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   2266篇
  免费   192篇
  国内免费   1篇
  2021年   10篇
  2020年   10篇
  2018年   16篇
  2017年   14篇
  2016年   36篇
  2015年   40篇
  2014年   54篇
  2013年   185篇
  2012年   102篇
  2011年   133篇
  2010年   62篇
  2009年   57篇
  2008年   120篇
  2007年   102篇
  2006年   102篇
  2005年   111篇
  2004年   125篇
  2003年   130篇
  2002年   134篇
  2001年   47篇
  2000年   53篇
  1999年   49篇
  1998年   38篇
  1997年   37篇
  1996年   29篇
  1995年   22篇
  1994年   32篇
  1993年   27篇
  1992年   48篇
  1991年   30篇
  1990年   42篇
  1989年   38篇
  1988年   45篇
  1987年   35篇
  1986年   28篇
  1985年   27篇
  1984年   19篇
  1983年   14篇
  1982年   22篇
  1981年   10篇
  1980年   17篇
  1979年   25篇
  1978年   26篇
  1977年   18篇
  1975年   16篇
  1974年   16篇
  1973年   15篇
  1971年   10篇
  1970年   15篇
  1968年   13篇
排序方式: 共有2459条查询结果,搜索用时 15 毫秒
21.
Change in the localization of the antigen recognized by the proteinuria-inducing monoclonal antibody (MA) 5-1-6 in experimental nephrosis was studied by indirect and biotin-avidin immunofluorescence, and immunoperoxidase at light and electron microscopical levels. The proteinuric state was induced by the administration of the aminonucleoside of puromycin (PAN) or adriamycin. The antigen decreased in quantity and/or its distribution changed with an increase in the amount of protein excreted in both experimental models. Recovery from the alterations observed during the development and proteinuria appeared to occur when PAN-induced proteinuria subsided. This antigenic molecule may thus be essential for maintaining the normal permselectivity of glomerular capillary walls.  相似文献   
22.
A method that makes use of polyacrylamide gel electrophoresis was developed for the analysis of intramolecular disulfide bonds in proteins. Proteins with different numbers of cleaved disulfide bonds are alkylated with iodoacetic acid or iodoacetamide as the first step. The disulfide bonds remaining were reduced by excess dithiothreitol, and the newly generated free sulfhydryl groups were alkylated with the reagent not yet used (iodoacetamide, iodoacetic acid, or vinyl-pyridine) as the second step. This treatment made it possible for lysozyme (Mr, 14,000; 4 disulfides), the N-terminal half-molecule of conalbumin (Mr, 36,000; 6 disulfides), the C-terminal half-molecule of conalbumin (Mr, 40,000; 9 disulfides), and whole conalbumin (Mr, 78,000; 15 disulfides) to be separated by acid-urea polyacrylamide gel electrophoresis into distinct bands depending on the number of disulfide bonds cleaved. The method allowed us to determine the total number of disulfide bonds in native proteins and to assess the cleaved levels of disulfide bonds in partially reduced proteins. Two-step alkylation used in combination with radioautography was especially useful for the analysis of disulfide bonds in proteins synthesized in complex biological systems.  相似文献   
23.
Kikuchi  Yoshiaki  Ishida  Teruo 《Hydrobiologia》1988,167(1):401-407
Preliminary comparisons are presented, of certain diagnostic characters of four species of Canthocamptus, all the specimens examined here being collected from freshwater bodies throughout Japan. The geographical distribution of each species is also discussed.Contribution No. 69 from the Itako Hydrobiological Station, Ibaraki University.  相似文献   
24.
