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   35167篇
  免费   92篇
  国内免费   86篇
系统科学   298篇
丛书文集   686篇
教育与普及   72篇
理论与方法论   130篇
现状及发展   15993篇
研究方法   1274篇
综合类   16331篇
自然研究   561篇
  2013年   195篇
  2012年   403篇
  2011年   987篇
  2010年   158篇
  2008年   490篇
  2007年   547篇
  2006年   594篇
  2005年   586篇
  2004年   677篇
  2003年   566篇
  2002年   496篇
  2001年   997篇
  2000年   977篇
  1999年   614篇
  1992年   602篇
  1991年   502篇
  1990年   544篇
  1989年   496篇
  1988年   502篇
  1987年   523篇
  1986年   534篇
  1985年   688篇
  1984年   518篇
  1983年   469篇
  1982年   398篇
  1981年   404篇
  1980年   505篇
  1979年   1113篇
  1978年   920篇
  1977年   887篇
  1976年   728篇
  1975年   835篇
  1974年   1100篇
  1973年   928篇
  1972年   966篇
  1971年   1136篇
  1970年   1485篇
  1969年   1152篇
  1968年   1073篇
  1967年   1097篇
  1966年   933篇
  1965年   730篇
  1964年   218篇
  1959年   425篇
  1958年   685篇
  1957年   507篇
  1956年   430篇
  1955年   400篇
  1954年   409篇
  1948年   284篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Summary A novel sesquiterpene lactone, 9--hydroxyparthenolide (1) was isolated from a chloroform extract ofAnvillea garcini that was collected in Iran. The structure of1 was assigned on the basis of high field NMR decoupling experiments and other spectroscopic evidence. This -methylene lactone has shown significant activity in both the 9KB cell culture and P388 mouse leukemia test systems.The authors acknowledge the support of contract No. N01-CM-97296 from the National Cancer Institute and the use of the Purdue University Biochemical Magnetic Resonance Laboratory (NIH grant No. RR01077). This is paper 16 in the series Potential Antitumor Agents.  相似文献   
152.
Summary A needle type of colloid osmometer has been devised with special attachments which made it useable with 3-l samples. It has been used in oncometry of fresh water teleosts to give the following results: 5.1±1.0 mm Hg for goldfish, 5.2±0.71 mm Hg for carp, and 14.3±0.75 mm Hg for eel.This study was supported in part by Research Grant 387036 from the Ministry of Education of Japan.invited to National Institute of Physiological Sciences, Okazaki, Japan.  相似文献   
153.
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   
154.
155.
156.
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   
157.
Summary There are wide individual variations in the thermal stability of human plasma dopamine--hydroxylase (DBH). Thermal stability variations have proven of value in biochemical genetic studies of many enzymes. The development of DBH thermolability depends on the exposure of plasma to oxygen. This observation may help to elucidate the biochemical basis of the genetic regulation of DBH.This work was supported in part by NIH grants HL 17487 and NS 11014.  相似文献   
158.
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   
159.
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   
160.
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