全文获取类型
收费全文 | 2158篇 |
免费 | 378篇 |
出版年
2021年 | 23篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 54篇 |
2014年 | 53篇 |
2013年 | 116篇 |
2012年 | 90篇 |
2011年 | 82篇 |
2010年 | 68篇 |
2009年 | 55篇 |
2008年 | 78篇 |
2007年 | 77篇 |
2006年 | 81篇 |
2005年 | 60篇 |
2004年 | 56篇 |
2003年 | 63篇 |
2002年 | 65篇 |
2001年 | 87篇 |
2000年 | 68篇 |
1999年 | 62篇 |
1998年 | 38篇 |
1997年 | 41篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 30篇 |
1993年 | 36篇 |
1992年 | 52篇 |
1991年 | 38篇 |
1990年 | 60篇 |
1989年 | 44篇 |
1988年 | 49篇 |
1987年 | 48篇 |
1986年 | 66篇 |
1985年 | 39篇 |
1984年 | 41篇 |
1983年 | 42篇 |
1982年 | 39篇 |
1981年 | 29篇 |
1980年 | 26篇 |
1979年 | 41篇 |
1978年 | 34篇 |
1977年 | 29篇 |
1976年 | 31篇 |
1975年 | 21篇 |
1974年 | 22篇 |
1973年 | 18篇 |
1972年 | 17篇 |
1971年 | 19篇 |
1967年 | 18篇 |
排序方式: 共有2536条查询结果,搜索用时 15 毫秒
51.
Extracts of Chromobacterium violaceum catalyzed all of the reactions involved in synthesizing tryptophan from chorismic acid. Tryptophan auxotrophs which had lost any of these activities did not produce the characteristic purple pigment, violacein, when grown on a medium in which tryptophan was limiting. Gel filtration of extracts allowed us to estimate molecular weights for the tryptophan enzymes. All of the enzymes appeared to have molecular weights below 100,000. No enzymes were observed to occur in aggregates. The specific activities of the enzymes of the tryptophan pathway did not change when mutants were grown under conditions of limiting or excess tryptophan. The first enzyme in the pathway, anthranilate synthetase, was subject to feedback control by the end product, tryptophan. Tryptophan acted as a noncompetitive inhibitor with respect to glutamine, one of the substrates for anthranilate synthetase, and as a competitive inhibitor of the reaction when chorismate, the other substrate, was varied. The nonlinearity observed in the Lineweaver-Burk plot in the latter case suggests that there may be more than one chorismate-binding site on anthranilate synthetase. 相似文献
52.
53.
54.
55.
V P Crawford 《Journal of theoretical biology》1990,145(1):83-94
This paper studies the correspondence between Nash equilibrium and evolutionary stability in large- and finite-population "playing the field" models. Whenever the fitness function is sufficiently continuous, any large-population ESS corresponds to a symmetric Nash equilibrium in the game that describes the simultaneous interaction of the individuals in the population, and any strict, symmetric Nash equilibrium in that game corresponds to a large-population ESS. This correspondence continues to hold, approximately, in finite populations; and it holds exactly for strict pure-strategy equilibria in sufficiently large finite populations. By contrast, a sequence of (mixed-strategy) finite-population ESSs can converge, as the population grows, to a limit that is not a large-population ESS, and a large-population ESS need not be the limit of any sequence of finite-population ESSs. 相似文献
56.
57.
Paula K. Donnelly James A. Entry Don L. Crawford Kermit Cromack Jr 《Microbial ecology》1990,20(1):289-295
The concentration of lignin in plant tissue is a major factor controlling organic matter degradation rates in forest ecosystems.
Microbial biomass and lignin and cellulose decomposition were measured for six weeks in forest soil microcosms in order to
determine the influence of pH, moisture, and temperature on organic matter decomposition. Microbial biomass was determined
by chloroform fumigation; lignin and cellulose decomposition were measured radiometrically. The experiment was designed as
a Latin square with soils of pH of 4.5, 5.5, and 6.5 adjusted to 20, 40, or 60% moisture content, and incubated at temperatures
of 4, 12, or 24°C. Microbial biomass and lignin and cellulose decomposition were not significantly affected by soil acidity.
