全文获取类型
收费全文 | 73篇 |
免费 | 0篇 |
专业分类
现状及发展 | 25篇 |
研究方法 | 6篇 |
综合类 | 41篇 |
自然研究 | 1篇 |
出版年
2012年 | 3篇 |
2011年 | 11篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有73条查询结果,搜索用时 31 毫秒
61.
62.
63.
Adult skeletal muscle robustly regenerates throughout an organism's life, but as the muscle ages, its ability to repair diminishes and eventually fails. Previous work suggests that the regenerative potential of muscle stem cells (satellite cells) is not triggered in the old muscle because of a decline in Notch activation, and that it can be rejuvenated by forced local activation of Notch. Here we report that, in addition to the loss of Notch activation, old muscle produces excessive transforming growth factor (TGF)-beta (but not myostatin), which induces unusually high levels of TGF-beta pSmad3 in resident satellite cells and interferes with their regenerative capacity. Importantly, endogenous Notch and pSmad3 antagonize each other in the control of satellite-cell proliferation, such that activation of Notch blocks the TGF-beta-dependent upregulation of the cyclin-dependent kinase (CDK) inhibitors p15, p16, p21 and p27, whereas inhibition of Notch induces them. Furthermore, in muscle stem cells, Notch activity determines the binding of pSmad3 to the promoters of these negative regulators of cell-cycle progression. Attenuation of TGF-beta/pSmad3 in old, injured muscle restores regeneration to satellite cells in vivo. Thus a balance between endogenous pSmad3 and active Notch controls the regenerative competence of muscle stem cells, and deregulation of this balance in the old muscle microniche interferes with regeneration. 相似文献
64.
Summary Transverse slicing is a new technique whereby a mammalian muscle can be freely grafted with success. This method eliminates contamination of the early graft by surviving muscle fibres and allows one to measure the development of contractile properties on a uniform population of regenerating muscle fibres.Supported in part by a grant from the Muscular Dystrophy Associations of America, Inc.Part of this research was carried out while on a scientific exchange between the US and Czechoslovak Academies of Sciences. 相似文献
65.
The genome of Theobroma cacao 总被引:2,自引:0,他引:2
Argout X Salse J Aury JM Guiltinan MJ Droc G Gouzy J Allegre M Chaparro C Legavre T Maximova SN Abrouk M Murat F Fouet O Poulain J Ruiz M Roguet Y Rodier-Goud M Barbosa-Neto JF Sabot F Kudrna D Ammiraju JS Schuster SC Carlson JE Sallet E Schiex T Dievart A Kramer M Gelley L Shi Z Bérard A Viot C Boccara M Risterucci AM Guignon V Sabau X Axtell MJ Ma Z Zhang Y Brown S Bourge M Golser W Song X Clement D Rivallan R Tahi M Akaza JM Pitollat B Gramacho K D'Hont A Brunel D Infante D Kebe I Costet P 《Nature genetics》2011,43(2):101-108
We sequenced and assembled the draft genome of Theobroma cacao, an economically important tropical-fruit tree crop that is the source of chocolate. This assembly corresponds to 76% of the estimated genome size and contains almost all previously described genes, with 82% of these genes anchored on the 10 T. cacao chromosomes. Analysis of this sequence information highlighted specific expansion of some gene families during evolution, for example, flavonoid-related genes. It also provides a major source of candidate genes for T. cacao improvement. Based on the inferred paleohistory of the T. cacao genome, we propose an evolutionary scenario whereby the ten T. cacao chromosomes were shaped from an ancestor through eleven chromosome fusions. 相似文献
66.
67.
A model previously developed by Lackman (C. L. Lackman, Forecasting commercial paper rates. Journal of Business Finance and Accounting 15 (1988) 499–524) for the period 1960 to 1985 is updated to include the 1990s and incorporate statistical techniques relating to tests for stationary conditions not available in 1988. As in the previous model, the demand for commercial paper by each institution (Households (HH), Life Insurance Companies (LIC), Non‐Financial Corporations (CRP) and Finance Corporations (FC)) and the total demand is simulated. Simulations of the commercial paper rate are also generated—using just the demand equations (total supply exogenous) and then employing the entire model (supply endogenous) to determine the rate. Simulation periods are from 1960:2 to 2001:4 for all demand simulations. The dynamic simulation of the total demand for commercial paper performs well. The resulting root mean square error, 3.485, compares favourably with the Federal Reserve Boston–Massachusetts Institute of Technology (FRB–MIT) estimate of the commercial paper rate (deLeeuw and Granlich, 1968). Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
68.
Burg TP Godin M Knudsen SM Shen W Carlson G Foster JS Babcock K Manalis SR 《Nature》2007,446(7139):1066-1069
Nanomechanical resonators enable the measurement of mass with extraordinary sensitivity. Previously, samples as light as 7 zeptograms (1 zg = 10(-21) g) have been weighed in vacuum, and proton-level resolution seems to be within reach. Resolving small mass changes requires the resonator to be light and to ring at a very pure tone-that is, with a high quality factor. In solution, viscosity severely degrades both of these characteristics, thus preventing many applications in nanotechnology and the life sciences where fluid is required. Although the resonant structure can be designed to minimize viscous loss, resolution is still substantially degraded when compared to measurements made in air or vacuum. An entirely different approach eliminates viscous damping by placing the solution inside a hollow resonator that is surrounded by vacuum. Here we demonstrate that suspended microchannel resonators can weigh single nanoparticles, single bacterial cells and sub-monolayers of adsorbed proteins in water with sub-femtogram resolution (1 Hz bandwidth). Central to these results is our observation that viscous loss due to the fluid is negligible compared to the intrinsic damping of our silicon crystal resonator. The combination of the low resonator mass (100 ng) and high quality factor (15,000) enables an improvement in mass resolution of six orders of magnitude over a high-end commercial quartz crystal microbalance. This gives access to intriguing applications, such as mass-based flow cytometry, the direct detection of pathogens, or the non-optical sizing and mass density measurement of colloidal particles. 相似文献
69.
Thrombospondins are large secreted, multimodular, calcium-binding glycoproteins that have complex roles in mediating cellular
processes. Determination of high-resolution structures of thrombospondins has revealed unique and interesting protein motifs.
Here, we review this progress and discuss implications for function. By combining structures of modules from thrombospondins
and related extracellular proteins it is now possible to prepare an overall model of the structure of thrombospondin-1 and
thrombospondin-2 and discern features of other thrombospondins. (Part of a multi-author Review) 相似文献
70.
The bacteriophage 434 repressor regulates gene expression by binding with differing affinities to the six operator sites on the phage chromosome. The symmetrically arrayed outer eight base pairs (four in each half-site) of these 14-base-pair operators are highly conserved but the middle four bases are divergent. Although these four base pairs are not in contact with repressor, operators with A.T or T.A base pairs at these positions bind repressor more strongly than those bearing C.G or G.C, suggesting that these bases are important for the repressor's ability to discriminate between operators. There is evidence that the central base pairs influence operator function by constraining the twisting and/or bending of DNA. Here we show that there is a relationship between the intrinsic twist of an operator, as determined by the sequence of its central bases, and its affinity for repressor; an operator with a lower affinity is undertwisted relative to an operator with higher affinity. In complex with repressor, the twist of both high- and low-affinity operators is the same. These results indicate that the intrinsic twist of DNA and its twisting flexibility both affect the affinity of 434 operator for repressor. 相似文献