全文获取类型
收费全文 | 192篇 |
免费 | 7篇 |
出版年
2023年 | 1篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 10篇 |
2010年 | 14篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 13篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 12篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 16篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有199条查询结果,搜索用时 62 毫秒
71.
Claire L. Ryall Katrina Viloria Fadel Lhaf Anthony J. Walker Aileen King Peter Jones David Mackintosh Rosemary McNeice Hemant Kocher Malin Flodstrom-Tullberg Charlotte Edling Natasha J. Hill 《The Journal of biological chemistry》2014,289(44):30614-30624
Understanding the mechanisms regulating islet growth and survival is critical for developing novel approaches to increasing or sustaining β cell mass in both type 1 and type 2 diabetes patients. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that is important for the regulation of cell growth and adhesion. Increased SPARC can be detected in the serum of type 2 diabetes patients. The aim of this study was to investigate the role of SPARC in the regulation of β cell growth and survival. We show using immunohistochemistry that SPARC is expressed by stromal cells within islets and can be detected in primary mouse islets by Western blot. SPARC is secreted at high levels by pancreatic stellate cells and is regulated by metabolic parameters in these cells, but SPARC expression was not detectable in β cells. In islets, SPARC expression is highest in young mice, and is also elevated in the islets of non-obese diabetic (NOD) mice compared with controls. Purified SPARC inhibits growth factor-induced signaling in both INS-1 β cells and primary mouse islets, and inhibits IGF-1-induced proliferation of INS-1 β cells. Similarly, exogenous SPARC prevents IGF-1-induced survival of primary mouse islet cells. This study identifies the stromal-derived matricellular protein SPARC as a novel regulator of islet survival and β cell growth. 相似文献
72.
73.
The early adaptive evolution of calmodulin 总被引:7,自引:0,他引:7
Baba ML; Goodman M; Berger-Cohn J; Demaille JG; Matsuda G 《Molecular biology and evolution》1984,1(6):442-455
Interaction between gene duplication and natural selection in molecular
evolution was investigated utilizing a phylogenetic tree constructed by the
parsimony procedure from amino acid sequences of 50 calmodulin- family
protein members. The 50 sequences, belonging to seven protein lineages
related by gene duplication (calmodulin itself, troponin-C, alkali and
regulatory light chains of myosin, parvalbumin, intestinal calcium-binding
protein, and glial S-100 phenylalanine-rich protein), came from a wide
range of eukaryotic taxa and yielded a denser tree (more branch points
within each lineage) than in earlier studies. Evidence obtained from the
reconstructed pattern of base substitutions and deletions in these
ancestral loci suggests that, during the early history of the family,
selection acted as a transforming force on expressed genes among the
duplicates to encode molecular sites with new or modified functions. In
later stages of descent, however, selection was a conserving force that
preserved the structures of many coadapted functional sites. Each branch of
the family was found to have a unique average tempo of evolutionary change,
apparently regulated through functional constraints. Proteins whose
functions dictate multiple interaction with several other macromolecules
evolved more slowly than those which display fewer protein-protein and
protein-ion interactions, e.g., calmodulin and next troponin-C evolved at
the slowest average rates, whereas parvalbumin evolved at the fastest. The
history of all lineages, however, appears to be characterized by rapid
rates of evolutionary change in earlier periods, followed by slower rates
in more recent periods. A particularly sharp contrast between such fast and
slow rates is found in the evolution of calmodulin, whose rate of change in
earlier eukaryotes was manyfold faster than the average rate over the past
1 billion years. In fact, the amino acid replacements in the nascent
calmodulin lineage occurred at residue positions that in extant metazoans
are largely invariable, lending further support to the Darwinian hypothesis
that natural selection is both a creative and a conserving force in
molecular evolution.
相似文献
74.
Proteolytic enzymes have been used both to modify properties of the cell membrane and to dissociate cells from many tissues including pituitary (4, 5, 12). Exposure of secretory tissues to pronase can alter their secretory response. Thus incubation of pancreatic islets of Langerhans in the presence of low concentrations of pronase increased the subsequent release of insulin in the presence of stimulatory and nonstimulatory glucose concentrations (7). The purpose of the present investigation was to determine whether low concentrations of pronase have the same stimulatory effect on the release of a pituitary hormone, growth hormone. Such an effect on hormone release could be of some importance in view of the development of dissociated cell systems as models for the study of the control of hormone release (4, 5). 相似文献
75.
76.
