全文获取类型
收费全文 | 559294篇 |
免费 | 67625篇 |
国内免费 | 2642篇 |
出版年
2021年 | 5022篇 |
2018年 | 5544篇 |
2017年 | 4981篇 |
2016年 | 7416篇 |
2015年 | 10783篇 |
2014年 | 12310篇 |
2013年 | 16549篇 |
2012年 | 19182篇 |
2011年 | 18942篇 |
2010年 | 12504篇 |
2009年 | 11507篇 |
2008年 | 16132篇 |
2007年 | 16324篇 |
2006年 | 14958篇 |
2005年 | 14469篇 |
2004年 | 14041篇 |
2003年 | 13450篇 |
2002年 | 12890篇 |
2001年 | 29230篇 |
2000年 | 29188篇 |
1999年 | 23115篇 |
1998年 | 7675篇 |
1997年 | 8027篇 |
1996年 | 7742篇 |
1995年 | 6988篇 |
1994年 | 6995篇 |
1993年 | 6679篇 |
1992年 | 17657篇 |
1991年 | 16782篇 |
1990年 | 16030篇 |
1989年 | 15828篇 |
1988年 | 14219篇 |
1987年 | 13408篇 |
1986年 | 12199篇 |
1985年 | 11939篇 |
1984年 | 9887篇 |
1983年 | 8523篇 |
1982年 | 6565篇 |
1981年 | 5853篇 |
1980年 | 5460篇 |
1979年 | 9253篇 |
1978年 | 7100篇 |
1977年 | 6478篇 |
1976年 | 5947篇 |
1975年 | 6363篇 |
1974年 | 6810篇 |
1973年 | 6661篇 |
1972年 | 5988篇 |
1971年 | 5561篇 |
1970年 | 4644篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Summary A derivative of Zymomonas mobilis ATCC 10988 has been isolated from cells treated with acridine orange. This derived strain, designated CU1, was found to have markedly decreased ethanol production and concomitant glucose utilisation capabilities when grown on high concentrations of glucose. Additionally, it was found that CU1 had altered alcohol dehydrogenase activity and also lacks at least one of the natural plasmids of Z.mobilis, the 3kb species. 相似文献
992.
D. Y. Sorokin E. N. Detkova G. Muyzer 《Extremophiles : life under extreme conditions》2010,14(1):71-77
Evidence on the utilization of simple fatty acids by sulfate-reducing bacteria (SRB) at extremely haloalkaline conditions are practically absent, except for a single case of syntrophy by Desulfonatronum on acetate. Our experiments with sediments from soda lakes of Kulunda Steppe (Altai, Russia) showed sulfide production with sulfate as electron acceptor and propionate and butyrate (but not acetate) as an electron donor at a pH 10–10.5 and a salinity 70–180 g l?1. With propionate as substrate, a highly enriched sulfidogenic culture was obtained in which the main component was identified as a novel representative of the family Syntrophobacteraceae. With butyrate as substrate, a pure SRB culture was isolated which oxidized butyrate and some higher fatty acids incompletely to acetate. The strain represents the first haloalkaliphilic representative of the family Desulfobacteraceae and is described as Desulfobotulus alkaliphilus sp. nov. 相似文献
993.
994.
Identification of an enzymatic activity that hydrolyzes protein-bound ADP-ribose in skeletal muscle 总被引:2,自引:0,他引:2
Y C Chang G Soman D J Graves 《Biochemical and biophysical research communications》1986,139(3):932-939
An enzymatic activity present in high-speed supernatant fluids of rat skeletal muscle was found that catalyzes the release of ADP-ribose from ADP-ribosylated-modified lysozyme. The nature of the product was proved by chromatographic studies and proton nuclear magnetic resonance spectroscopy. The enzyme activity is stimulated by Mg2+, dithioerythritol, and flouride. These results and those published earlier (Soman, G., Mickelson, J.R., Louis, C.F., and Graves, D.J. (1984) Biochem. Biophys. Res. Commun. 120, 973-980) show that ADP-ribosylation is a reversible process in skeletal muscle. 相似文献
995.
996.
Clinical interest in the lipoproteins stems mainly from the association between serum cholesterol concentrations and coronary heart disease. Investigations of lipoproteins should be performed in patients with premature coronary heart disease, with a strong family history of coronary heart disease, or with certain cutaneous stigmata of hyperlipoproteinaemia and when fasting serum samples are seen to be lipaemic. Family studies should be performed in appropriate cases to identify relatives at increased risk of developing coronary heart disease. Patients with conditions known to cause secondary hyperlipoproteinaemia should be investigated if they fall into one of these categories but only after treatment of the underlying condition. Non-specialist laboratories should be able to measure total cholesterol and triglyceride concentrations and high density lipoprotein cholesterol concentrations. Lipoprotein electrophoresis has a limited role in such laboratories and is not necessary as a routine procedure. Specialist laboratories should in addition be able to measure individual lipoproteins and identify apolipoprotein E phenotypes. 相似文献
997.
The evolution of the A family of chorion genes was examined by comparing new protein and DNA sequences from the silkmoths Antheraea pernyi and Bombyx mori with previously known sequences from Antheraea polyphemus. The comparisons indicated that the A family and its major subfamilies are ancient and revealed how parts of the genes corresponding to distinct regions of the protein structure have evolved, both by base substitutions and by segmental reduplications and deletions. 相似文献
998.
999.
D. G. Priest C. D. Veronee M. Mangum J. M. Bednarek M. T. Doig 《Molecular and cellular biochemistry》1982,43(2):81-87
Summary The folylpolyglutamate hydrolase activities of mouse liver, kidney, muscle and brain were examined by incorporation of methylenetetrahydrofolate polyglutamate reaction products into a stable ternary complex with tritiated fluorodeoxyuridylate and L. casei thymidylate synthetase. Complexes were separated electrophoretically on the basis of charge associated with the polyglutamyl moieties to determine distribution of chain lengths throughout the time course of the reaction. Tissue folylpolyglutamate hydrolase activities were allowed to utilize endogenous folylpolyglutamate as substrates by incubating crude tissue extracts at pH 7.4 and pH 4.5. Kidney and muscle contained relatively reactive hydrolases which were capable of generating intermediates of essentially all chain lengths from folylpentaglutamate, the predominant endogenous species. The relatively low activity in brain also gave rise to all possible intermediates. Liver contained a high concentration of methylenetetrahydrofolate but little hydrolase activity. The activity present in liver gave rise to essentially no intermediates but yielded only the monoglutamate form of the cofactor. When purified lysosomal preparations from liver and kidney were allowed to react with synthetic folylpolyglutamates, the same specificity with regard to reaction products was observed as with endogenous substrates. 相似文献
1000.