全文获取类型
收费全文 | 1596篇 |
免费 | 105篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 43篇 |
2015年 | 54篇 |
2014年 | 64篇 |
2013年 | 125篇 |
2012年 | 98篇 |
2011年 | 98篇 |
2010年 | 63篇 |
2009年 | 57篇 |
2008年 | 102篇 |
2007年 | 97篇 |
2006年 | 108篇 |
2005年 | 110篇 |
2004年 | 101篇 |
2003年 | 108篇 |
2002年 | 102篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 21篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 12篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1971年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有1701条查询结果,搜索用时 14 毫秒
1.
Masatoshi Kataoka Keizoh Kawamura Tamotsu Kondoh Yoichi Wakano Hiroshi Ishida 《FEMS microbiology letters》1993,107(1):111-114
Abstract A factor showing inhibitory activity against human gingival fibrolasts was extracted from the cytosol fraction of Actinobacillus actinomycetemcomitans Y4. The activity markedly inhibited the proliferation of human gingival fibrolasts, but had no effect on cell viability or gross morphology. No such activity was found in cytosol fractions from either Porphyromonas gingivalis 381 or Escherichia coli HB101. The extract from A. actinomycetemcomitans Y4 was then purified by anion-exchange chromatography, hydroxyapatite chromatography and gel-filtration chromatography to give a single band on SDS-PAGE with an apparent molecular mass of 65 kDa. The purification ratio was 183-fold with a recovery rate of 5% compared with the crude extract (starting material) when the activity was assessed by direct cell counts. 相似文献
2.
Koji Sode Nobuaki Hori Yoichi Mikami Isao Karube 《Biocatalysis and Biotransformation》1988,2(1):51-57
Asymmetric reduction of 2,6,6,-trimethyl-2-cyclohexene-l,4-dione (4-oxoisophrone) to (6R)-2,2,6-trimethyl-1,4-cyclohexane-dione((3R)-dihydro-4-oxoisophorone) was catalysed by immobilized thermophilic bacteria, Thermomonospora curvata JTS 321. Because of leakage of entrapped cells from gel beads during reactions using culture medium, we optimized the medium to allow the microbial conversion under conditions of controlled cell growth. Of the media screened, liver infusion medium was found to be the most suitable and microbial conversion was achieved without cell leakage from the immobilized gels. Immobilized T. curvata cells were repeatedly used for the asymmetric reduction of 4-oxoisophorone, more than 15 times, with an extent of conversion of 50%. 相似文献
3.
Camilynn I. Brannan Debra J. Gilbert Jeffrey D. Ceci Yoichi Matsuda Verne M. Chapman John A. Mercer Harvey Eisen Laura A. Johnston Neal G. Copeland Nancy A. Jenkins 《Genomics》1992,13(4):1075-1081
We have used an interspecific backcross between C57BL/6J and Mus spretus to derive a molecular genetic linkage map of chromosome 15 that includes 25 molecular markers and spans 93% of the estimated length of chromosome 15. Using a second interspecific backcross that was analyzed with a centromere-specific marker, we were also able to position our map with respect to the chromosome 15 centromere. This map provides molecular access to many discrete regions on chromosome 15, thus providing a framework for establishing relationships between cloned DNA markers and known mouse mutations and for identifying homologous genes in mice and humans that may be involved in disease. 相似文献
4.
Monica J. Justice Bebra J. Gilbert Kenneth W. Kinzler Bert Vogelstein Authur M. Buchberg Jeffrey D. Ceci Yoichi Matsuda Verne M. Chapman Christos Patriotis Antonios Makris Philip N. Tsichlis Nancy A. Jenkins Neal G. Copeland 《Genomics》1992,13(4):1281-1288
An interspecific backcross between C57BL/6J and Mus spretus was used to generate a molecular genetic linkage map of mouse chromosome 18 that includes 23 molecular markers and spans approximately 86% of the estimated length of the chromosome. The Apc, Camk2a, D18Fcr1, D18Fcr2, D18Leh1, D18Leh2, Dcc, Emb-rs3, Fgfa, Fim-2/Csfmr, Gnal, Grl-1, Grp, Hk-1rs1, Ii, Kns, Lmnb, Mbp, Mcc, Mtv-38, Palb, Pdgfrb, and Tpl-2 genes were mapped relative to each other in one interspecific backcross. A second interspecific backcross and a centromere-specific DNA satellite probe were used to determine the distance of the most proximal chromosome 18 marker to the centromere. The interspecific map extends the known regions of linkage homology between mouse chromosome 18 and human chromosomes 5 and 18 and identifies a new homology segment with human chromosome 10p. It also provides molecular access to many regions of mouse chromosome 18 for the first time. 相似文献
5.
