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   7359篇
  免费   591篇
  国内免费   40篇
  7990篇
  2024年   10篇
  2023年   36篇
  2022年   111篇
  2021年   163篇
  2020年   119篇
  2019年   182篇
  2018年   223篇
  2017年   197篇
  2016年   326篇
  2015年   446篇
  2014年   479篇
  2013年   547篇
  2012年   683篇
  2011年   657篇
  2010年   481篇
  2009年   376篇
  2008年   478篇
  2007年   449篇
  2006年   384篇
  2005年   331篇
  2004年   314篇
  2003年   283篇
  2002年   279篇
  2001年   45篇
  2000年   65篇
  1999年   61篇
  1998年   38篇
  1997年   37篇
  1996年   24篇
  1995年   26篇
  1994年   19篇
  1993年   10篇
  1992年   10篇
  1991年   16篇
  1990年   5篇
  1989年   5篇
  1988年   7篇
  1987年   7篇
  1986年   6篇
  1985年   4篇
  1984年   4篇
  1983年   3篇
  1979年   4篇
  1976年   4篇
  1975年   5篇
  1974年   3篇
  1972年   3篇
  1968年   3篇
  1964年   3篇
  1963年   2篇
排序方式: 共有7990条查询结果,搜索用时 15 毫秒
61.
62.
Kim MN  Kim N  Lee SH  Park YS  Hwang JH  Kim JW  Jeong SH  Lee DH  Kim JS  Jung HC  Song IS 《Helicobacter》2008,13(4):261-268
Background: This study was performed to evaluate whether the addition of probiotics to proton pump inhibitor (PPI)‐based triple therapy increases the likelihood of successful Helicobacter pylori eradication. Materials and Methods: Three hundred and forty‐seven H. pylori‐infected patients were randomized into a triple‐plus‐yogurt group (yogurt group, n = 168) or a triple‐only group (control group, n = 179). Triple therapy consisted of PPI b.i.d., clarithromycin 500 mg b.i.d., and amoxicillin 1 g b.i.d. for 7 days. Yogurt group received triple therapy for 1 week and one bottle of Will yogurt per day for at 3 weeks, starting on the first day of triple therapy. Will yogurt (a Korean brand) contains Lactobacillus acidophilus HY2177, Lactobacillus casei HY2743, Bifidobacterium longum HY8001, and Streptococcus thermophilus B‐1. 13C‐urea breath test was performed at least 4 weeks after completion of triple therapy. Eradication rates, compliances, and adverse events were compared. Results: By intention‐to treat analysis the H. pylori eradication rates in the yogurt group 79.2% (133 of 168) was similar to that in the control group 72.1% (129 of 179) (p = .124). However, by per‐protocol (PP) analysis, the eradication rate in the yogurt group, 87.5% (133 of 152) was higher than that in the control group, 78.7% (129 of 164) (p = .037). Common adverse events were metallic taste (11.8%) and diarrhea (8.6%). The frequency of adverse effects in the yogurt group 41.1% (69/168) were higher than in the control group, 26.3% (47 of 179) (p = .003). However, most adverse events were mild to moderate in intensity, and the severities of adverse effects were similar in both groups (p = .401). Conclusions: The addition of Will yogurt to triple therapy did not reduce the side‐effects of triple therapy. But it increased the H. pylori eradication rate by PP analysis, encouraging more research in this field.  相似文献   
63.
The expression of 4 pluripotency genes (Oct4, Sox2, c-Myc and Klf4) in mouse embryonic fibroblasts can reprogramme them to a pluripotent state. We have investigated the expression of these pluripotency genes when human somatic 293T cells are permeabilized and incubated in extracts of mouse embryonic stem (ES) cells. Expression of all 4 genes was induced over 1–8 h. Gene expression was associated with loss of repressive histone H3 modifications and increased recruitment of RNA polymerase II at the promoters. Lamin A/C, which is typically found only in differentiated cells, was also removed from the nuclei. When 293T cells were returned to culture after exposure to ES cell extract, the expression of the pluripotency genes continued to rise over the following 48 h of culture, suggesting that long-term reprogramming of gene expression had been induced. This provides a methodology for studying the de-differentiation of somatic cells that can potentially lead to an efficient way of reprogramming somatic cells to a pluripotent state without genetically altering them.  相似文献   
64.
65.
Microorganisms capable of degrading crude oil were isolated and grown in soybean oil as a sole carbon source. The microbial cultures were used to control green peach aphids in vitro. Approximately 60% mortality of aphids was observed when the cultures were applied alone onto aphids. To examine the cultures as a pesticide formulation mixture, the cultures were combined with a low dose of the insecticide imidacloprid (one-fourth dose of recommended field-application rate) and applied onto aphids. The cultures enhanced significantly the insecticidal effectiveness of imidacloprid, which was higher than imidacloprid alone applied at the low dose. The isolated microorganisms exhibited high emulsifying index values and decreased surface tension values after being grown in soybean oil media. GC/MS analyses showed that microorganisms degraded soybean oil to fatty acids. The cultures were suggested to play the roles of wetting, spreading, and sticking agents to improve the effectiveness of imidacloprid. This is the first report on the control of aphids by using oil-degrading microbial cultures.  相似文献   
66.
