全文获取类型
收费全文 | 4365篇 |
免费 | 361篇 |
国内免费 | 5篇 |
出版年
2023年 | 20篇 |
2022年 | 29篇 |
2021年 | 67篇 |
2020年 | 42篇 |
2019年 | 48篇 |
2018年 | 60篇 |
2017年 | 50篇 |
2016年 | 111篇 |
2015年 | 181篇 |
2014年 | 195篇 |
2013年 | 227篇 |
2012年 | 324篇 |
2011年 | 304篇 |
2010年 | 182篇 |
2009年 | 181篇 |
2008年 | 260篇 |
2007年 | 273篇 |
2006年 | 227篇 |
2005年 | 248篇 |
2004年 | 226篇 |
2003年 | 224篇 |
2002年 | 214篇 |
2001年 | 57篇 |
2000年 | 64篇 |
1999年 | 68篇 |
1998年 | 58篇 |
1997年 | 38篇 |
1996年 | 32篇 |
1995年 | 51篇 |
1994年 | 52篇 |
1993年 | 39篇 |
1992年 | 41篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 43篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 21篇 |
1985年 | 36篇 |
1984年 | 22篇 |
1983年 | 28篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1973年 | 13篇 |
1971年 | 14篇 |
1967年 | 8篇 |
1965年 | 9篇 |
排序方式: 共有4731条查询结果,搜索用时 15 毫秒
21.
Influences of the salt concentration on the fatty acid composition of Ectothiorhodospira species and other phototrophic purple bacteria have been analysed. Major fatty acids in bacteria of the genera Rhodobacter, Rhodopseudomonas, Chromatium, and Ectothiorhodospira were straight chain saturated and monounsaturated C-16 and C-18 fatty acids. Salt-dependent responses of all investigated bacteria revealed relations to their salt optima. Minimum values of C-16 and saturated fatty acids and maximum values of C-18 and unsaturated fatty acids were found at or close to the salt optima. Responses of Ectothiorhodospira mobilis upon changes in salinity were nearly identical, whether cells were grown in batch culture or in continuous culture with identical dilution rates at all salt concentrations. With increasing temperature, the fatty acid composition of Ectothiorhodospira mobilis and Ectothiorhodospira halophila strains showed decreasing portions of C-18 and of unsaturated fatty acids, while the contents of C-16 and saturated fatty acids increased. The results are discussed with respect to bilayer stabilisation and membrane fluidity.Abbreviations PC
phosphatidylcholine
- PG
phosphatidylglycerol
- CL
cardiolipin
- PE
phosphatidylethanolamine 相似文献
22.
Chromophoric [4-(dimethylamino)cinnamoyl]imidazole reacts with the serine protease alpha-chymotrypsin to form an acyl enzyme. At pHs below 4.0, the acyl enzyme turns over very slowly to yield the free acid. During this slow deacylation it is possible to obtain a very good resonance Raman spectrum of the acyl intermediate by using the 350.7-nm line of the krypton laser. The resonance Raman carbonyl frequency of the covalently bonded substrate and its wavelength at maximum intensity in the absorption spectrum of the acyl enzyme have been taken and used to monitor the active site environment. A comparison has been made of the absorption and Raman spectra of the acyl enzyme and those of the corresponding chromophoric methyl ester, aldehyde, and imidazole model compounds. A linear correlation is found between the wavelength of maximum absorption and the Raman frequency of the carbonyl group over a wide range of solvent conditions for each of the model compounds. By combining the Raman carbonyl frequency with the absorption maximum, we can determine that the bond order changes in the carbonyl bond of the bound substrate are not due to changes in the solvent, since the carbonyl frequency and the absorption maximum of the acyl enzyme do not fall on any of the linear correlations for the model compounds. The unusual spectroscopic properties of the bound substrate appear to be due to some specific enzyme-induced change in the substrate when it is bound at the active site. Thermal unfolding of the acyl enzymes changes both the carbonyl frequency of the acyl enzyme and its absorption maximum to completely different values.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
23.