Fractal properties of human muscle sympathetic nerve activity 总被引:1,自引:0,他引:1
Fadel PJ Orer HS Barman SM Vongpatanasin W Victor RG Gebber GL 《American journal of physiology. Heart and circulatory physiology》2004,286(3):H1076-H1087
Muscle sympathetic nerve activity (MSNA) in resting humans is characterized by cardiac-related bursts of variable amplitude that occur sporadically or in clusters. The present study was designed to characterize the fluctuations in the number of MSNA bursts, interburst interval, and burst amplitude recorded from the peroneal nerve of 15 awake, healthy human subjects. For this purpose, we used the Allan and Fano factor analysis and dispersional analysis to test whether the fluctuations were time-scale invariant (i.e., fractal) or random in occurrence. Specifically, we measured the slopes of the power laws in the Allan factor, Fano factor, and dispersional analysis curves. In addition, the Hurst exponent was calculated from the slope of the power law in the Allan factor curve. Whether the original time series contained fractal fluctuations was decided on the basis of a comparison of the values of these parameters with those for surrogate data blocks. The results can be summarized as follows. Fluctuations in the number of MSNA bursts and interburst interval were fractal in each of the subjects, and fluctuations in burst amplitude were fractal in four of the subjects. We also found that fluctuations in the number of heartbeats and heart period (R-R interval) were fractal in each of the subjects. These results demonstrate for the first time that apparently random fluctuations in human MSNA are, in fact, dictated by a time-scale-invariant process that imparts "long-term memory" to the sequence of cardiac-related bursts. Whether sympathetic outflow to the heart also is fractal and contributes to the fractal component of heart rate variability remains an open question. 相似文献
77.
78.
Thu Ly Inna Krieger Dmitri Tolkatchev Cheyenna Krone Timothy Moural Fadel A. Samatey ChulHee Kang Alla S. Kostyukova 《Protein science : a publication of the Protein Society》2018,27(2):498-508
The missense mutation R21H in striated muscle tropomyosin is associated with hypertrophic cardiomyopathy, a genetic cardiac disease and a leading cause of sudden cardiac death in young people. Tropomyosin adopts conformation of a coiled coil which is critical for regulation of muscle contraction. In this study, we investigated the effects of the R21H mutation on the coiled‐coil structure of tropomyosin and its interactions with its binding partners, tropomodulin and leiomodin. Using circular dichroism and isothermal titration calorimetry, we found that the mutation profoundly destabilized the structural integrity of αTM1a1‐28Zip, a chimeric peptide containing the first 28 residues of tropomyosin. The mutated αTM1a1‐28Zip was still able to interact with tropomodulin and leiomodin. However, the mutation resulted in a ~30‐fold decrease of αTM1a1‐28Zip's binding affinity to leiomodin. We used a crystal structure of αTM1a1‐28Zip that we solved at 1.5 Å resolution to study the mutation's effect in silico by means of molecular dynamics simulation. The simulation data indicated that while the mutation disrupted αTM1a1‐28Zip's coiled‐coil structure, most notably from residue Ala18 to residue His31, it may not affect the N‐terminal end of tropomyosin. The drastic decrease of αTM1a1‐28Zip's affinity to leiomodin caused by the mutation may lead to changes in the dynamics at the pointed end of thin filaments. Therefore, the R21H mutation is likely interfering with the regulation of the normal thin filament length essential for proper muscle contraction. 相似文献
79.
80.
K M Gallagher P J Fadel S A Smith K H Norton R G Querry A Olivencia-Yurvati P B Raven 《Journal of applied physiology》2001,91(5):2351-2358
This investigation was designed to determine the role of intramuscular pressure-sensitive mechanoreceptors and chemically sensitive metaboreceptors in affecting the blood pressure response to dynamic exercise in humans. Sixteen subjects performed incremental (20 W/min) cycle exercise to fatigue under four conditions: control, exercise with thigh cuff occlusion of 90 Torr (Cuff occlusion), exercise with lower body positive pressure (LBPP) of 45 Torr, and a combination of thigh cuff occlusion and LBPP (combination). Indexes of central command (heart rate, oxygen uptake, ratings of perceived exertion, and electromyographic activity), cardiac output, stroke volume, and total peripheral resistance were not significantly different between the four conditions. Mechanical stimulation during LBPP and combination conditions resulted in significant elevations in intramuscular pressure and mean arterial pressure from control at rest and throughout the incremental exercise protocol (P < 0.05). Conversely, there existed no significant changes in mean arterial pressure when the metaboreflex was stimulated by cuff occlusion. These findings suggest that under normal conditions the mechanoreflex is tonically active and is the primary mediator of exercise pressor reflex-induced alterations in arterial blood pressure during submaximal dynamic exercise in humans. 相似文献