全文获取类型
收费全文 | 4471篇 |
免费 | 257篇 |
国内免费 | 3篇 |
专业分类
4731篇 |
出版年
2023年 | 17篇 |
2022年 | 32篇 |
2021年 | 47篇 |
2020年 | 36篇 |
2019年 | 47篇 |
2018年 | 76篇 |
2017年 | 77篇 |
2016年 | 91篇 |
2015年 | 169篇 |
2014年 | 200篇 |
2013年 | 297篇 |
2012年 | 280篇 |
2011年 | 337篇 |
2010年 | 192篇 |
2009年 | 154篇 |
2008年 | 281篇 |
2007年 | 308篇 |
2006年 | 280篇 |
2005年 | 302篇 |
2004年 | 253篇 |
2003年 | 263篇 |
2002年 | 242篇 |
2001年 | 44篇 |
2000年 | 29篇 |
1999年 | 58篇 |
1998年 | 67篇 |
1997年 | 45篇 |
1996年 | 59篇 |
1995年 | 47篇 |
1994年 | 29篇 |
1993年 | 38篇 |
1992年 | 36篇 |
1991年 | 17篇 |
1990年 | 23篇 |
1989年 | 31篇 |
1988年 | 16篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有4731条查询结果,搜索用时 0 毫秒
51.
Minoru Yonezawa Masahiro Takahata Naoko Banzawa Nobuyuki Matsubara Yasuo Watanabe Hirokazu Narita 《Microbiology and immunology》1995,39(4):243-247
Artificial mutations of Gyrase A protein (GyrA) in Escherichia coli by site-directed mutagenesis were generated to analyze quinolone-resistant mechanisms. By genetic analysis of gyrA genes in a gyrA temperature sensitive (Ts) background, exchange of Ser at the NH2-terminal 83rd position of GyrA to Trp, Leu, Phe, Tyr, Ala, Val, and Ile caused bacterial resistance to the quinolones, while exchange to Gly, Asn, Lys, Arg and Asp did not confer resistance. These results indicate that it is the most important for the 83rd amino acid residue to be hydrophobic in expressing the phenotype of resistance to the quinolones. These findings also suggest that the hydroxyl group of Ser would not play a major role in the quinolone-gyrase interaction and Ser83 would not interact directly with other amino acid residues. 相似文献
52.
Masahiro Goto Hiroshi Sumura Kojiro Abe Fumiyuki Nakashio 《Biotechnology Techniques》1995,9(2):101-104
Summary A novel preparation method for surfactant-coated enzymes has been developed using a W/O emulsion. The enzymatic activity of chymotrypsin in isooctane significantly increased with the coating of surfactants. The surfactant-coated chymotrypsin showed a high enzymatic activity for amidation, although powdered chymotrypsin did not show the activity. Further, the coated enzyme showed a remarkably high storage stability. 相似文献
53.
54.
The effect of auxin on the molecular weight (Mw) distributionof cell wall xyloglucans was investigated by gel permeationchromatography using coleoptile segments of Avena sativa L.cv. Victory, and the following results were obtained.
- The water-insoluble hemicellulose (HC-A) mainly consisted ofxyloglucans. Iodine staining method revealed that relativelylarge amounts of xyloglucans were present in the water-solublehemicellulose (HC-B) and water-soluble polysaccharide (WS) fractions.
- IAA did not cause remarkable changes in xyloglucan contentsin the hemicellulose, but significantly increased the xyloglucancontent in the WS fraction.
- IAA substantially decreased theweight-average Mw of HC-A. Thiseffect became apparent within30 min of the incubation period,and was not affected by the0.15 M mannitol or 2% sucrose applied.Hydrogen ions also causeda decrease in the weight-average Mwof HC-A; its effect beingreversible.
- Neither IAA nor hydrogen ions caused any remarkablechangesin the weightaverage Mw of water-soluble xyloglucansin theHC-B.
55.
56.
