首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   741篇
  免费   33篇
  2022年   7篇
  2021年   18篇
  2019年   16篇
  2018年   9篇
  2017年   11篇
  2016年   21篇
  2015年   35篇
  2014年   38篇
  2013年   54篇
  2012年   58篇
  2011年   57篇
  2010年   34篇
  2009年   31篇
  2008年   44篇
  2007年   40篇
  2006年   32篇
  2005年   23篇
  2004年   30篇
  2003年   27篇
  2002年   22篇
  2001年   3篇
  2000年   7篇
  1999年   8篇
  1998年   8篇
  1997年   9篇
  1996年   8篇
  1995年   6篇
  1994年   5篇
  1993年   4篇
  1992年   9篇
  1991年   8篇
  1990年   6篇
  1989年   4篇
  1988年   7篇
  1987年   6篇
  1986年   5篇
  1985年   7篇
  1984年   4篇
  1983年   4篇
  1980年   5篇
  1979年   5篇
  1978年   4篇
  1975年   3篇
  1974年   4篇
  1973年   3篇
  1971年   3篇
  1969年   2篇
  1968年   2篇
  1958年   2篇
  1957年   3篇
排序方式: 共有774条查询结果,搜索用时 15 毫秒
61.
Adipose tissue‐derived mesenchymal stem cells (Ad‐MSC) and platelet derivatives have been used alone or in combination to achieve regeneration of injured tissues. We have tested the effect of platelet‐rich plasma (PRP) on Ad‐MSC and adipocyte function. PRP increased Ad‐MSC viability, proliferation rate and G1‐S cell cycle progression, by at least 7‐, 2‐, and 2.2‐fold, respectively, and reduced caspase 3 cleavage. Higher PRP concentrations or PRPs derived from individuals with higher platelet counts were more effective in increasing Ad‐MSC growth. PRP also accelerated cell migration by at least 1.5‐fold. However, PRP did not significantly affect mature adipocyte viability, differentiation and expression levels of PPAR‐γ and AP‐2 mRNAs, while it increased leptin production by 3.5‐fold. Interestingly, PRP treatment of mature adipocytes also enhanced the release of Interleukin (IL)‐6, IL‐8, IL‐10, Interferon‐γ, and Vascular Endothelial Growth Factor. Thus, data are consistent with a stimulatory effect of platelet derivatives on Ad‐MSC growth and motility. Moreover, PRP did not reduce mature adipocyte survival and increased the release of pro‐angiogenic factors, which may facilitate tissue regeneration processes. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc. J. Cell. Biochem. 116: 2408–2418, 2015. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.  相似文献   
62.
Mono‐ and bis‐alkaloid chiral auxiliaries with anthraquinone or phenanthryl cores were probed as chiral solvating agents (CSAs) for the enantiodiscrimination of chiral cyclic hemiesters. The dimeric anthraquinone derivative and the monomeric phenanthryl one showed remarkable efficiency in the nuclear magnetic resonance (NMR) differentiation of enantiomeric mixtures of hemiesters. An anthraquinone analogous with a single alkaloid unit was remarkably less effective. The conformational prevalence of the chiral auxiliaries were ascertained by NMR. Chirality 27:693–699, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   
63.
A survey of grapevine viruses present in the region of Calabria (southern Italy) was carried out, and the sanitary selection was conducted on various indigenous varieties. Serological (ELISA) and molecular (multiplex RT‐PCR) tests were used to detect the viruses included in the Italian certification programme: Arabis mosaic virus (ArMV), Grapevine fanleaf virus (GFLV), Grapevine leafroll associated virus 1 (GLRaV‐1), Grapevine leafroll associated virus 2 (GLRaV‐2), Grapevine leafroll associated virus 3 (GLRaV‐3), Grapevine virus A (GVA), Grapevine virus B (GVB) and Grapevine fleck virus (GFkV). The frequency with which the above viruses have been detected was 37.4, 32.6, 12.8, 7.7, 7.3, 1.9 and 0.3%, respectively, for GVA, GLRaV‐3, GFLV, GFKV, GLRaV‐1, GLRaV‐2 and GVB. ArMV was never found. The sanitary selection allowed for the detection of 6 putative clones of ‘Arvino’, 2 of ‘Magliocco dolce’ and 2 of the rootstock ‘17–37’ free of the above‐mentioned viruses. The necessary process for the commercialization of these clones as ‘certified’ propagation material was accomplished, and their official approval by the Italian Ministry of Agriculture is currently in progress.  相似文献   
64.
Fibrin is a natural biopolymer with many interesting properties, such as biocompatibility, bioresorbability, ease of processing, ability to be tailored to modify the conditions of polymerization, and potential for incorporation of both cells and cell mediators. Moreover, the fibrin network has a nanometric fibrous structure, mimicking extracellular matrix, and it can also be used in autologous applications. Therefore, fibrin has found many applications in tissue engineering, combined with cells, growth factors, or drugs. Because a major limitation of cardiac cell therapy is low cell engraftment, the use of biodegradable scaffolds for specific homing and in situ cell retention is desirable. Thus, fibrin-based injectable cardiac tissue engineering may enhance cell therapy efficacy. Fibrin-based biomaterials can also be used for engineering heart valves or cardiac patches. The aim of this review is to show cardiac bioengineering uses of fibrin, both as a cell delivery vehicle and as an implantable biomaterial.  相似文献   
65.
