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   1547篇
  免费   148篇
  2024年   1篇
  2023年   12篇
  2022年   7篇
  2021年   85篇
  2020年   50篇
  2019年   67篇
  2018年   70篇
  2017年   50篇
  2016年   74篇
  2015年   118篇
  2014年   114篇
  2013年   124篇
  2012年   139篇
  2011年   137篇
  2010年   76篇
  2009年   55篇
  2008年   96篇
  2007年   81篇
  2006年   52篇
  2005年   58篇
  2004年   54篇
  2003年   43篇
  2002年   38篇
  2001年   8篇
  2000年   3篇
  1999年   4篇
  1998年   12篇
  1997年   6篇
  1996年   5篇
  1995年   7篇
  1994年   5篇
  1993年   4篇
  1992年   7篇
  1991年   5篇
  1990年   5篇
  1989年   2篇
  1987年   1篇
  1986年   3篇
  1985年   2篇
  1984年   1篇
  1982年   4篇
  1981年   1篇
  1979年   2篇
  1977年   2篇
  1974年   2篇
  1973年   2篇
  1971年   1篇
排序方式: 共有1695条查询结果,搜索用时 390 毫秒
121.
Consumer complaints against the blandness of modern lean meat and the frequent reference to the more strongly flavored meat that was available years ago have prompted reconsideration of high fat-depositing typical pig breeds. Casertana and Large White pig breeds are characterized by a different tendency toward fat accumulation as they exhibit opposite genetic and physiological traits with respect to the energy metabolism. These physiological differences were investigated in longissimus lumborum muscles through proteomics (2-DE, MS/MS) and microarray approaches. Data were analyzed for pathway and network analyses, as well as GO term enrichment of biological functions. As a result, Casertana showed a greater amount of proteins involved in glycolitic metabolism and mainly rely on fast-mobilizable energy sources. Large White overexpressed cell cycle and skeletal muscle growth related genes. Metabolic behavior and other implications are discussed.  相似文献   
122.
Burkholderia glumae is an emerging rice pathogen in several areas around the world. Closely related Burkholderia species are important opportunistic human pathogens for specific groups of patients, such as patients with cystic fibrosis and patients with chronic granulomatous disease. Here we report that the first clinical isolate of B. glumae, strain AU6208, has retained its capability to be very pathogenic to rice. As previously reported for rice isolate B. glumae BGR1 (and also for the clinical isolate AU6208), TofI or TofR acyl homoserine lactone (AHL) quorum sensing played a pivotal role in rice virulence. We report that AHL quorum sensing in B. glumae AU6208 regulates secreted LipA lipase and toxoflavin, the phytotoxin produced by B. glumae. B. glumae AU6208 lipA mutants were no longer pathogenic to rice, indicating that the lipase is an important virulence factor. It was also established that type strain B. glumae ATCC 33617 did not produce toxoflavin and lipase and was nonpathogenic to rice. It was determined that in strain ATCC 33617 the LuxR family quorum-sensing sensor/regulator TofR was inactive. Introducing the tofR gene of B. glumae AU6208 in strain ATCC 33617 restored its ability to produce toxoflavin and the LipA lipase. This study extends the role of AHL quorum sensing in rice pathogenicity through the regulation of a lipase which was demonstrated to be a virulence factor. It is the first report of a clinical B. glumae isolate retaining strong rice pathogenicity and finally determined that B. glumae can undergo phenotypic conversion through a spontaneous mutation in the tofR regulator.  相似文献   
123.
124.
125.
Although the considerable progress against gastric cancer, it remains a complex lethal disease defined by peculiar histological and molecular features. The purpose of the present study was to investigate pRb2/p130, VEGF, EZH2, p53, p16(INK4A), p27(KIP1), p21(WAF1), Ki-67 expressions, and analyze their possible correlations with clinicopathological factors. The expression patterns were examined by immunohistochemistry in 47 patients, 27 evaluated of intestinal-type, and 20 of diffuse-type, with a mean follow up of 56 months and by Western blot in AGS, N87, KATO-III, and YCC-2, -3, -16 gastric cell lines. Overall, stomach cancer showed EZH2 correlated with high levels of p53, Ki-67, and cytoplasmic pRb2/p130 (P < 0.05, and P < 0.01, respectively). Increased expression of EZH2 was found in the intestinal-type and correlated with the risk of distant metastasis (P < 0.05 and P < 0.01, respectively), demonstrating that this protein may have a prognostic value in this type of cancer. Interestingly, a strong inverse correlation was observed between p27(KIP1) expression levels and the risk of advanced disease and metastasis (P < 0.05), and a positive correlation between the expression levels of p21(WAF1) and low-grade (G1) gastric tumors (P < 0.05), confirming the traditionally accepted role for these tumor-suppressor genes in gastric cancer. Finally, a direct correlation was found between the expression levels of nuclear pRb2/p130 and low-grade (G1) gastric tumors that was statistically significant (P < 0.05). Altogether, these data may help shed some additional light on the pathogenetic mechanisms related to the two main gastric cancer histotypes and their invasive potentials.  相似文献   
126.
