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   861篇
  免费   49篇
  910篇
  2022年   10篇
  2021年   18篇
  2020年   5篇
  2019年   3篇
  2018年   13篇
  2017年   7篇
  2016年   12篇
  2015年   28篇
  2014年   19篇
  2013年   46篇
  2012年   64篇
  2011年   59篇
  2010年   24篇
  2009年   27篇
  2008年   57篇
  2007年   43篇
  2006年   42篇
  2005年   38篇
  2004年   38篇
  2003年   53篇
  2002年   51篇
  2001年   29篇
  2000年   33篇
  1999年   18篇
  1998年   10篇
  1997年   11篇
  1996年   10篇
  1995年   16篇
  1994年   6篇
  1993年   7篇
  1992年   12篇
  1991年   14篇
  1990年   13篇
  1989年   9篇
  1988年   6篇
  1987年   9篇
  1986年   8篇
  1985年   5篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   3篇
  1979年   2篇
  1978年   4篇
  1977年   2篇
  1974年   5篇
  1973年   2篇
  1970年   2篇
  1967年   2篇
排序方式: 共有910条查询结果,搜索用时 0 毫秒
851.
MicroRNA (miRNA) expression profiling has proven useful in diagnosing and understanding the development and progression of several diseases. Microarray is the standard method for analyzing miRNA expression profiles; however, it has several disadvantages, including its limited detection of miRNAs. In recent years, advances in genome sequencing have led to the development of next-generation sequencing (NGS) technologies, which significantly advance genome sequencing speed and discovery. In this study, we compared the expression profiles obtained by next generation sequencing (NGS) with the profiles created using microarray to assess if NGS could produce a more accurate and complete miRNA profile. Total RNA from 14 hepatocellular carcinoma tumors (HCC) and 6 matched non-tumor control tissues were sequenced with Illumina MiSeq 50-bp single-end reads. Micro RNA expression profiles were estimated using miRDeep2 software. As a comparison, miRNA expression profiles for 11 out of 14 HCCs were also established by microarray (Agilent human microRNA microarray). The average total sequencing exceeded 2.2 million reads per sample and of those reads, approximately 57% mapped to the human genome. The average correlation for miRNA expression between microarray and NGS and subtraction were 0.613 and 0.587, respectively, while miRNA expression between technical replicates was 0.976. The diagnostic accuracy of HCC, p-value, and AUC were 90.0%, 7.22×10−4, and 0.92, respectively. In summary, NGS created an miRNA expression profile that was reproducible and comparable to that produced by microarray. Moreover, NGS discovered novel miRNAs that were otherwise undetectable by microarray. We believe that miRNA expression profiling by NGS can be a useful diagnostic tool applicable to multiple fields of medicine.  相似文献   
852.
The present study was conducted to clarify the relationship between histone H1 kinase (H1K) activity and events associated with in vitro fertilization of pig follicular oocytes matured in vitro. Histone H1 kinase has been shown to be homologous with a maturation promoting factor (MPF). Cumulus-oocyte complexes obtained from prepubertal gilts were cultured for 46 h in a modified Waymouth's MB752/1 medium and were then inseminated in vitro with frozen-thawed and preincubated epididymal boar spermatozoa. At 4, 6, 8 and 10 h post insemination, the oocytes were stained with 10 microg/ml Hoechst-33342 and examined under a fluorescent microscope for the stage of fertilization, according to morphological changes of oocyte nuclear chromatin and the extent of sperm penetration. Sperm penetration was observed to occur within 4 h post insemination (20.5%), and the percentage of fertilized oocytes increased (P < 0.01) to 72.9% at 8 h post insemination. Pronuclear formation was observed from 6 h post insemination (3.3%) and the percentage increased (P < 0.01) to 46.8% at 10 h post insemination. In each examination period, H1K activities in unfertilized oocytes at metaphase-II remained unchanged (112.0 fmol/h/oocyte) and were higher (P < 0.01) than those in fertilized oocytes (30.1 fmol/h/oocyte). The H1K activity in fertilized oocytes such as oocytes emitting a second polar body, oocytes with an enlarging sperm head(s) and oocytes with multiple pronuclei did not differ significantly. These results suggest that MPF in pig oocytes is inactivated shortly after sperm penetration and is maintained at the basal level throughout pronuclear formation.  相似文献   
853.
