全文获取类型
收费全文 | 673篇 |
免费 | 91篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 17篇 |
2017年 | 24篇 |
2016年 | 25篇 |
2015年 | 23篇 |
2014年 | 38篇 |
2013年 | 35篇 |
2012年 | 46篇 |
2011年 | 41篇 |
2010年 | 34篇 |
2009年 | 18篇 |
2008年 | 24篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 29篇 |
2003年 | 25篇 |
2002年 | 14篇 |
2001年 | 16篇 |
2000年 | 21篇 |
1999年 | 22篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有764条查询结果,搜索用时 31 毫秒
751.
Tomás Villaseñor Susana Brom Araceli Dávalos Luis Lozano David Romero Alejandro García-de los Santos 《BMC microbiology》2011,11(1):66
Background
A traditional concept in bacterial genetics states that housekeeping genes, those involved in basic metabolic functions needed for maintenance of the cell, are encoded in the chromosome, whereas genes required for dealing with challenging environmental conditions are located in plasmids. Exceptions to this rule have emerged from genomic sequence data of bacteria with multipartite genomes. The genome sequence of R. etli CFN42 predicts the presence of panC and panB genes clustered together on the 642 kb plasmid p42f and a second copy of panB on plasmid p42e. They encode putative pantothenate biosynthesis enzymes (pantoate-β-alanine ligase and 3-methyl-2-oxobutanoate hydroxymethyltransferase, respectively). Due to their ubiquitous distribution and relevance in the central metabolism of the cell, these genes are considered part of the core genome; thus, their occurrence in a plasmid is noteworthy. In this study we investigate the contribution of these genes to pantothenate biosynthesis, examine whether their presence in plasmids is a prevalent characteristic of the Rhizobiales with multipartite genomes, and assess the possibility that the panCB genes may have reached plasmids by horizontal gene transfer. 相似文献752.
Summary A new system for continuous juices clarification is presented. The bioreactor combines microporous plates commercially available and industrial pectinases immobilized on nylon membranes in a cross-flow configuration. The kinetic behaviour of the reactor for different recirculation flow rates has been determined. Fresh apricot juice has been continuously clarified in the bioreactor with excellent results. 相似文献
753.
754.
Panagrellus redivivus produced 24-methyl-23-dehydrocholesterol as 4.0% of the 4-desmethylsterols when propagated in a medium containing campesterol as the dietary sterol. The re-examination of previous data revealed that Caenorhabditis elegans produced 1.8% 24-methyl-23-dehydrocholesterol when propagated in medium containing campesterol. 24-Methyl-23-dehydrocholesterol was not detected when the nematodes were propagated in medium containing 22-dihydrobrassicasterol or 24-methylenecholesterol. This may be a result of the greater efficiency of dealkylation of the latter two sterols. This is the first report of the natural occurrence of this sterol in a non-photosynthetic organism, and the first report in organisms that dealkylate 24-alkylsterols. 相似文献
755.
756.
757.
The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus 总被引:1,自引:0,他引:1
Padgett RW; Loeb DD; Snyder LR; Edgell MH; Hutchison CA d 《Molecular biology and evolution》1987,4(1):30-45
Recombinant DNA clones have been isolated that contain 80 kb of the
beta-globin complex from the deer mouse, Peromyscus maniculatus.
Comparisons of this complex with that from the laboratory mouse, Mus
domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3,
Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin
complex since the two species diverged. Unlike other mammals studied thus
far, the deer mouse possesses three adult genes. Partial sequence analysis
indicates that each of the three adult genes is intact and hence may be
functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to
genomic blots from Peromyscus reveals that it has a homologous counterpart
in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO
and Hbb-bhl, are also found in Peromyscus. The strong hybridization between
the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO
genes suggest that both pairs are important for the ontogeny of these mice
although no known product has been identified for the Hbb-bhO genes. The
presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication
that created this related gene set occurred before the two lineages
diverged. A single gene for Hbb-y has been isolated from Peromyscus. The
adult region in Peromyscus has undergone significant divergence from the
same region in Mus, having three rather than two adult genes, the
acquisition of at least 15 kb of extra DNA relative to Mus, and possibly
the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in
contrast, contains the same set of genes apparently distributed over the
same amount of DNA as in the Mus beta- globin complex. This observation
suggests that the embryonic region of the complex is more evolutionarily
stable than the adult region.
相似文献
758.
The Na/K pump, or Na,K-ATPase, is a key enzyme to the homeostasis of osmotic pressure, cell volume, and the maintenance of
electrochemical gradients. Its α subunit, which holds most of its functions, belongs to a large family of ATPases known as
P-type, and to the subfamily IIC, which also includes H,K-ATPases. In this study, we attempt to describe the evolutionary
history of IIC ATPases by doing phylogenetic analysis with most of the currently available protein sequences (over 200), and
pay special attention to the relationship between their diversity and their osmoregulatory role. We include proteins derived
from many completed or ongoing genome projects, many of whose IIC ATPases have not been phylogenetically analyzed previously.
We show that the most likely origin of IIC proteins is prokaryotic, and that many of them are present in non-metazoans, such
as algae, protozoans or fungi. We also suggest that the pre-metazoan ancestor, represented by the choanoflagellate Monosiga brevicollis, whose genome has been sequenced, presented at least two IIC-type proteins. One of these proteins would have given rise to
most current animal IIC ATPases, whereas the other apparently evolved into a lineage that, so far, has only been found in
nematodes. We also propose that early deuterostomes presented a single IIC gene, from which all the extant diversity of vertebrate
IIC proteins originated by gene and genome duplications.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
759.
760.
F J Fernández-Belda F García-Carmona F García-Cánovas J A Lozano J C Gómez-Fernández 《Archives of biochemistry and biophysics》1982,215(1):40-46
Purified F1-ATPase is slowly inactivated by interaction, in a preincubation medium, with its substrate MgATP. Interaction with Mg2+ before addition of ATP to the preincubation medium is essential to induce the inactivation. This inactivation is different from other Mg2+-induced inhibitions previously described. Free ATP concentration is implicated in the inactivation process and a linear relationship can be established between this concentration and the number of turnovers which are necessary for total inactivation. ITP, 2′-dATP, and GTP can also induce inactivation. Although ITP and GTP are hydrolyzed at a lower rate than ATP and 2′-dATP, they induce inactivation after a smaller number of turnovers than the latter. This process closely follows a kinetics of the type described for suicide enzymes. A reaction scheme is suggested and discussed. 相似文献