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   53893篇
  免费   264篇
  国内免费   559篇
系统科学   1264篇
丛书文集   102篇
教育与普及   301篇
理论与方法论   552篇
现状及发展   30623篇
研究方法   789篇
综合类   18895篇
自然研究   2190篇
  2013年   824篇
  2012年   680篇
  2011年   2783篇
  2010年   473篇
  2009年   618篇
  2008年   927篇
  2007年   1004篇
  2006年   1111篇
  2005年   1318篇
  2004年   2488篇
  2003年   1997篇
  2002年   1705篇
  2001年   1181篇
  2000年   739篇
  1999年   864篇
  1998年   648篇
  1997年   778篇
  1996年   539篇
  1994年   692篇
  1993年   692篇
  1992年   814篇
  1991年   697篇
  1990年   760篇
  1989年   610篇
  1988年   591篇
  1987年   600篇
  1986年   668篇
  1985年   821篇
  1984年   730篇
  1983年   623篇
  1982年   770篇
  1981年   807篇
  1980年   883篇
  1979年   1269篇
  1978年   1160篇
  1977年   1149篇
  1976年   1041篇
  1975年   1020篇
  1974年   847篇
  1973年   1113篇
  1972年   1156篇
  1971年   1187篇
  1970年   1283篇
  1969年   1134篇
  1968年   1092篇
  1967年   965篇
  1966年   849篇
  1965年   670篇
  1964年   489篇
  1958年   503篇
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
621.
High-frequency generalised transduction by bacteriophage T4   总被引:30,自引:0,他引:30  
Wilson GG  Young KY  Edlin GJ  Konigsberg W 《Nature》1979,280(5717):80-82
  相似文献   
622.
Summary The effects of dosage and of cadmium pretreatment on the binding of cadmium in rat bile were studied. With increasing dose a higher cumulative biliary excretion of Cd was observed and a higher percentage of the Cd was excreted in a low-molecular-weight form. On the other hand, after cadmium pretreatment, a decrease in the cumulative biliary excretion of cadmium was observed but a greater percentage of that excreted into the bile was bound to high molecular weight compounds.  相似文献   
623.
Summary Cells from a murine fibrosarcoma (FSa) have been grown in vitro as multicell tumor spheroids (MTS). The growth rate of these MTS was determined. Follwing selected periods of growth, MTS were made into a single cell suspension and separated on linear density gradients of Renografin. While only 1 population of cells was separated from small spheroids (400 m diameter), at least 3 subpopulations of tumor cells were separated and isolated from large spheroids (800 m in diameter).This investigation was supported in part by grants numbered CA-18628 and CA-06294, awarded by the National Cancer Institute, DHEW.  相似文献   
624.
Summary The substrate- and inhibitor-related characteristics of monoamine oxidase (MAO) were studied on chick brain mitochondria. It was found that neither 5-hydroxytryptamine nor -phenylethylamine is the specific substrate for type A and type B MAO in chick brain.  相似文献   
625.
Summary Trans-4-hydroxy-3-methoxycinnamic acid (ferulic acid, FA) antagonized the effect of exogenous androgens on the ventral prostate (VP) in castrated rats as well as the effect of endogenous androgens in intact rats. FA, however, had no effect on the seminal vesicles (SV) and levator ani muscle (LAM), nor oestrogenic effect in female rats and mice. FA did not antagonize the receptor binding of testosterone nor inhibit the conversion of testosterone into 5-dihydrotestosterone (DHT).Supported in part by the project fund (grant 53-403) of Kawasaki Medical School.The authors would like to thank the Central Laboratory, Sankyo Pharmaceutical Co., Tokyo, for supplying 19-nortestosterone-17-ferulate.  相似文献   
626.
Summary Serum peptides containing classical anaphylatoxin (CAT) produce marked chemotactic orientation of human neutrophil granulocytes without modifying cell attachment to the substratum. Furthermore gradients of adhesion produced with gammaglobulins fail to induce morphological orientation of neutrophils. The results suggest that chemotaxis is not a special case of haptotaxis.The excellent technical assistance of Miss M. Schuster, Mrs A. Damschen and Mr M. Arnold is gratefully acknowledged. This work was supported by the Swiss National Science Foundation and the Sandoz-Stiftung zur Förderung der Medizinisch-Biologischen Forschung.  相似文献   
627.
Summary In 10 human subjects plasma dopamine--hydroxylase activity was found in the adrenal vein blood to be as high as in the periphery of the circulation. Adrenaline concentration in the adrenal vein blood was in the mean 170 times, noradrenaline concentration 11 times and dopamine concentration little higher than levels in the periphery.This study was supported by the Deutsche Forschungsgemeinschaft.  相似文献   
628.
Summary The immunoadjuvant activity of muramyl dipeptide seems to be critically dependent on the type of substitution of the -carboxyl group of the D-isoglutamine residue. Moreover the nonapeptide L-Ala-D-isoGlu-L-Lys-D-Ala-(Gly)5-OME also shows a definite effect.  相似文献   
629.
Summary Radiochemical precursor compounds for neurotransmitters were incubated withLimulus ventral nerve photoreceptor preparations. Octopamine was preferentially synthesized by a photoreceptor rich fraction of the nerve, acetylcholine was made by a photoreceptor poor fraction, and -aminobutyric acid was made about equally well in both fractions. The possibility that the ventral nerve photoreceptor cells serve a neurosecretory function in the adultLimulus is discussed.From the Neurobiology Course, Marine Biological Laboratory, Woods Hole, Mass. The Neurobiology Course is supported by grants from the Grass, Sloan and Sandoz Foundation and from Merck, Sharp and Dohme Research Institute.  相似文献   
630.
Bodmer WF 《Nature》1979,277(5697):509-510
  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