In the breeding season, the sexually mature male newt, Cynops pyrrhogaster, vibrates the tail in front of the female at an early stage of courtship. Effects of prolactin (PRL), gonadotropin (GTH), and sex steroids on this behavior were investigated in the male paired with the female receiving PRL and GTH. The behavior was elicited in the sexually inert male by injections of PRL of bovine, ovine, or bullfrog origin and human chorionic gonadotropin or bullfrog LH and FSH in combination. The effect of PRL or GTH alone was less marked than that of PRL plus GTH, especially in terms of frequency of the behavior. In the hypophysectomized male, combination of PRL and GTH significantly increased both the incidence and frequency of the behavior. However, PRL alone was not effective, and the effect of GTH alone was less pronounced than that in the intact animal receiving GTH injections. The effect of GTH was nullified by castration. In the PRL-treated castrated animal, testosterone or dihydrotestosterone, but not estradiol, was effective in inducing the behavior.  相似文献   
854.
855.
The late health effects of low-dose rate radiation exposure are still a serious public concern in the Fukushima area even four years after the accident at Fukushima Daiichi Nuclear Power Plant (FNPP). To clarify the factors associated with residents’ risk perception of radiation exposure and consequent health effects, we conducted a survey among residents of Kawauchi village in May and June 2014, which is located within 30 km of FNPP. 85 of 285 residents (29.8%) answered that acute radiation syndrome might develop in residents after the accident, 154 (54.0%) residents responded that they had anxieties about the health effects of radiation on children, and 140 (49.1%) residents indicated that they had anxieties about the health effects of radiation on offspring. Furthermore, 107 (37.5%) residents answered that they had concerns about health effects that would appear in the general population simply by living in an environment with a 0.23 μSv per hour ambient dose for one year, 149 (52.2%) residents reported that they were reluctant to eat locally produced foods, and 164 (57.5%) residents believed that adverse health effects would occur in the general population by eating 100 Bq per kg of mushrooms every day for one year. The present study shows that a marked bipolarization of the risk perception about the health effects of radiation among residents could have a major impact on social well-being after the accident at FNPP.  相似文献   
856.
Root-knot nematodes (RKNs, genus Meloidogyne) are a class of plant parasites that seek out and infect the roots of many plant species. The identification of RKN attractants can be used in agriculture in conjunction with nematode-trapping technology to redirect RKN movements and eventually reduce their prevalence in the field. Here, we discovered that some commercial silica gels can attract nematodes. Silica gels that attract nematodes contain calcium sulfate. Calcium sulfate and calcium carbonate showed strong nematode attraction properties. When plant seeds were surrounded by calcium sulfate or calcium carbonate, nematodes were not attracted to the plant seeds. We propose that calcium sulfate and calcium carbonate can be used in agriculture as a novel material to trap RKN.  相似文献   
857.
A novel Eubacterium cellulosolvens 5 gene encoding an endoglucanase (Cel5A) was cloned and expressed in Escherichia coli, and its enzymatic properties were characterized. The cel5A gene consists of a 3,444-bp open reading frame and encodes a 1,148-amino-acid protein with a molecular mass of 127,047 Da. Cel5A is a modular enzyme consisting of an N-terminal signal peptide, two glycosyl hydrolase family 5 catalytic modules, two novel carbohydrate-binding modules (CBMs), two linker sequences, and a C-terminal sequence with an unknown function. The amino acid sequences of the two catalytic modules and the two CBMs are 94% and 73% identical to each other, respectively. Two regions that consisted of one CBM and one catalytic module were tandemly connected via a linker sequence. The CBMs did not exhibit significant sequence similarity with any other CBMs. Analyses of the hydrolytic activity of the recombinant Cel5A (rCel5A) comprising the CBMs and the catalytic modules showed that the enzyme is an endoglucanase with activities with carboxymethyl cellulose, lichenan, acid-swollen cellulose, and oat spelt xylan. To investigate the functions of the CBMs and the catalytic modules, truncated derivatives of rCel5A were constructed and characterized. There were no differences in the hydrolytic activities with various polysaccharides or in the hydrolytic products obtained from cellooligosaccharides between the two catalytic modules. Both CBMs had the same substrate affinity with intact rCel5A. Removal of the CBMs from rCel5A reduced the catalytic activities with various polysaccharides remarkably. These observations show that CBMs play an important role in the catalytic function of the enzyme.  相似文献   
858.
