全文获取类型
收费全文 | 2909篇 |
免费 | 245篇 |
国内免费 | 4篇 |
出版年
2021年 | 36篇 |
2019年 | 29篇 |
2018年 | 25篇 |
2017年 | 32篇 |
2016年 | 41篇 |
2015年 | 77篇 |
2014年 | 88篇 |
2013年 | 128篇 |
2012年 | 171篇 |
2011年 | 151篇 |
2010年 | 96篇 |
2009年 | 90篇 |
2008年 | 119篇 |
2007年 | 146篇 |
2006年 | 116篇 |
2005年 | 130篇 |
2004年 | 134篇 |
2003年 | 134篇 |
2002年 | 126篇 |
2001年 | 35篇 |
2000年 | 32篇 |
1999年 | 51篇 |
1998年 | 50篇 |
1997年 | 35篇 |
1996年 | 28篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 29篇 |
1992年 | 39篇 |
1991年 | 35篇 |
1990年 | 25篇 |
1989年 | 30篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 28篇 |
1984年 | 37篇 |
1983年 | 20篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 39篇 |
1979年 | 20篇 |
1978年 | 28篇 |
1977年 | 27篇 |
1976年 | 26篇 |
1975年 | 20篇 |
1974年 | 27篇 |
1973年 | 28篇 |
1972年 | 20篇 |
1971年 | 22篇 |
排序方式: 共有3158条查询结果,搜索用时 625 毫秒
11.
Species specificity of bacterial palindromic units 总被引:8,自引:0,他引:8
Eric Gilson David Perrin William Saurin Maurice Hofnung 《Journal of molecular evolution》1987,25(4):371-373
We described previously a family of dispersed palindromic sequences highly repeated in Escherichia coli and Salmonella typhimurium genomes. These sequences, called PU (palindromic units), are located outside structural genes. We report here observations suggesting that PU may have a role in bacterial speciation. 相似文献
12.
Michael K. Dahl Eric Francoz William Saurin Winfried Boos Michael D. Manson Maurice Hofnung 《Molecular & general genetics : MGG》1989,218(2):199-207
Summary The malE and malK genes from Salmonella typhimurium, and the MalEFG operon and a portion of malK from Enterobacter aerogenes were cloned and sequenced. Plasmid-borne malE genes from both species and the malF and malG genes from E. aerogenes were expressed normally in Escherichia coli, and their products function in maltose transport. This shows that the malB products from the three species are interchangeable, at least in the combinations tested. The general genetic organization of the malB region is conserved. Potential binding sites and distances between them are highly conserved in the regulatory intervals. An unexpected conserved region was detected, which we call the U box, and which could be another target for a regulatory protein. This hypothesis is supported by the presence of the U box in the regulatory, region of the pulA-malX operon in Klebsiella pneumoniae. The intergenic region between malE and malF from S. typhimurium and E. aerogenes, contains inverted repeats similar to the palindromic units (PU or REP) found at the same location in E. coli. The predicted amino acid sequence of the encoded proteins showed 90% or more identity in every pairwise comparison of species. 相似文献
13.
The kinetic properties of ribulose 1,5-bisphosphate carboxylase(RuBPC) appear to have been modified during evolution of photosynthesisto adjust to changes in substrate availability. C4 plants areconsidered to have a higher concentration of CO2 available toRuBPC than C3plants. In this study, the Km(CO2 and catalyticcapacity (kcat) of RuBPC and the ratio of RuBPC protein to totalsoluble protein from several Flaveria species, including C3,C3-C4 intermediate, and C4 species, were determined. The C3and intermediate species had similar Km(CO2) values while theC4 species on average had higher Km(CO2) values. The mean ratioof Kcat/Km for species of each group was similar, supportingthe hypothesis that changes in Km and Kcat, are linked. Theallocation of total soluble protein to RuBPC was lowest in theC4 Flaveria species, intermediate in the C3-C4 species, andhighest in the C3 species. The results suggest that during evolutionof C4 photosynthesis adjustments may occur in the quantity ofRuBPC prior to changes in its kinetic properties. (Received January 4, 1989; Accepted April 11, 1989) 相似文献
14.
In this paper the authors present a comparative study of the actions of the antibiotics primycin and gramicidin on the erythrocyte membrane permeability. It has been found that both antibiotics have a nonlinear effect on the membrane permeability. Above a threshold antibiotic concentration, which is characteristic of the type of the antibiotic, the cation permeability of the erythrocyte membranes increases sharply. In the range of nonlinearity the transport-kinetic curves level off before achieving the equilibrium radioactive ion distribution between the extra- and intracellular spaces. A stochastic model of the cooperative and aspecific incorporation of antibiotic molecules into the membrane explains the experimental findings. The authors conclude that membrane permeability increases at the places where two or more antibiotic molecules form aggregates in the membrane. 相似文献
15.
