全文获取类型
收费全文 | 110478篇 |
免费 | 13251篇 |
国内免费 | 412篇 |
专业分类
124141篇 |
出版年
2018年 | 990篇 |
2017年 | 964篇 |
2016年 | 1258篇 |
2015年 | 1550篇 |
2014年 | 1942篇 |
2013年 | 2461篇 |
2012年 | 2861篇 |
2011年 | 2810篇 |
2010年 | 1886篇 |
2009年 | 1847篇 |
2008年 | 2358篇 |
2007年 | 2343篇 |
2006年 | 2332篇 |
2005年 | 2132篇 |
2004年 | 2069篇 |
2003年 | 2103篇 |
2002年 | 2073篇 |
2001年 | 9640篇 |
2000年 | 9509篇 |
1999年 | 7195篇 |
1998年 | 1614篇 |
1997年 | 1792篇 |
1996年 | 1580篇 |
1995年 | 1407篇 |
1994年 | 1308篇 |
1993年 | 1249篇 |
1992年 | 4792篇 |
1991年 | 4522篇 |
1990年 | 3992篇 |
1989年 | 4012篇 |
1988年 | 3608篇 |
1987年 | 3084篇 |
1986年 | 2776篇 |
1985年 | 2678篇 |
1984年 | 1973篇 |
1983年 | 1729篇 |
1982年 | 1230篇 |
1981年 | 983篇 |
1980年 | 913篇 |
1979年 | 1762篇 |
1978年 | 1361篇 |
1977年 | 1199篇 |
1976年 | 1028篇 |
1975年 | 1149篇 |
1974年 | 1166篇 |
1973年 | 1162篇 |
1972年 | 1033篇 |
1971年 | 955篇 |
1970年 | 822篇 |
1969年 | 743篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
Bacillus subtilis plasmid pGR71 is a promoter-probe shuttle vector derived from pUB110. The expression of the cat gene on pGR71 in B. subtilis requires the insertion of a Bacillus promoter and a ribosomal binding site (RBS) into the HindIII cloning site immediately upstream from the cat gene. A recombinant plasmid of pGR71, named pGR71-369, was obtained by a spontaneous deletion of a fragment containing most of the inserted HindIII fragment and the replication origin necessary for multiplication in Escherichia coli. The expression of the cat gene in B. subtilis cells carrying this plasmid was inducible by heat. Nucleotide sequence analysis of the upstream region of the cat gene, deletion analysis, and dot blot hybridization analysis of mRNA in various conditions revealed that the cat gene was expressed by heat-inducible translational coupling and that the regulatory region of heat inducibility was present in the upstream region of the cat gene. 相似文献
994.
995.
996.
997.
998.
999.
Eleven mutations resulting in partially deleted or truncated LEU3 protein were generated by linker insertion or other modifications at restriction sites, deletion of restriction fragments, or oligonucleotide-directed mutagenesis. Functional studies of these mutants showed the following: (i) A specific DNA binding region is contained within the 173 N-terminal residues, but other regions of the protein are required for optimal binding. (ii) Activation of LEU2 expression depends on the C-terminal 113 residues of the LEU3 protein. (iii) Deletion of part or all of a central section of LEU3 eliminates the ability of the LEU3 protein to respond to the co-activator alpha-isopropylmalate, i.e. creates an unmodulated activator. (iv) Overproduction of unmodulated activator slows down cell growth. (v) Specific deletion of two short acidic regions, including one with net charge - 19, has only minor effects on activation and modulation. 相似文献
1000.
P1 nuclease defines a subpopulation of active SV40 chromatin--a new nuclease hypersensitivity assay. 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)
Under exhaustive digestion conditions P1 nuclease was found to cleave a subpopulation of intracellular SV40 chromatin only once. The major P1 cleavage site in SV40 DNA was mapped at the origin of DNA replication, and the two minor sites at the SV40 enhancers. The P1-sensitive SV40 chromatin subpopulation was found to have higher superhelical density than the bulk of the intracellular SV40 chromatin. Furthermore, pulse labeled SV40 DNA which had higher superhelical density than that of the steady state viral DNA (S.S.Chen and M.T.Hsu, J.Virol 51:14-19, 1984) was also found to be preferentially cleaved by P1 nuclease. These results are consistent with a supercoil-dependent alteration of chromatin conformation near the regulatory region of the viral genome that can be recognized by P1 nuclease. Since P1 nuclease cleaves the subpopulation of SV40 chromatin only once without further degradation, this nuclease can be used as a general tool to define viral or cellular chromatin fraction with altered chromatin conformation and to map nuclease hypersensitive sites. Preliminary studies indicate that P1 makes limited double stranded cleavages in cellular chromatin to generate large DNA fragments. 相似文献