全文获取类型
收费全文 | 666450篇 |
免费 | 75855篇 |
国内免费 | 313篇 |
专业分类
742618篇 |
出版年
2018年 | 5777篇 |
2016年 | 7699篇 |
2015年 | 10153篇 |
2014年 | 12092篇 |
2013年 | 16797篇 |
2012年 | 19013篇 |
2011年 | 19617篇 |
2010年 | 13290篇 |
2009年 | 12527篇 |
2008年 | 17846篇 |
2007年 | 18510篇 |
2006年 | 17646篇 |
2005年 | 16859篇 |
2004年 | 16764篇 |
2003年 | 16031篇 |
2002年 | 15678篇 |
2001年 | 31371篇 |
2000年 | 31524篇 |
1999年 | 24731篇 |
1998年 | 8203篇 |
1997年 | 8637篇 |
1996年 | 8053篇 |
1995年 | 7464篇 |
1994年 | 7321篇 |
1993年 | 7515篇 |
1992年 | 20164篇 |
1991年 | 20040篇 |
1990年 | 19358篇 |
1989年 | 18873篇 |
1988年 | 17965篇 |
1987年 | 17025篇 |
1986年 | 15679篇 |
1985年 | 15445篇 |
1984年 | 12610篇 |
1983年 | 10949篇 |
1982年 | 8194篇 |
1981年 | 7305篇 |
1980年 | 7036篇 |
1979年 | 11940篇 |
1978年 | 9339篇 |
1977年 | 8554篇 |
1976年 | 7974篇 |
1975年 | 8806篇 |
1974年 | 9680篇 |
1973年 | 9493篇 |
1972年 | 8671篇 |
1971年 | 7953篇 |
1970年 | 7035篇 |
1969年 | 6915篇 |
1968年 | 6452篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
N-Methyl-D-Aspartate receptors in acquisition of the short-term memory in the honeybeeApis mellifera
N. G. Lopatina I. V. Ryzhova E. G. Chesnokova L. A. Dmitrieva 《Journal of Evolutionary Biochemistry and Physiology》2000,36(3):294-300
Role of NMDA receptors in the process of associative learning has been studied in the honeybeeApis mellifera L. in behavior experiments, using method of conditional reflexes. To determine pharmacological profile of NMDA receptors,
effects of Mg2+ ions, NMDA, glycine (Gly), antagonist of the glycine site 5,7-dichlorokynurenic acid (DCK), competitive antagonists of NMDA
receptors: D,L-2-aminophosphovalerate (APV), L-2-aminophosphobutyrate (APB), and D-glutamyl-aminomethylphosphonic acid (GAMP)
as well of antagonists of NMDA receptor ion channels MK-801 and ketamine (Ket) were studied on acquisition of alimentary conditional
reflex and its retention in memory. NMDA increased capacity for learning by stimulating shortterm memory. The NMDA receptor
co-agonist Gly activated this NMDA effect. DCK eliminated the NMDA and Gly stimulatoty effects. All tested antagonists at
millimolar concentrations inhibited associative function. The data obtained confirm our hypothesis about participation of
NMDA receptors in processes of formation of short-term memory in the honeybeeApis mellifera and suggest that functional characteristics of the NMDA receptors involved in the process of associative learning in the
honeybee resemble those in mammals. 相似文献
943.
Chen Chen Raymond Dagnino Jr. Charles Q. Huang James R. McCarthy Dimitri E. Grigoriadis 《Bioorganic & medicinal chemistry letters》2001,11(24):3165-3168
Cyclizations of alkylhydrazines with N-acyl-S-methylisothioureas, readily synthesized from acyl chlorides, sodium thioisocyanate, dialkylamines then methyl iodide in a one-pot reaction, gave 1-alkyl-3-dialkylamino-5-phenyltriazoles 7 as major products. The regioisomers were assigned through the use of NOE NMR experiments. While bearing a N-bis(cyclopropyl)methyl-N-propylamino group, this series of compounds shows very good binding affinity on the human CRF1 receptor. Among them, 1-methyl-3-[N-bis(cyclopropyl)methyl-N-propylamino]-5-(2,4-dichlorophenyl)-1H-[1,2,4]triazole 7a had the best binding affinity for the CRF1 receptor (Ki=9 nM). 相似文献
944.
945.
The GTP-induced dissociation of T alpha from T beta gamma initiates the release of transducin from photolyzed rhodopsin and the subsequent activation of the cGMP phosphodiesterase. In this study, site-specific proteolysis and immunoprecipitation were used to map the domain of T alpha that interacts with T beta gamma. We found that Staphylococcus aureus V8 protease rapidly removes a small fragment from T alpha under native conditions, resulting in the formation of a single 38-kDa polypeptide (T alpha'). Under the same conditions, T beta gamma remains intact. A 4.5-fold decrease in the rate of T alpha cleavage by S. aureus protease was observed in the presence of T beta gamma, suggesting T beta gamma binding blocks the protease-sensitive site on T alpha. Amino acid sequence analysis indicated that T alpha' is derived from the cleavage of T alpha at Glu-21. The ability of T alpha' to interact with and activate the retinal phosphodiesterase is not diminished. However, T alpha' is unable to participate in T beta gamma-dependent activities such as the light-stimulated binding of guanine nucleotides, binding to photoexcited rhodopsin, and ADP-ribosylation catalyzed by pertussis toxin. Moreover, the anti-T alpha monoclonal antibody TF16 was able to precipitate T beta gamma in the presence of T alpha, but not with either T alpha' or T alpha-guanosine 5'-O-(3-thiotriphosphate). We conclude that the amino-terminal region of T alpha participates in T beta gamma interaction and discuss our results with respect to the known structure and function of transducin. 相似文献
946.
S F Brooks T Herget S Broad E Rozengurt 《The Journal of biological chemistry》1992,267(20):14212-14218
947.
948.
Reconstitution of RecBC DNase activity from purified Escherichia coli RecB and RecC proteins 总被引:8,自引:0,他引:8
I D Hickson C N Robson K E Atkinson L Hutton P T Emmerson 《The Journal of biological chemistry》1985,260(2):1224-1229
The Escherichia coli RecB protein, normally synthesized in low amounts, has been amplified by linkage of the recB gene to the phage lambda leftward promoter in an expression plasmid. From strains harboring this plasmid, RecB protein has been purified to homogeneity by a simple procedure which includes affinity chromatography on a column of RecC protein bound to agarose. The purified RecB protein has DNA-dependent ATPase activity but no exonuclease activity. RecC protein alone has neither ATPase nor exonuclease activity. However, when combined together, the RecB and RecC proteins show the ATP-dependent double-stranded exonuclease properties characteristic of the RecBC DNase. 相似文献
949.
G. E. Walker 《Plant and Soil》1984,78(3):431-432
Summary
Aphelenchus avenae and various unidentified bacteria and actinomycetes were cultured from soil samples taken from a pine-forest and a wheat-field.
The nematode failed to reproduce in significant numbers on cultures of these micro-organisms and was apparently unable to
utilize them as food sources. 相似文献
950.