduction velocity of peristaltic movements of the canine ureter was measured under anaesthesia with a new type of diameter gauge using an image sensor. The peristaltic velocity was 34.1±6.2 mm/sec in 10 experiments. Noradrenaline at a low dosage of 1 g/kg i.v. reduced the resting diameter, increased the conduction velocity to 47–56 mm/sec, and approximately doubled the frequency of contraction. The application of acetylcholine also caused an increase in both frequency and conduction velocity (42–46 mm/sec). A plot of the conduction velocity against the mean period of peristaltic contraction was hyperbolic in shape.  相似文献   
293.
    
Summary -Galactosidase activity in intact cells of 21 species ofStreptomyces was measured using ONPG hydrolysis, without addition of a permeabilizing agent. Differences in the induction efficiency of ONPG-hydrolytic activity by lactose or galactose, which could have taxonomic implications, were observed among the species.  相似文献   
294.
Summary Adult spontaneously hypertensive rats (SHR) are less sensitive to painful stimuli than their normotensive controls, Wistar-Kyoto (WKY) rats. This difference can be eliminated by the specific opiate antagonist, naloxone, and by the -adrenergic blocking agent, propranol.Acknowledgment. The author wishes to thank Miss R. L. Holcomb for her editorial assistance.  相似文献   
295.
Summary A simple device is described, which permits us to quantify several parameters of spontaneous behaviour of small animals. Using this device with mice we obtained statistically satisfactory results, showing a strong genetic influence on the behavioural characteristics tested.We wish to thank Mr R. Laplace for technical help, Mr J. P. Arnould for electronic work as well as I.N.S.E.R.M.-SCR 3.  相似文献   
296.
Summary Several peptides were separated from-chymotrypsin-treated physalaemin by high voltage paper electrophoresis, and inhibition of the excitability of a molluscan giant neurone (tonically autoactive neurone) by the tripeptide, Lys-Phe-Tyr, was demonstrated.We thank Dr Sadaaki Iwanaga of Osaka University and Dr Atsuo Inoue of Daiichi Pharmaceutical CO for their helpful advice and the donation of the tripeptide (Lys-Phe-Tyr).  相似文献   
297.
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   
298.
In vivo studies indicated that the primary effects of E. coli endotoxin on hepatic clearance of sulfobromophthalein were at the excretory level. Newborns were more sensitive to the LPS than older animals.  相似文献   
299.
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   
300.
Summary The radiations coming from Blanc Brillant de Luxe' fluorescent stimulate the growth and ramification of protonema ofCeratodon purpureus (Hedw.) Brid. This stimulation is caused by red light (660 nm). Multidirectional lightening is more favorable than unidirectional exposition.  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