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   791140篇
  免费   89132篇
  国内免费   443篇
  880715篇
  2018年   6708篇
  2016年   9148篇
  2015年   12939篇
  2014年   14887篇
  2013年   21561篇
  2012年   24090篇
  2011年   24648篇
  2010年   16541篇
  2009年   15229篇
  2008年   21794篇
  2007年   22808篇
  2006年   21066篇
  2005年   20387篇
  2004年   20203篇
  2003年   19491篇
  2002年   18915篇
  2001年   34112篇
  2000年   34333篇
  1999年   27628篇
  1998年   10094篇
  1997年   10495篇
  1996年   10099篇
  1995年   9257篇
  1994年   9278篇
  1993年   9111篇
  1992年   22968篇
  1991年   22402篇
  1990年   22110篇
  1989年   21813篇
  1988年   20080篇
  1987年   19176篇
  1986年   17656篇
  1985年   17921篇
  1984年   15029篇
  1983年   13029篇
  1982年   10196篇
  1981年   9200篇
  1980年   8566篇
  1979年   14341篇
  1978年   11214篇
  1977年   10464篇
  1976年   9872篇
  1975年   10572篇
  1974年   11481篇
  1973年   11275篇
  1972年   10428篇
  1971年   9522篇
  1970年   8068篇
  1969年   8021篇
  1968年   7266篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
We examined the relationships among reproductive hormone concentrations and bone mineral density (BMD) in 43 women runners classified as eumenorrheic (n = 24), oligomenorrheic (n = 8), or amenorrheic (n = 11). Results were compared with a eumenorrheic nonrunner control group (n = 11). Serum 17 beta-estradiol, progesterone, and dehydroepiandrosterone sulfate concentrations were determined in daily blood samples for 21 days, and integrated concentrations (areas under the curve) were calculated. BMD was assessed at the lumbar spine and proximal femur by dual-photon absorptiometry. As expected, 17 beta-estradiol, progesterone, and lumbar spine BMD were higher in the control and eumenorrheic runner groups than in the oligomenorrheic and amenorrheic runner groups (P less than 0.05). Progesterone concentration was significantly correlated with lumbar spine BMD in the eumenorrheic runners (r = 0.61). None of the steroid hormones was significantly related to BMD in the oligomenorrheic/amenorrheic group. The present data suggest that circulating levels of gonadal steroid hormones affect axial BMD in eumenorrheic runners.  相似文献   
993.
994.
995.
996.
During an ultrastructural study of small-intestinal mucosa from a patient suffering from alpha-chain disease organisms were identified within the epithelial cytoplasm which showed the fine structural features of the coccidian group. Though coccidiosis is well recognized as causing a diarrhoeal and often lethal illness in animals it has been neglected as a cause of disease in man. Thus this finding may be significant and warrants further investigation into its possible role in the pathogenesis of alpha-chain disease.  相似文献   
997.
998.
999.
1000.
The role of cortisol as a factor controlling the deposition of glycogen in the pig fetus was examined by infusing either a low dose (1 mg/day) or a high dose (3 mg/day) of cortisol into chronically-catheterized hypophysectomized fetal pigs for five days beginning on day 100-104 of gestation. After infusion, liver glycogen was significantly higher (P less than 0.05) and lung glycogen significantly lower (P less than 0.05) than in uninfused hypophysectomized litter mates although concentrations were significantly different from intact litter mates (P less than 0.05). Although skeletal and cardiac muscle content increased after infusion this difference was not significant. Changes in tissue glycogen content were similar for both the low and high rates of infusion. These observations indicate that exogenous cortisol alone is able to stimulate liver glycogen deposition and reverse the effect of hypophysectomy. Although other factors may be necessary for maximal response this suggests that cortisol is an important stimulant for liver glycogen deposition in the fetal pig. The effect of cortisol on muscle glycogen was equivocal suggesting that other hormones may play a more important role in this tissue.  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