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   268篇
  免费   19篇
  国内免费   1篇
  288篇
  2021年   4篇
  2018年   4篇
  2017年   7篇
  2016年   7篇
  2015年   8篇
  2014年   9篇
  2013年   6篇
  2012年   13篇
  2011年   9篇
  2010年   14篇
  2009年   13篇
  2008年   15篇
  2007年   15篇
  2006年   7篇
  2005年   8篇
  2004年   9篇
  2003年   7篇
  2002年   2篇
  2001年   8篇
  2000年   7篇
  1999年   4篇
  1998年   10篇
  1997年   6篇
  1996年   4篇
  1994年   4篇
  1993年   7篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1987年   3篇
  1986年   4篇
  1983年   2篇
  1982年   2篇
  1981年   8篇
  1979年   4篇
  1978年   2篇
  1976年   2篇
  1975年   6篇
  1974年   3篇
  1973年   2篇
  1972年   3篇
  1971年   2篇
  1969年   2篇
  1964年   3篇
  1963年   3篇
  1962年   1篇
  1961年   2篇
  1957年   2篇
  1956年   3篇
  1933年   1篇
排序方式: 共有288条查询结果,搜索用时 15 毫秒
261.

Background

Familial adenomatous polyposis (FAP) is a disease characterized by the development of hundreds to thousands of adenomatous polyps in the colorectum early in life. Virtually all patients with FAP will develop colorectal cancer before the age of 40 to 50 years, unless prophylactic colectomy is performed, which significantly improves their prognosis. The mortality pattern has changed and duodenal cancer now is one of the main cancer-related causes of death in these patients. Practically all patients with FAP develop premalignant duodenal adenomas, which may develop to duodenal cancer in approximately 3-7% of patients. Duodenal cancer in patients with FAP has a poor prognosis. The clinical challenge is to identify patients at high-risk for duodenal carcinoma. Chemoprevention would be desirable to avoid duodenectomy. The main goal of this study is to identify risk markers in normal duodenal mucosa of patients with FAP, that could help identify patients at increased risk for malignant transformation.

Methods

Messenger RNA (mRNA) levels of glutathione S-transferase A1 (GSTA1), glutathione S-transferase P1 (GSTP1), KIAA1199, E-cadherin, peroxisome proliferative activated receptor δ (PPARδ), caspase-3, cyclin D1, β-catenin, and cyclooxygenase-2 (COX-2) were measured in duodenal mucosa, using the QuantiGene 2.0 Plex assay. Levels in normal appearing mucosa of patients with FAP (n?=?37) were compared with levels in non-FAP patient controls (n?=?16). In addition, levels before and after treatment with either celecoxib & ursodeoxycholic acid (UDCA, n?=?14) or celecoxib & placebo (n?=?13) were evaluated in patients with FAP.

Results

mRNA levels of glutathione S-transferase A1 (28.16% vs. 38.24%, p?=?0.008) and caspase-3 (3.30% vs. 5.31%, p?=?0.001) were significantly lower in patients with FAP vs. non-FAP patient controls, respectively. COX-2 mRNA levels in normal duodenal mucosa of patients with FAP were found to be unexpectedly low. None of the potential risk markers was influenced by celecoxib or celecoxib & UDCA.

Conclusions

Protection against toxins and carcinogens (GSTA1) and apoptosis (caspase-3) is low in patients with FAP, which could contribute to increased susceptibility for malignant transformation of duodenal mucosa.

Trial registration

http://ClinicalTrials.gov number NCT00808743
  相似文献   
262.
The phylogenetic affinities of the chaetognaths: a molecular analysis   总被引:5,自引:3,他引:5  
The chaetognaths, or arrowworms, constitute a small and enigmatic phylum of marine invertebrates whose phylogenetic affinities have long been uncertain. A popular hypothesis is that the chaetognaths are the sister group of the major deuterostome phyla: chordates, hemichordates, and echinoderms. Here we attempt to determine the affinities of the chaetognaths by using molecular sequence data. We describe the isolation and nucleotide sequence determination of 18S ribosomal DNA from one species of chaetognath and one acanthocephalan. Extensive phylogenetic analyses employing a suite of phylogenetic reconstruction methods (maximum parsimony, maximum likelihood, evolutionary parsimony, and two distance methods) suggest that the hypothesized relationship between chaetognaths and the deuterostomes is incorrect. In contrast, we propose that the lineage leading to the chaetognaths arose prior to the advent of the coelomate metazoa.   相似文献   
263.
The epoxidation of zeaxanthin (Zx) to violaxanthin after exposure to different light stress conditions has been studied in Arabidopsis (Arabidopsis thaliana). Formation of Zx was induced by illumination of intact leaves for up to 8 h at different light intensities and temperatures. The kinetics of epoxidation was found to be gradually retarded with increasing light stress during pre-illumination, indicating a gradual down-regulation of the Zx epoxidase activity. Retardation of the epoxidation rates by a factor of up to 10 was inducible either by increasing the light intensity or by extending the illumination time or by decreasing the temperature during pre-illumination. The retardation of the epoxidation kinetics was correlated with a decrease of the PSII quantum efficiency after the pre-illumination treatment. Experiments with the stn7/stn8 mutant of Arabidopsis indicated that the thylakoid protein kinases STN7 and STN8, which are required for the phosphorylation of PSII proteins, are not involved in the short-term down-regulation of Zx epoxidation. However, the retardation of Zx epoxidation was maintained in thylakoids isolated from pre-illuminated leaves, indicating that a direct modification of the Zx epoxidase is most likely involved in the light-induced down-regulation.  相似文献   
264.
265.
266.
267.
268.
The 1/4-inch mesh eliminates the raw nose caused by specimens rubbing their noses on fine screening. The fine screening keeps new-born garter snakes, crickets, and other surprises from escaping. A light fixture and a 15-watt sign bulb will keep your specimens more active, feeding more often, and growing faster. Even a 40-watt bulb can be used with comparative safety. Colored gravels or carpet tiles give a splash of color and are easily cleaned. The double-strength glass adds weight and strength to the top. Extra weight may be added to ensure that there will be no escapees. Cleaning is accomplished by removing both pieces of glass. The terrarium may also be used as a greenhouse.  相似文献   
269.
Molecular evolution of the period gene in Drosophila athabasca   总被引:1,自引:0,他引:1  
We measured nucleotide variability within and between the three semispecies of the Drosophila athabasca complex, at the period (per) gene by using a polymerase chain reaction-based four-cutter restriction- enzyme analysis. The levels of polymorphism varied considerably between the three semispecies. Our results for per, combined with previous data for X-linked allozymes, suggest that the X chromosome in the western- northern semispecies is less variable than expected under an equilibrium-neutral model. Both the pattern of divergence between the semispecies and a cladistic clustering of per haplotypes support the previously hypothesized grouping of eastern A and eastern B as the two most recently diverged semispecies. A 21-bp in-frame segment in the region of per which shares sequence similarity with the neuronal development gene single minded is deleted in all eastern A and eastern B flies examined but is present in all of the western-northern flies and all other published per sequences. Despite these hints that there may be significant differences at the per gene between the semispecies, especially the western-northern group versus the two eastern groups, there is no compelling evidence that per is involved in the mating song differences between the semispecies.   相似文献   
270.
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