全文获取类型
收费全文 | 916篇 |
免费 | 127篇 |
专业分类
1043篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 17篇 |
2020年 | 13篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 27篇 |
2016年 | 31篇 |
2015年 | 48篇 |
2014年 | 41篇 |
2013年 | 51篇 |
2012年 | 58篇 |
2011年 | 53篇 |
2010年 | 33篇 |
2009年 | 31篇 |
2008年 | 40篇 |
2007年 | 42篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 31篇 |
2003年 | 36篇 |
2002年 | 28篇 |
2001年 | 36篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1966年 | 3篇 |
1960年 | 2篇 |
排序方式: 共有1043条查询结果,搜索用时 0 毫秒
1.
Existence of two populations of cyclin/proliferating cell nuclear antigen during the cell cycle: association with DNA replication sites 总被引:81,自引:14,他引:67 下载免费PDF全文
Pulse-chase experiments have revealed that cyclin, the auxiliary protein of DNA polymerase-delta, is stable during the transition from growth to quiescence in 3T3 cells. Immunoblotting together with immunofluorescence analysis has shown that the amount of cyclin after 24 h of quiescence is 30-40% of that of growing cells and that it presents a nucleoplasmic staining. Immunofluorescence studies show the existence of two populations of cyclin during the S phase, one that is nucleoplasmic as in quiescent cells and is easily extracted by detergent, and another that is associated to specific nuclear structures. By using antibromodeoxyuridine immunofluorescence to detect the sites of DNA synthesis, it was shown that the staining patterns of the replicon clusters and their order of appearance throughout the S phase are identical to those observed for cyclin. Two-dimensional gel analysis of Triton-extracted cells show that 20-30% of cyclin remains associated with the replicon clusters. This population of cyclin could not be released from the nucleus using high-salt extractions. This demonstrates that cyclin is tightly associated to the sites of DNA replication and that it must have a fundamental role in DNA synthesis in eukaryotic cells. 相似文献
2.
3.
Fanconi's anemia lymphocytes: effect of caffeine, adenosine and niacinamide during G2 prophase 总被引:1,自引:0,他引:1
In this investigation peripheral blood lymphocytes from 3 Fanconi's anemia (FA) patients, 2 FA heterozygotes and 4 normal subjects were treated with caffeine and/or adenosine, and/or niacinamide during G2 prophase. Caffeine dramatically increased breakage levels in homozygote and heterozygote cells. Niacinamide and adenosine decreased the amount of chromosomal aberrations detected in FA homozygote and heterozygote lymphocytes treated and untreated with caffeine during G2 prophase. Caffeine sensitivity of heterozygote lymphocytes is proposed as a new clinical test to explore heterozygosis in individuals of FA families. 相似文献
4.
Killing of Escherichia coli cells modulated by components of the stability system ParD of plasmid R1
Alicia Bravo Sagrario Ortega Gertrudis de Torrontegui Ramón Díaz 《Molecular & general genetics : MGG》1988,215(1):146-151
Summary The proteins P10 and P12 have been shown to be gene products of a new stability system, ParD, of plasmid R1. It is now shown that an R1 miniplasmid, pAB112, carrying a trans-complementable amber mutation in the gene of the P10 protein, is lethal for the host in the absence of suppression. This lethal effect is suppressed in a supF background and also by deletions in pAB112 that affect the gene of the P12 protein. These data indicate that the P12 protein has a lethal effect on the host and that this effect is neutralized by the P10 protein. The possibility that the stabilization conferred by the ParD system could be due to a counterselection, mediated by P12, of cells that lose the plasmid at cell division, is discussed. 相似文献
5.
The replication of covalently closed circular supercoiled (form I) DNA in prokaryotes is generally controlled at the initiation level by a rate-limiting effector. Once initiated, replication proceeds via one of two possible modes (theta or sigma replication) which do not rely on functions involved in DNA repair and general recombination. Recently, a novel plasmid replication mode, leading to the accumulation of linear multigenome-length plasmid concatemers in both gram-positive and gram-negative bacteria, has been described. Unlike form I DNA replication, an intermediate recombination step is most probably involved in the initiation of concatemeric plasmid DNA replication. On the basis of structural and functional studies, we infer that recombination-dependent plasmid replication shares important features with phage late replication modes and, in several aspects, parallels the synthesis of plasmid concatemers in phage-infected cells. The characterization of the concatemeric plasmid replication mode has allowed new insights into the mechanisms of DNA replication and recombination in prokaryotes. 相似文献
6.
