全文获取类型
收费全文 | 2947篇 |
免费 | 48篇 |
国内免费 | 163篇 |
出版年
2023年 | 8篇 |
2022年 | 28篇 |
2021年 | 36篇 |
2020年 | 72篇 |
2019年 | 62篇 |
2018年 | 74篇 |
2017年 | 56篇 |
2016年 | 29篇 |
2015年 | 78篇 |
2014年 | 235篇 |
2013年 | 201篇 |
2012年 | 200篇 |
2011年 | 280篇 |
2010年 | 172篇 |
2009年 | 142篇 |
2008年 | 146篇 |
2007年 | 105篇 |
2006年 | 98篇 |
2005年 | 100篇 |
2004年 | 93篇 |
2003年 | 94篇 |
2002年 | 59篇 |
2001年 | 56篇 |
2000年 | 49篇 |
1999年 | 44篇 |
1998年 | 46篇 |
1997年 | 48篇 |
1996年 | 47篇 |
1995年 | 34篇 |
1994年 | 41篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 46篇 |
1990年 | 30篇 |
1989年 | 27篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 43篇 |
1983年 | 38篇 |
1982年 | 35篇 |
1981年 | 23篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1974年 | 2篇 |
1952年 | 1篇 |
排序方式: 共有3158条查询结果,搜索用时 15 毫秒
1.
The photon flux autocorrelation function of a fluorescent label attached to a bacterial motor shaft is calculated for the case in which the bacterial motor is considered to be actively but idly rotating. It is shown that even when the fluorescent label has a very short lifetime, fluorescence correlation spectroscopy should provide a useful tool for determining the rate of revolution of the bacterial motor under various solution conditions. 相似文献
2.
Abstract Both the intracellular and the extracellular concentration of cyclic AMP increases logarithmically in synchronously growing cultures of Escherichia coli . Thus, cyclic AMP by itself cannot regulate growth and division of the bacterium during the cell cycle. 相似文献
3.
Abstract A short-term oral administration of live Saccharomyces cerevisiae cells, strain Sillix Hansen DSM 1883, resulted in enhanced resistance of mice toward infections with K. pneumoniae, S. pneumoniae and S. pyogenes A produced by intranasal inoculation. Yeast pre-treatment also increased the efficacy of antibiotic therapy in bacterial infections and of antiviral drugs in viral infections. Yeast treatment of animals stimulated phagocytosis, activated the complement system and induced interferon which are likely to represent the main mechanisms of action whereby pretreatment of mice with live S. cerevisiae cells increases resistance to infection. It is concluded that preventive administration of live Saccharomyces cerevisiae cells should be used for increasing resistance to bacterial infections, in particular of the respiratory tract, or to viral infections, as well as an adjunct to antibiotic and antiviral drug therapy. 相似文献
4.
5.
Victor M. Luque-Almagro Verity J. Lyall Stuart J. Ferguson M. Dolores Roldán David J. Richardson Andrew J. Gates 《The Journal of biological chemistry》2013,288(41):29692-29702
Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression. 相似文献
6.
The pathway construction and allosteric regulation of phenylalanine and tyrosine biosynthesis was examined in Neisseria gonorrhoeae. A single 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase enzyme sensitive to feedback inhibition by l-phenylalanine was found. Chorismate mutase and prephenate dehydratase appear to co-exist as catalytic components of a bifunctional enzyme, known to be present in related genera. The latter enzyme activities were both feedback inhibited by l-phenylalanine. Prephenate dehydratase was strongly activated by l-tyrosine. NAD+-linked prephenate dehydrogenase and arogenate dehydrogenase activities coeluted following ion-exchange chromatography, suggesting their identity as catalytic properties of a single broad-specificity cyclohexadienyl dehydrogenase. Each dehydrogenase activity was inhibited by 4-hydroxyphenylpyruvate, but not by l-tyrosine. Two aromatic aminotransferases were resolved, one preferring the l-phenylalanine:2-ketoglutarate substrate combination and the other preferring the l-tyrosine: 2-ketoglutarate substrate combination. Each aminotransferase was also able to transaminate prephenate. The overall picture of regulation is one in which l-tyrosine modulates l-phenylalanine synthesis via activation of prephenate dehydratase. l-Phenylalanine in turn regulates early-pathway flow through inhibition of DAHP synthase. The recent phylogenetic positioning of N. gonorrhoeae makes it a key reference organism for emerging interpretations about aromatic-pathway evolution. 相似文献
7.
A.L. Smith P.D. Jenny L. Langley P. Verdugo M. Villalon J. Unadkat D. Luchtel 《Journal of microbiological methods》1989,10(4):265-280
We developed a kinetic assay using a monolayer of differentiated respiratory epithelium in culture to assess bacterial adherence. Mean residence time of bacteria in the tissue culture chamber was estimated from a model-independent (moment) analysis of the rate of bacterial washout from perfused Rose chambers. Results with this method compared favorably with visual assessment of adherence and double radiolabel method with H. influenzae. Adherence was assessed with low inoculae of H. influenzae, P. cepacia and P. aeruginosa avoiding cytotoxic effects seen when large inoculae are added to eukaryotic cells. This method will provide a means of assessing adherence of pathogenic respiratory bacteria to their cellular target at low inoculae. 相似文献
8.
Frank G. Rodgers Richard P. Blakemore Nancy A. Blakemore Richard B. Frankel Dennis A. Bazylinski Denise Maratea Christine Rodgers 《Archives of microbiology》1990,154(1):18-22
A many-called magnetotactic prokaryote obtained from brackish water was observed to possess intercellular connections at points of contact between the outer membranes of constituent cells. Each aggregate organism consisted of 10 to 30 individual Gram-negative cells containing material with the appearance of poly--hydroxybutyrate and magnetosomes of unusual arrangement, structure and composition. The aggregate, which possessed prokaryotic-type flagella arranged at the outwards surfaces of each cell, showed motility indicative of co-ordination between individual component cells. These results suggest that this organism could be a multicellular prokaryote. 相似文献
9.
D.W. Bruno 《FEMS microbiology letters》1988,51(2-3):135-139
Abstract The cell surface hydrophobicity of Renibacterium salmoninarum strains was examined using a salt aggregation method. Those strains which were virulent in the test animal were sticky, auto-agglutinating and possessed a hydrophobic cell surface. Those strains with a low virulence were non-sticky, non-agglutinating and failed to aggregate in a high molar salt. Strains could not be distinguished using biochemical tests. There was no change in hydrophobicity following re-isolation of the bacteria from experimentally infected rainbow trout, Salmo gairdneri . 相似文献
10.
M. A. Malek N. A. Chowdhury Q. M. Youssouf N. Choudhury 《Enzyme and microbial technology》1988,10(12):750-753
Five locally isolated bacterial strains produced extracellular cellulase enzymes, primarily CMCase, when grown on different natural and commercial cellulosic substrates. Extracellular CMCase and avicelase activity was higher with the strain CLS-32, a Cytophaga sp., compared to four other strains. The whole-cell preparations of these isolates were found to saccharify cellulosic substrates to reducing sugars. Maximum release of reducing sugar (5.75 mg ml−1) was obtained with CLS-32 using sugar cane bagasse as growth and hydrolysis substrates. 相似文献