全文获取类型
收费全文 | 7297篇 |
免费 | 592篇 |
国内免费 | 2篇 |
专业分类
7891篇 |
出版年
2023年 | 43篇 |
2022年 | 121篇 |
2021年 | 196篇 |
2020年 | 124篇 |
2019年 | 137篇 |
2018年 | 165篇 |
2017年 | 134篇 |
2016年 | 232篇 |
2015年 | 415篇 |
2014年 | 449篇 |
2013年 | 518篇 |
2012年 | 659篇 |
2011年 | 587篇 |
2010年 | 381篇 |
2009年 | 379篇 |
2008年 | 486篇 |
2007年 | 446篇 |
2006年 | 380篇 |
2005年 | 323篇 |
2004年 | 279篇 |
2003年 | 306篇 |
2002年 | 270篇 |
2001年 | 65篇 |
2000年 | 55篇 |
1999年 | 78篇 |
1998年 | 54篇 |
1997年 | 50篇 |
1996年 | 33篇 |
1995年 | 43篇 |
1994年 | 45篇 |
1993年 | 37篇 |
1992年 | 37篇 |
1991年 | 26篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 17篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 20篇 |
1979年 | 17篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 13篇 |
1973年 | 9篇 |
1972年 | 8篇 |
1970年 | 15篇 |
1969年 | 9篇 |
排序方式: 共有7891条查询结果,搜索用时 0 毫秒
101.
Belinda Martineau H. Jane Smith Caroline Dean Pamela Dunsmuir John Bedbrook Laurens J. Mets 《Plant molecular biology》1989,13(4):419-426
We report the successful transformation, via Agrobacterium tumefaciens infection, and regeneration of two species of the genus Flaveria: F. brownii and F. palmeri. We document the expression of a C3 plant gene, an abundantly expressed ribulose 1,5-bisphosphate carboxylase/oxygenase small subunit gene isolated from petunia, in these C4 plants. The organ-specific expression of this petunia gene in Flaveria brownii is qualitatively identical to its endogenous pattern of expression. 相似文献
102.
An electro-transformation procedure was established for Bacillus cereus ATCC 14579. Using early growth-stage culture and high electric field, the ectroporation efficiency was up to 2 x 10(9) cfu microg(-1) ml(-1) with pC194 plasmid DNA. The procedure was tested with three other plasmids, of various sizes, replication mechanisms and selection markers, and the transformation efficiencies ranged between 2 x 10(6) and 1 x 10(8) cfu microg(-1) ml(-)(1). The effects of two wall-weakening agents on electroporation rates were also evaluated. The transformation rate that was reached with our procedure is 10(3) times higher than that previously obtained with members of the Bacillus genus with similar plasmids, and 10(6) times superior than that achieved with available protocols for B. cereus. The proposed method is quick, simple, efficient with small rolling circle plasmids and large theta replicating plasmids with low copy number per cell, and suitable for many genetic manipulations that are not possible without high-efficiency transformation protocols. 相似文献
103.
Qiu Z Norflus F Singh B Swindell MK Buzescu R Bejarano M Chopra R Zucker B Benn CL DiRocco DP Cha JH Ferrante RJ Hersch SM 《The Journal of biological chemistry》2006,281(24):16672-16680
104.
105.
106.
Polymorphic analysis of the three MHC-linked HSP70 genes 总被引:10,自引:0,他引:10
Three genes encoding members of the M
r 70 000 heat shock protein family (HSP70) are known to lie in the class III region of the human major histocompatibility complex. IN order to determine whether these genes or their protein products exhibit any polymorphism the three genes have been specifically amplified from genomic DNA and sequenced. The HSP70-1 and HSP70-2 genes encode the major heat-inducible HSP70. A comparison of the nucleotide sequences of these genes from B8, SC01, DR3, B18, F1C30, DR3, and B7, SC30, DR2 haplotypes has revelad only very limited sequence variation which is not associated with any amino acid polymorphism. The HSP70-Hom gene encodes a protein that is highly related to HSP70-1, but which is not heat-inducible. Nucleotide sequence analysis of this gene from different haplotypes has revealed a Met Thr amino acid substitution at residue 493 in a number of the haplotypes tested. This variable amino acid lies in the proposed peptide-binding site of the HSP70-Hom protein.
Address correspondence and offprint requests to: R. D. Campbell. 相似文献
107.
108.
The Mre11 complex is required for ATM activation and the G2/M checkpoint 总被引:25,自引:0,他引:25 下载免费PDF全文
Carson CT Schwartz RA Stracker TH Lilley CE Lee DV Weitzman MD 《The EMBO journal》2003,22(24):6610-6620
The maintenance of genome integrity requires a rapid and specific response to many types of DNA damage. The conserved and related PI3-like protein kinases, ataxia-telangiectasia mutated (ATM) and ATM-Rad3-related (ATR), orchestrate signal transduction pathways in response to genomic insults, such as DNA double-strand breaks (DSBs). It is unclear which proteins recognize DSBs and activate these pathways, but the Mre11/Rad50/NBS1 complex has been suggested to act as a damage sensor. Here we show that infection with an adenovirus lacking the E4 region also induces a cellular DNA damage response, with activation of ATM and ATR. Wild-type virus blocks this signaling through degradation of the Mre11 complex by the viral E1b55K/E4orf6 proteins. Using these viral proteins, we show that the Mre11 complex is required for both ATM activation and the ATM-dependent G(2)/M checkpoint in response to DSBs. These results demonstrate that the Mre11 complex can function as a damage sensor upstream of ATM/ATR signaling in mammalian cells. 相似文献
109.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
110.
Lilian Da-Croce Greicy Helen Ribeiro Gambarini-Paiva Patrícia Caroline Angelo Eduardo Alves Bambirra Antônio Carlos Vieira Cabral Ana Lúcia Brunialti Godard 《Cell and tissue banking》2013,14(1):65-76
The tissue cryopreservation maintains the cellular metabolism in a quiescence state and makes the conservation possible for an indefinite period of time. The choice of an appropriate cryopreservation protocol is essential for maintenance of cryopreserved tissue banks. This study evaluated 10 samples of umbilical cord, from which small fragments of tissue (Wharton’s jelly and cord lining membrane) were subjected to two protocols of cryopreservation: slow cooling and vitrification. The samples were frozen for a period of time ranging from 5 to 78 days. The efficiency of cryopreservation was evaluated by testing cell viability, histological analysis, cell culture, cytogenetic analysis and comparison with the results of the fresh samples. The results showed that the slow cooling protocol was more efficient than the vitrification for cryopreservation of umbilical cord tissue, because it has caused fewer changes in the structure of tissue (edema and degeneration of the epithelium) and, despite the significant decrease cell viability compared to fresh samples, the ability of cell proliferation in vitro was preserved in most samples. In conclusion, this study showed that it is possible to cryopreserve small fragments of tissue from the umbilical cord and, to obtain viable cells capable of proliferation in vitro after thawing, contributing to the creation of a frozen tissue bank. 相似文献