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   8576篇
  免费   931篇
  国内免费   4篇
  2021年   96篇
  2019年   65篇
  2018年   74篇
  2017年   71篇
  2016年   151篇
  2015年   203篇
  2014年   234篇
  2013年   319篇
  2012年   389篇
  2011年   418篇
  2010年   265篇
  2009年   243篇
  2008年   316篇
  2007年   367篇
  2006年   297篇
  2005年   307篇
  2004年   308篇
  2003年   303篇
  2002年   306篇
  2001年   243篇
  2000年   226篇
  1999年   189篇
  1998年   111篇
  1997年   97篇
  1996年   92篇
  1995年   91篇
  1994年   90篇
  1993年   74篇
  1992年   165篇
  1991年   152篇
  1990年   137篇
  1989年   154篇
  1988年   145篇
  1987年   121篇
  1986年   101篇
  1985年   108篇
  1984年   120篇
  1983年   91篇
  1982年   118篇
  1981年   87篇
  1980年   99篇
  1979年   112篇
  1978年   97篇
  1977年   88篇
  1976年   104篇
  1975年   90篇
  1974年   92篇
  1973年   89篇
  1972年   80篇
  1971年   68篇
排序方式: 共有9511条查询结果,搜索用时 15 毫秒
1.
2.
1. Ants are widespread in tropical rainforests, including in the canopy where territorially dominant arboreal species represent the main part of the arthropod biomass. 2. By mapping the territories of dominant arboreal ant species and using a null model analysis and a pairwise approach this study was able to show the presence of an ant mosaic on the upper canopy of a primary Neotropical rainforest (c. 1 ha sampled; 157 tall trees from 28 families). Although Neotropical rainforest canopies are frequently irregular, with tree crowns at different heights breaking the continuity of the territories of dominant ants, the latter are preserved via underground galleries or trails laid on the ground. 3. The distribution of the trees influences the structure of the ant mosaic, something related to the attractiveness of tree taxa for certain arboreal ant species rather than others. 4. Small‐scale natural disturbances, most likely strong winds in the area studied (presence of canopy gaps), play a role by favouring the presence of two ant species typical of secondary formations: Camponotus femoratus and Crematogaster levior, which live in parabiosis (i.e. share territories and nests but lodge in different cavities) and build conspicuous ant gardens. In addition, pioneer Cecropia myrmecophytic trees were recorded.  相似文献   
3.
4.
5.
6.
7.
During an HIV-1 prevention clinical trial in East Africa, we observed 16 cases of primary HIV-1 infection in women coincident with pregnancy or breastfeeding. Nine of eleven pregnant women initiated rapid combination antiretroviral therapy (ART), despite having CD4 counts exceeding national criteria for ART initiation; breastfeeding women initiated ART or replacement feeding. Rapid ART initiation during primary HIV-1 infection during pregnancy and breastfeeding is feasible in this setting.  相似文献   
8.
Dealing with patients'' sex-related complaints is uncomfortable for many physicians. It can become more comfortable if the physician learns to apply his or her clinical knowledge of sexuality in combination with specific interpersonal interviewing skills. The level of comfort can be increased if the physician accepts his or her professional limitations in providing therapy and knows what other sources of care are available.  相似文献   
9.
Brief admission of the new diabetic child and of a parent to an enlightened hospital for stabilisation, preliminary education, and familiarisation with hospital and community staff is well worth while. The greater the demand for constant control of the highest quality, the greater the need for a close understanding of the psychosocial factors concerned and for clinical skill. The nature of the home and the family relationships should in theory be available from the child''s general practitioner at the time of the first referral since he has so much information about the whole family. With the virtual disappearance, however, of mutual consultation in the patient''s home in many places, the opportunity for oral communication has declined, and availability on the telephone is not always easy. The busy general practitioner (far less an unknown physician from a deputising service without access to the records) has little time to write a comprehensive letter. In practice a relatively small hospital-based mobile team of specially experienced sisters who are keen to communicate in the home, the GP''s surgery, and the school makes a major contribution to the diabetic care of a young population vulnerable to major handicap in what should be the prime of life. Their cost effectiveness may be difficult to prove but it is not at all in doubt--especially when the sisters as in this area deal in the community with a wider range of chronic illnesses and handicaps in children.  相似文献   
10.
A study was conducted investigating the possibility that the immunosuppressive action of methimazole (the active metabolite of the antithyroid drug carbimazole) might be due to an effect on the production of oxygen radicals by monocytes. Techniques comprised measurement of luminol dependent chemoluminescence in monocytes and a spectrophotometric assay for production of hydrogen peroxide. The results showed definite inhibition of formation of oxygen radicals by resting and stimulated monocytes, which may explain the immunosuppressive action of the drug in Graves'' disease. The findings also suggest that the formation of oxygen radicals and the initiation of the immune response may be closely related.  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