全文获取类型
收费全文 | 4727篇 |
免费 | 476篇 |
专业分类
5203篇 |
出版年
2024年 | 3篇 |
2023年 | 32篇 |
2022年 | 76篇 |
2021年 | 162篇 |
2020年 | 78篇 |
2019年 | 95篇 |
2018年 | 117篇 |
2017年 | 122篇 |
2016年 | 169篇 |
2015年 | 289篇 |
2014年 | 341篇 |
2013年 | 337篇 |
2012年 | 443篇 |
2011年 | 402篇 |
2010年 | 254篇 |
2009年 | 217篇 |
2008年 | 321篇 |
2007年 | 273篇 |
2006年 | 277篇 |
2005年 | 247篇 |
2004年 | 244篇 |
2003年 | 185篇 |
2002年 | 211篇 |
2001年 | 45篇 |
2000年 | 19篇 |
1999年 | 30篇 |
1998年 | 25篇 |
1997年 | 25篇 |
1996年 | 28篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 7篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1973年 | 3篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有5203条查询结果,搜索用时 0 毫秒
141.
142.
Clara Erice O. Yipkin Calhan Lilian Kisiswa Sean Wyatt Alun M. Davies 《Developmental neurobiology》2019,79(4):317-334
Members of the TNF and TNF receptor superfamilies acting by both forward and reverse signaling are increasingly recognized as major physiological regulators of axon growth and tissue innervation in development. Studies of the experimentally tractable superior cervical ganglion (SCG) neurons and their targets have shown that only TNF reverse signaling, not forward signaling, is a physiological regulator of sympathetic innervation. Here, we compared SCG neurons and their targets with prevertebral ganglion (PVG) neurons and their targets. Whereas all SCG targets were markedly hypoinnervated in both TNF‐deficient and TNFR1‐deficient mice, PVG targets were not hypoinnervated in these mice and one PVG target, the spleen, was significantly hyperinnervated. These in vivo regional differences in innervation density were related to in vitro differences in the responses of SCG and PVG neurons to TNF reverse and forward signaling. Though TNF reverse signaling enhanced SCG axon growth, it did not affect PVG axon growth. Whereas activation of TNF forward signaling in PVG axons inhibited growth, TNF forward signaling could not be activated in SCG axons. These latter differences in the response of SCG and PVG axons to TNF forward signaling were related to TNFR1 expression, whereas PVG axons expressed TNFR1, SCG axons did not. These results show that both TNF reverse and forward signaling are physiological regulators of sympathetic innervation in different tissues. 相似文献
143.
144.
145.
The trade‐off between the allocation of resources toward somatic maintenance or reproduction is one of the fundamentals of life history theory and predicts that females invest in offspring at the expense of their longevity or vice versa. Mate quality may also affect life history trade‐offs through mechanisms of sexual conflict; however, few studies have examined the interaction between mate quality and age at first mating in reproductive decisions. Using house crickets (Acheta domesticus), this study examines how survival and reproductive trade‐offs change based on females’ age at first reproduction and exposure to males of varying size. Females were exposed to either a large (presumably high‐quality) or small male at an early (young), middle (intermediate), or advanced (old) age, and longevity and reproductive investment were subsequently tracked. Females mated at a young age had the largest number of eggs but the shortest total lifespans while females mated at older ages produced fewer eggs but had longer total lifespans. The trade‐off between age at first mating and eggs laid appears to be mediated through higher egg‐laying rates and shorter postmating lifespans in females mated later in life. Exposure to small males resulted in shorter lifespans and higher egg‐laying rates for all females indicating that male manipulation of females, presumably through spermatophore contents, varies with male size in this species. Together, these data strongly support a trade‐off between age at first reproduction and lifespan and support the role of sexual conflict in shaping patterns of reproduction. 相似文献
146.