L V Schagina K Blaskó A E Grinfeldt Y E Korchev A A Lev 《Biochimica et biophysica acta》1989,978(1):145-150
The exchange diffusions of tracer cations (22Na+, 86Rb+) are studied on gramicidin-A-treated red blood cell (RBC) membranes. A time-dependent decrease in cation permeability has been observed and has been considered to be the result of a channel inactivation process. The channel inactivation appears at 20 and 30 degrees C but not at a temperature as low as 6 degrees C. The gramicidin A channel inactivation can be monitored by a conductivity decay of molecular lipid membranes (BLM) prepared either from cholesterol or from a mixture of cholesterol and phospholipids but not of pure phosphatidylethanolamine. The role of cholesterol in the channel inactivation is discussed. 相似文献
16.
17.
18.
Calcium-Independent Release of Acetylcholine from Electric Organ Synaptosomes and Its Changes by Depolarization and Cholinergic Drugs 总被引:4,自引:4,他引:0
Vladimír Doleal Marie Françoise Diebler† Sylvie Lazereg† Maurice Israël † Stanislav Tuek 《Journal of neurochemistry》1988,50(2):406-413
Chemiluminescent detection was applied to measure the continuous spontaneous Ca2+-independent liberation of acetylcholine (ACh) from Torpedo electric organ synaptosomes. Differentiation between the release of ACh and choline was achieved by inhibiting cholinesterases with phospholine, and a way to quantify the continuous release was devised. The method permitted measurements during short time intervals from minute amounts of tissue and without an accumulation of ACh in the medium. Synaptosomes continuously liberated small amounts of ACh during incubations in the presence of 3 mM K+ and in the absence of Ca2+. The spontaneous liberation of ACh was similar both quantitatively and qualitatively at pH values of 8.6 and 7.8. It was unaltered by MgCl2 (10.4 mM), 2-(4-phenylpiperidino)cyclohexanol (10 microM), ouabain (104 microM), atropine (10 microM), and valinomycin (102 nM). Carbamoylcholine brought about a decrease, which could be partially reversed by atropine. The Ca2+-independent output of ACh was increased considerably when the concentration of K+ ions was raised (eightfold at 103 and 35-fold at 203 mM K+). Carbamoylcholine (104 microM) blocked the increase in ACh release produced by high K+; this effect of carbamoylcholine was not reversed by atropine (10 microM). When Ca2+ was added to synaptosomes depolarized by a high concentration of K+, the amount of ACh released during the first 1-3 min after the addition of Ca2+ was at least 20 times higher than in the absence of Ca2+, but the release returned rapidly to predepolarization values. Similarly high values of ACh release could be achieved by adding Ca2+ plus the ionophore A23187 and even higher values by adding Ca2+ plus gramicidin.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
19.
Production and Characterization of Monoclonal Antibodies to Wall-Localized Peroxidases from Corn Seedlings 总被引:2,自引:1,他引:1 下载免费PDF全文
Sung-Ha Kim Maurice E. Terry Pepper Hoops Marianne Dauwalder Stanley J. Roux 《Plant physiology》1988,88(4):1446-1453
A library of 22 hybridomas, which make antibodies to soluble wall antigens from the coleoptiles and primary leaves of etiolated corn (Zea mays L.) seedlings, was raised and cloned three times by limit dilution to assure monoclonal growth and stability. Two of these hybridomas made immunoglobulin G antibodies, designated mWP3 and mWP19, which both effectively immunoprecipitated peroxidase activity from crude and partially purified preparations of wall peroxidases. Direct peroxidase-binding assays revealed that both antibodies bound enzymes with peroxidase activity. As judged by immunoblot analyses, mWP3 recognized a Mr 98,000 wall peroxidase with an isoelectric point near 4.2, and mWP19 recognized a Mr 58,000 wall peroxidase. Immunogold localization studies showed both peroxidases are predominately in cell walls. 相似文献
20.
The addition of antimycin A during the logarithmic phase of growth of heterotrophic Euglena gracilis cultures (in lactate or glucose medium) was immediately followed by decreased respiration and a cessation of grwoth. Induced cyanideresistent respiration appeared 5 h after the addition of the inhibitor then the cells started to grow again and could be cultured in the presence of antimycin A. Thus the cells exhibited a cyanide-and antimycin-resistant respiration which was, in addition, sensitive to salicylhydroxamic acid and propylgallate. Antimycin-adapted Euglena and control cells were compared for their biomass production and protein synthesis. The difference in growth yield between control and antimycin-adapted cells was not as high as would be expected if only the first phosphorylation site of the normal respiratory chain was active in the presence of antimycin A. Furthermore, the ability to incorporate labelled valine into proteins, under resting-cell conditions, was not changed. Strong correlations were established between the effects of respiratory effectors on O2 consumption and valine incorporation. These results suggest that sufficient energy for protein synthesis and growth is provided by the operation of the cyanide-resistant respiratory pathway in antimycin-adapted Euglena.Abbreviations DNP
dinitrophenol
- PG
propylgallate
- SHAM
salicylhydroxamic acid 相似文献