Bernhard Knig Patricia A. DiNitto Peter M. Blumberg 《Journal of cellular biochemistry》1985,29(1):37-44
The major phorbol ester receptor is the Ca++-activated, phospholipid-dependent protein kinase C. Diacylglycerol stimulates protein kinase C in a fashion similar to the phorbol esters. Likewise, it inhibits phorbol ester binding competitively. Both results suggest that diacylglycerol is the/an endogenous phorbol ester analogue. Alternatively, the diacylglycerol might simply be acting to modify the phospholipid environment of the protein. If diacylglycerol were indeed functioning as an analogue, it should interact with the receptor stoichiometrically. This interaction can be quantitated by measuring the perturbation in apparent diacylglycerol binding affinity as a function of the ratio of diacylglycerol to receptor. We report here that 1,2-dioleoylglycerol interacts with the receptor with the predicted stoichiometry. 相似文献
24.
Bernhard Reinicke Peter Blümel Harald Labischinski Peter Giesbrecht 《Archives of microbiology》1985,141(4):309-314
In contrast to what has been postulated, penicillin G at its optimal lytic concentration of 0.1 g per ml did not lead to a detectable activation of autolytic wall processes in staphylococci in terms of the release of uniformly labelled wall fragments from cells pretreated with the drug for 1 h. Rather a considerable inhibition of this release was observed. A similarly profound inhibition of the release of peptidoglycan fragments occurred when staphylococci pretreated for 1 h with 0.1 g penicillin per ml acted as a source of crude autolysins on peptidoglycan isolated from labelled normal cells of the same strain. This clearly demonstrated that the overall inhibition of autolytic wall processes caused by penicillin was mainly due to a decreased total autolysin action rather than to an altered wall structure. Furthermore, no substantial penicillin-induced inhibition of the incorporation of 14C-N-acetylglucosamine into the staphylococcal wall could be observed before bacteriolysis started, i. e., approximately during the first 80 min of penicillin action. These results are not consistent with any of the models hitherto proposed for the action of penicillin.Dedicated to Prof. Dr. Gerhart Drews on the occasion of his 60th birthday 相似文献
25.
Bernhard Ronacher Heiner Römer 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,157(5):631-642
In recordings from single tympanic receptor fibres in C. biguttulus, the response to synthesized sounds (rectangularly modulated white noise) interrupted by very brief (a few milliseconds) gaps was examined. In behavioral tests, females of the species respond very differently to such 'model syllables' at moderate intensities, depending on the gap width. If the gaps (in a moderate-intensity syllable) are larger than 2 ms, the stimulus fails to elicit a response, whereas stimuli with gaps smaller than 1 ms are as effective as uninterrupted syllables (D. von Helversen 1972; O. von Helversen 1979). Neither the mean spike count nor the interspike-interval distribution of the single receptor response contains the information sufficient to distinguish uninterrupted syllables from syllables with gaps. On the other hand, examination of the temporal distribution of the spikes reveals that gaps (or the pulse onsets following the gaps) cause spike synchronization. An index of synchronization (IS) was defined as a measure of this gap-induced effect. Analysis of the receptor responses based on IS revealed differences that correspond quantitatively to the abrupt abolition of the behavioral response at a gap-width between 1 and 2 ms. From the hypothesis that such brief gaps are detected by the nervous system by way of spike synchronization in the tympanic nerve, one can predict certain features of the behavioral response to high-intensity stimuli. The gap-induced spike synchronization was more pronounced at higher temperatures. This effect was demonstrated in both summated recordings from the tympanic nerve and single fibre recordings. Experiments with primary auditory fibres of Locusta migratoria showed that the receptors in this species respond very similarly to the same stimuli. That is, the receptors of C. biguttulus are not specially adapted for detecting very brief gaps. Synchronization of the spikes in parallel receptor fibres of the tympanal nerve is probably a general feature of acridids; we infer that in C. biguttulus this gap-induced synchronized activity is detected by special processing in higher auditory centres. 相似文献
26.
