全文获取类型
收费全文 | 1888篇 |
免费 | 229篇 |
出版年
2022年 | 15篇 |
2021年 | 38篇 |
2020年 | 17篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 49篇 |
2015年 | 84篇 |
2014年 | 69篇 |
2013年 | 101篇 |
2012年 | 97篇 |
2011年 | 91篇 |
2010年 | 71篇 |
2009年 | 56篇 |
2008年 | 101篇 |
2007年 | 83篇 |
2006年 | 90篇 |
2005年 | 77篇 |
2004年 | 76篇 |
2003年 | 63篇 |
2002年 | 56篇 |
2001年 | 53篇 |
2000年 | 46篇 |
1999年 | 44篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 18篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 27篇 |
1990年 | 37篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 33篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 16篇 |
1979年 | 17篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 11篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 21篇 |
1972年 | 11篇 |
1970年 | 13篇 |
排序方式: 共有2117条查询结果,搜索用时 15 毫秒
1.
2.
3.
N. J. Belshaw S. Hakola H. Nevalainen M. Penttil? P. Suominen D. B. Archer 《Molecular & general genetics : MGG》1997,256(1):18-27
Three DNA fragments, trs1, 2 and 3, were isolated from the Trichoderma reesei genome on the basis of their ability to promote autonomous replication of plasmids in Saccharomyces cerevisiae. Each trs element bound specifically to the isolated T. reesei nuclear matrix in vitro, and two of them bound in vivo, indicating that they are matrix attachment regions (MARs). A similar
sequence previously isolated from Aspergillus nidulans (ans1) was also shown to bind specifically to the T. reesei nuclear matrix in vitro. The T. reesei MARs are AT-rich sequences containing 70%, 86% and 73% A+T over 2.9, 0.8 and 3.7 kb, respectively for trs1, 2 and 3. They exhibited no significant sequence homology, but were shown to contain a number of sequence motifs that occur frequently
in many MARs identified in other eukaryotes. However, these motifs occurred as frequently in the trs elements as in randomly generated sequences with the same A+T content. trs1 and 3 were shown to be present as single copies in the T. reesei genome. The presence of the trs elements in transforming plasmids enhanced the frequency of integrative transformation of T. reesei up to five fold over plasmids without a trs. No evidence was obtained to suggest that the trs elements promoted efficient replication of plasmids in T. reseei. A mechanism for the enhancement of transformation frequency by the trs elements is proposed.
Received: 1 March 1997 / Accepted: 13 May 1997 相似文献
4.
Benedict G. Archer 《Analytical biochemistry》1981,113(2):439-443
A gel filtration method has been developed for the complete removal of sodium dodecyl sulfate (SDS) from proteins and peptides. The protein or peptide (20 μg–10 mg) containing SDS (up to 30–60 mg) is dissolved in a mixture of propionic acid, formic acid, and water (2:1:2, ). Under these conditions, protein-SDS (or peptide-SDS) complexes, as well as SDS micelles, are dissociated. Subsequently, protein and SDS can be separated on a small Sephadex G-25 superfine column. The recovery of protein is typically 90% or more. 相似文献
5.
Summary An improved method for separating analogues of coenzyme F420 by isocratic reversed-phase high performance liquid chromatography is described. The method offers improved resolution, shorter chromatography runs and requires less complex apparatus. 相似文献
6.
7.
Within- and between-species patterns of allocation to pulp and seed in vertebrate dispersed plants 总被引:1,自引:0,他引:1
Will Edwards 《Oikos》2005,110(1):109-114
Non-uniform scaling of pulp and seed mass has been shown to alter dispersal probabilities in vertebrate dispersed species. Since dispersal in tropical forests is strongly linked to establishment success, processes determining allocation to pulp and seed are likely to impact on parental fitness, and therefore should be under the control of natural selection. In this study I examine size-dependent dry mass allocation pattern to pulp and seed mass both among and within 20 fruit-producing plant species of tropical rainforest in northeast Queensland, Australia. Reduced major axis analyses using mean values for each species showed significant isometry, indicating that at the community level, plant species that employ vertebrates as a means of seed dispersal tend to allocate an equivalent mean relative proportion of the overall dry weight investment in fruit to pulp. However, identical analyses conducted for each species separately revealed that relationships within individual species do not reflect the inter-specific relationship. These results imply two influences on dry mass allocation to fruit components; the first (within-species allometry) determines how fruits vary within each species. The second (between-species allometry) operates in a similar manner across species to produce equal ratios of mean pulp and seed mass independent of within-species allometries. 相似文献
8.
Alicia P. Higueruelo Adrian Schreyer G. Richard J Bickerton Tom L. Blundell Will R. Pitt 《PloS one》2012,7(12)
Efforts to increase affinity in the design of new therapeutic molecules have tended to lead to greater lipophilicity, a factor that is generally agreed to be contributing to the low success rate of new drug candidates. Our aim is to provide a structural perspective to the study of lipophilic efficiency and to compare molecular interactions created over evolutionary time with those designed by humans. We show that natural complexes typically engage in more polar contacts than synthetic molecules bound to proteins. The synthetic molecules also have a higher proportion of unmatched heteroatoms at the interface than the natural sets. These observations suggest that there are lessons to be learnt from Nature, which could help us to improve the characteristics of man-made molecules. In particular, it is possible to increase the density of polar contacts without increasing lipophilicity and this is best achieved early in discovery while molecules remain relatively small. 相似文献
9.
10.
D. A. Peterson D. C. Peterson S. L. Archer E. K. Weir 《Redox report : communications in free radical research》2013,18(4):263-265
SummaryPolyunsaturated fatty acids (PUFAs) have been shown to modulate the activity of ionic channels by an unknown mechanism. Some channels are activated (i.e. certain delayed-rectifier, potassium channels) and others are inhibited (i.e. certain calcium, sodium and other potassium channels). We have previously demonstrated that PUFAs can act as electron carriers. It is known that ionic channels can be redox modulated. The ability of fatty acids to serve as electron shuttling agents is proportional to their unsaturation. These PUFAs cause reduction of disulfides through a superoxide radical-independent mechanism, probably related to enhanced electron delocalization. The present study shows that there is a strong correlation between the ability of a PUFA to transfer an electron to a disulfide and its reported ability to modulate ionic channels. This suggests that electron transfer could be the mechanism of PUFAs action on particular ionic channels. 相似文献