Hyaluronan-based scaffold were used for in vitro commitment of human and rat bone marrow mesenchymal stem cells (MSC). Cells were cultured either in monolayer and in 3D conditions up to 35 days. In order to monitor the differentiating processes molecular biology and morphological studies were performed at different time points. All the reported data supported the evidence that both human and rat MSC grown onto hyaluronan-derived three-dimensional scaffold were able to acquire a unique phenotype of chondrocytes and osteocytes depending on the presence of specific differentiation inducing factors added into the culture medium without significative differences in term of time expression of extracellular matrix proteins.  相似文献   
127.
Herein we report the results of mutation analysis of the ATP7B gene in a group of 134 Wilson disease (WD) families (268 chromosomes) prevalently of Italian origin. Using the SSCP and sequencing methods we identified 71 disease-causing mutations. Twenty-four were novel, while 19 more mutations already described, were identified in new populations in this study. A known mutation G591D showed a regional distribution, since it was only detected in 38.5% of the analyzed chromosomes in WD patients originating from Apulia, a region of South Italy. Detection of new mutations in the ATP7B gene increases our capability of molecular analysis that is essential for early diagnosis and treatment of WD.  相似文献   
128.
Chloroplast genomes in land plants harbor approximately 20 group II introns. Genetic approaches have identified proteins involved in the splicing of many of these introns, but the proteins identified to date cannot account for the large size of intron ribonucleoprotein complexes and are not sufficient to reconstitute splicing in vitro. Here, we describe an additional protein that promotes chloroplast group II intron splicing in vivo. This protein, RNC1, was identified by mass spectrometry analysis of maize (Zea mays) proteins that coimmunoprecipitate with two previously identified chloroplast splicing factors, CAF1 and CAF2. RNC1 is a plant-specific protein that contains two ribonuclease III (RNase III) domains, the domain that harbors the active site of RNase III and Dicer enzymes. However, several amino acids that are essential for catalysis by RNase III and Dicer are missing from the RNase III domains in RNC1. RNC1 is found in complexes with a subset of chloroplast group II introns that includes but is not limited to CAF1- and CAF2-dependent introns. The splicing of many of the introns with which it associates is disrupted in maize rnc1 insertion mutants, indicating that RNC1 facilitates splicing in vivo. Recombinant RNC1 binds both single-stranded and double-stranded RNA with no discernible sequence specificity and lacks endonuclease activity. These results suggest that RNC1 is recruited to specific introns via protein-protein interactions and that its role in splicing involves RNA binding but not RNA cleavage activity.  相似文献   
129.
Endo-polygalacturonases (endoPGs) belong to the glycoside hydrolase family 28 and hydrolyze the alpha-1,4 glycosidic bond present in the smooth regions of pectins. Pectic substances are among the principal macromolecular components of the primary plant cell walls and are subjected to enzymatic degradation not only in the course of important physiological processes such as plant senescence and ripening, but also during infection events by plant pathogens. Here we report, for the first time, the isolation and the purification of an endoPG (PehA) from the supernatant of the plant pathogen Burkholderia cepacia strain ATCC 25416. In order to obtain adequate amounts of protein required for structural and functional studies, the gene coding for pehA was PCR-amplified and cloned in Escherichia coli cells. The recombinant protein was purified to homogeneity and characterized. PehA exhibited a pI value of 8.0 and an optimal activity at pH 3.5. Far-UV circular dichroism (CD) measurements show that PehA assumes a beta-helix fold super-secondary structural motif.  相似文献   
130.
Gram-negative bacteria most often use N-acyl homoserine lactones (AHLs) as intercellular quorum-sensing signal molecules. In this study, it was demonstrated that rice plants contain AHL mimic molecules that are very sensitive to the highly specific AiiA lactonase enzyme and can activate three different AHL bacterial biosensors, indicating that the compounds have a homoserine lactone structure and could be AHLs. The possible source and biological significance of this finding are discussed.  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