Carol Burck James A. Shapiro Bernhard Hauer 《Molecular & general genetics : MGG》1984,194(1-2):340-342
Summary A pCM2 replicon derived by an N– deletion from ::Tn9 which carries the imm434 immunity region is incompatible with some (but not all) IncP-1 plasmids. The imm pCM1 replicon does not show the same incompatibility behavior. 相似文献
27.
Cytochromec oxidase was isolated from human hearts and separated by SDS gel electrophoresis. The identity of polypeptide bands with known subunits was demonstrated by immunoblotting with monospecific antisera to rat liver cytochromec oxidase subunits. The polarographically determined kinetics of cytochromec oxidation were similar to those reported for the bovine heart enzyme. 相似文献
28.
Bernhard Kadenbach 《Journal of bioenergetics and biomembranes》1986,18(1):39-54
The present view on the regulation of respiration and ATP synthesis in higher organisms implies only Michaelis-Menten type kinetics and respiratory control as regulatory principles. Recent experimental observations, suggesting further regulatory mechanisms at respiratory chain complexes, are reviewed. A new hypothesis is presented implying regulation of respiration and ATP synthesis in higher organisms mainly via allosteric modification of respiratory chain complexes, in particular of cytochromec oxidase. The allosteric effectors, e.g., metabolites, cofactors, ions, hormones, and the membrane potential are suggested to change the activity and the coupling degree of cytochromec oxidase by binding to specific sites at nuclear coded subunits. Recent results on the structure and activity of cytochromec oxidase, supporting the hypothesis, are reviewed.Dedicated to Professor Dr. Carl Martius on the occasion of his 80th birthday. 相似文献
29.
From anaerobic freshwater enrichment cultures with 3-hydroxybenzoate as sole substrate, a slightly curved rod-shaped bacterium was isolated in coculture with Desulfovibrio vulgaris as hydrogen scavenger. The new isolate degraded only 3-hydroxybenzoate or benzoate, and depended on syntrophic cooperation with a hydrogenoxidizing methanogen or sulfate reducer. 3-Hydroxybenzoate was degraded via reductive dehydroxylation to benzoate. With 2-hydroxybenzoate (salicylate), short coccoid rods were enriched from anaerobic freshwater mud samples, and were isolated in defined coculture with D. vulgaris. This isolate also fermented 3-hydroxybenzoate or benzoate in obligate syntrophy with a hydrogen-oxidizing anaerobe. The new isolates were both Gram-negative, non-sporeforming strict anaerobes. They fermented hydroxybenzoate or benzoate to acetate, CO2, and, presumably, hydrogen which was oxidized by the syntrophic partner organism. With hydroxybenzoates, but not with benzoate, Acetobacterium woodii could also serve as syntrophic partner. Other substrates such as sugars, alcohols, fatty or amino acids were not fermented. External electron acceptors such as sulfate, sulfite, nitrate, or fumarate were not reduced. In enrichment cultures with 4-hydroxybenzoate, decarboxylation to phenol was the initial step in degradation which finally led to acetate, methane and CO2. 相似文献
30.
Abstract A method for extraction of microbial populations from wood samples was worked out which gave good recovery of both aerobic and anaerobic microorganisms in agar shake dilution and plating enumerations. This method was applied to the quantification of microbial populations in three European white firs ( Abies alba Mill.) which were afflicted with the European fir disease. Low numbers of aerobic microorganisms (102 −104 colony- forming units (cfu) per g fresh tissue) were detected in sapwood irrespective of the degree of affliction. Anaerobic bacteria were usually 1–2 orders of magnitude less frequent. Wetwood of highly diseased firs contained significantly higher numbers of aerobic microorganisms (105 −107 ), whereas the number of anaerobes was not enhanced significantly. Among the prevalent aerobic microorganisms in wetwood were Protaminobacter, Pseudomonas strains, and a yeast. In anaerobic counts from wetwood, Klebsiella and Vibrio strains predominated. The sapwood contained Bacillus, Beijerinckia, Staphylococcus , and Clostridium spp. High numbers of aerobic microorganisms were also detected in the roots and lower stem of a diseased vine plant ( Vitis vinifera L.). The importance of microbial populations in wetwood formation and disease expression is discussed. 相似文献