全文获取类型
收费全文 | 3220篇 |
免费 | 243篇 |
国内免费 | 1篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 38篇 |
2021年 | 78篇 |
2020年 | 59篇 |
2019年 | 58篇 |
2018年 | 95篇 |
2017年 | 75篇 |
2016年 | 100篇 |
2015年 | 182篇 |
2014年 | 180篇 |
2013年 | 222篇 |
2012年 | 292篇 |
2011年 | 288篇 |
2010年 | 163篇 |
2009年 | 168篇 |
2008年 | 221篇 |
2007年 | 225篇 |
2006年 | 169篇 |
2005年 | 151篇 |
2004年 | 140篇 |
2003年 | 135篇 |
2002年 | 124篇 |
2001年 | 28篇 |
2000年 | 12篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 23篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1969年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有3464条查询结果,搜索用时 15 毫秒
21.
This work investigates the influence of environmental inducers on the organization of cell regulation networks, using a connectionist approach. Protein interactions are modeled by an asymmetrical recurrent network, the units of which take continuous values. In contrast to classical models, we explicitly introduce a genome to encode the architecture of the system. This feature enables us to introduce an evolution model, in which a genetic algorithm that mimics the effects of evolution on proteins mutual interactions is used. We assume an efficient system to respond to persistent environmental stimuli, independently of their amplitude. Results are presented that show a structuration of the network with the emergence of specialized hierarchical structures. These structures seem to drive the system at the edge of chaos, so that it can present adapted responses to significant environmental changes. 相似文献
22.
Summary Crude, cell-free protein-synthesizing systems were prepared from follicles of two different stages of development in the ovariole of the silkmothAntherea pernyi. The efficiency of the translation of natural and synthetic mRNAs in these systems was compared with that in a cell-free wheat germ system. A postmitochondrial extract (S-30) from the follicles almost completely inhibited protein synthesis in a polyribosome-dependent, cell-free systems. A specific ribonuclease, obtained from the post mitochondrial extract by ammonium sulphate precipitation, heat denaturation and DEAE-cellulose chromatography, inhibited polyribosome-dependent protein synthesis. The effect of this specific ribonuclease on the structural integrity of radioactive RNAs and ribosomal subunits, which were isolated from Ehrlich ascites tumor cells, was also studied. 相似文献
23.
The subunit MW of Dioscorea bulbifera polyphenol oxidase (MW 115 000 ± 2000) determined by SDS-PAGE is ca. 31 000 indicating that the enzyme is an oligomeric protein with four subunits. Ki values of various inhibitors and their modes of inhibition have been determined with catechol and pyrogallol as substrates. p-Nitrophenol, p-cresol, quinoline and resorcinol are competitive inhibitors of catechol binding while only orcinol and p-nitrophenol behave in the same way towards pyrogallol as substrate. From the effect of pH on Vmax, groups with pK values ca. 4.7 and 6.8 have been identified to be involved in catalytic activity. The Arrhenius activation energy (Ea) at pH 4.0 is 8.9 kcal/mol between 40–65°. At pH 7.0, the value is 22.1 kcal/mol between 40 and 60°. The enthalpies (ΔH) at pH 4.0 and pH 7.0 are 2.3 kcal/mol and 32.4 kcal/mol respectively. The results are discussed considering the conformational changes of the enzyme during substrate binding. 相似文献
24.
Effects of Feeding and Drinking on Acetylcholine Release in the Nucleus Accumbens, Striatum, and Hippocampus of Freely Behaving Rats 总被引:4,自引:0,他引:4
Gregory P. Mark Pedro Rada Emmanuel Pothos Bartley G. Hoebel 《Journal of neurochemistry》1992,58(6):2269-2274
Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatum (STR), and hippocampus (HIPP) using microdialysis in 30-min intervals before, during, and after free-feeding in 20-h food-deprived rats. The effects on ACh in the NAC and STR were also observed in response to water intake in 20-h water-deprived animals. Neostigmine was used in the perfusate to improve ACh recovery. Basal ACh was sensitive to tetrodotoxin and low calcium, and therefore largely neuronal in origin. Feeding caused a 38% increase in extracellular ACh in the NAC and no change in the STR or HIPP. Dopamine was also increased in the NAC (48%) and to a lesser extent in the STR (21%) following feeding. Drinking caused 18-20% increases in ACh release in both the NAC and STR. In a separate experiment, ACh release in the NAC was monitored in 10-min intervals during free-feeding; ACh increased in the interval immediately following maximal food intake. These results suggest a site-specific increase in ACh release following feeding that cannot be solely attributed to the activation associated with this behavior. 相似文献
25.
Michael O. Eze Emmanuel I. Okafor Charles E. Okoronkwo 《Applied microbiology and biotechnology》1982,16(1):52-55
Summary The influence of the microenvironment on the metabolic behaviour of immobilized cells is discussed in relation to literature data. A model is proposed in which decreased water activity and/or oxygen deficiency result in changed yields and/or new metabolic behaviour of the immobilized cells. 相似文献
26.
In a comparison of the polyphenol oxidase activity of various species of yam tubers the greatest enzyme activity was found in D. bulbifera. The enzyme was purified from acetone powder extracts of this plant. Ammonium sulphate fractionation, followed by ion exchange chromatography and gel filtration gave 22-fold purification. The final product gave a single band on polyacrylamide disc gel electrophoresis. The purified enzyme showed activity towards catechol, pyrogallol and dl-β-3,4-dihydroxyphenylalanine (dl-DOPA) and had a MW 115000 ± 2000. It was characterized by response to various inhibitors. β-Mercaptoethanol, dithioerythritol, l-cysteine, sodium metabisulphite and KCN inhibited strongly. 相似文献
27.
Grard Morel Paul Dubois Claudine Benassayag Emmanuel Nunez Christine Radanyi Grard Redeuilh Hlne Richard-Foy Etienne-Emile Baulieu 《Experimental cell research》1981,132(2):249-257
Antiserum against calf uterus oestradiol receptor has been used for detecting oestradiol receptor in rat pituitary cells at the ultrastructural level after immunochemical reaction according to Sternberger. The gonadotropic, lactotropic and somatotropic cells were positive, but not the thyrotropic and corticotropic cells. In peripubertal and adult rats, both cytoplasmic and nuclear receptors were seen, but in a long-term castrated rat, the receptor was found only in the cytoplasm. After oestradiol administration to 21-day-old animals, the cytoplasmic receptor decreased and the nuclear receptor increased in gonadotropic cells, supporting the concept of hormone-receptor complex translocation. Antibodies against α1-foetoprotein demonstrated the presence of this oestrogen-binding plasma protein in all pituitary cells, but only in the cytoplasmic area. These results and the immunological controls related to antibody specificity give the first evidence of steroid receptor at the ultrastructural level. 相似文献
28.
29.
Bernard Banaigs Christian Francisco Emmanuel Gonzalez Louis Codomier 《Phytochemistry》1984,23(12):2951-2952
Two new diunsaturated lipids, related to palmitic acid, were isolated from the brown alga Cystoseira barbata, one of which is toxic to mice during P388 lymphocytic leukemia tests. 相似文献