全文获取类型
收费全文 | 2029篇 |
免费 | 121篇 |
出版年
2022年 | 6篇 |
2021年 | 14篇 |
2019年 | 12篇 |
2018年 | 26篇 |
2017年 | 25篇 |
2016年 | 32篇 |
2015年 | 55篇 |
2014年 | 57篇 |
2013年 | 175篇 |
2012年 | 114篇 |
2011年 | 125篇 |
2010年 | 66篇 |
2009年 | 67篇 |
2008年 | 102篇 |
2007年 | 132篇 |
2006年 | 107篇 |
2005年 | 98篇 |
2004年 | 106篇 |
2003年 | 112篇 |
2002年 | 120篇 |
2001年 | 23篇 |
2000年 | 30篇 |
1999年 | 36篇 |
1998年 | 31篇 |
1997年 | 29篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 27篇 |
1992年 | 31篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 25篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 12篇 |
1969年 | 5篇 |
排序方式: 共有2150条查询结果,搜索用时 15 毫秒
61.
Tetsuo Suami Shigeru Nishiyama Yasuhide Ishikawa Shinichi Katsura 《Carbohydrate research》1976,52(1):187-196
The aminocyclitol antibiotic neamine has been chemically modified at the hydroxyl group on C-6 of the 2-deoxystreptamine moiety. The partially acetylated neamine derivatives, 6,3′,4′-tri-O-acetyl- (3) and 5,3′,4′-tri-O-acetyl-1,3,2′,6′-tetra-N-(ethoxycarbonyl)neamine (4), were prepared by random hydrolysis of the 5,6-O-ethoxyethylidene derivative (2), followed by chromatographic purification. Condensation of 4 and 2,3,5-tri-O-benzoyl-d-ribofuranosyl chloride led to 6-O-(β-d-ribofuranosyl)neamine (7). Analogous condensation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide or 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide afforded the corresponding 6-O-(d-hexopyranosyl)neamines. 相似文献
62.
The effect of NADP+ on light-induced steady-state redox changes of membrane-bound cytochromes was investigated in membrane fragments prepared from the blue-green algae Nostoc muscorum (Strain 7119) that had high rates of electron transport from water to NADP+ and from an artificial electron donor, reduced dichlorophenolindophenol (DCIPH2) to NADP+. The membrane fragments contained very little phycocyanin and had excellent optical properties for spectrophotometric assays. With DCIPH2 as the electron donor, NADP+ had no effect on the light-induced redox changes of cytochromes: with or without NADP+, 715- or 664-nm illumination resulted mainly in the oxidation of cytochrome f and of other component(s) which may include a c-type cytochrome with an α peak at 549 nm. With 664 nm illumination and water as the electron donor, NADP+ had a pronounced effect on the redox state of cytochromes, causing a shift toward oxidation of a component with a peak at 549 nm (possibly a c-type cytochrome), cytochrome f, and particularly cytochrome b559. Cytochrome b559 appeared to be a component of the main noncyclic electron transport chain and was photooxidized at physiological temperatures by Photosystem II. This photooxidation was apparent only in the presence of a terminal acceptor (NADP+) for the electron flow from water. 相似文献
63.
Several compounds containing a thiomethyl group were found to replace vitamin B12 in a protozoan, Ochromonas malhamensis. The order of the effectiveness was as follows: 5-methylthioadenosine > S-adenosylmethionine > 5-methylthioribose > L-methionine. A similar order was obtained with respect to the permeability of these compounds into the protozoan cells, except for S-adenosylmethionine. 5-Methylthioadenosine and 5-methylthioribose as well as l-methionine markedly increased the intracellular content of l-methionine. The level of S-adenosylmethionine was also increased by them, but to a lesser degree. The thiomethyl group of the compounds was established to be incorporated into S-adenosylmethionine. The metabolic fate of the thiomethyl group of 5-methylthioadenosine cannot be distinguished from that of l-methionine. A high activity of 5-methylthioadenosine nucleosidase was detected in the cell-free extracts of the protozoan. These results strongly suggest that 5-methylthioadenosine would be metabolized to l-methionine via 5-methylthioribose and then the l-methionine would be converted to S-adenosylmethionine. Like l-methionine and vitamin B12, 5-methylthioadenosine and 5-methylthioribose may play an important role in maintenance of the C-1 pool in Ochromonas malhamensis.Neither 5-methylthioadenosine nor 5-methylthioribose replaced vitamin B12 in some vitamin B12-requiring bacteria. This result is consistent with the fact that neither compounds was significantly taken up by these bacteria.Abbreviations MTA
5-methylthioadenosine
- AdoMet
S-adenosylmethionine
- MTR
5-methylthioribose
- TCA
trichloroacetic acid
Paper II in the series. The first paper of the series has been published (Sugimoto and Fukui, 1974) 相似文献
64.