Several physicochemical parameters of ovalbumin were examined at acid pH. The intrinsic viscosity and far UV-CD spectrum at pH 2 did not differ from those at pH 7. But the near UV-CD spectrum, difference absorption spectrum around 250-320 nm, and fluorescence spectrum showed micro-environmental changes around the aromatic amino acid residues in acid solution. The reactivity of one of the four sulfhydryl groups with 2,2'-dithiodipyridine increased at pH below 5. The rate of denaturation by urea and that of surface tension decay were high in the low pH range. We concluded that at low pH (around 2), ovalbumin molecules kept their native globular conformation, but that their chain flexibility increased and they were very susceptible to denaturation. This state might be equivalent to the molten-globule state observed with some globular proteins in acidic region.  相似文献   
25.
The crystal structure of title complex has been analyzed by X-ray diffraction method as a model for elucidating the possible interaction between the phenylalanyl residue of proteins and the N7-protonated or methylated guanine base of nucleic acids. The guanine base is associated with the benzene ring of phenylalanine by stacking interaction, and further connected with the carboxyl group by the formation of a pair of hydrogen bonds. These two interaction modes are suggested to be responsible for the specific recognition of base sequence by protein.  相似文献   
26.
The spontaneous release of [3H] gamma-aminobutyric acid ([3H]GABA) in various areas of rat brain injected with [3H]putrescine was examined using a push-pull perfusion technique. The release in a 25-min perfusate was highest in the caudate-putamen. The effect of high K+ stimulation on the release of [3H]GABA formed from [3H]putrescine was examined in the caudate-putamen. The release was enhanced by high K+ solution in a Ca2+-dependent manner.  相似文献   
27.
The efficient expression in Escherichia coli of the Tn9-derived chloramphenicol acetyltransferase (EC 2.3.1.28) gene fused distal to the promoter and N terminus of the Bacillus subtilis aprA gene was dependent on the initiation of translation from the ribosome-binding site in the aprA gene.  相似文献   
28.
A novel penicillin-binding protein, PBP-2' (Mr about 75,000), is known to be induced in excessively large amount by most beta-lactam compounds in cells of a clinically isolated strain of Staphylococcus aureus, TK784, that is highly resistant to beta-lactams and also most other antibiotics. This protein has very low affinities to most beta-lactam compounds and has been supposed to be the cause of the resistance of the cells to beta-lactams. A 14-kilobase DNA fragment was isolated from the cells that carried the gene encoding this penicillin-binding protein and also a genetically linked marker that is responsible for the resistance to tobramycin. This DNA was cloned on plasmid pACYC184 and was shown to cause both production of PBP-2' and resistance to tobramycin in Escherichia coli cells. However, the formation of PBP-2' in E. coli was only moderate and was independent of normal inducer beta-lactams. The PBP-2' formed in the E. coli cells showed slow kinetics of binding to beta-lactams similar to that of PBP-2' formed in the original S. aureus cells and gave a similar pattern of peptides to the latter when digested with the proteolytic V8 enzyme of S. aureus.  相似文献   
29.
The single-stranded region of the amino acid acceptor stem corresponding to the 3'-end of E. coli tRNAMetf was replaced by ligation of chemically synthesized ribooligonucleotides, in order to change the length of the single-stranded CCA terminus. The chemically synthesized ribooligomers, CCA, ACCA, AACCA and CAACCA, were ligated to nuclease-treated E. coli tRNAMetf, which lacked the ACCA sequence at the 3'-end. The methionine acceptor activities of these modified tRNAs were examined using E. coli methionyl-tRNA synthetase. Ligation of the chemically synthesized pentamer (AACCA) to the acceptor terminus restored the methionine acceptor activity, whereas ligation of the hexamer (CAACCA) or trimer (CCA) to the acceptor terminus did not Modification of the acceptor terminus had no effect on the formylation of accepted methionine.  相似文献   
30.
The membrane potential and the ionic activity gradients of K+and Cl across the surface membrane of cytoplasmic dropletsprepared from Chara australis internodal cells, were measuredin high and low ionic strength bathing solutions using liquidion exchange microelectrodes selective for K+ and Cl.Our results indicate that K+ is close to electrochemical equilibriumwhereas Cl is not. 1 Present address: ICI Japan, Palace Hotel Annex Building, Marunouchi,Tokyo, Japan.  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