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   6178篇
  免费   364篇
  国内免费   1篇
  2023年   58篇
  2022年   94篇
  2021年   192篇
  2020年   135篇
  2019年   182篇
  2018年   222篇
  2017年   176篇
  2016年   244篇
  2015年   382篇
  2014年   398篇
  2013年   466篇
  2012年   497篇
  2011年   478篇
  2010年   276篇
  2009年   274篇
  2008年   319篇
  2007年   301篇
  2006年   306篇
  2005年   231篇
  2004年   180篇
  2003年   168篇
  2002年   137篇
  2001年   109篇
  2000年   107篇
  1999年   71篇
  1998年   46篇
  1997年   29篇
  1996年   29篇
  1995年   31篇
  1994年   24篇
  1993年   15篇
  1992年   33篇
  1991年   32篇
  1990年   20篇
  1989年   25篇
  1988年   15篇
  1987年   18篇
  1986年   25篇
  1985年   22篇
  1984年   16篇
  1983年   13篇
  1982年   12篇
  1981年   15篇
  1979年   16篇
  1978年   9篇
  1975年   9篇
  1974年   12篇
  1973年   8篇
  1970年   8篇
  1968年   7篇
排序方式: 共有6543条查询结果,搜索用时 15 毫秒
81.
Sitosterol and the following terpenic compounds have been isolated from the bark of Podocarpus lambertius: 3β-hydroxytotarol, 4β-carboxynortotarol, and macrophyllic and lambertic acids. The leaves yielded sitosterol, stigmastan-3β,5α-diol-6-one, isopimaric acid, phyllocladene, isophyllocladene, 8,9-abieten-15-ol and 17-isophyllocladenol.  相似文献   
82.
83.
84.
85.
Retinoids (vitamin A and derivatives) are recognized as essential factors for central nervous system (CNS) development. Retinol (vitamin A) also was postulated to be a major antioxidant component of diet as it modulates reactive species (RS) production and oxidative stress in biological systems. Oxidative stress plays a major role either in pathogenesis or development of neurodegenerative diseases, or even in both. Here we investigate the role of retinol supplementation to human neuron-derived SH-SY5Y cells over RS production and biochemical markers associated to neurodegenerative diseases expressed at neuronal level in Parkinson’s disease and Alzheimer’s disease: α-synuclein, β-amyloid peptide, tau phosphorylation and RAGE. Retinol treatment (24 h) impaired cell viability and increased intracellular RS production at the highest concentrations (7 up to 20 µM). Antioxidant co-treatment (Trolox 100 µM) rescued cell viability and inhibited RS production. Furthermore, retinol (10 µM) increased the levels of α-synuclein, tau phosphorylation at Ser396, β-amyloid peptide and RAGE. Co-treatment with antioxidant Trolox inhibited the increased in RAGE, but not the effect of retinol on α-synuclein, tau phosphorylation and β-amyloid peptide accumulation. These data indicate that increased availability of retinol to neurons at levels above the cellular physiological concentrations may induce deleterious effects through diverse mechanisms, which include oxidative stress but also include RS-independent modulation of proteins associated to progression of neuronal cell death during the course of neurodegenerative diseases.  相似文献   
86.
87.

Oral mucositis is an inflammation of the oral mucosa mainly resulting from the cytotoxic effect of 5-fluorouracil (5-FU). The literature shows anti-inflammatory action of l-cysteine (l-cys) involving hydrogen sulfide (H2S). In view of these properties, we investigate the effect of l-cys in oral mucositis induced by 5-FU in hamsters. The animals were divided into the following groups: saline 0.9%, mechanical trauma, 5-FU 60–40 mg/kg, l-cys 10/40 mg and NaHS 27 µg/kg. 5-FU was administered on days 1st to 2nd; 4th day excoriations were made on the mucosa; 5th–6th received l-cys and NaHS. For data analysis, histological analyses, mast cell count, inflammatory and antioxidants markers, and immunohistochemistry (cyclooxygenase-2(COX-2)/inducible nitric oxide synthase (iNOs)/H2S) were performed. Results showed that l-cys decreased levels of inflammatory markers, mast cells, levels of COX-2, iNOS and increased levels of antioxidants markers and H2S when compared to the group 5-FU (p < 0.005). It is suggested that l-cys increases the H2S production with anti-inflammatory action in the 5-FU lesion.

  相似文献   
88.
Data on intestinal parasite infections for South American Indians in prehistoric times as revealed by coprolite analysis are being used to support transoceanic migration routes from the Old World to the New World. These same findings on modern semi-isolated aborigines, considered persisting prehistoric patterns, are also of great importance as indicators of pre-Columbian peopling of South America. This is the case for the Lengua Indians from Paraguay, studied in the 1920s, and the Yanomami and the Salum? from Brazil, studied in the 1980s. The intestinal parasitic profile of these groups can be empirically associated with culture change, but no clear correlations with the population biology of their hosts can be made at present because of scarcity of data.  相似文献   
89.
90.
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