Refinement of the AMBER force field for nucleic acids: improving the description of alpha/gamma conformers 下载免费PDF全文
Pérez A Marchán I Svozil D Sponer J Cheatham TE Laughton CA Orozco M 《Biophysical journal》2007,92(11):3817-3829
We present here the parmbsc0 force field, a refinement of the AMBER parm99 force field, where emphasis has been made on the correct representation of the alpha/gamma concerted rotation in nucleic acids (NAs). The modified force field corrects overpopulations of the alpha/gamma = (g+,t) backbone that were seen in long (more than 10 ns) simulations with previous AMBER parameter sets (parm94-99). The force field has been derived by fitting to high-level quantum mechanical data and verified by comparison with very high-level quantum mechanical calculations and by a very extensive comparison between simulations and experimental data. The set of validation simulations includes two of the longest trajectories published to date for the DNA duplex (200 ns each) and the largest variety of NA structures studied to date (15 different NA families and 97 individual structures). The total simulation time used to validate the force field includes near 1 mus of state-of-the-art molecular dynamics simulations in aqueous solution. 相似文献
147.
Brown NM Martin SM Maurice N Kuwana T Knudson CM 《The Journal of biological chemistry》2007,282(4):2144-2155
Cytokine deprivation has been classically used to study molecular processes of apoptosis. Following interleukin (IL)-3 withdrawal in FL5.12 cells, Bax undergoes a conformational change that results in its mitochondria targeting, cytochrome c release, activation of caspase-9, and apoptosis. Cells overexpressing Casp9DN (dominant negative caspase-9) or treated with the caspase inhibitor Q-VD-OPh increased viability but failed to increase clonogenic survival. We find that caspase-inhibited cells had a significant fraction of viable cells (herein termed "rescued" cells) that failed to initiate cell division after IL-3 add back. The "rescued" cells had reduced mitochondrial potential, stained for active Bax, and had reduced staining with dihydroethidium, an agent sensitive to superoxide levels. Readdition of IL-3 after deprivation demonstrated that Bax activation was reversed, whereas altered 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide and dihydroethidium staining persisted for days. Furthermore, the "rescued" cells were resistant to rotenone, an inhibitor of mitochondrial respiration. The cells were highly sensitive to 2-deoxyglucose, an inhibitor of glycolysis and proposed anti-cancer agent. We conclude that the inhibition of caspase-9 allows cells to retain viability, but cells have prolonged mitochondrial dysfunction and enter a unique nondividing state that shares some properties with malignant cells. 相似文献
148.
149.
Kassen SC Ramanan V Montgomery JE T Burket C Liu CG Vihtelic TS Hyde DR 《Developmental neurobiology》2007,67(8):1009-1031
Constant intense light causes apoptosis of rod and cone photoreceptors in adult albino zebrafish. The photoreceptors subsequently regenerate from proliferating inner nuclear layer (INL) progenitor cells that migrate to the outer nuclear layer (ONL) and differentiate into rods and cones. To identify gene expression changes during this photoreceptor regeneration response, a microarray analysis was performed at five time points during the light treatment. The time course included an early time point during photoreceptor death (16 h), later time points during progenitor cell proliferation and migration (31, 51, and 68 h) and a 96 h time point, which likely corresponds to the initial photoreceptor differentiation. Mean expression values for each gene were calculated at each time point relative to the control (0 h light exposure) and statistical analysis by one-way ANOVA identified 4567 genes exhibiting significant changes in gene expression along the time course. The genes within this data set were clustered based on their temporal expression patterns and proposed functions. Quantitative real-time PCR validated the microarray expression profiles for selected genes, including stat3 whose expression increased markedly during the light exposure. Based on immunoblots, both total and activated Stat3 protein expression also increased during the light treatment. Immunolocalization of Stat3 on retinal tissue sections demonstrated increased expression in photoreceptors and Müller glia by 16 h of light exposure. Some of the Stat3-positive Müller cells expressed PCNA at 31 h, suggesting that Stat3 may play a role in signaling a subset of Müller cells to proliferate during the regeneration response. 相似文献
150.
Paslaru L Davidson S Popescu I Morange M 《Journal of cellular and molecular medicine》2007,11(2):369-371
Cyclosporine A (CsA) is a powerful immunosuppressive drug which significantly improved the success of organ transplantation; however, the major limiting factors for the drug's clinical use are its long and short term adverse effects. The present study was conducted to examine, in a dose-dependent manner, in a model of cardiogenesis, the effect of CsA on cardiomyocytes differentiation. 相似文献