全文获取类型
收费全文 | 8032篇 |
免费 | 494篇 |
国内免费 | 1358篇 |
出版年
2024年 | 43篇 |
2023年 | 156篇 |
2022年 | 271篇 |
2021年 | 319篇 |
2020年 | 348篇 |
2019年 | 322篇 |
2018年 | 272篇 |
2017年 | 273篇 |
2016年 | 291篇 |
2015年 | 256篇 |
2014年 | 355篇 |
2013年 | 683篇 |
2012年 | 309篇 |
2011年 | 385篇 |
2010年 | 279篇 |
2009年 | 482篇 |
2008年 | 497篇 |
2007年 | 418篇 |
2006年 | 382篇 |
2005年 | 399篇 |
2004年 | 268篇 |
2003年 | 261篇 |
2002年 | 243篇 |
2001年 | 172篇 |
2000年 | 150篇 |
1999年 | 151篇 |
1998年 | 128篇 |
1997年 | 149篇 |
1996年 | 142篇 |
1995年 | 142篇 |
1994年 | 161篇 |
1993年 | 143篇 |
1992年 | 117篇 |
1991年 | 103篇 |
1990年 | 114篇 |
1989年 | 87篇 |
1988年 | 62篇 |
1987年 | 50篇 |
1986年 | 69篇 |
1985年 | 85篇 |
1984年 | 80篇 |
1983年 | 41篇 |
1982年 | 45篇 |
1981年 | 37篇 |
1980年 | 29篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1977年 | 37篇 |
1976年 | 14篇 |
1975年 | 5篇 |
排序方式: 共有9884条查询结果,搜索用时 15 毫秒
81.
Abstract The thermophilic facultatively phototrophic green bacterium Chloroflexus aurantiacus strain Ok-70-fl was shown to possess sulfide-repressed hydrogenase activity. Biosynthesis of the enzyme was severely repressed by S2− (5.7 mM) and stimulated specifically by Ni2+ and by molecular hydrogen. The hydrogenase was shown to be localized in the cytoplasmic membrane and could be solubilized from the latter by the detergent Triton X-100 in a state forming one enzymatically active band ( M r 170 × 103 ) in polyacrylamide gels. In the membraneous state, the hydrogenase had its maximal activity at 73°C and was active with methyl viologen, methylene blue, menadione and flavins, but not with NAD or NADP as electron acceptors. Solubilization of the enzyme with Triton X-100 resulted in a drastic increase in the FAD/FMN-linked activity. 相似文献
82.
Corrado Fogher Ilona Dusha∗ Patricia Barbot Claudine Elmerich∗ 《FEMS microbiology letters》1985,30(1-2):245-249
Abstract Probes containing the nod and hsn regions of Rhizobium meliloti and the fixABC genes of Rhizobium japonicum were used to perform hybridization experiments with endonuclease-restricted DNA from Azospirillum brasilense strains and 2 Azospirillum lipoferum strains. Homology to nod, hsn and fixA was found in the 4 Azospirillum strains. 相似文献
83.
84.
85.
The phylogenetically related phototrophic bacteria Rhodospirillum tenue and Rhodocyclus purpureus modulate activity of their glutamine synthetases by adenylylation/deadenylylation. Evidence for covalent modification includes the inhibitory effect of Mg2+ on the activity of glutamine synthetase extracted from cells of either species grown on excess ammonia, and the lack of Mg2+ inhibition of activity of the enzyme isolated from N2-(R. tenue) or glutamine (R. purpureus)-grown cells. In addition, snake venom phosphodiesterase treatment of glutamine synthetase from either species grown on excess ammonia relieved Mg2+ inhibition of the enzyme (as measured via the -glutamyl transferase assay), and changed the cation specificity from Mn2+ to Mg2+ (in the biosynthetic assay). 相似文献
86.
Antisera have been developed against the wholecell antigens of Desulfovibrio africanus Benghazi and Walvis Bay, D. vulgaris Hildenborough, D. salexigens British Guiana, D. gigas, and D. desulfuricans Essex 6. An enzymelinked immunoadsorption assay (ELISA) was developed to measure the reaction of these antisera with the homologous and heterologous antigens. The ELISA method demonstrated a reaction between pre-immune sera and cells of D. africanus, D. gigas and D. desulfuricans, suggesting the presence of a lectin-like substance on these cell surfaces. Extensive cross-reactions were seen between the antisera and heterologous cells, suggesting the sharing of a number of surface antigens amongst the Desulfovibrio. However, the pattern of these cross-reactions was different from that observed for an ELISA reaction developed for the cytochrome c3 from various Desulfovibrio.Abbreviation ELISA
enzyme-linked immunoadsorption assay 相似文献
87.
