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   39158篇
  免费   67篇
  国内免费   99篇
系统科学   201篇
丛书文集   863篇
教育与普及   111篇
理论与方法论   257篇
现状及发展   17282篇
研究方法   1627篇
综合类   18433篇
自然研究   550篇
  2013年   266篇
  2012年   560篇
  2011年   1135篇
  2010年   243篇
  2008年   701篇
  2007年   720篇
  2006年   769篇
  2005年   778篇
  2004年   677篇
  2003年   729篇
  2002年   745篇
  2001年   1126篇
  2000年   1041篇
  1999年   695篇
  1992年   654篇
  1991年   542篇
  1990年   571篇
  1989年   585篇
  1988年   596篇
  1987年   594篇
  1986年   601篇
  1985年   741篇
  1984年   574篇
  1983年   491篇
  1982年   420篇
  1981年   409篇
  1980年   533篇
  1979年   1209篇
  1978年   1038篇
  1977年   1023篇
  1976年   727篇
  1975年   773篇
  1974年   1162篇
  1973年   980篇
  1972年   1016篇
  1971年   1226篇
  1970年   1614篇
  1969年   1249篇
  1968年   1219篇
  1967年   1234篇
  1966年   1034篇
  1965年   751篇
  1964年   208篇
  1959年   445篇
  1958年   685篇
  1957年   574篇
  1956年   488篇
  1955年   414篇
  1954年   458篇
  1948年   282篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
Summary Pentobarbital concentrations of 10–100 M selectively inhibited the noradrenaline release evoked by activation of the nicotinic receptors on the terminals sympathetic nerves of the rabbit heart. Higher concentrations also decreased the noradrenaline release induced by KCl or by electrical stimulation of the nerve axons.This paper is dedicated to Professor Dr. G. Malorny on the occasion of his 65th birthday.Acknowledgment: We thank Mrs G. Thielecke for technical assistance.  相似文献   
252.
Summary It was shown in the rat that mobilization of intramuscular triglyceride during exercise is controlled by the adrenergic system.Acknowledgments. The work was supported by the Polish Academy of Sciences, grant No. 10.4.2.01.3.2.  相似文献   
253.
Summary The cytoplasm of the restrictive form of the amycelial mutant ofNeurospora crassa, growing on sucrosemedium, contains paracrystalline, microfilamentous inclusions and mitochondria with internal membranous whorls lacking in acetate-grown cultures.The support of the Fonds national suisse de la recherche scientifique is gratefully acknowledged.  相似文献   
254.
Summary A 2-dimensional thin-layer method has been developed for the separation on cellulose of adenine and guanine derivatives. Using incubated rat cerebral cortex slices it was shown that noradrenaline and acetylcholine stirnulated cAMP and cGMP production respectively but glutamate and -aminobutyric acid stimulated production of both cyclic nucleotides.  相似文献   
255.
Summary The effects of L-glutamic acid and of some glutamate analogues have been studied on the central nervous system of the snailHeobania vermiculata, using conventional electrophysiological techniques. The glutamate H-response had the mean equilibrium value of-(57±4) mV and was associated with a Cl conductance change. The D-response to glutamate application showed an involvement of sodium ions. Aspartate was agonist of glutamate action and displayed similar equilibrium value of the H-response, whereas quisqualate H-response was non-invertible.The authors wish to express their thanks to Prof. A. Curatolo for his continual interest and advice, and to Dr J. Stinnakre for the criticism of the text.  相似文献   
256.
Summary Eradication of replicating bone marrow cells of rat by means of combined administration of single doses of hydroxyurea and vinblastin is followed within 9–10 h by an inflow of lymphoid cells of extramedullary origin in the range of 13,200,000/femur. The rat bone marrow with a high content of lymphoid cells was previously shown to be concentrated in stem cells. The factor(s) which convey the information of decrease of replicating marrow cells to extramedullary sites is at present unknown.Acknowledgment. This study was supported by a grant from the Chief Scientist Office, Ministry of Health, Israel.Hydroxyurea for this investigation was given as a gift by the Squibb Institute of Medical Research, Princeton, N.J. USA, to which the authors are indebted.  相似文献   
257.
Summary Cyclophosphamide given to rats 2 or 5 days after an injection of Yoshida ascites sarcoma cured approximately the same proportion of animals, but the resistance to a subsequent tumor challenge was found only in rats treated with the drug 5 days after tumor injection.  相似文献   
258.
The effect ofγ-irradiation on soil enzyme stability   总被引:1,自引:0,他引:1  
Summary Arylsulphatase, -1,3 glucanase, phosphatase and urease responded differently to -irradiation (5–50 Mrad) in air-dried and moist soils. In all instances phosphatase was the most stable. The variability between enzymes may be due to inherent biochemical and stuctural characteristics or to their location within the soil microenvironment.Supported by a grant from the NERC.  相似文献   
259.
Summary Large-scale purification of hepatitis B surface antigen, applicable to the preparation of potential vaccines for prevention of hepatitis B, is described. The method involves the following steps: precipitation of serum with polyethylene glycol 6000, affinity chromatography on concanavalin A-Sepharose and on -aminononyl-Sepharose, and isopycnic centrifugation.This study was supported by grant 09011 from the National Heart, Lung and Blood Institute. We thank Dr. B. Hollinger for testing HBsAg samples by a complement fixation test.  相似文献   
260.
The behavioural study, in particular rearing environmental conditions, of the mutant mouse staggerer has shown that such animals may live more than 90 days. (he behavioural diagnosis of this mutation has been possible from the second week of life, using specific tests. A typical "bat posture" permits one to recognize the mutant from the normal Mouse. Locomotory and feeding behaviours also present late and various qualitatige particularities.  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