Ayako Ueki Yukiko Fukushima Tetsuo Kimoto 《Virchows Archiv. B, Cell pathology including molecular pathology》1976,22(1):315-321
The presence of C3 receptor sites on the cell surfaces of WI-38 fibroblasts was reported in a previous paper. Here the effect of dexamethasone
sodium sulfate of C3 receptor site function was studied. The incubation of WI-38 fibroblasts with dexamethasone sodium sulfate produces the biphasic
mode of action, i.e., the growth-stimulating phase with low doses (90–230 μg/ml) and the growth-inhibiting phase with high
doses (450–900 μg/ml). The function of C3 receptor sites on WI-38 fibroblasts seems to be very stable and cannot be suppressed by the pretreatment of WI-38 fibroblasts
with dexamethasone in high concentrations, where the cell growth is inhibited. 相似文献
65.
Hyaluronic acid synthesis in cultured cells usually occurs during the growth phase. The relation between hyaluronic acid synthetase activity and cell proliferation is studied. The synthetase activity in rat fibroblasts is high during the growth phase, but low in the stationary phase. When the old medium of stationary cultures is renewed with fresh medium containing 20% calf serum, DNA synthesis occurs synchronously between 12 and 20 hours, followed by cell division. Under these conditions, the hyaluronic acid synthetase activity is significantly induced within two hours, reaching a maximum level at 5–8 hours, and then decreases gradually. This induction of the synthetase, which shows a high turnover rate, requires continued synthesis of both RNA and protein. Furthermore, the induction of both DNA and hyaluronic acid synthesis is found to be caused by calf serum added in the medium. However, dialysis and ultrafiltration of the serum permit us to concentrate an active fraction with a high molecular weight, which induces the synthetase activity, but not DNA synthesis. 相似文献
66.
For the purpose of clarifying the mechanism of plaque formation in HeLa cell cultures by coxsackievirus A9, which does not show definite CPE in fluid cultures, we investigated the growth pattern of the virus in HeLa cells, comparing plaque (HeLA)-forming and non-plaque (HeLa)-forming viruses. It was revealed that the yield of both viruses per cell was nearly the same, but non- plaque (HeLa)-forming virus was far less efficient in infecting HeLa cells. Dextran sulfate was effective in releasing more virus from cells, when HeLa cell cultures were infected with plaque (HeLa)-forming virus, but not in cultures infected with non-plaque (HeLa)-forming virus. From these experimental results, the mechanism by which plaques are formed in HeLa cell cultures by coxsackievirus A9 was discussed. 相似文献
67.
68.
69.
The synthesis of the OmpF porin in Escherichia coli K-12 was highly and reversibly inhibited by 5 mM salicylate in the bacterial growth medium, and salicylate also inhibited the OmpC porin synthesis, although only weakly. The full expression of the salicylate effect was presumed to require the ompB gene product on comparison between the wild type and ompB mutant strains. The salicylate effect was also observed for the porin protein synthesis in Klebsiella pneumoniae and Serratia marcescens, although an ompB-like gene remains to be identified in both species. 相似文献
70.
Identification and Expression of the Genes Encoding a Reactivating Factor for Adenosylcobalamin-Dependent Glycerol Dehydratase 总被引:10,自引:0,他引:10
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Takamasa Tobimatsu Hideki Kajiura Michio Yunoki Muneaki Azuma Tetsuo Toraya 《Journal of bacteriology》1999,181(13):4110-4113
Adenosylcobalamin-dependent glycerol dehydratase undergoes inactivation by glycerol, the physiological substrate, during catalysis. In permeabilized cells of Klebsiella pneumoniae, the inactivated enzyme is reactivated in the presence of ATP, Mg2+, and adenosylcobalamin. We identified the two open reading frames as the genes for a reactivating factor for glycerol dehydratase and designated them gdrA and gdrB. The reactivation of the inactivated glycerol dehydratase by the gene products was confirmed in permeabilized recombinant Escherichia coli cells coexpressing GdrA and GdrB proteins with glycerol dehydratase. 相似文献