Glucose transport in adipose cells is regulated by changing the distribution of glucose transporter 4 (GLUT4) between the cell interior and the plasma membrane (PM). Insulin shifts this distribution by augmenting the rate of exocytosis of specialized GLUT4 vesicles. We applied time-lapse total internal reflection fluorescence microscopy to dissect intermediates of this GLUT4 translocation in rat adipose cells in primary culture. Without insulin, GLUT4 vesicles rapidly moved along a microtubule network covering the entire PM, periodically stopping, most often just briefly, by loosely tethering to the PM. Insulin halted this traffic by tightly tethering vesicles to the PM where they formed clusters and slowly fused to the PM. This slow release of GLUT4 determined the overall increase of the PM GLUT4. Thus, insulin initially recruits GLUT4 sequestered in mobile vesicles near the PM. It is likely that the primary mechanism of insulin action in GLUT4 translocation is to stimulate tethering and fusion of trafficking vesicles to specific fusion sites in the PM.  相似文献   
859.
A giant mitochondrion that branches and connects as a single mitochondrion in a cell has been observed during specific phases of the cell cycle of unicellular green algae, but has not been observed in multicellular algae. The genus Ulva is a green macroalga in which the haploid and diploid phases are isomorphic and its gametes develop parthenogenetically. The existence or absence of the giant mitochondrion, and its behavior in Ulva partita, were investigated using a parthenogenesis system. To observe the parthenogenesis of gametes and the dynamics of mitochondria by fluorescence microscopy, we developed an experimental system for culturing and observing U. partita on cover slips: gametes were suspended in 6‐well plates filled with artificial seawater, and cover slips were placed on the well bottoms. The gametes settled on the cover slips as spherical cells (1‐cell S phase). These cells grew into larger cells, losing their eyespot (1‐cell L phase), and developed into multicellular thalli. Gene introduction using the polyethylene glycol (PEG) method is available with transformation efficiencies of 9.0–15.1%. Transformation was performed using a plasmid encoding green fluorescent protein (GFP) fused to the mitochondrial targeting sequence, and mitochondria were labeled by GFP fluorescence. This revealed a string‐shaped giant mitochondrion in a cell of the 1‐cell S phase. In the 1‐cell L phase, a reticular mitochondrion was observed. After the initiation of cell division, the reticular mitochondrion was fragmented, and small oval mitochondria were observed in the 5‐cell phase.  相似文献   
860.
Adult cardiac stem cells are multipotent and support myocardial regeneration   总被引:99,自引:0,他引:99  
The notion of the adult heart as terminally differentiated organ without self-renewal potential has been undermined by the existence of a subpopulation of replicating myocytes in normal and pathological states. The origin and significance of these cells has remained obscure for lack of a proper biological context. We report the existence of Lin(-) c-kit(POS) cells with the properties of cardiac stem cells. They are self-renewing, clonogenic, and multipotent, giving rise to myocytes, smooth muscle, and endothelial cells. When injected into an ischemic heart, these cells or their clonal progeny reconstitute well-differentiated myocardium, formed by blood-carrying new vessels and myocytes with the characteristics of young cells, encompassing approximately 70% of the ventricle. Thus, the adult heart, like the brain, is mainly composed of terminally differentiated cells, but is not a terminally differentiated organ because it contains stem cells supporting its regeneration. The existence of these cells opens new opportunities for myocardial repair.  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