全文获取类型
收费全文 | 322000篇 |
免费 | 21686篇 |
国内免费 | 61篇 |
出版年
2021年 | 2689篇 |
2020年 | 2211篇 |
2019年 | 2516篇 |
2018年 | 5457篇 |
2017年 | 5159篇 |
2016年 | 6655篇 |
2015年 | 7634篇 |
2014年 | 8923篇 |
2013年 | 12399篇 |
2012年 | 14898篇 |
2011年 | 14963篇 |
2010年 | 10110篇 |
2009年 | 8126篇 |
2008年 | 12858篇 |
2007年 | 13120篇 |
2006年 | 12347篇 |
2005年 | 11512篇 |
2004年 | 11331篇 |
2003年 | 10730篇 |
2002年 | 10342篇 |
2001年 | 11207篇 |
2000年 | 10821篇 |
1999年 | 8602篇 |
1998年 | 2826篇 |
1997年 | 2509篇 |
1996年 | 2314篇 |
1995年 | 2155篇 |
1992年 | 6596篇 |
1991年 | 6727篇 |
1990年 | 6582篇 |
1989年 | 6467篇 |
1988年 | 6022篇 |
1987年 | 5561篇 |
1986年 | 5091篇 |
1985年 | 5379篇 |
1984年 | 4316篇 |
1983年 | 3537篇 |
1982年 | 2416篇 |
1979年 | 3882篇 |
1978年 | 2993篇 |
1977年 | 2751篇 |
1976年 | 2693篇 |
1975年 | 3220篇 |
1974年 | 3533篇 |
1973年 | 3509篇 |
1972年 | 3057篇 |
1971年 | 2916篇 |
1970年 | 2494篇 |
1969年 | 2424篇 |
1968年 | 2279篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
E. Molina Grima J. A. Sánchez Pérez F. García Camacho F. G. Acién Fernández J. M. Fernández Sevilla F. Valdés Sanz 《Biotechnology letters》1994,16(10):1035-1040
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. 相似文献
103.
Initiation of the extrinsic pathway of coagulation. Association of factor VIIa with a cell line expressing tissue factor 总被引:3,自引:0,他引:3
We have examined initial assembly of the extrinsic pathway of blood coagulation on cell surfaces with radiolabeled human factor VIIa and a human fetal lung cell line possessing abundant functional tissue factor activity. Binding of factor VIIa to these cells was observed and was time- and temperature-dependent. Binding of factor VIIa was quantitatively equivalent at 37 and 6 degrees C, although the kinetics of binding differed. The radiolabeled ligand bound by the cell was indistinguishable by sodium dodecyl sulfate-polyacrylamide gel analysis from the factor VIIa offered. Factor VIIa binding was influenced by calcium ions. The binding appears to involve at least two classes of calcium-dependent binding sites. Optimal binding occurred at 2 mM calcium for both classes of sites, and there was inhibition of binding to the high affinity sites at higher calcium. Association of factor VIIa was specific, saturable, had a Kd of 123 +/- 37 pm, and factor VIIa interacted with about 100,000 binding sites per cell. Once established, specific binding was rapidly reversible. Direct cellular binding of human factor X also was observed and was calcium, time- and temperature-dependent. Factor X binding was specific and saturable with half-maximal binding at 87.6 +/- 27.4 nM to 6.03 +/- 1.03 X 10(6) sites per cell. Specific high affinity binding of factor VIIa correlated with generation of factor Xa. A direct linear relationship was observed at low factor VIIa binding; however, at higher bound factor VIIa, the relationship was nonstoichiometric, i.e. less factor Xa was formed per mole of factor VIIa. Expression of specific binding sites for factors VIIa and X provides further substantiation for the molecular assembly hypothesized to initiate the extrinsic coagulation protease cascade on cells. 相似文献
104.
105.
Conformational similarity among amino acid residues, a property derived by analysing (φ, ψ)-probability distributions of 20 proteinous amino acids from 38 different globular proteins, is used to arrive at a set of six ‘obligatory’ amino acids of primitive proteins. The amino acids Ser, Val, Leu, Asp, Gly and Pro have been argued to be ‘obligatory’ and to represent, conformationally, the remaining amino acids. The reasons for consideration of these six residues as ‘obligatory’ are discussed. Methods to check the validity of our proposition are suggested. 相似文献
106.
107.
108.
109.
Marco Filice Marzia Marciello Lorena Betancor Alfonso V. Carrascosa Jose M. Guisan Gloria Fernandez‐Lorente 《Biotechnology progress》2011,27(4):961-968
Rhizomucor miehei lipase (RML) is greatly hyperactivated (around 20‐ to 25‐fold toward small substrates) in the presence of sucrose laurate. Hyperactivation appears to be an intramolecular process because it is very similar for soluble enzymes and covalently immobilized derivatives. The hyperactivated enzyme was immobilized (in the presence of sucrose laurate) on cyanogen bromide‐activated Sepharose (very mild covalent immobilization through the amino terminal residue), on glyoxyl Sepharose (intense multipoint covalent immobilization through the region with the highest amount of Lys residues), and on different anion exchangers (by multipoint anionic exchange through the region with the highest density of negative charges). Covalent immobilization does not promote the fixation of the hyperactivated enzyme, but immobilization on Sepharose Q retains the hyperactivated enzyme even in the absence of a detergent. The hydrolysis of fish oils by these hyperactivated enzyme derivatives was sevenfold faster than by covalently immobilized derivatives and three and a half times faster than by the enzyme hyperactivated on octyl‐Sepharose. The open structure of the hyperactivated lipase is fairly exposed to the medium, and no steric hindrance should interfere with the hydrolysis of large substrates. These new hyperactivated derivatives seem to be more suitable for hydrolysis of oils by RML immobilized inside porous supports. In addition, the hyperactivated derivatives are fairly stable against heat and organic cosolvents. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011 相似文献
110.
Ia I Serkiz A I Lipskaia L B Pinchuk V V Trishin Iu F Kataevski? G N Koval' 《Radiobiologiia》1991,31(5):629-634
Irradiation conditions in which laboratory animals were kept in experimental laboratories of Chernobyl and Kiev after the accident at the Chernobyl A.P.S. are described. The data are presented on the spectral structural and activity of radionuclides in the diet as well as in the organs and tissues of the animals. The radiation loads have been estimated with regard to an external gamma component and the internal one contributed by the incorporated radionuclides. It has been shown that radiation doses received by the animals during their lifetime due to these contributions do not exceed units of cGy. 相似文献