全文获取类型
收费全文 | 766篇 |
免费 | 80篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 3篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 24篇 |
2017年 | 25篇 |
2016年 | 27篇 |
2015年 | 33篇 |
2014年 | 31篇 |
2013年 | 42篇 |
2012年 | 50篇 |
2011年 | 47篇 |
2010年 | 39篇 |
2009年 | 28篇 |
2008年 | 29篇 |
2007年 | 47篇 |
2006年 | 37篇 |
2005年 | 32篇 |
2004年 | 35篇 |
2003年 | 23篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 22篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1964年 | 1篇 |
排序方式: 共有846条查询结果,搜索用时 15 毫秒
1.
2.
The inhibition of respiratory chain activities in rat liver, rat heart and bovine heart mitochondria by the anthracycline antibiotic adriamycin was measured in order to determine the adriamycin-sensitive sites. It appeared that complex III and IV are efficiently affected such that their activities were reduced to 50% of control values at 175 +/- 25 microM adriamycin. Complex I displayed a minor sensitivity to the drug. Of the complex-I-related activities tested, only duroquinone oxidation appeared sensitive (50% inhibition at approx. 450 microM adriamycin). Electron-transfer activities catalyzed by complex II remained essentially unaltered up to high drug concentrations. Of the activities measured for this complex, only duroquinone oxidation was significantly affected. However, the adriamycin concentration required to reduce this activity to 50% exceeded 1 mM. Mitochondria isolated from rat liver, rat heart and bovine heart behaved essentially identical in their response to adriamycin. These data support the conclusion that, in these three mitochondrial systems, the major drug-sensitive sites lie in complex III and IV. Cytochrome c oxidase and succinate oxidase activity in whole mitochondria exhibited a similar sensitivity towards adriamycin, as inner membrane ghosts, suggesting that the drug has direct access to its inner membrane target sites irrespective of the presence of the outer membrane. By measuring NADH and succinate oxidase activities in the presence of exogenously added cytochrome c, it appeared that adriamycin was less inhibitory under these conditions. This suggests that adriamycin competes with cytochrome c for binding to the same site on the inner membrane, presumably cardiolipin. 相似文献
3.
The internal pH of peroxisomes in the yeasts Hansenula polymorpha, Candida utilis and Trichosporon cutaneum X4 was estimated by 31P nuclear magnetic resonance (NMR) spectroscopy. 31P NMR spectra of suspensions of intact cells of these yeasts, grown under conditions of extensive peroxisomal proliferation, displayed two prominent Pi-peaks at different chemical shift positions. In control cells grown on glucose, which contain very few peroxisomes, only a single peak was observed. This latter peak, which was detected under all growth conditions, was assigned to cytosolic Pi at pH 7.1. The additional peak present in spectra of peroxisome-containing cells, reflected Pi at a considerably lower pH of approximately 5.8–6.0. Experiments with the protonophore carbonyl cyanide m-chlorophenylhydrazon (CCCP) and the ionophores valinomycin and nigericin revealed that separation of the two Pi-peaks was caused by a pH-gradient across a membrane separating the two pools. Experiments with chloroquine confirmed the acidic nature of one of these pools. In a number of transfer experiments with the yeast H. polymorpha it was shown that the relative intensity of the Pi-signal at the low pH-position was correlated to the peroxisomal volume fraction. These results strongly suggest that this peak has to be assigned to Pi in peroxisomes, which therefore are acidic in nature. The presence of peroxisome-associated Pi was confirmed cytochemically.Abbreviations CCCP
Carbonyl cyanide m-chlorophenylhydrazon
- DCCD
N,N-dicyclohexylcarbodiimide 相似文献
4.
Summary The protease fromC. ficifolia was applied to stickwater prior to evaporation. The evaporator was operated at reduced viscosities with an increase in solid concentration beyond 50% as compared to the untreated substrate. 相似文献
5.
Abstract The influence of a seed-dressing with rhizosphere bacteria on the infection of sugarbeet by fungi of the genus Pythium I. Antagonistic effect of different bacterial isolates towards Pythium spp.
Seed treatment with selectively isolated rhizosphere bacteria from the fluorescent pseudomonad group can protect sugar beet seedlings from damping-off caused by species of Pythium. The antagonistic rhizobacteria were equally effective in different soil substrates, both unsterilized and steam-sterilized. Antagonistic activity of an isolate was similar within seeds of a sugarbeet cultivar but different when different cultivars were compared. The number of bacteria adhering to the seed of eachcultivar which influenced the level of antagonism to Pythium infection, varied with seed morphology. A mixture of the three different isolates did not increase antagonistic activity when compared to the activity of the isolates individually. 相似文献
Seed treatment with selectively isolated rhizosphere bacteria from the fluorescent pseudomonad group can protect sugar beet seedlings from damping-off caused by species of Pythium. The antagonistic rhizobacteria were equally effective in different soil substrates, both unsterilized and steam-sterilized. Antagonistic activity of an isolate was similar within seeds of a sugarbeet cultivar but different when different cultivars were compared. The number of bacteria adhering to the seed of eachcultivar which influenced the level of antagonism to Pythium infection, varied with seed morphology. A mixture of the three different isolates did not increase antagonistic activity when compared to the activity of the isolates individually. 相似文献
6.
