全文获取类型
收费全文 | 10631篇 |
免费 | 658篇 |
国内免费 | 112篇 |
出版年
2023年 | 91篇 |
2022年 | 105篇 |
2021年 | 232篇 |
2020年 | 179篇 |
2019年 | 185篇 |
2018年 | 402篇 |
2017年 | 335篇 |
2016年 | 435篇 |
2015年 | 383篇 |
2014年 | 472篇 |
2013年 | 728篇 |
2012年 | 804篇 |
2011年 | 808篇 |
2010年 | 509篇 |
2009年 | 366篇 |
2008年 | 429篇 |
2007年 | 383篇 |
2006年 | 420篇 |
2005年 | 252篇 |
2004年 | 244篇 |
2003年 | 228篇 |
2002年 | 204篇 |
2001年 | 177篇 |
2000年 | 185篇 |
1999年 | 168篇 |
1998年 | 101篇 |
1997年 | 103篇 |
1996年 | 94篇 |
1995年 | 109篇 |
1994年 | 87篇 |
1993年 | 76篇 |
1992年 | 96篇 |
1991年 | 83篇 |
1990年 | 64篇 |
1989年 | 70篇 |
1988年 | 65篇 |
1987年 | 76篇 |
1986年 | 66篇 |
1985年 | 76篇 |
1984年 | 72篇 |
1983年 | 73篇 |
1982年 | 79篇 |
1981年 | 76篇 |
1980年 | 63篇 |
1979年 | 73篇 |
1978年 | 63篇 |
1977年 | 65篇 |
1974年 | 67篇 |
1973年 | 59篇 |
1969年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
2.
3.
4.
The production of L-lysine fromDL-α-amino-ε-caprolactam (DL-ACL) by new strains producingL-α-amino-ε-caprolactamase and aminocaprolactam racemase is described. Optimal conditions for hydrolysis ofL-ACL byCryptococcus sp. and for racemization of ACL by cells of a strain isolated in nature and identified asPseudomonas sp. were determined. Synthesis ofL-α-amino-ε-caprolactamase is induced byDL-ACL orL-lysine with the same effectivity. A positive effect of phosphates (potassium salts) on reduction of the induction lag was
detected, the synthesis of this enzyme was found to be repressed by glucose and some possibilities of the reversion of this
repressive effect were demonstrated. Under conditions optimal for the production of both enzymes a quantitative theoretical
conversion of 10 % aqueousDL-ACL toL-lysine by a mixture of native cells in a mass ratio of 1: 2 (producer of ACL-hydrolase to producer of ACL-racemase) occurred
in 8 h at 40 °C and pH 8.0 相似文献
5.
Effect of precursors on biosynthesis of monensins A and B 总被引:1,自引:0,他引:1
Precursors of monensins (acetate, propionate, butyrate, isobutyrate) affect the total production and the relative proportion of monensins A and B. Addition of propionate into the fermentation medium causes a prevalence of monensin B whereas butyrate and isobutyrate stimulate the production of monensin A and suppress the production of monensin B. 相似文献
6.
7.
Barbora Straková Michail Rovatsos Lukáš Kubička Lukáš Kratochvíl 《BioEssays : news and reviews in molecular, cellular and developmental biology》2020,42(10):2000050
Frequent independent origins of environmental sex determination (ESD) are assumed within amniotes. However, the phylogenetic distribution of sex-determining modes suggests that ESD is likely very ancient and may be homologous across ESD groups. Sex chromosomes are demonstrated to be old and stable in endothermic (mammals and birds) and many ectothermic (non-avian reptiles) lineages, but they are mostly non-homologous between individual amniote lineages. The phylogenetic pattern may be explained by ancestral ESD with multiple transitions to later evolutionary stable genotypic sex determination. It is pointed out here that amniote ESD shares several key aspects with sequential hermaphroditism of fishes such as a lack of sex differences in genomes, biased population sex ratios, and potentially also molecular mechanism related to general stress responses. Here, it is speculated that ESD evolves via a heterochronic shift of the sensitive period of sex change from the adult to the embryonic stage in a hermaphroditic amniote ancestor. Also see the video abstract here https://youtu.be/q2mjtlCefu4 . 相似文献
8.
Kai-For Mo 《Carbohydrate research》2009,344(4):439-1494
The synthesis of laminarahexaose is described. NMR studies of several of the intermediates leading to the β-1,3-glucan show anomalously small coupling constants for some of the C-1 hydrogens. An X-ray structure for the protected hexasaccharide shows that the small coupling constants are due to some of the glucopyranose rings adopting a twist-boat conformation. The X-ray studies also explain other unexpected NMR observations. 相似文献
9.
10.
Jaroslav Dršata Martin Beránek VladimÍr Palička 《Journal of enzyme inhibition and medicinal chemistry》2013,28(1):31-36
Incubation of 50 mM d -glucose with aspartate aminotransferase (AST, EC 2.6.1.1) preparations (purified pig heart enzyme or a rat liver 20,000 × g supernatant) at 25°C had no effect on enzyme activity. 50 mM d -fructose or d -ribose gradually inhibited pig heart AST under the same conditions to zero activity after 14 days. 50 mM dl -glyceraldehyde decreased enzyme activity to zero after 6 days of incubation. The inhibition of pig heart AST by 50 mM d -fructose or d -ribose was marked even at a temperature of 4°C but it was less pronounced than at 25°C. There was no effect of 0.5 mM 2-oxoglutarate on AST activity during incubation, while the presence of 25 mM l -aspartate decreased it rapidly. 0.5 mM 2-oxoglutarate partly prevented inhibition of AST by d -ribose or d -fructose, while an analogous experiment with 25 mM aspartate resulted in a rapid decline similar to that in the absence of sugars. 相似文献