全文获取类型
收费全文 | 1267篇 |
免费 | 17篇 |
国内免费 | 75篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 10篇 |
2018年 | 13篇 |
2017年 | 24篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 37篇 |
2013年 | 35篇 |
2012年 | 27篇 |
2011年 | 47篇 |
2010年 | 25篇 |
2009年 | 53篇 |
2008年 | 56篇 |
2007年 | 43篇 |
2006年 | 43篇 |
2005年 | 43篇 |
2004年 | 42篇 |
2003年 | 48篇 |
2002年 | 46篇 |
2001年 | 30篇 |
2000年 | 31篇 |
1999年 | 42篇 |
1998年 | 26篇 |
1997年 | 37篇 |
1996年 | 44篇 |
1995年 | 37篇 |
1994年 | 43篇 |
1993年 | 32篇 |
1992年 | 41篇 |
1991年 | 46篇 |
1990年 | 49篇 |
1989年 | 38篇 |
1988年 | 61篇 |
1987年 | 55篇 |
1986年 | 25篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1359条查询结果,搜索用时 31 毫秒
51.
Noriko Arase-Fukushi Hisashi Arase Bingyan Wang Mari Hirano Kazumasa Ogasawara Robert A. Good Kazunori Ono 《Microbiology and immunology》1993,37(11):883-894
Allo-chimerism and clonal elimination of self antigen (Ag) (Ia + Mls-1a) reactive Vβ6+ T cells were analyzed and compared between allogeneic bone marrow (BM) chimeras reconstituted with BM cells which had been treated with anti-Thy-1 monoclonal antibody (mAb) plus complement (C) (T– chimeras) and BM chimeras which had been reconstituted with BM cells pretreated with anti-Thy-1 mAb alone (T+ chimeras). When lethally irradiated AKR (Mls-1a) mice were reconstituted with BM cells from B10 or B10 H-2 congenic mice, both T+ and T– chimeras were entirely free of signs of graft-versus-host reaction (GVHR). However, complete replacement of the AKR lymphoid tissues by donor BM cells was accomplished at an early stage in T+ chimeras but not in T– chimeras. On the other hand, clonal elimination of Vβ6+ T cells reactive to the recipient Ag (Mls-1a) was abolished in T+ chimeras but successfully induced in T– chimeras. The Vβ6+ T cells not eliminated in T+ chimeras showed depressed responses against Mls-1a antigens. The findings herein demonstrate that T cells which contaminate a BM inoculum survive in recipient mice after treatment with anti-Thy-1 mAb without C in vitro followed by BMT. The surviving T cells have been estimated to represent fewer than 0.5% of the BM cells inoculated. These cells appear to accelerate the full replacement of recipient lymphoid tissues by donor cells. Furthermore, the T cells which survive in the marrow inoculum influence eventually the development of a tolerant state in the T cell repertoire of the donor. 相似文献
52.
53.
基于结构比较的蛋白质同源模建系统及其评估Ⅱ侧链的安装 总被引:1,自引:0,他引:1
至今,有关蛋白质侧链的同源模建,除了在本体模板上安装侧链和少数限制条件下在同源模板上安装侧链的报道外,系统的研究和实施似乎还未见报道。本软件系统PMODELING采用同源移植和“死端排除“相结合的侧链安装策略,对与模板蛋白相应践基具有相似大小和形状的目标残基采用直接移植的方法。其余铡链则用广义“死端排除定则”安装。经众多蛋白的测试,达到了较好的模建品质。 相似文献
54.
Plasmid rolling circle replication and its control 总被引:10,自引:0,他引:10
Manuel Espinosa Gloria del Solar Fernando Rojo Juan C. Alonso 《FEMS microbiology letters》1995,130(2-3):111-120
Abstract This review summarises current information on rolling circle replicating plasmids originally isolated from Gram-positive bacteria with a low guanine and cytosine content in their DNA. It focuses on the peculiar biological features of these small, high copy number plasmids that replicate via an asymmetric RC mechanism. The regulation of plasmid copy number is also discussed. 相似文献
55.
Changes in DNA supertwist as a response of Bacillus subtilis towards different kinds of stress 总被引:1,自引:0,他引:1
Abstract The silent parD ( kis/kid ) stability operon of plasmid R1 is normally repressed by the co-ordinated action of the Kis and Kid proteins. In this report it is shown that a mutation in repA , the gene of the plasmid replication protein, that reduces two-fold the copy number of the plasmid, leads to the derepression of the parD system. This derepression can be prevented by a suppressor mutation in copB, a copy number control gene of plasmid R1, that increases the efficiency of replication of the repA mutant. Derepression of the wild-type parD system leads to high plasmid stability. These data show the activation of a plasmid stability operon by a mutation that reduces the efficiency of wild-type plasmid replication. 相似文献
56.
