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   948篇
  免费   79篇
  1027篇
  2022年   9篇
  2021年   12篇
  2019年   7篇
  2018年   13篇
  2017年   10篇
  2016年   15篇
  2015年   27篇
  2014年   30篇
  2013年   38篇
  2012年   55篇
  2011年   60篇
  2010年   36篇
  2009年   23篇
  2008年   41篇
  2007年   38篇
  2006年   41篇
  2005年   37篇
  2004年   25篇
  2003年   37篇
  2002年   35篇
  2001年   20篇
  2000年   37篇
  1999年   26篇
  1998年   10篇
  1997年   12篇
  1996年   12篇
  1995年   11篇
  1994年   6篇
  1993年   6篇
  1992年   23篇
  1991年   18篇
  1990年   18篇
  1989年   16篇
  1988年   18篇
  1987年   9篇
  1986年   18篇
  1985年   13篇
  1984年   14篇
  1983年   10篇
  1982年   6篇
  1981年   6篇
  1979年   12篇
  1978年   8篇
  1977年   7篇
  1975年   16篇
  1974年   17篇
  1973年   10篇
  1972年   8篇
  1971年   6篇
  1967年   5篇
排序方式: 共有1027条查询结果,搜索用时 6 毫秒
141.
OBJECTIVE: To assess the relation of smoking and alcohol and coffee consumption to active Helicobacter pylori infection. DESIGN: Cross sectional study of patients attending a general practitioner. Active H pylori infection was measured by the 15C-urea breath test and detailed quantitative information on smoking and on alcohol and coffee consumption was obtained by a standardised self administered questionnaire. SETTING: One general practice in Germany. SUBJECTS: 447 patients aged 15-79 who had not had peptic ulcer disease or treatment for H pylori infection. MAIN OUTCOME MEASURES: Prevalence of H pylori infection according to smoking and alcohol and coffee consumption. RESULTS: Overall prevalence of infection was 21% (94/447). There was no significant relation between smoking and active H pylori infection. Alcohol consumption showed a negative dose-response relation and coffee consumption a positive dose-response relation with active infection. After adjustment for potential confounders, the odds ratios for patients who drank < or = 75 g and > 75 g of ethanol a week compared with non-drinkers were 0.90 (95% confidence interval 0.55 to 1.59) and 0.33 (0.16 to 0.68), respectively (P value for trend 0.005, assuming that 1 litre of beer and 0.51 of wine contain on average 50 g of ethanol in south Germany). Adjusted odds ratios for patients who drank < 3 cups and > or = 3 cups of coffee per day compared with those who did not drink coffee were 1.49 (0.71 to 3.12) and 2.49 (1.23 to 5.03), respectively (P value for trend 0.007). CONCLUSION: These results suggest a protective effect of alcohol consumption against active infection with H pylori and an opposite effect of coffee consumption.  相似文献   
142.
143.
Great-granny’s Garden: a living archive and a sensory garden   总被引:1,自引:0,他引:1  
Since 2003, the Botanical Garden in Oslo has been involved in a project coordinated by the Norwegian Genetic Resource Centre. The wide range of work supervised by this centre includes conservation of ornamental plants. Our garden has been responsible for the registration and collecting of ornamentals in Southeast-Norway and has a special responsibility for the conservation of Paeonia species and cultivars. As a result of the project, Great-granny’s Garden was opened to the public in 2008. It has two objectives. Firstly, it shall be a living archive of Norway’s horticultural heritage. Although proven hardy, easy to grow, and long-lived, old varieties of traditional ornamentals are rapidly disappearing. We aim to keep these old-fashioned varieties for sustainable use in future horticulture and encourage people to use them in present day gardening, both in new gardens and in the restoration of old ones. Secondly, the garden is designed as a sensory garden for people with dementia, in cooperation with Oslo’s Resource Centre for Dementia and Psychiatric Care of the Elderly. It is enclosed by a picked fence and by shrubs, offers rest on several benches, and has a paved and easy to follow round-walk among traditional garden elements and plants with a lush variety of colours, forms, and scents. A sensory garden stimulates many senses, evokes pleasant emotions, brings out long-forgotten memories, and stimulates communication. Sensory gardens are therefore considered an important tool in the therapy of dementia.  相似文献   
144.
145.
146.
147.
Mutants of Pichia guilliermondii were isolated that lacked homoaconitate hydratase (lys4), homoisocitrate dehydrogenase (lys10) or α-aminoadipate reductase (lys2) and were able to excrete homocitrate into the culture medium. The effects of incubation time and lysine concentration in the medium on the excretion of homocitrate were examined. In the presence of 600 mg of L-lysine/1 in a minimum salt medium P. guilliermondii G75 (lys2) produced about 280 mg homocitrate/1 during 48 h of growth. A simple procedure to isolate homocitrate from the medium is described.  相似文献   
148.
149.
150.
In the presence of two or polyvalent cations, e. g., Mg2+, protonated ethylenediamine, protonated spermidine, and protonated spermine, poly U forms an ordered structure in aqueous solution. At elevated temperatures, the secondary structure is lost by a cooperative process. The melting temperature Tm rises with the size of the cations. Using IR-spectroscopy, we could show that the secondary structure of poly U is stabilized by hydrogen bonds. Both carbonyl groups of the uracil are involved in the hydrogen bonding. This experimental result enables us to choose the right arrangement for UU base pairing.  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