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   30922篇
  免费   62篇
  国内免费   115篇
系统科学   367篇
丛书文集   683篇
教育与普及   75篇
理论与方法论   105篇
现状及发展   14007篇
研究方法   1292篇
综合类   14171篇
自然研究   399篇
  2013年   157篇
  2012年   433篇
  2011年   871篇
  2010年   177篇
  2009年   172篇
  2008年   529篇
  2007年   609篇
  2006年   576篇
  2005年   591篇
  2004年   555篇
  2003年   581篇
  2002年   510篇
  2001年   1005篇
  2000年   984篇
  1999年   611篇
  1992年   570篇
  1991年   456篇
  1990年   504篇
  1989年   455篇
  1988年   441篇
  1987年   482篇
  1986年   501篇
  1985年   580篇
  1984年   449篇
  1983年   395篇
  1982年   341篇
  1981年   398篇
  1980年   452篇
  1979年   1027篇
  1978年   809篇
  1977年   817篇
  1976年   600篇
  1975年   661篇
  1974年   975篇
  1973年   809篇
  1972年   774篇
  1971年   935篇
  1970年   1229篇
  1969年   976篇
  1968年   825篇
  1967年   929篇
  1966年   784篇
  1965年   556篇
  1959年   339篇
  1958年   539篇
  1957年   376篇
  1956年   338篇
  1955年   291篇
  1954年   289篇
  1948年   196篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
Summary Crude coralloid root extract ofCycas revoluta showed significant antiviral activity against viruses of the tomato plant (PVX, PVY, TMV, TAV and TRSV) when applied 24 h before virus inoculation, or when mixed with different virus inocula before virus inocultion, in hypersensitive and systemic hosts. No such inhibition was observed when extract was applied 24 h after virus inoculation. TAV did not show any inhibitory response in a systemic host.Authors are thankful to Dr S. N. Gupta and Dr (Smt.) K. Shukla for their valuable guidance and providing laboratory facilities and U.G.C. for financial assistance.  相似文献   
932.
Summary Amniotic fluid was obtained from 19-day-old rat fetuses by aspiration. Pooled samples measured at 4 different dilutions demonstrated parallelism with standard rat TSH. It is concluded that rat amniotic fluid has TSH immunoactivity.This work was supported by Hong Kong University Research Grant No. 335/034/5727.The authors wish to acknowledge with thanks the gift of rat TSH RIA kit from Dr A. F. Parlow and the Rat Pituitary Programme of NIAMDD.  相似文献   
933.
J P Kabayo  M Taher  H Barnor 《Experientia》1988,44(9):802-803
Comparison of the survival, fecundity and offspring size of Glossina palpalis palpalis females fed reconstituted oven-dried blood, fresh, frozen/thawed, or reconstituted freeze-dried blood showed that oven-drying at 45 degrees C does not diminish the nutritional quality of blood. The significance of this finding is discussed with a view to optimizing costs and conditions of blood-diet storage and transportation in the context of mass-rearing of tsetse flies.  相似文献   
934.
The need for national HIV databases   总被引:1,自引:0,他引:1  
S P Layne  T G Marr  S A Colgate  J M Hyman  E A Stanley 《Nature》1988,333(6173):511-512
Researchers and public health officials involved in surveying and forecasting the course of the HIV epidemic require complete and unfiltered information from many sources. Governments should respond by establishing national HIV databases.  相似文献   
935.
The efficacy of different hexacyanoferrates(II) in preventing the enteral absorption of 134Cs was studied in piglets. As compared to the controls, oral application of 134Cs together with KFe[Fe(CN)6], NH4Fe[Fe(CN)6], or Fe4[Fe(CN)6]3 resulted in a strong reduction of the 134 Cs-uptake by more than 97%. The decrease in enteral absorption depends on the dose of administered hexacyanoferrate(II), whereas differences between the compounds under study were small. The biological half-life of 134Cs in non-hexacyanoferrate(II) treated piglets was 21.6 +/- 3.3 days (mean +/- SD).  相似文献   
936.
Summary Using two independent techniques, ultracentrifugation in a KBr-gradient, and native pore polyacrylamide gel electrophoresis in combination with [3H]-epoxyfarnesyldiazoacetate photoaffinity labeling, we showed that in the hemolymph ofPeriplaneta americana, and probably also inLeptinotarsa decemlineata JH-III binds to the lipophorin, whereas inLocusta migratoria JH-III binds to a different protein.  相似文献   
937.
Summary Formation of green islands in the host (mustard leaves) beneath the infection-drops containing germinating conidia ofAlternaria brassicicola (Schw.) Wiltsch. has been correlated with the secretion of cytokinins by the pathogen.A. brassicicola also synthesized cytokinins in the liquid synthetic medium. Cytokinins produced in vitro were extracted, and their application on the detached mustard leaves evoked the formation of green islands.  相似文献   
938.
939.
Recognition of myelin-associated glycoprotein by the monoclonal antibody HNK-1   总被引:16,自引:0,他引:16  
R C McGarry  S L Helfand  R H Quarles  J C Roder 《Nature》1983,306(5941):376-378
Myelin-associated glycoprotein (MAG) is a quantitatively minor component in both peripheral and central myelin sheaths that is thought to have a role in cell-cell interactions within the nervous system. We show here that a mouse monoclonal antibody, HNK-1, which is directed against human natural killer cells also recognizes an antigenic determinant of human central and peripheral nervous system white matter by immunoperoxidase staining of tissue sections. Immunoblot analysis of myelin proteins and purified extracted MAG indicates that the antigen recognized is MAG.  相似文献   
940.
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