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   46027篇
  免费   249篇
  国内免费   542篇
系统科学   1221篇
丛书文集   98篇
教育与普及   281篇
理论与方法论   508篇
现状及发展   29657篇
研究方法   152篇
综合类   12712篇
自然研究   2189篇
  2014年   396篇
  2013年   802篇
  2012年   427篇
  2011年   2407篇
  2009年   594篇
  2008年   625篇
  2007年   683篇
  2006年   805篇
  2005年   962篇
  2004年   2112篇
  2003年   1709篇
  2002年   1369篇
  2001年   978篇
  2000年   512篇
  1999年   728篇
  1998年   640篇
  1997年   771篇
  1996年   528篇
  1994年   680篇
  1993年   687篇
  1992年   688篇
  1991年   599篇
  1990年   665篇
  1989年   486篇
  1988年   463篇
  1987年   471篇
  1986年   566篇
  1985年   669篇
  1984年   640篇
  1983年   543篇
  1982年   714篇
  1981年   758篇
  1980年   828篇
  1979年   1107篇
  1978年   1031篇
  1977年   1049篇
  1976年   935篇
  1975年   902篇
  1974年   676篇
  1973年   986篇
  1972年   1057篇
  1971年   1000篇
  1970年   991篇
  1969年   969篇
  1968年   944篇
  1967年   794篇
  1966年   655篇
  1965年   559篇
  1964年   462篇
  1963年   414篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
481.
Summary In reserpinized mice the occurrence of goldthioglucose hypothalamic lesions was significantly lower than in control mice. Some protection was also conferred by serotonin-receptor blockers and by treatment with nialamide+DL--methyldopa, but the protective effect of reserpine was not reversed by serotonergic and dopaminergic agonists, alone or in combination, nor by insulin.  相似文献   
482.
    
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   
483.
Summary Stroma-free hemoglobin solutions present some drawbacks when used as blood substitutes, essentially because the hemoprotein has a low vascular retention, due to its small hydrodynamic volume. Covalent coupling of the protein with dextran derivatives artificially increases its size and affords polymeric conjugates whose oxygen-binding properties (Barcroft's curve, Hill coefficient) depend on the molecular weight.The authors wish to thank Prof. J. Neel and Prof. C. Vigneron for useful discussions and criticism.  相似文献   
484.
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   
485.
Summary Several high molecular weight polyacetylenes have been isolated from the spongePetrosia ficiformis found in dark caves. These compounds are related to, but different from, the polyacetylenes isolated from the same sponge living in its usual habitat.This work is a part of the Progetto finalizzato per l'Oceanografia e i Fondi Marini, CNR, Roma.The authors thank Mr G. Scognamiglio for the HPLC work, Mr C. Di Pinto for the NMR spectra and Mr G. Villani for the collection of the sponge.  相似文献   
486.
Summary Claviceps purpurea 275 F.I. fed with -aminobutyric acid produces ergostine with the corresponding -hydroxy--aminoacid undiluted by endogenous aminoacid. Almost all the -aminobutyric acid not incorporated into the ergostine remains unchanged in the medium. The significance of these results in the biosynthesis of ergot alkaloids is discussed.  相似文献   
487.
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   
488.
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   
489.
Summary The purified chitin from the cuticle of a pentastomid was examined by X-ray method. The X-ray photograph discloses that the chitin in question is of -type. Since the arthropod cuticle contains -chitin, it is suggested that Pentastomida may be considered an independent phylum.Thanks are due to Prof. Dr. G. Sundara Rajulu for guidance and encouragement.  相似文献   
490.
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   
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