The influence of variation of the phospholipid composition in model membranes composed of phosphatidylcholine and phosphatidylethanolamine on the hydrolysis of these phospholipids by rat liver mitochondrial phospholipase A2 was investigated. With the pure phospholipids, phosphatidylethanolamine was hydrolyzed over 30-times faster than phosphatidylcholine. Upon increasing the mole percentage of phosphatidylethanolamine in mixtures, a gradual, though non-linear, increase in the initial rate of hydrolysis of this phospholipid was observed. By contrast, phosphatidylcholine hydrolysis remained constant up to about 50 mol% phosphatidylethanolamine, whereafter a sudden fall-off of activity was observed. This drop in the hydrolysis rate coincided with a transition of the phospholipid structure from bilayer to an as yet unidentified organization characterized by an isotropic signal in the 31P-NMR spectra recorded in the presence of Ca2+. The occurrence of this phase was clearly dependent on Ca2+, since mixtures with identical composition in the absence of Ca2+ remained largely in bilayer configuration. That the structure adopted by phospholipids is of importance for their susceptibility to attack by this intracellular phospholipase A2 became evident also in studies with the single phospholipids in the absence or presence of Triton X-100 above the critical micellar concentration. While phosphatidylcholine hydrolysis was inhibited in mixed micelles as compared to its bilayer organization, the hydrolysis of phosphatidylethanolamine in mixed micelles was 3-fold that in the hexagonal HII phase. 相似文献
7.
Milan Höfer Klaas Nicolay George Robillard 《Journal of bioenergetics and biomembranes》1985,17(3):175-182
The electrochemical gradient of protons,
, was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH0 range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP+) for negative above pH0 4.5, and thiocyanate (SCN–) for positive below pH0 4.5. The chemical gradient of H+ was determined by measuring the chemical shift of intracellular Pi by31P-NMR at given pH0 values. The values of pHi increased almost linearly from 7.3 at pH0 3 to 7.8 at pH0 8.5. In the physiological pH0 range from 3.5 to 6,
was fairly constant at values between 17–18 KJ mol–1, gradually decreasing at pH0 above 6. In deenergized cells, the intracellular pHi decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH0 4.5 or 7.5. There was no membrane potential detectable in deenergized cells. 相似文献
8.
In vivo 31P and 13C nuclear magnetic resonance studies of acetate metabolism in Chromatium vinosum 总被引:2,自引:1,他引:1 下载免费PDF全文
K Nicolay H van Gemerden K J Hellingwerf W N Konings R Kaptein 《Journal of bacteriology》1983,155(2):634-642
31P and 13C nuclear magnetic resonance (NMR) experiments were performed on suspensions of the phototrophic bacterium Chromatium vinosum incubated anaerobically in the dark. 31P NMR spectra revealed that during prolonged dark incubation high ATP levels are maintained. This phenomenon was independent of the presence of the energy reserves polyglucose and polyphosphate. 13C NMR experiments revealed that the amino acids glutamate, aspartate, and alanine are the major products of acetate incorporation in the dark. Apart from these amino acids, poly-beta-hydroxybutyrate was also formed. Acetate metabolism was markedly stimulated by the presence of polyglucose. The specific 13C activity of glutamate C-2 was approximately 50% that of glutamate C-4. The idea is discussed that this difference is the consequence of the maintenance of redox balance during entry of acetate into cell metabolism. 相似文献
9.
Oxidation of Neurospora crassa NADP-specific glutamate dehydrogenase by activated oxygen species. 总被引:2,自引:1,他引:1 下载免费PDF全文
The glutamine synthetase and the NADP-specific glutamate dehydrogenase activities of Neurospora crassa were lost in a culture without carbon source only when in the presence of air. Glutamine synthetase was previously reported to be liable to in vitro and in vivo inactivation by activated oxygen species. Here we report that NADP-specific glutamate dehydrogenase was remarkably stable in the presence of activated oxygen species but was rendered susceptible to oxidative inactivation when chelated iron was bound to the enzyme and either ascorbate or H2O2 reacted on the bound iron. This reaction gave rise to further modifications of the enzyme monomers by activated oxygen species, to partial dissociation of the oligomeric structure, and to precipitation and fragmentation of the enzyme. The in vitro oxidation reaction was affected by pH, temperature, and binding to the enzyme of NADPH. Heterogeneity in total charge was observed in the purified and immunoprecipitated enzymes, and the relative amounts of enzyme monomers with different isoelectric points changes with time of the oxidizing reaction. 相似文献
10.
Neuropeptide Y-like immunoreactivity was studied in the thalamus of the cat using an indirect immunoperoxidase method. The densest network of immunoreactive fibers was observed in the nucleus (n.) paraventricularis anterior. In the anterior, intralaminar and midline thalamic nuclei, as well as in the n. geniculatum medialis, n. geniculatum lateralis, n. habenularis lateralis, n. medialis dorsalis, n. lateralis posterior and n. pulvinar a low density of neuropeptide Y-like immunoreactive fibers was observed. Neuropeptide Y-like fibers were totally absent in the n. ventralis lateralis, n. ventralis medialis, n. ventralis postero-medialis and n. ventralis postero-lateralis. In addition, neuropeptide Y-like perikarya were found in the n. parafascicularis, n. suprageniculatus, n. geniculatum lateralis ventralis, n. medialis dorsalis and n. lateralis posterior. 相似文献