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   1308653篇
  免费   115354篇
  国内免费   1391篇
  1425398篇
  2021年   17741篇
  2020年   12568篇
  2019年   16126篇
  2018年   17453篇
  2017年   16145篇
  2016年   27759篇
  2015年   42191篇
  2014年   50206篇
  2013年   76412篇
  2012年   34339篇
  2011年   22210篇
  2010年   42635篇
  2009年   44383篇
  2008年   21496篇
  2007年   19215篇
  2006年   25092篇
  2005年   26312篇
  2004年   25413篇
  2003年   23113篇
  2002年   21280篇
  2001年   34491篇
  2000年   31826篇
  1999年   31596篇
  1998年   25319篇
  1997年   25133篇
  1996年   24666篇
  1995年   22753篇
  1994年   22619篇
  1993年   21732篇
  1992年   27116篇
  1991年   25592篇
  1990年   23980篇
  1989年   24893篇
  1988年   22929篇
  1987年   21479篇
  1986年   20294篇
  1985年   22128篇
  1984年   22019篇
  1983年   19483篇
  1982年   20118篇
  1981年   19444篇
  1980年   18074篇
  1979年   17851篇
  1978年   17035篇
  1977年   16349篇
  1976年   15469篇
  1975年   14842篇
  1974年   15095篇
  1973年   15526篇
  1972年   12943篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
OBJECTIVE--To examine the relation between bone density and indices of calcium metabolism including parathyroid hormone and 25-hydroxyvitamin D concentrations in middle aged women. DESIGN--A cross sectional study. SETTING AND SUBJECTS--138 women volunteers aged 45-65 with no known osteoporosis and unselected for disease status recruited for a dietary assessment study from the community using general practice registers. Volunteer rate was 20%. MAIN OUTCOME MEASURE--Bone mineral density measured with dual energy x ray absorptiometry. RESULTS--Bone density at the lumbar spine and neck and trochanteric regions of the femur was inversely related to serum intact parathyroid hormone concentrations and positively related to serum 25-hydroxyvitamin D concentrations. These associations were independent of possible confounding factors, including age, body mass index, cigarette smoking habit, menopausal status, and use of diuretics and postmenopausal hormone replacement therapy. These associations were apparent throughout the whole distribution of bone density and 25-hydroxyvitamin D and parathyroid hormone concentrations within the normal range, suggesting a physiological relation. CONCLUSIONS--The findings are consistent with the hypothesis that parathyroid hormone and 25-hydroxyvitamin D concentrations influence bone density in middle aged women. Findings from this study together with other work suggest that the role of vitamin D in osteoporosis should not be neglected. The associations with parathyroid hormone also indicate plausible biological mechanisms. The roughly 5-10% difference in bone density between top and bottom tertiles of serum 25-hydroxyvitamin D concentrations, though not large in magnitude, may have considerable public health implications in terms of prevention of osteoporosis and its sequelae, fractures.  相似文献   
102.
103.
104.
Zooplankton data collected during September 1995 in the NorthWest Atlantic at 4139'N, 4958'W (the location of the siteof the ‘Titanic’ wreck) were analysed. The regioninvestigated was characterized by a very sharp frontal zonebetween the Gulf Stream and the main stream of the LabradorCurrent. The total plankton biomass in the water column wasvery high. The macroplankton biomass values below the 600 mlayer were significantly higher as compared with the similarvalues measured before in other productive boreal regions ofthe Atlantic and Pacific oceans. A lot of dead mesoplanktonanimals occurred in the deep layers. The reason was that thecold-water mesoplankton advected by the Labrador Current diedoff intensively within the deep layers of the frontal zone andwere used as a food resource by the macroplankton carnivoresand scavengers that were very abundant there.  相似文献   
105.
106.
107.
Trigger finger is a relatively common clinical entity, most frequently caused by stenosing tenosynovitis. Several other conditions not related to tenosynovitis also have been described as a cause of triggering, and these have been reviewed. We present a rare anomaly of the fourth lumbrical muscle insertion as a cause of triggering of the right little finger. This was completely relieved following excision of the anomalous muscle. This rare anatomic variant should be added to the list of potential causes of trigger finger.  相似文献   
108.
109.
110.
Besides vobtusine and vobtusine-lactone, deoxyvobtusine was isolated from the leaves of Voacanga grandifolia (Miq. Rolfe. Spectral and chemical evi  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