The human DnaJ homolog Hdj2 is a cochaperone containing a cysteine-rich zinc finger domain. We identified a specific interaction of Hdj2 with the cellular redox enzyme thioredoxin using a yeast two-hybrid assay and a coimmunoprecipitation assay, thereby investigating how the redox environment of the cell regulates Hdj2 function. In reconstitution experiments with Hsc70, we found that treatment with H2O2 caused the oxidative inactivation of Hdj2 cochaperone activity. Hdj2 inactivation paralleled the oxidation of cysteine thiols and concomitant release of coordinated zinc, suggesting a role of cysteine residues in the zinc finger domain of Hdj2 as a redox sensor of chaperone-mediated protein-folding machinery. H2O2-induced negative regulation of Hdj2 cochaperone activity was also confirmed in mammalian cells using luciferase as a foreign reporter cotransfected with Hsc70 and Hdj2. The in vivo oxidation of cysteine residues in Hdj2 was detected only in thioredoxin-knockdown cells, implying that thioredoxin is involved in the in vivo reduction. The oxidative inactivation of Hdj2 was reversible. Wild-type thioredoxin notably recovered the oxidatively inactivated Hdj2 activity accompanied by the reincorporation of zinc, whereas the catalytically inactive mutant thioredoxin (Cys32Ser/Cys35Ser) did not. Taken together, we propose that oxidation and reduction reversibly regulate Hdj2 function in response to the redox states of the cell.  相似文献   
67.
Human hair follicle dermal papilla cells (HFDPCs) located in hair follicles (HFs) play a pivotal role in hair follicle morphogenesis, hair cycling, and hair growth. Over the past few decades, probiotic bacteria (PB) have been reported to have beneficial effects such as improved skin health, anti-obesity, and immuno-modulation for conditions including atopic dermatitis and inflammatory bowel disease (IBD). PB can secrete 50~150 nm sized extracellular vesicles (EVs) containing microbial DNA, miRNA, proteins, lipids, and cell wall components. These EVs can regulate communication between bacteria or between bacteria and their host. Although numerous biological effects of PB-EVs have been reported, the physiological roles of Leuconostoc holzapfelii (hs-Lh), which is isolated from human scalp tissue, and the extracellular vesicles derived from them (hs-LhEVs) are largely unknown. Herein, we investigated the effects of hs-LhEVs on hair growth in HFDPCs. We show that hs-LhEVs increase cell proliferation, migration, and regulate the cell cycle. Furthermore, hs-LhEVs were found to modulate the mRNA expression of hair-growth-related genes in vitro. These data demonstrate that hs-LhEVs can reduce apoptosis by modulating the cell cycle and promote hair growth by regulation via the Wnt/β-catenin signal transduction pathway.  相似文献   
68.
The exocyst is a key factor in vesicle transport and is involved in cell secretion, cell growth, cell division and other cytological processes in eukaryotes. EXO70 is the key exocyst subunit. We obtained a gene, SHORT-ROOT 1 (SR1), through map-based cloning and genetic complementation. SR1 is a conserved protein with an EXO70 domain in plants. SR1 mutation affected the whole root-development process: producing shorter radicles, adventitious roots and lateral roots, and demonstrating abnormal xylem development, resulting in dwarfing and reduced water potential and moisture content. SR1 was largely expressed in the roots, but only in developing root meristems and tracheary elements. The shortness of the sr1 mutant roots was caused by the presence of fewer meristem cells. The in situ histone H4 expression patterns confirmed that cell proliferation during root development was impaired. Tracheary element dysplasia was caused by marked decreases in the inner diameters of and distances between the perforations of adjacent tracheary elements. The membrane transport of sr1 mutants was blocked, affecting cell division in the root apical region and the development of root tracheary elements. The study of SR1 will deepen our understanding of the function of EXO70 genes in Oryza sativa (rice) and guide future studies on the molecular mechanisms involved in plant root development.  相似文献   
69.
Highly effective and safe drugs for the treatment of neuropathic pain are urgently required and it was shown that blocking T-type calcium channels can be a promising strategy for drug development for neuropathic pain. We have developed pyrrolidine-based T-type calcium channel inhibitors by structural hybridization and subsequent assessment of in vitro activities against Cav3.1 and Cav3.2 channels. Profiling of in vitro ADME properties of compounds was also carried out. The representative compound 17h showed comparable in vivo efficacy to gabapentin in the SNL model, which indicates T-type calcium channel inhibitors can be developed as effective therapeutics for neuropathic pain.  相似文献   
70.
Keratin 8 (K8) is a type II keratin that is associated with the type I keratins K18 or K19 in single layered epithelia. We generated a bacterial artificial chromosome (BAC) transgenic mouse line that expresses the tamoxifen inducible CreER(T2) inserted into the endogenous murine K8 gene. The transgenic mouse line contains two copies of the BAC transgene. To determine the expression specificity and inducibility of CreER(T2), the K8-CreER(T2) mice were bred with a Gt(ROSA 26)( ACTB-tdTomato-EGFP ) fluorescent protein-based reporter transgenic mouse line. We demonstrated that CreER(T2) and the endogenous K8 gene share the same patterns of expression and that the enzymatic activity of CreER(T2) can be efficiently induced by tamoxifen in all K8-expressing tissues. This mouse line will be useful for studying gene function in development and homeostasis of simple epithelia, and investigating both tissue lineage hierarchy and the identity of the cells of origin for epithelial cancers.  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