全文获取类型
收费全文 | 359篇 |
免费 | 32篇 |
专业分类
391篇 |
出版年
2023年 | 2篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 3篇 |
2016年 | 14篇 |
2015年 | 25篇 |
2014年 | 21篇 |
2013年 | 15篇 |
2012年 | 34篇 |
2011年 | 22篇 |
2010年 | 14篇 |
2009年 | 15篇 |
2008年 | 26篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1996年 | 7篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 6篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1969年 | 3篇 |
1968年 | 1篇 |
1967年 | 3篇 |
1963年 | 1篇 |
排序方式: 共有391条查询结果,搜索用时 0 毫秒
1.
Colchicine (COL) elevates the frequency of micronucleated polychromatic erythrocytes (PE), the ratio of normochromatic to polychromatic erythrocytes (N/PE) and the frequency of large PE due to spindle disruption. Simultaneous i.p. injection of L-cysteine (CYS) does not influence the effects of COL while if administered 1 h prior to COL, CYS suppresses the N/PE ratio and frequency of large PE but not the frequency of micronucleated PE elevated by COL. Preincubation of CYS with COL at 37 degrees C for 1 h results in a significant decrease in all the COL effects. The modulatory effect of exogenous CYS appears to be due to its competition with the endogenous tubulin cysteine residues for interacting with COL. 相似文献
2.
The influence of intracellular levels of cAMP on the lipid synthesis of Microsporum gypseum has been examined by exogenous supplementation of dibutyryl cAMP and its activators/inhibitors. Incorporation of [14C]acetate into various lipid fractions of M. gypseum was markedly enhanced in the presence of dibutyryl cAMP and its modulators, probably as a consequence of increased intracellular cAMP levels, which, in turn, affected the lipid biosynthesis. Increased activities of phosphatidic acid phosphatase, glycerol kinase, ethanolamine kinase and choline kinase in the presence of these additives supports the enhanced synthesis of phospholipids and suggests that lipid biosynthesis is being controlled by cAMP in M. gypseum. 相似文献
3.
Simultaneous reduction in alkaloid yield and level of phosphatases by high concentrations of phosphate was observed inClaviceps sp. SD-58. Tryptophan-induced culture showed an increase in alkaloid yield and the level of phosphatases. Phosphate caused repression of both acid phosphatase (isoenzyme I) and alkaline phosphatase (isoenzymes III and V). 相似文献
4.
5.
Surface-active components, both reactants and products, are frequently encountered in two-phase, aqueous-organic, biocatalytic reactions, When such reaction are carried out in a membrane reactor, employing a membrane selectively wetted by one of the two reactants, changes in the content of these surfactants- as a consequence of the progress of the reaction-can lead to wetting transitions at the two membrane-liquid interfaces as a result of adsorption of the tenside. This can lead to a decrease in the pressure required to cause the, initially, nonwetting phase to break through the membrane. Such effects render difficult the operation of two-phase membrane bioreactors. Hence, it is necessary to make a careful selection of the membrane material and type by considering factors such as UF versus MF and low MWCO versus high MWCO to enable the reactor to be operated without breakthrough, but without significantly compromising the reaction rates that can be maintained.The phenomena leading to breakthrough effects are discussed in this paper, and experimental results for the hydrolysis of ethyl laurate by lipase from Candida rugosa in a batch flat sheet membrane reactor are presented with the reactor operated with a variety of membranes. An experimental result showing the decrease in the pressure required to cause breakthrough of the organic phase (for the system ethyl laurate-lauric acid-water) as the content of the highly surface-active lauric acid in the organic phase is increased is also presented for an asymmetric, hydrophilic meta-aramid ultrafiltration membrane. (c) 1994 John Wiley & Sons, Inc. 相似文献
6.
The blue-green algaeChroococcus, Oscillatoria and Nostoc, excrete vitamin B12 and pantothenic acid in the culture filtrates during the phase of active growth. The excretion has an ecological significance. 相似文献
7.
B M Braganca A V Hospattankar S E Electricwalla N R Vaidya 《Analytical biochemistry》1979,92(2):453-461
An accurate micromethod suitable for the assay of polyamines in concentrations of 2 to 30 nmol is described. It is based on the oxidation of polyamines by purified fractions of crude l-amino acid oxidase from Russell's viper venom. By a combination of two enzyme fractions, one which oxidizes polyamines and amino acids (AAP) and another which oxidizes only amino acids (AA), the technique can accurately determine polyamine concentrations in extracts of sera which may not be free of amino acids. Experiments described show 90 to 100% recovery of added polyamines in the presence of varying amounts of amino acids. Polyamines added to serum also showed recoveries ranging from 96 to 98%. The enzymes do not oxidize histamine and epinephrine and are very stable. The method does not require sophisticated equipment and is suitable for screening of large number of clinical samples to assess the importance of polyamines as a diagnostic test or their prognostic value in diseases like cancer. 相似文献
8.
Genetic Studies of the Prp17 Gene of Saccharomyces Cerevisiae: A Domain Essential for Function Maps to a Nonconserved Region of the Protein 总被引:1,自引:0,他引:1 下载免费PDF全文
The PRP17 gene product is required for the second step of pre-mRNA splicing reactions. The C-terminal half of this protein bears four repeat units with homology to the β transducin repeat. Missense mutations in three temperature-sensitive prp17 mutants map to a region in the N-terminal half of the protein. We have generated, in vitro, 11 missense alleles at the β transducin repeat units and find that only one affects function in vivo. A phenotypically silent missense allele at the fourth repeat unit enhances the slow-growing phenotype conferred by an allele at the third repeat, suggesting an interaction between these domains. Although many missense mutations in highly conserved amino acids lack phenotypic effects, deletion analysis suggests an essential role for these units. Only mutations in the N-terminal nonconserved domain of PRP17 are synthetically lethal in combination with mutations in PRP16 and PRP18, two other gene products required for the second splicing reaction. A mutually allele-specific interaction between prp17 and snr7, with mutations in U5 snRNA, was observed. We therefore suggest that the functional region of Prp17p that interacts with Prp18p, Prp16p, and U5 snRNA is in the N terminal region of the protein. 相似文献
9.
10.