全文获取类型
收费全文 | 13317篇 |
免费 | 991篇 |
国内免费 | 31篇 |
出版年
2023年 | 102篇 |
2022年 | 81篇 |
2021年 | 181篇 |
2020年 | 148篇 |
2019年 | 162篇 |
2018年 | 468篇 |
2017年 | 401篇 |
2016年 | 486篇 |
2015年 | 581篇 |
2014年 | 657篇 |
2013年 | 970篇 |
2012年 | 1087篇 |
2011年 | 1082篇 |
2010年 | 697篇 |
2009年 | 500篇 |
2008年 | 605篇 |
2007年 | 571篇 |
2006年 | 605篇 |
2005年 | 457篇 |
2004年 | 406篇 |
2003年 | 409篇 |
2002年 | 351篇 |
2001年 | 200篇 |
2000年 | 182篇 |
1999年 | 183篇 |
1998年 | 108篇 |
1997年 | 100篇 |
1996年 | 101篇 |
1995年 | 101篇 |
1994年 | 80篇 |
1993年 | 64篇 |
1992年 | 95篇 |
1991年 | 93篇 |
1990年 | 86篇 |
1989年 | 102篇 |
1988年 | 91篇 |
1987年 | 97篇 |
1986年 | 88篇 |
1985年 | 93篇 |
1984年 | 75篇 |
1983年 | 75篇 |
1982年 | 68篇 |
1981年 | 75篇 |
1980年 | 55篇 |
1979年 | 84篇 |
1978年 | 70篇 |
1977年 | 72篇 |
1975年 | 53篇 |
1974年 | 70篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
33.
E. Janchen A. Ginzberger K. Redinger Elise Hofmann B. Schussnig Fr. Knoll 《Plant Systematics and Evolution》1937,86(3):227-238
Ohne Zusammenfassung 相似文献
34.
35.
36.
37.
Substrate particle size affects pit building decision and pit size in the antlion larvae Euroleon nostras (Neuroptera: Myrmeleontidae) 总被引:2,自引:0,他引:2
Abstract. The larvae of the antlion Euroleon nostras are pit-builders, constructing pitfall traps in loose sand. The number of pits and the pit diameter are recorded when larvae are kept in substrates with different particle sizes. The most convenient pit-building sand fractions are two fractions with fine sand (≤ 0.23 mm; 0.23–0.54 mm). The largest pits are constructed in sand with a particle size of 0.23–0.54 mm. In this sand fraction, larvae of all three instars most readily build pits. No pits are constructed in sand with a particle size greater than 1.54 mm. First- and second-instar larvae avoid building pits in substrates of particle size 1–1.54 mm, but third-instar larvae construct pits in this sand fraction. It is assumed that the antlion is capable of distinguishing between substrate types and this hypothesis is tested by giving larvae the choice of building a pit in one of four particle-size fractions. Larvae of all three instars prefer to build pits in the fraction with a particle size of 0.23–0.54 mm. Only third-instar larvae build pits in all four fractions, but only occasionally in the coarser fraction. 相似文献
38.
Jaroslav Votruba Jarmila Pazlarová Milada Dvořáková Kalju Vanatalu Libuše Váchová Marie Strnadová Helena Kučerová Jiří Chaloupka 《Applied microbiology and biotechnology》1987,26(4):373-377
Summary A mathematical model was formulated to describe the kinetics and stoichiometry of growth and proteinase production in Bacillus megaterium. Synthesis of the extracellular proteinase in a batch culture is repressed by amino acids. The specific rate of formation of the enzyme (r
E) can be described by the formula {ie373-1}, where k
2 and k
3 stand for the non-repressible and repressible part of enzyme synthesis respectively, k
S
2 is a repression coefficient and S
2 indicates the concentration of amono acids; the values of k
2 and k
S
2 depend on the composition of the mixture of amino acids. Even in a high concentration, a single amino acid is less effective than a mixture of amino acids. The dependence of the proteinase repression on the concentration of an external amino acid (leucine) follows the same course as its rate of incorporation into proteins, approaching saturation at concentrations higher than 50 M (half saturation approximately 10 M). However, the total uptake of leucine did not exhibit any saturation even at 500 M external concentration.Symbols
X
biomass concentration, g/l
-
E
proteinase concentration, unit/l
-
t
time, h
-
S
1
concentration of glucose, g/l
-
S
2
concentration of amino acids, g/l
-
specific growth rate, l/h
-
rE
specific rate of enzyme production, unit/g/h
-
k
1
growth kinetic constant, l/h
-
k
2
product formation kinetic constant (for non-repressible part of enzyme synthesis), unit/g
-
k
3
product formation kinetic constant (for repressible portion of enzyme synthesis), unit/g
-
k
S
1
saturation constant, g/l
-
k
S
2
repression coefficient for a certain amino acid or amino acids mixture, g/l 相似文献
39.
The crystal structure of the beta-lactamase of Streptomyces albus G at 0.3 nm resolution. 总被引:10,自引:3,他引:7
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
O Dideberg P Charlier J P Wéry P Dehottay J Dusart T Erpicum J M Frère J M Ghuysen 《The Biochemical journal》1987,245(3):911-913
The crystal structure of the beta-lactamase of Streptomyces albus G has been solved at 0.3 nm resolution by X-ray-diffraction methods. The enzyme is a typical two-domain protein. One domain consists of five alpha-helices, and the other is five-stranded beta-sheet with alpha-helices on both sides of the sheet. The active-site serine residue (Ser-48) is within a cleft located between the two domains. 相似文献
40.