Colour polymorphism in vertebrates is usually under genetic control and may be associated with variation in physiological traits. The melanocortin 1 receptor (Mc1r) has been involved repeatedly in melanin-based pigmentation but it was thought to have few other physiological effects. However, recent pharmacological studies suggest that MC1R could regulate the aspects of immunity. We investigated whether variation at Mc1r underpins plumage colouration in the Eleonora's falcon. We also examined whether nestlings of the different morphs differed in their inflammatory response induced by phytohemagglutinin (PHA). Variation in colouration was due to a deletion of four amino acids at the Mc1r gene. Cellular immune response was morph specific. In males, but not in females, dark nestling mounted a lower PHA response than pale ones. Although correlative, our results raise the neglected possibility that MC1R has pleiotropic effects, suggesting a potential role of immune capacity and pathogen pressure on the maintenance of colour polymorphism in this species.  相似文献   
66.
Chlamydia pneumoniae is an obligate intracellular Gram-negative bacterium that causes recurrent pharyngitis, pneumonia and chronic inflammation induced by cycles of persistence and productive infection that might also explain the association with chronic diseases. The aim of this study was to determine whether C. pneumoniae can invade and survive within human osteoblasts and whether this infection elicits the secretion of proinflammatory cytokines.Our results demonstrated that C. pneumoniae was able to infect the SaOS-2 osteoblastic cell line and to replicate in the osteoblasts in a time-dependent manner and was associated to an increase in the cell number and cell viability.In addition, infection of the SaOS-2 cell line with C. pneumoniae at MOI of 4 is correlated to a proinflammatory response. Infected osteoblasts produced increased levels of cytokines IL-6, IL-8, IL-17, and IL-23. The production of cytokines increased with subsequent interaction between osteoblasts and monocytes and the maximum levels of cytokines released were detected 72 h after infection with C. pneumoniae. Thus, controlling the release of chemokines, e.g., IL-23, may be a therapeutic strategy for preventing inflammatory bone disease and counteract inflammation and bone destruction.  相似文献   
67.
Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high-shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained when PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible. The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress-strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.  相似文献   
68.
Vascular Endothelial Growth Factor (VEGF) is the main player in angiogenesis. Because of its crucial role in this process, the study of the genetic factors controlling VEGF variability may be of particular interest for many angiogenesis-associated diseases. Although some polymorphisms in the VEGF gene have been associated with a susceptibility to several disorders, no genome-wide search on VEGF serum levels has been reported so far. We carried out a genome-wide linkage analysis in three isolated populations and we detected a strong linkage between VEGF serum levels and the 6p21.1 VEGF region in all samples. A new locus on chromosome 3p26.3 significantly linked to VEGF serum levels was also detected in a combined population sample. A sequencing of the gene followed by an association study identified three common single nucleotide polymorphisms (SNPs) influencing VEGF serum levels in one population (Campora), two already reported in the literature (rs3025039, rs25648) and one new signal (rs3025020). A fourth SNP (rs41282644) was found to affect VEGF serum levels in another population (Cardile). All the identified SNPs contribute to the related population linkages (35% of the linkage explained in Campora and 15% in Cardile). Interestingly, none of the SNPs influencing VEGF serum levels in one population was found to be associated in the two other populations. These results allow us to exclude the hypothesis that the common variants located in the exons, intron-exon junctions, promoter and regulative regions of the VEGF gene may have a causal effect on the VEGF variation. The data support the alternative hypothesis of a multiple rare variant model, possibly consisting in distinct variants in different populations, influencing VEGF serum levels.  相似文献   
69.
Interacting in the peripersonal space requires coordinated arm and eye movements to visual targets in depth. In primates, the medial posterior parietal cortex (PPC) represents a crucial node in the process of visual-to-motor signal transformations. The medial PPC area V6A is a key region engaged in the control of these processes because it jointly processes visual information, eye position and arm movement related signals. However, to date, there is no evidence in the medial PPC of spatial encoding in three dimensions. Here, using single neuron recordings in behaving macaques, we studied the neural signals related to binocular eye position in a task that required the monkeys to perform saccades and fixate targets at different locations in peripersonal and extrapersonal space. A significant proportion of neurons were modulated by both gaze direction and depth, i.e., by the location of the foveated target in 3D space. The population activity of these neurons displayed a strong preference for peripersonal space in a time interval around the saccade that preceded fixation and during fixation as well. This preference for targets within reaching distance during both target capturing and fixation suggests that binocular eye position signals are implemented functionally in V6A to support its role in reaching and grasping.  相似文献   
70.
There are only few reviews concerning visceral aneurysms in cirrhotics, and a small number of papers on visceral aneurysms in liver transplant patients. The present paper investigates this condition in both groups of patients in a 10-year-retrospective study.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号