Microbial biomass was greater at higher soil moisture contents. Lignin and cellulose decomposition significantly increased
at higher soil temperatures and moisture contents. Soil moisture was more important in affecting microbial biomass than either
soil temperature or soil pH. 相似文献
58.
Bioremediation of soils contaminated with the herbicide 2-sec-butyl-4,6-dinitrophenol (dinoseb). 总被引:3,自引:2,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
R H Kaake D J Roberts T O Stevens R L Crawford D L Crawford 《Applied microbiology》1992,58(5):1683-1689
A novel soil treatment method for achieving the removal of dinoseb (2-sec-butyl-4,6-dinitrophenol) from contaminated soils was investigated. One soil contained dinoseb as the major contaminant, although several other hazardous compounds were also present. A second soil was highly contaminated with dinoseb. Dinoseb was not degraded in these soils under the aerobic conditions at each site. Pretreatment of the soils by the addition of a starchy potato-processing by-product and flooding with phosphate buffer stimulated the consumption of oxygen and nitrate from the soils, thereby lowering the redox potential and creating anaerobic conditions. Anaerobiosis (Eh less than -200 mV) promoted the establishment of an anaerobic microbial consortium that degraded dinoseb completely, without the formation of the polymerization products seen under aerobic or microaerophilic conditions. When dinoseb was present at low concentrations in a chronically contaminated soil, the natural microflora was capable of establishing anaerobic conditions and degrading dinoseb as a result of starch degradation. Inoculation of this soil with an aerobic starch-degrading microorganism and then an acclimated, anaerobic, dinoseb-degrading consortium did not improve dinoseb degradation. In a second acutely contaminated soil, these inoculations improved dinoseb degradation rates over those of uninoculated controls. 相似文献
59.
Comparison of extracellular peroxidase- and esterase-deficient mutants of Streptomyces viridosporus T7A. 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Peroxidase-deficient mutants of the lignin-degrading bacterium Streptomyces viridosporus T7A were screened for their production of acid-precipitable polymeric lignin, extracellular peroxidases and esterases, and immunoreactivities against a polyclonal antibody produced against electrophoretically purified peroxidase isoform P3 of wild-type S. viridosporus. The mutants showed diminished abilities to solubilize lignin and produce acid-precipitable polymeric lignin. Their peroxidase activities were decreased, and their esterase production patterns were altered. Western immunoblots demonstrated that the mutants produced proteins immunologically reactive with the antibody, but with different mobilities from those of wild-type proteins. These findings confirm a direct role for peroxidases in lignin solubilization. They also indicate a possible role for esterases. 相似文献
60.
A lignin peroxidase gene was cloned from Streptomyces viridosporus T7A into Streptomyces lividans TK64 in plasmid pIJ702. BglII-digested genomic DNA (4-10 kb) of S. viridosporus was shotgun-cloned into S. lividans after insertion into the melanin (mel+) gene of pIJ702. Transformants expressing pIJ702 with insert DNA were selected based upon the appearance of thiostrepton resistant (tsrr)/mel-colonies on regeneration medium. Lignin peroxidase-expressing clones were isolated from this population by screening of transformants on a tsr-poly B-411 dye agar medium. In the presence of H2O2 excreted by S. lividans, colonies of lignin peroxidase-expressing clones decolorized the dye. Among 1000 transformants screened, 2 dye-decolorizing clones were found. One, pIJ702/TK64.1 (TK64.1), was further characterized. TK64.1 expressed significant extracellular 2,4-dichlorophenol (2.4-DCP) peroxidase activity (= assay for S. viridosporus lignin peroxidase). Under the cultural conditions employed, plasmidless S. lividans TK64 had a low background level of 2.4-DCP oxidizing activity. TK64.1 excreted an extracellular peroxidase not observed in S. lividans TK64, but similar to S. viridosporus lignin peroxidase ALip-P3, as shown by activity stain assays on nondenaturing polyacrylamide gels. The gene was located on a 4 kb fragment of S. viridosporus genomic DNA. When peroxidase-encoding plasmid, pIJ702.LP, was purified and used to transform three different S. lividans strains (TK64, TK23, TK24), all transformants tested decolorized poly B-411. When grown on lignocellulose in solid state processes, genetically engineered S. lividans TK64.1 degraded the lignocellulose slightly better than did S. lividans TK64. This is the first report of the cloning of a bacterial gene coding for a lignin-degrading enzyme. 相似文献