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   26352篇
  免费   51篇
  国内免费   92篇
系统科学   189篇
丛书文集   312篇
教育与普及   77篇
理论与方法论   132篇
现状及发展   11086篇
研究方法   1199篇
综合类   12999篇
自然研究   501篇
  2013年   167篇
  2012年   410篇
  2011年   940篇
  2010年   157篇
  2009年   155篇
  2008年   444篇
  2007年   521篇
  2006年   527篇
  2005年   532篇
  2004年   592篇
  2003年   496篇
  2002年   485篇
  2001年   792篇
  2000年   778篇
  1999年   521篇
  1992年   475篇
  1991年   380篇
  1990年   417篇
  1989年   395篇
  1988年   368篇
  1987年   416篇
  1986年   425篇
  1985年   521篇
  1984年   418篇
  1983年   336篇
  1982年   274篇
  1981年   285篇
  1980年   355篇
  1979年   842篇
  1978年   647篇
  1977年   626篇
  1976年   506篇
  1975年   538篇
  1974年   767篇
  1973年   663篇
  1972年   632篇
  1971年   801篇
  1970年   1087篇
  1969年   772篇
  1968年   661篇
  1967年   765篇
  1966年   701篇
  1965年   485篇
  1959年   261篇
  1958年   454篇
  1957年   305篇
  1956年   295篇
  1955年   232篇
  1954年   218篇
  1948年   234篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
181.
Summary The influence of somatostatin on tumor cell growth was studied in vivo in mice (sarcoma 180 ascites tumor and Lewis lung tumor) and in vitro on nontransformed and polyoma-transformed cell lines. 4 or 20 g/100 g of cyclic somatostatin and 4 g/100 g of linear protamin Zn-bound somatostatin were injected s.c. twice daily in the in vivo study. Cyclic somatostatin (1, 4 or 10 g/ml) was added twice daily to the cell cultures. Somatostatin administration influenced neither the survival of animals nor the growth rate of cultured cell lines. *** DIRECT SUPPORT *** A2025117 00011  相似文献   
182.
183.
Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner.  相似文献   
184.
    
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   
185.
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   
186.
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   
187.
Summary Aldosterone (15 g BID) and methylprednisolone (8 mg QD) administration to female guinea-pigs augmented both the total and the specific activity of NaK-ATPase but not the activity of adenylate cyclase in the cardiac sarcolemma. The rise in NaK-ATPase was due to increase in the number of enzyme molecules; catalytic activity and ouabain-sensitivity of individual molecules did not change.Acknowledgments. This work was supported by grant 1 R01 HL16611 from the National Heart and Lung Institute of the National Institutes of Health, United States Public Health Service. I thank Mr Kooil Kang for his excellent technical assistance.  相似文献   
188.
Summary Mouse foetuses were treated by Thalidomide on days 11–12 in order to verify whether the drug would induce blood abnormalities leading to circulatory troubles. About 18% of the treated foetuses showed both severe limb haemorrhages on day 14, and obvious alterations of the nucleated red blood cells of vitelline origin. These blood abnormalities, occurring suddenly during the well-known critical stage of foetal development, could be responsible for circulatory blocks leading to necrosis.  相似文献   
189.
    
Summary Unambiguous assignment of the1H-NMR. resonances due to the hydrogen atoms in the -position of homoserine indicates that the hydrogen which is exchanged and removed in the cystathionine--synthase catalyzed reactions holds the pro-R configuration.  相似文献   
190.
Summary RIA of ecdysones are made on nymphal extracts ofPisaura mirabilis during the intermoulting cycle. The hormone level is low during exuviation and the greatest part of the intermoulting period but increases notably before and after ecdysis. The main hormonal peak or pre-ecdysial peak is due to -ecdysone, characterized by combined TLC/RIA.Acknowledgment. We wish to thank Dr M. Hirn for his help during the manipulations and J. Britton who has translated the text into English.  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