全文获取类型
收费全文 | 186篇 |
免费 | 17篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有203条查询结果,搜索用时 15 毫秒
11.
Cet1, the RNA triphosphatase component of the yeast mRNA capping apparatus, catalyzes metal-dependent gamma phosphate hydrolysis within the hydrophilic interior of a topologically closed 8-strand beta barrel (the "triphosphate tunnel"). We used structure-guided alanine scanning to identify 6 side chains within the triphosphate tunnel that are essential for phosphohydrolase activity in vitro and in vivo: Arg393, Glu433, Arg458, Arg469, Asp471 and Thr473. Alanine substitutions at two positions, Asp377 and Lys409, resulted in partial catalytic defects and a thermosensitive growth phenotype. Structure-function relationships were clarified by introducing conservative substitutions. Five residues were found to be nonessential: Lys309, Ser395, Asp397, Lys427 Asn431, and Lys474. The present findings, together with earlier mutational analyses, reveal an unusually complex active site in which 15 individual side chains in the tunnel cavity are important for catalysis, and each of the 8 strands of the beta barrel contributes at least one functional constituent. The active site residues fall into three classes: (i) those that participate directly in catalysis via coordination of the gamma phosphate or the metal; (ii) those that make critical water-mediated contacts with the gamma phosphate or the metal; and (iii) those that function indirectly via interactions with other essential side chains or by stabilization of the tunnel structure. 相似文献
12.
Catford JG Staehelin C Lerat S Piché Y Vierheilig H 《Journal of experimental botany》2003,54(386):1481-1487
Roots of legumes establish symbiosis with arbuscular mycorrhizal fungi (AMF) and nodule-inducing rhizobia. The existing nodules systemically suppress subsequent nodule formation in other parts of the root, a phenomenon termed autoregulation. Similarly, mycorrhizal roots reduce further AMF colonization on other parts of the root system. In this work, split- root systems of alfalfa (Medicago sativa) were used to study the autoregulation of symbiosis with Sinorhizobium meliloti and the mycorrhizal fungus Glomus mosseae. It is shown that nodulation systemically influences AMF root colonization and vice versa. Nodules on one half of the split-root system suppressed subsequent AMF colonization on the other half. Conversely, root systems pre-colonized on one side by AMF exhibited reduced nodule formation on the other side. An inhibition effect was also observed with Nod factors (lipo-chito-oligosaccharides). NodSm-IV(C16:2, S) purified from S. meliloti systemically suppressed both nodule formation and AMF colonization. The application of Nod factors, however, did not influence the allocation of (14)C within the split-root system, excluding competition for carbohydrates as the regulatory mechanism. These results indicate a systemic regulatory mechanism in the rhizobial and the arbuscular mycorrhizal association, which is similar in both symbioses. 相似文献
13.
D. Leblanc A. Morin D. Gu X.M. Zhang J.-G. Bisaillon M. Paquet H. Dubeau 《Biotechnology letters》1998,20(12):1127-1131
Thirteen commercial lipases in hexane and seventeen bacterial cell suspensions in aqueous media were screened for the production of ethyl valerate and ethyl butyrate. The highest esterifying activity was obtained with commercial Pancrealipase (Biozymes Inc.) and Candida rugosa lipase (Amano Enzyme Ltd) and with bacterial cell suspension from Pseudomonas fragi CRDA 446. Commercial enzymes gave molar conversion yield of 68% over 24 h as compared to 17% with whole cells in aqueous medium. However, a comparison of both sources of biocatalyst i.e. whole microbial cells and commercial lipases, based on the amount of ester produced per g of protein for a complete reaction, indicated similar activities. © Rapid Science Ltd. 1998 相似文献
14.
M. Joanne Morgan Jean-Guy J. Godin 《Ethology : formerly Zeitschrift fur Tierpsychologie》1985,70(3):236-246
Fish schools are believed to provide antipredator benefits to their members. Two potential antipredator benefits, the dilution and confusion effects, of schooling were investigated in the laboratory using banded killifish (Fundulus diaphanus). Individual risk of being attacked and killed by a fish predator (white perch, Morone americana) declined with increasing killifish school size in a manner closely predicted by the dilution hypothesis. Perch were apparently not confused by schooling killifish since fish in groups of one did not suffer a disproportionately greater predation rate than fish in all larger school sizes. However, killifish straggling from the school were preferentially attacked and more successfully captured compared with school members. Schooling in the banded killifish therefore confers a considerable antipredator benefit to individual group members, at least through a dilution effect, and straying from a school has an associated increased risk of mortality to predation, which selects for schooling behaviour. 相似文献
15.
16.
David Navarro Marie Couturier Gabriela Ghizzi Damasceno da Silva Jean-Guy Berrin Xavier Rouau Marcel Asther Christophe Bignon 《Microbial cell factories》2010,9(1):58
Background
To reduce the production cost of bioethanol obtained from fermentation of the sugars provided by degradation of lignocellulosic biomass (i.e., second generation bioethanol), it is necessary to screen for new enzymes endowed with more efficient biomass degrading properties. This demands the set-up of high-throughput screening methods. Several methods have been devised all using microplates in the industrial SBS format. Although this size reduction and standardization has greatly improved the screening process, the published methods comprise one or more manual steps that seriously decrease throughput. Therefore, we worked to devise a screening method devoid of any manual steps. 相似文献17.
Examination of the folding pathway of the antigenomic hepatitis delta virus ribozyme reveals key interactions of the L3 loop 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《RNA (New York, N.Y.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
With the goal of gaining insight into the tertiary structure of the hepatitis delta virus ribozyme, cross-linking experiments using 4-thiouridine residues introduced in either the 5'-end portion of the substrate, or at seven strategic positions within the ribozyme, were performed. Mapping of the newly formed covalent bonds in cross-linked species obtained under various conditions, as well as using several mutated ribozymes, permitted monitoring of the formation of the ribozyme-substrate complex as the ribozyme proceeded along the folding pathway. In order to aid visualization of the tertiary structure transformation, an in silico animation of the "on" folding pathway was developed. In combination with those of the cleavage assays of structured substrates, these data shed light on the key contribution of the L3 loop in the formation of an active tertiary complex. 相似文献
18.
19.
20.