Emergence of tetracycline resistance due to a multiple drug resistance plasmid in Vibrio cholerae O139 总被引:2,自引:0,他引:2
Tatsuo Yamamoto G.Balakrish Nair Yoshifumi Takeda 《FEMS immunology and medical microbiology》1995,11(2):131-136
Abstract Of the 173 clinical strains of Vibrio cholerae O139 isolated from India, Bangladesh, and Thailand tested, six strains from India were resistant to tetracycline, ampicillin, chloramphenicol, kanamycin, and gentamicin. These six strains harbored a self-transmissible plasmid that mediated resistance to tetracycline, ampicillin, chloramphenicol, kanamycin, gentamicin, sulfamethoxazole, trimethoprim, and O/129. The multiple drug resistance plasmids were 200 kb in size and belonged to the incompatibility group C. Although a majority of the O139 strains (94.8%) were highly resistant to streptomycin, sulfamethoxazole, trimethoprim, and O/129, the tetracycline-susceptible strains so far tested were plasmid-negative. The data suggest the existence of two distinct multiple antimicrobial agent resistance (MAR) patterns in V. cholerae O139. 相似文献
57.
N. A. Kozyrovskaya R. I. Gvozdyak V. A. Muras V. A. Kordyum 《Archives of microbiology》1984,137(4):338-343
Transfer of plasmid pRD1 from Escherichia coli K12J62-1 to phytopathogenic bacteria, Agrobacterium tumefaciens, Xanthomonas beticola and Erwinia carotovora subsp. carotovora caused changes in conjugant properties not determined by the plasmid and the emergence of the properties not present in the parent strains. Clones have been obtained with intermediate properties between donor and recipient, including those with altered or lost virulence. In transconjugants of A. tumefaciens virulence increased. In transconjugants of X. beticola and E. carotovora subsp. carotovora highly virulent as well as avirulent forms have been observed. The loss of virulence in X. beticola correlated with the Nif* phenotype. Plasmid pRD1 also affected the biochemical properties of the new hosts. 相似文献
58.
Aphid transmission and a polypeptide are specified by a defined region of the cauliflower mosaic virus genome 总被引:15,自引:0,他引:15
Infection of young turnip leaves with an aphid-transmissible isolate, Cabb B-JI, of cauliflower mosaic virus (CaMV) causes synthesis of an Mr 18 000 polypeptide (p18) which co-purifies with virus inclusion bodies. This polypeptide is not detectable in leaves infected with either of two aphid non-transmissible isolates. Campbell and CM4-184. Construction in vitro, of hybrid genomes between Cabb B-JI and Campbell isolates demonstrates that aphid transmissibility and presence of p18 is dependent on the small genome fragment from the BstEII site to the XhoI site. A deletion made in this fragment within open reading frame (ORF) II causes loss of aphid transmissibility and also terminates production of p18. We conclude that aphid transmissibility and the presence of p18 are related to the expression of ORF II of the CaMV genome. 相似文献
59.
Summary We compared the DNA sequence of the yeas 2-μm plasmidcis-actingSTB andtrans-actingREP1 partition loci of laboratory haploid and industrial amphiploid strains. Several industrial strains had a uniqueSTB sequence (type 1) sharing only 70% homology with laboratorySTB (type 2). Type 1 plasmids had a REP1 protein with 6–10% amino acid substitutions when compared to REP1 of type 2 plasmids.
All 2-μm variants that shared a similarSTB consensus sequence exhibited a high degree ofREP1 nucleotide and amino acid sequence conservation. These observations suggest molecular coevolution oftrans-acting elements with cognate target DNA structure. Based on DNA sequencing and Southern hybridization analyses, we classified
2-μm variants into two main evolutionary lineages that differ atSTB as well asREP1 loci. The role of molecular coevolution in yeast intra- and interspecies plasmid evolution was discussed. 相似文献
60.
Howard T. Jacobs 《Journal of molecular evolution》1991,32(4):333-339
Summary Subunit 8 of mitochondrial ATP synthase (A8), a mitochondrially encoded polypeptide, has no known homologue in any prokaryotic or plastid ATP synthase, suggesting that it has been recruited to its present role in the enzyme from an extraneous source. The polypeptide is poorly conserved at the primary sequence level, but shows a well-conserved hydropathy profile. The hydropathy profiles of A8 from diverse taxa were compared with those of thehok family of prokaryotic respiratory toxins, some of whose members are involved in plasmid maintenance, through postsegregational killing of cells that lose the plasmid at cell division. Such comparisons revealed a highly significant degree of similarity, suggesting a functional relationship. Based on these findings, it is proposed that A8 evolved from ahok-like protein, whose original role was the maintenance of an extrachromosomal replicon in the endosymbiont ancestor of mitochondria. An aggressive mechanism for the evolutionary maintenance of mitochondrial DNA overcomes many of the failings of traditional explanations for its retention as a separate genome. 相似文献