Escherichia coli RuvC protein is an endonuclease that resolves the Holliday structure. 总被引:24,自引:10,他引:14 下载免费PDF全文
Genetic evidence suggests that the Escherichia coli ruvC gene is involved in DNA repair and in the late step of RecE and RecF pathway recombination. To study the biochemical properties of RuvC protein, we overproduced and highly purified the protein. By employing model substrates, we examined the possibility that RuvC protein is an endonuclease that resolves the Holliday structure, an intermediate in genetic recombination in which two double-stranded DNA molecules are linked by single-stranded crossover. RuvC protein cleaves cruciform junctions, which are formed by the extrusion of inverted repeat sequences from a supercoiled plasmid and which are structurally analogous to Holliday junctions, by introducing nicks into strands with the same polarity. The nicked ends are ligated by E.coli or T4 DNA ligases. Analysis of the cleavage sites suggests that DNA topology rather than a particular sequence determines the cleavage site. RuvC protein also cleaves Holliday junctions which are formed between gapped circular and linear duplex DNA by the function of RecA protein. However, it does not cleave a synthetic four-way junction that does not possess homology between arms. The active form of RuvC protein, as studied by gel filtration, is a dimer. This is mechanistically suited for an endonuclease involved in swapping DNA strands at the crossover junctions. From these properties of RuvC protein and the phenotypes of the ruvC mutants, we infer that RuvC protein is an endonuclease that resolves Holliday structures in vivo. 相似文献
6.
Properties of the Escherichia coli RuvA and RuvB proteins involved in DNA repair, recombination and mutagenesis 总被引:4,自引:0,他引:4
The ruvA and ruvB genes constitute an operon, which is regulated by the SOS system and involved in DNA repair, recombination and mutagenesis. RuvA protein binds to both single-stranded and double-stranded DNA. RuvB protein has weak ATPase activity. RuvA bound to DNA greatly enhances ATPase activity of RuvB. UV-irradiation to supercoiled DNA further enhances the stimulatory effect of RuvA on the RuvB ATPase activity. In the presence of ATP the RuvA-RuvB complex has an activity that renatures cruciform structures formed by heating and gradually cooling supercoiled DNA with an inverted repeat. These findings suggest that the RuvA-RuvB complex interacts with an irregular conformation in damaged DNA and induces conformational changes in DNA using energy provided by ATP hydrolysis, so that it facilitates DNA repair, recombination and error prone replication. 相似文献
7.
Ken-ichi Yamamoto Osamu Hirano Yoichi Hara Hiroshi Yoshikawa 《Ichthyological Research》1987,33(4):399-404
A cyprinid fish,Pseudogobio esocinus showed gradual bradycardia at oxygen saturation (%) of less than 29.7±4.6 (1.89±0.29 ml/l of oxygen concentration), surfacing at 14.7±1.3 (0.94±0.09ml/l), drastic decrease of oxygen consumption at less than 14.2±0.8 (0.91 ±0.06ml/l) and asphyxia at 9.7±1.4 (0.62±0.09ml/l). The fish avoided water having low oxygen saturation of less than 54.0± 5.4 (3.38±0.30ml/l), and markedly at less than 26.2±3.4 (1.62±0.16 ml/l). 相似文献
8.
9.
Severe combined immune deficiency (scid) mice are assumed to have two types of abnormalities: one is high radiosensitivity and the other is abnormal recombination
in immunoglobulin and T-cell receptor genes. The human chromosome 8 q1.1 region has an ability to complement the scid aberrations. Moreover, the localization of the subunit DNA-dependent protein kinase [DNA-PKcs] participating in DNA double-strand break repair in the same locus was clarified. In scid mouse cells, the number of DNA-PKcs products and extent of DNA-PK activity remarkably decrease. These observations gave rise to the assumption that DNA-PKcs is the scid factor itself. In order to determine whether the DNA-PK
cs
gene is the scid gene, we isolated the mouse DNA-PK
cs
gene and investigated its chromosomal locus by fluorescence in situ hybridization (FISH). Consequently, it became clear that
the mouse DNA-PK
cs
gene existed in the centromeric region of mouse chromosome 16, determined by cross-genetic study, as a scid locus. This finding strongly suggests that mouse DNA-PK
cs
is the scid gene.
Received: 22 March 1996 相似文献
10.
Tetsuo Ajiki Takahiro Fujimori Hideo Ikehara Yoichi Saitoh Sakan Maeda 《Biotechnic & histochemistry》1995,70(2):90-94
To investigate the relationship of oncogene analysis to morphology, we analyzed K-ras gene mutations by dot-blot hybridization with and without consideration of histological atypias in individual colorectal adenomas. Each of 54 colon polyps were divided into two parts after fixation. One part was used as a mass to assess point mutations; the remaining portion of each polyp was paraffin-embedded, stained with hematoxylin and eosin, and examined for point mutations related to histological atypias. In the first part of our study, K-ras gene mutations at codon 12 were detected in 13 cases (24%). In the second part of our study, 12 cases had distinctly different histological atypias. From each of these 12 cases, two areas, one with higher or one with lower grade atypia in the same polyp were excised to analyze for K-ras gene mutation. Two of these 12 cases (17%) had the mutation in different areas of the same tumor. These two cases contained the mutation only in the areas with higher grade atypia, and only one case added information regarding ras mutation upon microdissection when compared to the entire biopsy. These results suggest that oligonucleotide hybridization can identify the majority of cases containing ras mutations despite regional morphologic variation. Individual cases, however, may contain clonal subpopulations within adenomas with different ras sequences from other regions within the same adenoma. 相似文献