全文获取类型
收费全文 | 78530篇 |
免费 | 3234篇 |
国内免费 | 7155篇 |
出版年
2023年 | 683篇 |
2022年 | 1085篇 |
2021年 | 1415篇 |
2020年 | 1504篇 |
2019年 | 2797篇 |
2018年 | 1810篇 |
2017年 | 1499篇 |
2016年 | 1911篇 |
2015年 | 3038篇 |
2014年 | 4016篇 |
2013年 | 5447篇 |
2012年 | 3446篇 |
2011年 | 4750篇 |
2010年 | 3466篇 |
2009年 | 3513篇 |
2008年 | 3731篇 |
2007年 | 3979篇 |
2006年 | 3597篇 |
2005年 | 3149篇 |
2004年 | 2621篇 |
2003年 | 2302篇 |
2002年 | 2013篇 |
2001年 | 1630篇 |
2000年 | 1444篇 |
1999年 | 1436篇 |
1998年 | 1322篇 |
1997年 | 1148篇 |
1996年 | 1038篇 |
1995年 | 1259篇 |
1994年 | 1176篇 |
1993年 | 1115篇 |
1992年 | 1138篇 |
1991年 | 949篇 |
1990年 | 876篇 |
1989年 | 826篇 |
1988年 | 829篇 |
1987年 | 814篇 |
1986年 | 530篇 |
1985年 | 954篇 |
1984年 | 1340篇 |
1983年 | 956篇 |
1982年 | 1309篇 |
1981年 | 923篇 |
1980年 | 929篇 |
1979年 | 880篇 |
1978年 | 507篇 |
1977年 | 418篇 |
1976年 | 341篇 |
1975年 | 263篇 |
1973年 | 263篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
881.
882.
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
883.
884.
Nonrandom insertion of Tn5 into cloned human adenovirus DNA 总被引:4,自引:0,他引:4
885.
Megumi Kono Koji O'hara Yoshihiro Arai Hideyuki Fukuda Misaki Asakawa Hideomi Nakahara 《FEMS microbiology letters》1985,28(2):213-217
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
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
886.
887.
888.
889.