全文获取类型
收费全文 | 418篇 |
免费 | 48篇 |
国内免费 | 1篇 |
出版年
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 30篇 |
2012年 | 43篇 |
2011年 | 43篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1969年 | 3篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有467条查询结果,搜索用时 15 毫秒
461.
Nitrogenase biosynthesis in Klebsiella pneumoniae including mutant strains, which produce nitrogenase in the presence of NH+4 (Shanmugam, K.T., Chan, Irene, and Morandi, C. (1975) Biochim. Biophys. Acta 408, 101--111) is repressed by a mixture of L-amino acids. Biochemical analysis shows that glutamine synthetase activity in strains SK-24, SK-28, and SK-29 is also repressed by amino acids, with no detectable effect on glutamate dehydrogenase. Among the various amino acids, L-glutamine in combination with L-aspartate was found to repress nitrogenase biosynthesis completely. In the presence of high concentrations of glutamine (1 mg/ml) even NH+4 repressed nitrogenase biosynthesis in the strains SK-27, SK-37, SK-55 and SK-56. Under these conditions, increased glutamate dehydrogenase activity was also detected. Physiological studies show that nitrogenase derepressed strains are unable to utilize NH+4 as sole source of nitrogen for biosynthesis of glutamate for biosynthesis of glutamate, whereas back mutations leading to NH+4 utilization results in sensitivity to repression by NH+4. These findings suggest that amino acids play an important role as regulators of nitrogen fixation. 相似文献
462.
Two major DNA binding proteins of molecular weights 34,000 and 38,000 have been identified in the 30,000 g supernatant (S-30)
fraction of rat thigh muscle extracts. The presence of 38 KD DNA binding protein in the muscle S-30 could be demonstrated
only if Triton X-100 treated extracts were used for Afinity chromatography suggesting that this protein may be a membrane
associated DNA binding protein. The 38 KD DNA binding protein differed from the 34 KD DNA binding protein also in its chromatographic
behaviour in DE-52 columns in which the 38 KD protein was retained, while the 34 KD protein came out in the flow-through in
an electrophoretically pure form. The 34 KD DNA binding protein can also be purified by precipitation with MgCl2. Incubation of 0 15 M NaCl eluates (containing the 38 KD and/or 34 KD DNA binding protein) in the presence of 100 mM Mg2+ resulted in the specific precipitation of the 34 KD protein. Prolonged incubation (30 days) of the 0.15 M NaCl eluates containing
the two DNA binding proteins at 4°C led to the preferential degradation of the 34 KD DNA binding protein. Nitrocellulose filter
binding assays indicated selective binding of purified 34 KD protein to ss DNA. Purified 34 KD DNA binding protein cleaved
pBR 322 supercoiled DNA, and electrophoresis of the cleavage products in agarose gels revealed a major DNA band corresponding
to the circular form of DNA. 相似文献
463.
DNA binding proteins present in the cytoplasm and nuclei of term placenta were isolated by DNA-cellulose chromatography and analysed by electrophoresis in high resolution polyacrylamide gradient gels. A denatured DNA specific protein of approximate molecular weight 34 000 daltons was the predominant DNA binding protein of the cytoplasm; this protein consisted of over 65% of the total DNA binding proteins of the 0.15 M NaCl eluate of the cytoplasm. The cytoplasmic extracts contained two additional DNA binding proteins of molecular weight 24 000 and 18 000 daltons and these proteins bound preferentially to ds DNA. All the three DNA binding proteins were also present in the nuclei and electrophoresis of histones in adjacent lanes indicated that they are not histones. The 34 000-dalton DNA binding protein has been purified by ammonium sulphate fractionation followed by phosphocellulose (PC) chromatography. The DBP eluted from the PC column between 0.125–0.15M potassium phosphate. PC fractions containing electrophoretically pure 34KD DBP showed an endonuclease activity capable of converting plasmid pBR 322 DNA to the linear form. Maximum endonucleolytic activity was observed in the presence of 3–5 mM Mg2+ and the enzyme activity was completely inhibited by 3 mM ethylenediamine tetraacetate. 相似文献
464.
465.
Utilisation (uptake) of hydrogen gas by whole cells of Rhizobium japonicum was found to be influenced by the carbon source(s) present in the growth medium, with activity being highest in a medium containing sugars. Tricarboxylic acid cycle intermediates, such as malate, significantly reduced H2 utilisation. No reduction in the hydrogenase activity is observed when the enzyme is assayed directly by the tritium exchange method, indicating that the decrease in hydrogen uptake activity is not due to repression of hydrogenase biosynthesis. Cyclic AMP was found to alleviate the inhibition of H2 uptake by malate, and this requires new protein synthesis. Addition of chloramphenicol or rifampicin simultaneously with cyclic AMP eliminated the stimulation of H2 uptake in the malate medium. These results show that in R. japonicum cyclic AMP plays a major role in the regulation of H2 metabolism. 相似文献
466.
The steady state kinetics of ligninperoxidase catalysed reaction using n-propanol as the organic substrate and monitoring the formation of propanaldehyde at lambda = 300 nm spectrophotometerically as functions of different reaction parameters has been studied. It has been concluded that n-propanol can be used as a substrate for analysing the activity of ligninperoxidase. The turnover number of ligninperoxidase of Phanerochaete chrysosporium using n-propanol as substrate has been found to be higher approximately by a factor of 10(3) as compared to that using veratryl alcohol as the substrate. The method works in assaying the activity of ligninperoxidase produced by Aspergillus fumigatus indicating that it can be used for assaying the ligninperoxidase activities produced by other microorganisms also and is not limited to assaying the ligninase activity produced by Phanerochaete chrysosporium alone. Under identical experimental conditions, horseradish peroxidase does not show peroxidase activity using n-propanol as substrate indicating that the method does not interfere with the activities of other peroxidases. 相似文献
467.
Molybdate transport and regulation in bacteria 总被引:11,自引:0,他引:11