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   1099761篇
  免费   88395篇
  国内免费   1350篇
  1189506篇
  2021年   17511篇
  2020年   12504篇
  2019年   16056篇
  2018年   16515篇
  2017年   15262篇
  2016年   27125篇
  2015年   41665篇
  2014年   49591篇
  2013年   75856篇
  2012年   28537篇
  2011年   14937篇
  2010年   40605篇
  2009年   42888篇
  2008年   15337篇
  2007年   12509篇
  2006年   19452篇
  2005年   20608篇
  2004年   19999篇
  2003年   17751篇
  2002年   15999篇
  2001年   19000篇
  2000年   15860篇
  1999年   20022篇
  1998年   23670篇
  1997年   23421篇
  1996年   23267篇
  1995年   21383篇
  1994年   21284篇
  1993年   20268篇
  1992年   18195篇
  1991年   16633篇
  1990年   15406篇
  1989年   16664篇
  1988年   15179篇
  1987年   14329篇
  1986年   13837篇
  1985年   15969篇
  1984年   17455篇
  1983年   15590篇
  1982年   17877篇
  1981年   17507篇
  1980年   16270篇
  1979年   13363篇
  1978年   13885篇
  1977年   13609篇
  1976年   13036篇
  1975年   11887篇
  1974年   11909篇
  1973年   12423篇
  1972年   10175篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Hoyt  J. C.  Lin  H. -P. P.  Reeves  H. C. 《Current microbiology》1994,28(2):67-69
Isocitrate lyase inEscherichia coli and inAcinetobacter calcoaceticus is phosphorylated when the cells are grown with acetate as the sole carbon source in low-phosphate mineral salts medium containing32P inorganic phosphate. The level of32P incorporation into the enzyme in both microorganisms appears to be constant throughout the entire growth cycle. Further, theresults of immunoblots and rocket immunoelectrophoresis suggest that the amount of isocitrate lyase protein, although at different levels in each microorganism, also remains constant throughout the growth cycle.  相似文献   
992.
Numerous data suggested that the pharmacological and biochemical properties of 5-hydroxytryptamine1A (5-HT1A) receptors exhibit some regional differences in the CNS, notably within the raphe nuclei compared with various forebrain areas (such as the hippocampus). This possibility has been further investigated in the dorsal raphe nucleus and two areas within the hippocampus, the dentate gyrus and the CA1 area, using the quantitative autoradiographic technique. The potencies of 5'-guanylylimidodiphosphate to inhibit the specific binding of 125I-Bolton-Hunter-8-methoxy-2-(N-propyl-N-propylamino)tetralin (125I-BH-8-MeO-N-PAT) to 5-HT1A sites and of N-ethylmaleimide to block these sites irreversibly were identical in the dorsal raphe nucleus and the hippocampal areas in rat brain sections. In contrast, slight but significant differences were noted in the pH dependence and pharmacological properties of 5-HT1A sites labeled by 125I-BH-8-MeO-N-PAT in these three regions. Similarly, heat denaturation experiments and tissue exposure to either phospholipase A2 or the alkylating agent 8-methoxy-2-(N-2'-chloropropyl,N-propyl)aminotetraline revealed regional differences in the properties of 5-HT1A sites. However, in most cases, the observed variations were of greater amplitude between the CA1 area and the dentate gyrus, where 5-HT1A sites are located postsynaptically, than between any one of these areas and the dorsal raphe nucleus where they act as (presynaptic) somatodendritic autoreceptors. These data further support that subtypes of 5-HT1A receptors probably exist in the rat brain, but this heterogeneity seems unrelated to the pre- or post-synaptic location of these receptors.  相似文献   
993.
P. Vargas  T. Cabello 《BioControl》1985,30(3):225-230
Trichogramma cordubensis n. sp. is a parasite ofHeliothis armigera Hb. eggs in cotton crops in western Andalusia. Reproduced onEphestia kuehniella Zeller eggs, it is described morphologically and compared withT. chilonis Ishii andT. evanescens Westwood as both present similarities with this species.T. cordubensis can be distinguished in the male genitalia by the shape of the dorsal expansion of the gonobase and the size, shape and relative position of the median ventral projection. Male antennal setae are longer inT. cordubensis than in the other 2 species. In addition, unlikeT. chilonis andT. evanescens, T. cordubensis is thelytokous at 20°C. in our laboratory, though males and gynandromorphs can be obtained by altering the rearing temperature, this being another difference of this species.  相似文献   
994.
Exploratory behavior and locomotor activity is enhanced in male rat pups (aged 10 to 20 days) whose dams received a chronic dose (1.25 ml/l) of Tween 80 via their drinking water. This enhancement manifests itself during the diurnal period of the day. These data suggest that Tween 80 has an effect on the CNS which could lead to misinterpretation of results in toxicology studies that use this compound as a dosage vehicle.  相似文献   
995.
996.
997.
998.
999.
Tetraspore development has been studied in Chondria tenuissimausing light and electron microscopy. The transformation of tetrasporangialmother cells into mature tetrasporangia involves a series ofstructural changes, especially of dictyosomes and of the nucleus.The youngest stage of tetrasporogenesis consists of a uninucleatetetraspore mother cell with synaptonemal complexes present duringearly prophase of meiosis I. Mitochondria are aggregated aroundthe nucleus, dictyosome activity is low, and proplastids occurin the peripheral cytoplasm. The cleavage furrows are initiatedalmost concomitantly with commencement of meiosis. When thecleavage furrows are initiated, spherical bodies bounded bytwo membranes are found within the cytoplasm; they develop intovacuoles with fibrillar contents (fv1), which increase in sizeduring tetraspore development by fusing with each other andwith Golgi vesicles. The Golgi vesicles and the vacuoles withfibrillar contents (fv1) contribute material to the developingtetraspore wall. During the middle stage of tetraspore formationthe vacuoles with fibrillar contents (fv1) are dominant, dictyosomeactivity increases, as well as the number of plastids and mitochondria;starch formation also increases. Stacked cisternae of the endoplasmicreticulum are found within the peripheral part of the nucleus.The same nuclear structures are also observed in tetrasporangiaof the marine red alga Gastroclonium clavalum. The final stageis characterized by the disappearance of vacuoles with fibrillarcontents (fv1) and of the stacked ER within the nucleus, presenceof straight, large dictyosomes which produce cored vesicles,an abundance of starch grains and by the formation of fullydeveloped chlorqplasts. The cored vesicles contain Thiéry-positivematerial and contribute to the formation of vacuoles with fibrouscontents (fv2) as they are dominant in the tetraspores beforetheir liberation. Rhodophlyla, Chondria, tetrasporogenesis, ultrastructure, Golgi apparatus  相似文献   
1000.
H. Haibach  Y. W. Yesus  J. J. Doggett 《CMAJ》1984,130(9):1165-1166
A 46-year-old man with pentazocine-induced agranulocytosis is described. In previously reported cases of a complete absence of mature neutrophils in the peripheral blood and bone marrow the patients had undergone marrow-depressing treatment with radiation and antineoplastic drugs. This case is unique in that the patient had complete agranulocytosis without predisposing factors.  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