全文获取类型
收费全文 | 180篇 |
免费 | 8篇 |
专业分类
188篇 |
出版年
2015年 | 1篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 2篇 |
2001年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1959年 | 13篇 |
1958年 | 20篇 |
1957年 | 18篇 |
1956年 | 18篇 |
1955年 | 16篇 |
1954年 | 20篇 |
1953年 | 16篇 |
1952年 | 13篇 |
1951年 | 6篇 |
1950年 | 4篇 |
1949年 | 1篇 |
1948年 | 3篇 |
排序方式: 共有188条查询结果,搜索用时 15 毫秒
151.
152.
Several factors which influence the speed of fermentation of quickly dried yeast are investigated. If the yeast is washed and the bulk of coenzymes and phosphate is removed, addition of 0.5 μmole diphosphopyridine nucleotide (DPN) and 0.5 μmole adenosine triphosphate (ATP) per cc. is necessary for maximal speed. In the optimal pH range, which lies between 6.6 and 6.2, and with optimal amounts of cofactors, there is no influence of nicotinamide mononucleotide (NMN), but with suboptimal amounts of DPN, the speed is raised by synthesis to DPN.The dialyzate of boiled juice contains factors which raise the speed of washed yeast by 20–30% of the maximum obtained in the presence of the usual cofactors. A phosphate concentration of 0.01–0.02 M is likewise necessary even if the phosphate is only partly esterified. At pH 6.0 to 5.9 the speed is less than half that at pH 6.5.Fermentation is completely absent without either K+ or NH4+ and without Mg. The optimal amount of the monovalent ions is 5 × 10?2M. Sodium alone is unable to allow fermentation but is only slightly harmful if enough K+ or NH4+ is present.Addition of small amounts of phosphoglycerate at optimal potassium phosphate concentration and pH increases the rate of sugar fermentation and gives rise to an extra CO2 formation during the time of phosphoglycerate decomposition of about 3 to 5 times the amount added. 相似文献
153.
Neurospora diphosphopyridine nucleotidase 总被引:17,自引:0,他引:17
154.
155.
156.
O. HADAS R. PINKAS N. MALINSKY‐RUSHANSKY A. NISHRI A. KAPLAN A. RIMMER A. SUKENIK 《Freshwater Biology》2012,57(6):1214-1227
1. We propose that the appearance and establishment of Nostocales (cyanobacteria) species of the genera Aphanizomenon and Cylindrospermopsis in the warm subtropical Lake Kinneret (Sea of Galilee, Israel) from 1994 was linked to changes in climate conditions and summer nitrogen (N) availability. 2. From 1994 to 2009, an increase in frequency of events of elevated water temperature (>29 °C) in summer, and to some extent a greater frequency of lower summer wind speed events, affected water turbulence and water column stratification, thus providing better physical conditions for the establishment of these populations. 3. In recent years, N‐depleted conditions in Lake Kinneret in early summer have promoted the development and domination of Nostocales that could gain an ecological advantage owing to their N2‐fixing capability. 4. Nitrogen fixation rates coincided both with heterocyst abundance and with Nostocales biomass. The N supplied to the lake via nitrogen fixation ranged from negligible quantities when Nostocales represented only a minor component of the phytoplankton community to 123 tonnes when Cylindrospermopsis bloomed in 2005. This high N2 fixation rate equals the average summer dissolved inorganic nitrogen load to the lake via the Jordan River. 相似文献
157.
Lathe WC rd; Burke WD; Eickbush DG; Eickbush TH 《Molecular biology and evolution》1995,12(6):1094-1105
R1 is a non-long terminal repeat (non-LTR) retrotransposable element that
inserts into a specific sequence of insect 28S ribosomal RNA genes. We have
previously shown that this element has been maintained through vertical
transmission in the melanogaster species subgroup of Drosophila. To address
whether R1 elements have been vertically transmitted for longer periods of
evolutionary time, the analysis has been extended to 11 other species from
four species groups of the genus Drosophila (melanogaster, obscura,
testecea, and repleta). All sequenced elements appeared functional on the
basis of the preservation of their open-reading frames and consistently
higher rate of substitution at synonymous sites relative to replacement
sites. The phylogenetic relationships of the R1 elements from all species
analyzed were congruent with the species phylogenies, suggesting that the
R1 elements have been vertically transmitted since the inception of the
Drosophila genus, an estimated 50-70 Mya. The stable maintenance of R1
through the germ line appears to be the major mechanism for the widespread
distribution of these elements in Drosophila. In two species, D.
neotestecea of the testecea group and D. takahashii of the melanogaster
group, a second family of R1 elements was also present that differed in
sequence by 46% and 31%, respectively, from the family that was congruent
with the species phylogeny. These second families may represent occasional
horizontal transfers or, alternatively, they could reflect the ability of
R1 elements to diverge into new families within a species and evolve
independently.
相似文献
158.
159.
160.