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   560篇
  免费   38篇
  2022年   2篇
  2021年   7篇
  2019年   4篇
  2018年   6篇
  2017年   5篇
  2016年   12篇
  2015年   18篇
  2014年   23篇
  2013年   33篇
  2012年   32篇
  2011年   28篇
  2010年   27篇
  2009年   21篇
  2008年   38篇
  2007年   32篇
  2006年   34篇
  2005年   32篇
  2004年   47篇
  2003年   26篇
  2002年   29篇
  2001年   7篇
  2000年   14篇
  1999年   8篇
  1998年   13篇
  1997年   4篇
  1996年   8篇
  1995年   6篇
  1994年   10篇
  1993年   6篇
  1992年   6篇
  1991年   8篇
  1990年   5篇
  1988年   2篇
  1987年   2篇
  1985年   3篇
  1984年   2篇
  1983年   3篇
  1982年   2篇
  1981年   5篇
  1980年   1篇
  1979年   1篇
  1978年   3篇
  1977年   3篇
  1976年   2篇
  1975年   5篇
  1974年   2篇
  1973年   4篇
  1972年   1篇
  1971年   2篇
  1969年   1篇
排序方式: 共有598条查询结果,搜索用时 281 毫秒
591.
Identifying metabolic biomarkers of frailty, an age-related state of physiological decline, is important for understanding its metabolic underpinnings and developing preventive strategies. Here, we systematically examined 168 nuclear magnetic resonance-based metabolomic biomarkers and 32 clinical biomarkers for their associations with frailty. In up to 90,573 UK Biobank participants, we identified 59 biomarkers robustly and independently associated with the frailty index (FI). Of these, 34 associations were replicated in the Swedish TwinGene study (n = 11,025) and the Finnish Health 2000 Survey (n = 6073). Using two-sample Mendelian randomization, we showed that the genetically predicted level of glycoprotein acetyls, an inflammatory marker, was statistically significantly associated with an increased FI (β per SD increase = 0.37%, 95% confidence interval: 0.12–0.61). Creatinine and several lipoprotein lipids were also associated with increased FI, yet their effects were mostly driven by kidney and cardiometabolic diseases, respectively. Our findings provide new insights into the causal effects of metabolites on frailty and highlight the role of chronic inflammation underlying frailty development.  相似文献   
592.
593.
594.
595.
Samples of 130 metastatic melanomas from 92 patients were analyzed by DNA flow cytometry. DNA aneuploidy was observed in 67% of the patients. DNA indices were evenly distributed from 0.6 to 2.6 Tumors originating from primary lesions in the lower extremities were more frequently DNA aneuploid than those of other sites. S-phase fraction (SPF) was evaluable from 73 tumors. DNA aneuploid tumors had a significantly higher SPF than diploid tumors, and females had a higher SPF than males. Furthermore, distant metastases had a higher SPF than metastases in regional lymph nodes and in transit metastases, probably indicating a higher growth potential in metastases spreading to distant sites.  相似文献   
596.
Summary Methods for the isolation and thin-layer chromatographic identification of amino-terminal tryptophyl-peptides presumably responsible for histochemical tryptophyl-peptide reactions in the ACTH cells of the rat hypophysis are described. In the hypophyseal extract several tryptophylpeptide bands — depending on the homogenization solution — were demonstrated on thin-layer chromatograms. Tryptophyl-peptides were demonstrated from their fluorescence induced 1) with glyoxylic acid (glyoxylic acid introduced into the homogenization solution), 2) by exposure of the chromatographic plates to combined formaldehyde and chloral vapour or 3) by exposure to combined formaldehyde and acetyl chloride vapour. A positive PAS reaction was demonstrated in some tryptophyl-peptide bands. Thus, some tryptophyl-peptides seem to contribute to the observed PAS positivity of the ACTH cells.This investigation was supported by grants from the Jalmari and Rauha Ahokas Foundation and the J.K. Paasikivi Foundation  相似文献   
597.
Numerous species of microscopic fungi inhabit mosses and hepatics. They are severely overlooked and their identity and nutritional strategies are mostly unknown. Most of these bryosymbiotic fungi belong to the Ascomycota. Their fruit‐bodies are extremely small, often reduced and simply structured, which is why they cannot be reliably identified and classified by their morphological and anatomical characters. A phylogenetic hypothesis of bryosymbiotic ascomycetes is presented. New sequences of 78 samples, including 61 bryosymbionts, were produced, the total amount of terminals being 206. Of these, 202 are Ascomycetes. Sequences from the following five gene loci were used: rDNA SSU, rDNA LSU, RPB2, mitochondrial rDNA SSU, and rDNA 5.8S. The program TNT was used for tree search and support value estimation. We show that bryosymbiotic fungi occur in numerous lineages, one of which represents a newly discovered lineage among the Ascomycota and exhibits a tripartite association with cyanobacteria and sphagna. A new genus Trizodia is proposed for this basal clade. Our results demonstrate that even highly specialized life strategies can be adopted multiple times during evolution, and that in many cases bryosymbionts appear to have evolved from saprobic ancestors. © The Willi Hennig Society 2009.  相似文献   
598.
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