The immediate-early growth response in regenerating liver and insulin-stimulated H-35 cells: comparison with serum-stimulated 3T3 cells and identification of 41 novel immediate-early genes. 总被引:30,自引:8,他引:22 下载免费PDF全文
K L Mohn T M Laz J C Hsu A E Melby R Bravo R Taub 《Molecular and cellular biology》1991,11(1):381-390
Liver regeneration provides a unique system for analysis of mitogenesis in intact, fully developed animals. Cellular immediate-early genes likely play an important role in cell cycle regulation and have been extensively studied in mitogen-stimulated fibroblasts lymphocytes but not in liver. We have begun to characterize the immediate-early growth response genes of mitogen-stimulated liver cells, specifically, regenerating liver and insulin-stimulated Reuber H-35 hepatoma cells, and to address differences in growth response between different cell types. Through subtraction and differential screening of cDNA libraries from regenerating liver and insulin-treated H-35 cells, we have extensively characterized 341 differentially expressed clones and identified 52 immediate-early genes. These genes have been partially sequenced and subjected to Northern (RNA) blot analysis, and 41 appear to be novel. Surprisingly, two-thirds of these genes are also expressed in BALB/c 3T3 cells, but only 10 were identified in previous studies of 3T3 cells, and of these, 6 include well-known genes like jun and fos, and only 4 are novel. Approximately one-third of the immediate-early genes identified in mitogen-stimulated liver cells or serum-stimulated NIH 3T3 cells are expressed in a tissue-specific fashion, indicating that cell type-specific regulation of the proliferative response occurs during the immediate-early period. Our findings indicate that the immediate-early response is unusually complex for the first step in a regulatory cascade, suggesting that multiple pathways must be activated. The abundance of immediate-early genes and the highly varied pattern of their expression in different cell types suggest that the tissue specificity of the proliferative response arises from the particular set of these genes expressed in a given tissue. 相似文献
7.
Introduction of the Escherichia coli gdhA gene into Rhizobium phaseoli: effect on nitrogen fixation. 总被引:1,自引:1,他引:0 下载免费PDF全文
Rhizobium phaseoli lacks glutamate dehydrogenase (GDH) and assimilates ammonium by the glutamine synthetase-glutamate synthase pathway. A strain of R. phaseoli harboring the Escherichia coli GDH structural gene (gdhA) was constructed. GDH activity was expressed in R. phaseoli in the free-living state and in symbiosis. Nodules with bacteroids that expressed GDH activity had severe impairment of nitrogen fixation. Also, R. phaseoli cells that lost GDH activity and assimilated ammonium by the glutamine synthetase-glutamate synthase pathway preferentially nodulated Phaseolus vulgaris. 相似文献
8.
Specific proteins synthesized during the viral lytic cycle in vaccinia virus-infected HeLa cells: analysis by high-resolution, two-dimensional gel electrophoresis. 总被引:4,自引:3,他引:1 下载免费PDF全文
The proteins synthesized in vaccinia-infected HeLa cells have been analyzed at different times after infection by using two-dimensional gel electrophoresis. Vaccinia-infected cells present up to 198 polypeptides (138 acidic, isoelectric focusing; 60 basic, nonequilibrium pH gradient electrophoresis) not detected in control cells. Cells infected in the presence of cycloheximide show 81 additional polypeptides after cycloheximide removal, resulting in a total estimate of 279 proteins induced after vaccinia infection. The glycoproteins made at various times postinfection were also analyzed. At least 13 proteins labeled with [3H]glucosamine were detected in vaccinia-infected HeLa cells. 相似文献
9.
Effects of N-fertilizers,straw, and dry fallow on the nitrogen balance of a flooded soil planted with rice 总被引:1,自引:0,他引:1
Teresita Santiago-Ventura Marjorie Bravo C. Daez V. Ventura I. Watanabe A. A. App 《Plant and Soil》1986,93(3):405-411
Summary Nitrogen balance studies were made on rice (Oryza sativa) grown in flooded soil in pots. A low rate of fertilizer (5.64 mg N. kg−1 soil) did not depress the N gain, but a high rate (99.72 mg N. kg−1 soil) elminated the N gain. Soil N loss was negligible since15N applied as ammonium sulfate and thoroughly mixed with the soil was recovered from the soil-plant system after 3 crops. The
observed N gain, therefore, was caused by N2-fixation, not by a reduction of soil N loss.
Straw enhanced N gain at the rate of 2–4 mg per g straw. However, this gain was not observed when soil N availability was
high. Dry fallow between rice crops decreased the N gain. 相似文献
10.