Respiratory chain phosphorylation has been investigated in the methylotrophic bacterium Methylophilus methylotrophus following the addition of oxidisable substrates to aerobic, whole cell suspensions. Initial-rate experiments showed that ATP synthesis occurred at the overall expense of AMP and inorganic phosphate via the sequential action of the ATP phosphohydrolase and adenylate kinase; some of the nascent ATP was rapidly used to synthesis nonadenine nucleoside triphosphates. After being corrected for ATP turnover, Pi/O quotients of 0.46 to 0.54, 0.77 and 1.37 nmol/ng-atom O were obtained for the oxidation of methanol dehydrogenase-linked substrates (methanol, ethanol and acetaldehyde), duroquinol and formate (NAD+-linked) respectively. These values were proportional to the H+/O and/or K+/O quotients exhibited by these substrates, and yielded an average H+/ATP (H+/Pi) quotient of 4.2 ng-ion H+/nmol. Steady-state experiments showed that the extent of cellular energisation varied with the respiration rate but was always in the order methanol > duroquinol > acetaldehyde, thus indicating that under these longer-term conditions methanol was completely oxidised to yield PQQH2 and 2NAD(P)H. These results are discussed in terms of the various reactions which lead to the generation or utilisation of the protonmotive force in this organism.Abbreviations FCCP
carbonylcyanide p-trifluoromethyxyphenyl-hydrazone
-
bulk phase, transmembrane electrochemical potential difference of protons (
)
- pH
bulk phase, transmembrane pH difference (pHin–pHout)
-
bulk phase, transmembrane electrical potential difference (in - out)
- [P]
concentration of anhydride phosphate bonds in adenine nucleotides (2[ATP]+[ADP])
- FPLC
fast protein liquid chromatography
- PQQ
pyrroloquinoline quinone
- Gp
phosphorylation potential 相似文献
88.
Andrew W. West H.D. Burges R.J. White C.H. Wyborn 《Journal of invertebrate pathology》1984,44(2):128-133
Spores and parasporal crystals of a Bacillus thuringiensis var. aizawai (H-serotype 7), strain HD137, streptomycin-resistant mutant were added to acidic (pH 5.0) natural and autoclaved soil and incubated at ?0.10 MPa, 25°C. Populations of B. thuringiensis in both soil treatments showed exponential rates of mortality which were represented by linear regression, the loss of viability being greater in natural than autoclaved soil. In natural soil, parasporal crystal insecticidal activity was lost at a complex, nonexponential rate. The initial, rapid decrease of activity gradually slowed, and the level of activity stabilized at 10% of the original inoculum level after 250 days incubation, until the cessation of sampling at >2 years. In autoclaved soil no significant (P > 0.2) loss of parasporal crystal insecticidal activity was detected over the same period, which suggested that soil microorganisms were responsible for the loss of crystal insecticidal activity in the natural, nonsterilized soil. The rate of loss of crystal activity in natural soil correlated well with assay data reported in the literature using Galleria mellonella, which measures the combined activity of spore and crystal. In autoclaved soil correlation was poor, probably due to variability in the bioassay data. 相似文献
89.
Dr. Paul A. Lespinat Yves M. Berlier Guy D. Fauque Rene Toci Gerard Denariaz Jean LeGall 《Journal of industrial microbiology & biotechnology》1987,1(6):383-388
Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D2–H+ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism. 相似文献
90.
Karsten Pedersen Carola Holmström Anna-Kerstin Olsson Amelie Pedersen 《Archives of microbiology》1986,145(1):1-8
A budding coccoid bacterium, (CH1), a Vibrio sp. and a Pseudomonas sp. were investigated for factors governing their attachment to glass surfaces in static batch culture and laminar flow continuous culture systems. An analysis of variance showed that the three species exhibited very different responses. For CH1 attachment was dependent on cell density, incubation time and nutrient concentration. The Vibrio sp. was affected by nutrient concentration while the attachment of the Pseudomonas sp. was independent of cell density, incubation time and nutrient concentration. A comparison of attachment to hydrophilic and hydrophobic surfaces showed that attachment of the Vibrio sp. and CH1 to hydrophilic surfaces was 3 and 10 times greater respectively than to hydrophobic surfaces while Pseudomonas attached in equal numbers to both surfaces. The continuous culture system with defined flow hydrodynamics and growth conditions at steady state revealed a random sampling effect 3 times smaller than the batch culture system did. When the biofilm development of Pseudomonas sp. was followed during 46 h at different fluid shear under laminar and turbulent flow conditions, the former biofilm reached 3.3·108 cells·cm-2 and the latter 8.2·107 cells·cm-2.Non-common abbreviation NSS
Nine salt solution 相似文献