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   33459篇
  免费   66篇
  国内免费   74篇
系统科学   215篇
丛书文集   719篇
教育与普及   79篇
理论与方法论   251篇
现状及发展   14663篇
研究方法   1489篇
综合类   15738篇
自然研究   445篇
  2013年   216篇
  2012年   510篇
  2011年   972篇
  2010年   241篇
  2008年   627篇
  2007年   606篇
  2006年   676篇
  2005年   674篇
  2004年   609篇
  2003年   629篇
  2002年   642篇
  2001年   996篇
  2000年   915篇
  1999年   617篇
  1992年   586篇
  1991年   483篇
  1990年   506篇
  1989年   499篇
  1988年   498篇
  1987年   517篇
  1986年   502篇
  1985年   613篇
  1984年   507篇
  1983年   416篇
  1982年   359篇
  1981年   349篇
  1980年   473篇
  1979年   1012篇
  1978年   895篇
  1977年   900篇
  1976年   595篇
  1975年   654篇
  1974年   979篇
  1973年   831篇
  1972年   858篇
  1971年   1055篇
  1970年   1389篇
  1969年   1052篇
  1968年   985篇
  1967年   1049篇
  1966年   869篇
  1965年   648篇
  1964年   163篇
  1959年   364篇
  1958年   529篇
  1957年   451篇
  1956年   366篇
  1955年   322篇
  1954年   372篇
  1948年   198篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
201.
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   
202.
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   
203.
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   
204.
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   
205.
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   
206.
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   
207.
A strain of Aspergillus fumigatus Fres., isolated from sugar-beet draffs, synthesizes in vitro four toxic metabolites which have not yet been described in these fungal species. Toxic effects of the most abundant of these metabolites "fumitoxin A" have been studed on chick embryo. Artemia salina larvae, cell cultures, and on mice.  相似文献   
208.
Triiodothyronine injected daily to pregnant rats for the last week of gestation (50 microgram/100 g b.wt) increased the specific activities of 5 acid glycosidases in the fetal forebrain and cerebellum. Cortisone (50 mg/100 g b.wt) administered in the same period had no effect on cerebellum acid hydrolases, but decreased their activity in the forebrain.  相似文献   
209.
Raloff J 《Science news》1978,114(6):92-3, 95
  相似文献   
210.
The construction of molecular models for the human serotransferrin glycans shows that they present one compact section linked to the protein and constituted by the pentasaccharide alpha-Man-(1 leads to 3)-[alpha-Man-(1 leads to 6)]-beta-Man-(1 leads to 4)-beta-GlcNAc-(1 leads to 4)-beta-GlcNAc-(1 leads to)-Asn to which are attached two "antennae" consisting of the trisaccharide alpha-NANA-(2 leads to 6)-beta-Gal-(1 leads to 4)-beta-GlcNAc. The trisaccharide sequence beta-Man-(1 leads to 4)-beta-GlcNAc-(1 leads to 4)-beta-GlcNAc adopts a flat and rigid conformation, stabilised by hydrogen bonds. In contrast, the sequence alpha-NANA-(1 leads to 6)-beta-Gal-(1 leads to 4)-beta-GlcNAc-(1 leads to 2)-alpha-Man takes up a helical configuration. The two "antennae" can be disposed on the pentasaccharide core to give two possible configurations, one Y-shaped and the other T-shaped. In both cases, the general conformation of the glycans is perfectly compatible with their postulated role as a recognition signal.  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