全文获取类型
收费全文 | 398篇 |
免费 | 61篇 |
专业分类
459篇 |
出版年
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 16篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 22篇 |
2012年 | 32篇 |
2011年 | 33篇 |
2010年 | 15篇 |
2009年 | 17篇 |
2008年 | 23篇 |
2007年 | 17篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 17篇 |
2003年 | 13篇 |
2002年 | 21篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1965年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有459条查询结果,搜索用时 0 毫秒
61.
62.
R Ravin PS Blank A Steinkamp SM Rappaport N Ravin L Bezrukov H Guerrero-Cazares A Quinones-Hinojosa SM Bezrukov J Zimmerberg 《PloS one》2012,7(6):e39421
Blast-Induced Traumatic Brain Injury (bTBI) describes a spectrum of injuries caused by an explosive force that results in changes in brain function. The mechanism responsible for primary bTBI following a blast shockwave remains unknown. We have developed a pneumatic device that delivers shockwaves, similar to those known to induce bTBI, within a chamber optimal for fluorescence microscopy. Abrupt changes in pressure can be created with and without the presence of shear forces at the surface of cells. In primary cultures of human central nervous system cells, the cellular calcium response to shockwaves alone was negligible. Even when the applied pressure reached 15 atm, there was no damage or excitation, unless concomitant shear forces, peaking between 0.3 to 0.7 Pa, were present at the cell surface. The probability of cellular injury in response to a shockwave was low and cell survival was unaffected 20 hours after shockwave exposure. 相似文献
63.
64.
Shay Covo Wenjian Ma James W. Westmoreland Dmitry A. Gordenin Michael A. Resnick 《Cell cycle (Georgetown, Tex.)》2012,11(21):3937-3944
Ultraviolet light (UV) can provoke genome instability, partly through its ability to induce homologous recombination (HR). However, the mechanism(s) of UV-induced recombination is poorly understood. Although double-strand breaks (DSBs) have been invoked, there is little evidence for their generation by UV. Alternatively, single-strand DNA lesions that stall replication forks could provoke recombination. Recent findings suggest efficient initiation of UV-induced recombination in G1 through processing of closely spaced single-strand lesions to DSBs. However, other scenarios are possible, since the recombination initiated in G1 can be completed in the following stages of the cell cycle. We developed a system that could address UV-induced recombination events that start and finish in G2 by manipulating the activity of the sister chromatid cohesion complex. Here we show that sister-chromatid cohesion suppresses UV-induced recombination events that are initiated and resolved in G2. By comparing recombination frequencies and survival between UV and ionizing radiation, we conclude that a substantial portion of UV-induced recombination occurs through DSBs. This notion is supported by a direct physical observation of UV-induced DSBs that are dependent on nucleotide excision repair. However, a significant role of nonDSB intermediates in UV-induced recombination cannot be excluded. 相似文献
65.
66.
Defining the molecular mechanisms of human cell immortalization. 总被引:31,自引:0,他引:31
Although the immortalization of human cells is a key step in oncogenic progression, the molecular mechanisms underlying this event are poorly understood. After reviewing the use of chemicals, physical agents, oncogenes and DNA tumor viruses as immortalizing agents, we consider the importance of negative regulators of cell growth (RB and p53), their inactivation, as well as genomic instability in the pathogenesis of cancer. Finally, a molecular model for human cell immortalization that integrates many of the above observations is presented along with supporting evidence. 相似文献
67.
Molecular cloning of an amino acid-regulated mRNA (amino acid starvation-induced) in rat hepatoma cells 总被引:1,自引:0,他引:1
Using the combination of a subtracted library and differential hybridization, a 409-base pair cDNA was identified that corresponds to a mRNA that is induced 2-3-fold when rat Fao hepatoma cells are subjected to amino acid starvation for 12 h. While this mRNA species was induced during starvation, others such as beta-actin, Cu-Zn superoxide dismutase, glyceraldehyde-3-P, and histone H4 were decreased in abundance to 25-50% of their original levels. The induction of the amino acid starvation-induced (ASI) mRNA was repressed when starved cells were returned to a medium supplemented with amino acids. Tissue distribution analysis showed the ASI mRNA, approximately 650 base pairs in length, to be present in every rat tissue tested. The cDNA clone has been sequenced and appears to correspond to the 3'-most end of the mRNA. The cDNA sequence includes the poly(A) tail, two potential polyadenylation signal sequences, and an open reading frame that we presume to be a portion of the coding sequence. The ASI cDNA will be used to investigate the molecular mechanisms for amino acid-dependent regulation of protein expression by mammalian cells. 相似文献
68.
Z. Gross Shay Nimri Claudia M. Barzilay Liliya Simkhovich 《Journal of biological inorganic chemistry》1997,2(4):492-506
A series of oxoiron(IV) porphyrin cation radical complexes was investigated as compound I analogs of cytochrome P-450. Both
the spectroscopic features and the reactivities of the complexes in oxygen atom transfer to olefins were examined as a function
of only one variable, the axial ligand trans to the oxoiron(IV) bond. The results disclosed two important kinetic steps – electron transfer from olefin to oxoiron(IV)
and intramolecular electron transfer from metal to porphyrin radical – which are affected differently by the axial ligands.
The large kinetic barrier of the latter step in the reaction of olefins with the perchlorato-bound oxoiron(IV) porphyrin cation
radical complex enabled the trapping of a reaction intermediate in which the metal, but not the porphyrin radical, is reduced.
The first electron transfer step is probably followed by σ-bond formation, which readily accounts for formation of isomerized
organic products at low temperatures. It is finally postulated that part of the enhanced oxygenation activities of cytochrome
P-450 monooxygenases and chloroperoxidases is due to a lowering of the energy barrier for the second electron transfer step
via participation of their redox-active cysteinate ligand.
Received: 16 January 1997 / Accepted: 24 May 1997 相似文献
69.
70.