全文获取类型
收费全文 | 9017篇 |
免费 | 640篇 |
国内免费 | 476篇 |
专业分类
10133篇 |
出版年
2024年 | 11篇 |
2023年 | 81篇 |
2022年 | 190篇 |
2021年 | 324篇 |
2020年 | 231篇 |
2019年 | 265篇 |
2018年 | 282篇 |
2017年 | 232篇 |
2016年 | 322篇 |
2015年 | 463篇 |
2014年 | 580篇 |
2013年 | 640篇 |
2012年 | 743篇 |
2011年 | 705篇 |
2010年 | 415篇 |
2009年 | 375篇 |
2008年 | 430篇 |
2007年 | 420篇 |
2006年 | 372篇 |
2005年 | 359篇 |
2004年 | 292篇 |
2003年 | 300篇 |
2002年 | 241篇 |
2001年 | 195篇 |
2000年 | 193篇 |
1999年 | 162篇 |
1998年 | 108篇 |
1997年 | 102篇 |
1996年 | 104篇 |
1995年 | 101篇 |
1994年 | 78篇 |
1993年 | 78篇 |
1992年 | 127篇 |
1991年 | 101篇 |
1990年 | 72篇 |
1989年 | 72篇 |
1988年 | 66篇 |
1987年 | 49篇 |
1986年 | 41篇 |
1985年 | 53篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
In Bombyx mori, ecdysteroidogenesis by the prothoracic glands (PGs) is controlled by both prothoracicotropic hormone (PTTH) and a factor secreted by the glands themselves. This factor, which is active both in vitro and in vivo, has been named 'autocrine factor' (AF). To find out whether or not this dual control also exists in other species, in particular in hemimetabolous ones, we applied similar methods as were used to discover AF in Bombyx to the locusts Locusta migratoria and Schistocerca gregaria. Our results unequivocally show that locust PGs also secrete an as yet unidentified autocrine factor. Possible roles of AF are discussed. 相似文献
932.
933.
934.
An acetylation/deacetylation-SUMOylation switch through a phylogenetically conserved psiKXEP motif in the tumor suppressor HIC1 regulates transcriptional repression activity
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
935.
Andrew J. Dugmore Douglas M. Borthwick Mike J. Church Alastair Dawson Kevin J. Edwards Christian Keller Paul Mayewski Thomas H. McGovern Kerry-Anne Mairs Guðrún Sveinbjarnardóttir 《Human ecology: an interdisciplinary journal》2007,35(2):169-178
In order to assess possible contributions of climate change to the human ecology of the North Atlantic islands we evaluate
the utility of cumulative deviations from the mean, calculated for the Greenland ice core storm frequency proxy (GISP2 Na+) and sea ice proxy (GISP2 chloride excess). Our aim is to identify episodes of unpredictable change in the context of long-term
trends of cultural and environmental development. Key changes are identified in the proxy climate records in 975 and 980 ad, 1025 and 1040 ad, 1180 ad, 1425 and 1450 ad, and 1520 and 1525 ad. Some of these changes are consistent with those inferred from new studies of the palaeoecological record of the Faroes.
This indicates that the cumulative deviation measure could give greatest prominence to the most important climate changes
affecting landscapes and settlement (such as the changes of 1425 and 1450 ad and their immediate aftermath), rather than extreme events, such as great single storms. 相似文献
936.
937.
Gu W Ding J Wang X de Kluyver RL Saunders NA Frazer IH Zhao KN 《Nucleic acids research》2007,35(14):4820-4832
Recently we reported that gene codon composition determines differentiation-dependent expression of the PV L1 genes in mouse primary keratinocytes (KCs) in vitro and in vivo (Zhao et al. 2005, Mol. Cell Biol. 25:8643–8655). Here, we investigated whether generalized substitution of isoencoding codons affects the duration of expression of PV L1 genes in mouse and human KCs in day 1 culture transiently transfected with native (Nat) and codon modified (Mod) L1 genes. Following transient transfection, KC continuously transcribed both Nat and Mod PV L1 genes for at least 12 days, with the levels of L1 mRNAs from the Mod L1 genes significantly higher than those from the Nat L1 genes. However, continuous L1 protein expression at day 9 post-transfection was observed for both mouse and human KCs transfected with the Nat L1 genes only. Further, aa-tRNAs prepared from D8 KC cultures enhanced translation of two PV Nat L1 DNAs in RRL lysate and PV Nat L1 mRNAs in D0 cell-free lysate, whereas aa-tRNAs from D0 KCs enhanced translation of PV Mod L1 mRNAs in D8 cell-free lysate. It appears that aa-tRNAs in less-differentiated and differentiated KCs differentially match the PV Nat and Mod L1 mRNAs to regulate their translations in vitro. 相似文献
938.
Cre reconstitution allows for DNA recombination selectively in dual-marker-expressing cells in transgenic mice 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Cre/LoxP-based DNA recombination has been used to introduce desired DNA rearrangements in various organisms, having for example, greatly assisted genetic analyses in mice. For most applications, single gene promoters are used to drive Cre production for conditional gene activation/inactivation or lineage-tracing experiments. Such a manipulation introduces Cre in all cells in which the utilized promoter is active. To overcome the limited selectivity of single promoters for cell-type-specific recombination, we have explored the ‘dual promoter combinatorial control’ of Cre activity, so that Cre activity could be restricted to cells that express dual protein markers. We efficiently reconstituted Cre activity from two modified, inactive Cre fragments. Cre re-association was greatly enhanced by fusing the Cre fragments separately to peptides that can form a tight antiparallel leucine zipper. The co-expressed Cre fusion fragments showed substantial activity in cultured cells. As proof of principle of the utility of this technique in vivo for manipulating genes specifically in dual-marker-positive cells, we expressed each inactive Cre fragments in transgenic mice via individual promoters. Result showed the effective reconstitution of Cre activates LoxP recombination in the co-expressing cells. 相似文献
939.
940.
A soil bacterium SW4, capable of degrading the sulfonylurea herbicide ethametsulfuron-methyl (ESM), was isolated from the
bottom soil of a herbicide factory. Based on physiological characteristics, biochemical tests and phylogenetic analysis of
the 16S rRNA gene sequence, the strain was identified as a Pseudomonas sp. The total degradation of ESM in the medium containing glucose was up to 84.6% after 6 days of inoculation with SW4 strain.
The inoculation of strain SW4 to soil treated with ESM resulted in a higher degradation rate than in noninoculated soil regardless
of the soil sterilized or nonsterilized. Five metabolites of ESM degradation were analyzed by liquid chromatography/mass spectrometry.
Based on the identified products, strain SW4 seemed to degrade ESM after two separate and different pathways: one leads to
the cleavage of the sulfonylurea bridge, whereas the other to the dealkylation and opening of the triazine ring of ESM. 相似文献