首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   89891篇
  免费   5086篇
  国内免费   10257篇
  2023年   1010篇
  2022年   1416篇
  2021年   1885篇
  2020年   2120篇
  2019年   3403篇
  2018年   2377篇
  2017年   2076篇
  2016年   2469篇
  2015年   3612篇
  2014年   4550篇
  2013年   6093篇
  2012年   3913篇
  2011年   5307篇
  2010年   3988篇
  2009年   4119篇
  2008年   4390篇
  2007年   4702篇
  2006年   4330篇
  2005年   3763篇
  2004年   3193篇
  2003年   2812篇
  2002年   2488篇
  2001年   2090篇
  2000年   1889篇
  1999年   1831篇
  1998年   1685篇
  1997年   1431篇
  1996年   1273篇
  1995年   1493篇
  1994年   1388篇
  1993年   1277篇
  1992年   1304篇
  1991年   1085篇
  1990年   1017篇
  1989年   939篇
  1988年   914篇
  1987年   897篇
  1986年   613篇
  1985年   1017篇
  1984年   1405篇
  1983年   1000篇
  1982年   1354篇
  1981年   947篇
  1980年   976篇
  1979年   893篇
  1978年   525篇
  1977年   430篇
  1976年   350篇
  1975年   267篇
  1973年   265篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Development of a high-frequency transforming vector for Aspergillus nidulans   总被引:18,自引:0,他引:18  
D J Ballance  G Turner 《Gene》1985,36(3):321-331
The pyr4 gene of Neurospora crassa, which codes for orotidine-5'-phosphate decarboxylase, is capable of transforming an Aspergillus nidulans pyrG mutant by chromosomal integration, despite low homology between the transforming DNA and the recipient genome. Integration of pFB6, a plasmid carrying pyr4 and capable of replication in Escherichia coli, was not observed at the pyrG locus. The efficiency of transformation was considerably enhanced (50-100 fold) by inclusion in the transforming vector of a 3.5-kb A.nidulans chromosomal sequence, ans1. Although this sequence was isolated on the basis of replicating activity in Saccharomyces cerevisiae, there was no evidence for such activity in A.nidulans. Part of the ans1 fragment appears to be reiterated in the A.nidulans genome, though it is not yet clear whether this is directly responsible for the high transformation frequency. The efficiency of transformation of A.nidulans by plasmids bearing ans1, using an improved protocol, was approx. 5 X 10(3) stable transformants per microgram of plasmid DNA.  相似文献   
992.
993.
Nonrandom insertion of Tn5 into cloned human adenovirus DNA   总被引:4,自引:0,他引:4  
  相似文献   
994.
Abstract A susceptibility of 63 clinical isolates of Klebsiella pneumoniae to inorganic and organic mercuric compounds was determined. 18 of them were found to be resistant to fluorescein mercuric acetate (FMA) and merbromin (MB). Moreover, all the resistant strains inactivate the antibacterial effect of FMA. The changes in the amount of organic mercury at the time of inactivation of the drug and the structures of the end products were examined in detail with the plasmid-bearing strain JK9 and its transconjugants of Escherichia coli .
The results showed that FMA was inactivated by an intracellular enzyme produced inducively and was degraded to fluorescein (sodium salt, uranine), which led to the sedimentation of metallic mercury. The discovery of the genes conferring inducible organic mercury-inactivating enzymes determined by plasmids was the next step and their application in the recovery of metallic mercury from organomercurials is now imminent.  相似文献   
995.
Isolation and characterization of a genomic DDD mouse interleukin-3 gene   总被引:1,自引:0,他引:1  
K Todokoro  A Yamamoto  H Amanuma  Y Ikawa 《Gene》1985,39(1):103-107
  相似文献   
996.
Q M Yi  J Lutkenhaus 《Gene》1985,36(3):241-247
  相似文献   
997.
998.
999.
1000.
cDNA clones coding for rat liver ribosomal proteins S17 and L30 have been isolated by positive hybridization-translation assay from a cDNA library prepared from 8-9S poly(A)+RNA from free polysomes of regenerating rat liver. The cDNA clone specific for S17 protein (pRS17-2) has a 466-bp insert with the poly(A) tail. The complete amino acid (aa) sequence of S17 protein was deduced from the nucleotide sequence of the cDNA. S17 protein consists of 134 aa residues with an Mr of 15 377. The N-terminal aa sequence of S17 protein determined by automatic Edman degradation is consistent with the sequence data. The aa sequence of S17 shows strong homology (76.9%) to that of yeast ribosomal protein 51 [Teem and Rosbash, Proc. Natl. Acad. Sci. USA 80 (1983) 4403-4407] in the two-thirds N-terminal region. The cDNA clone specific for L30 protein (pRL30) has a 394-bp insert. The aa sequence of L30 protein was deduced from the nucleotide sequence of the cDNA. The protein consists of 114 aa residues with an Mr of 12 652. When compared with the N-terminal aa sequence of rat liver L30 protein [Wool, Annu. Rev. Biochem. 48 (1979) 719-754], pRL30 was found not to contain the initiation codon and 5'-noncoding region. The cDNA showed twelve silent changes in the coding region, one point mutation and one base deletion in the 3'-noncoding region, compared with mouse genomic DNA for L30 protein [Wiedemann and Perry, Mol. Cell Biol. 4 (1984) 2518-2528].  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号