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   59269篇
  免费   5610篇
  国内免费   18篇
  64897篇
  2023年   276篇
  2022年   418篇
  2021年   732篇
  2020年   605篇
  2019年   659篇
  2018年   1138篇
  2017年   1018篇
  2016年   1667篇
  2015年   2744篇
  2014年   2633篇
  2013年   3538篇
  2012年   4079篇
  2011年   3703篇
  2010年   2404篇
  2009年   2086篇
  2008年   3016篇
  2007年   2936篇
  2006年   2714篇
  2005年   2528篇
  2004年   2424篇
  2003年   2127篇
  2002年   2074篇
  2001年   1359篇
  2000年   1326篇
  1999年   1232篇
  1998年   725篇
  1997年   639篇
  1996年   645篇
  1995年   622篇
  1994年   563篇
  1993年   588篇
  1992年   1069篇
  1991年   803篇
  1990年   815篇
  1989年   788篇
  1988年   685篇
  1987年   620篇
  1986年   630篇
  1985年   746篇
  1984年   577篇
  1983年   437篇
  1982年   377篇
  1981年   332篇
  1980年   272篇
  1979年   399篇
  1978年   360篇
  1977年   253篇
  1976年   253篇
  1974年   299篇
  1973年   259篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Two cases of right lower lobe oedema are presented as a supposedly very rare sign of left heart failure after myocardial infarction in the presence of acute mitral regurgitation. Causes of unilateral oedema and its clinical relevance in the diagnostic and therapeutic perspectives are discussed, and a review of the literature on this topic is presented.  相似文献   
52.
53.
54.
55.
56.
A method is described for the histochemical detection of horseradish peroxidase in Paraplast Plus embedded brain sections. The procedure uses 150-micron-thick Vibratome-cut slices of glutaraldehyde-paraformaldehyde-fixed brain tissue. Tetramethylbenzidine stabilized by diaminobenzidine/cobalt/H2O2 is used as chromogen. The Vibratome-cut slices are dehydrated through a graded series of acetone, cleared in toluol and flat-embedded in Paraplast Plus embedding medium. Serial sections can be cut as thin as 5-7 micron. The method is universal in its application and permits optimal visualization of labeled neurons with great morphological detail at the light-microscopic level.  相似文献   
57.
Symmetrical dialkyl carbonates and dibenzyl carbonates reacted with various nucleophiles in the presence of Candida antarctica lipase B in organic solvents. For example, reaction of dibutyl and dibenzyl carbonate with an alcohol gave a mixture of the mono- and disubstituted products. Aminolysis, however, afforded only the carbamates, without subsequent reaction to the ureum derivatives. The reaction rates were rather low compared with carboxylic esters; the reactivity increased in the order dimethyl相似文献   
58.
Activity-based protein profiling represents a powerful methodology to probe the activity state of enzymes under various physiological conditions. Here we present the development of a para-nitrophenol phosphonate activity-based probe with structural similarities to the potent agrochemical paraoxon. We demonstrate that this probes labels distinct serine hydrolases with the carboxylesterase CXE12 as the predominant target in Arabidopsis thaliana. The designed probe features a distinct labeling pattern and therefore represents a promising chemical tool to investigate physiological roles of selected serine hydrolases such as CXE12 in plant biology.  相似文献   
59.
Abstract Porcine Escherichia coli strains isolated from cases fo postweaning diarrhea or edema disease were analysed for the presence of fedA , the major subunit gene of F107 fimbriae. The E. coli isolates were known to contain colonisation factor '8813', or to express F107, 2134P or other fimbriae, different from F4, F5, F6, and F41. PCR with fedA -specific primers, restriction enzyme digestion of the PCR product, and nucleotide sequence analysis demonstrated that 2134P pili, colonisation factor '8813' and fimbriae identified on Australian strains of the O141 serotype belong to one family of F107 fimbrial antigens.  相似文献   
60.
The 10-subunit RNA exosome is involved in a large number of diverse RNA processing and degradation events in eukaryotes. These reactions are carried out by the single catalytic subunit, Rrp44p/Dis3p, which is composed of three parts that are conserved throughout eukaryotes. The exosome is named for the 3′ to 5′ exoribonuclease activity provided by a large C-terminal region of the Rrp44p subunit that resembles other exoribonucleases. Rrp44p also contains an endoribonuclease domain. Finally, the very N-terminus of Rrp44p contains three Cys residues (CR3 motif) that are conserved in many eukaryotes but have no known function. These three conserved Cys residues cluster with a previously unrecognized conserved His residue in what resembles a metal-ion-binding site. Genetic and biochemical data show that this CR3 motif affects both endo- and exonuclease activity in vivo and both the nuclear and cytoplasmic exosome, as well as the ability of Rrp44p to associate with the other exosome subunits. These data provide the first direct evidence that the exosome-Rrp44p interaction is functionally important and also provides a molecular explanation for the functional defects when the conserved Cys residues are mutated.  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