Growth Regulation of Dark-grown Dwarf Barley Coleoptile by the Endogenous IAA Content 总被引:1,自引:0,他引:1
Growth curves of dark-grown coleoptiles of 11 isogenic coleoptilardwarf strains of barley (Hordeum vulagare L. cv. Akashinriki:uzu, 5, 77, 97, 105, 125, 131, 133, 136, 145 and 148) were simulatedwith a logistic equation and the endogenous IAA contents ofthe barley strains were determined. Growth analysis of the dwarfbarley coleoptiles revealed that the final coleoptile lengthwas correlated with the growth rate on the 2nd day after germination(r=0.897), when the growth rate was about maximum. The endogenousIAA Content of the barley strains, measured fluorometrically,indicated that on the 2nd day, the dwarf strains contained lessendogenous IAA than the normal Strain. The IAA content on the2nd day was correlated to the growth rate on the 2nd day (r=0.907,except for Strain 145) and the final coleoptile length (r=0.933,except for strains 77 and 145). The correlation, however, wasnot significant on the 3rd day. These results suggested thatthe dwarfism of the dark-grown coleoptiles of the barley Strainsexamined is primarily controlled by the endogenous IAA content.
1 Present address: Department of Biology, Faculty of Science,Osaka City University, Osaka 558, Japan. (Received February 1, 1982; Accepted April 13, 1982) 相似文献
57.
58.
Toshihiko Ubuka Masahiro Kinuta Reiko Akagi Shozo Kiguchi Miyabi Azumi 《Analytical biochemistry》1982,126(2):273-277
A procedure for the simultaneous preparation of S-sulfo-l-cysteine and l-alanine 3-sulfinic acid is described. The method is based on the quantitative reaction between sulfite and S-(2-amino-2-carboxyethylsulfonyl)-l-cysteine. The yield was 95% for S-sulfo-l-cysteine and 91% for l-alanine 3-sulfinic acid. The reaction was also applied to the quantitative determination of sulfite in biological materials. In this procedure, sulfite reacts with S-(2-amino-2-carboxyethylsulfonyl)-l-cysteine. Separation of the reaction product, S-sulfo-l-cysteine, is done by ion-exchange fractionation, and it is determined with acid ninhydrin reagent 2 (M. K. Gaitonde, 1967, Biochem. J.104, 627–663). The recovery was 96.8 ± 0.3%. 相似文献
59.
Robert P. Clement Masahiro Kohashi Walter N. Piper 《Archives of biochemistry and biophysics》1982,214(2):657-667
Rat hepatic uroporphyrinogen III cosynthase has been isolated and purified 50-fold with a 36% yield by ammonium sulfate fractionation and sequential chromatography on DEAE-Sephacel and Sephadex G-100SF. Inhibition of uroporphyrinogen III formation with increasing porphobilinogen concentration was observed. Cosynthase was shown to be thermolabile, and a time-dependent loss of enzyme activity during reaction with uroporphyrinogen I synthase and porphobilinogen was observed. The pH optimum for the complete system (synthase and cosynthase) was pH 7.8 in 50 mm Tris-HCl or 50 mm sodium phosphate buffer. Various metals (KCl, NaCl, MgCl2, CaCl2) increased formation of Uroporphyrinogen III. Heavy metals including ZnCl2, CdCl2, and CuCl2 were shown to selectively inhibit cosynthase activity, whereas other metals (HgCl2, PbCl2) were less selective and inhibited both synthase and cosynthase at similar concentrations. 相似文献
60.
A β-N-acetylhexosaminidase [EC 3.2.1.30] has been purified ~98-fold from an extract of the digestive organs of Saxidomus purpuratus by using ammonium sulfate fractionation, and chromatography on Toyopearl HW-50, CM-cellulose, and Sepharose 4B. The purified enzyme, the molecular weight of which was estimated to be ~66,000 by gel filtration, was composed of two sub-units of molecular weight 30,000 as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The purified enzyme had a pH optimum of 3.8 and an optimum temperature of 55°, and its activity was enhanced ~2-fold in the presence of 0.1m sodium chloride. The Michaelis constants toward p-nitrophenyl 2-acetamido-2-deoxy-β-d-glucoside and -galactoside were 1.2 × 10?4 and 1.3 × 10?4m, respectively. 相似文献