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   1695篇
  免费   5篇
化学工业   43篇
机械仪表   2篇
建筑科学   4篇
能源动力   4篇
轻工业   35篇
水利工程   1篇
石油天然气   1篇
无线电   4篇
一般工业技术   17篇
冶金工业   1582篇
原子能技术   1篇
自动化技术   6篇
  2018年   2篇
  2017年   2篇
  2014年   1篇
  2013年   5篇
  2011年   7篇
  2010年   1篇
  2009年   5篇
  2008年   2篇
  2007年   3篇
  2006年   5篇
  2005年   4篇
  2004年   4篇
  2003年   4篇
  2002年   2篇
  2001年   3篇
  2000年   1篇
  1999年   50篇
  1998年   538篇
  1997年   273篇
  1996年   178篇
  1995年   94篇
  1994年   83篇
  1993年   114篇
  1992年   14篇
  1991年   22篇
  1990年   15篇
  1989年   20篇
  1988年   24篇
  1987年   16篇
  1986年   13篇
  1985年   16篇
  1984年   5篇
  1983年   3篇
  1982年   13篇
  1981年   11篇
  1980年   9篇
  1979年   4篇
  1978年   5篇
  1977年   44篇
  1976年   66篇
  1975年   4篇
  1974年   1篇
  1973年   2篇
  1972年   2篇
  1970年   2篇
  1969年   1篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1956年   1篇
排序方式: 共有1700条查询结果,搜索用时 5 毫秒
91.
92.
93.
Ten male Holstein calves were fed diets with or without 5% added animal fat in combination with low and high dietary calcium (.15 or .98%) for 4 wk. After 3 wk, the animals were orally dosed with calcium-45. One week later they were killed and tissue samples taken. Except for lower calcium-45 in bile, added dietary fat had no marked influence on calcium metabolism. Net absorption of calcium-45 (not excreted in feces) ranged from 82% for calves fed low calcium to 53% for those given high calcium. Calcium-45 in bone was substantially higher in calves fed .15% calcium. Tailbone biopsies revealed rapid uptake of calcium-45 with approximately as much incorporated during the 1st d as in the following 6 d. Calcium-45 in blood peaked 24 h following dosing. Calves fed .15% calcium had higher calcium-45 in blood and bile than those receiving .98% calcium. Calcium-45 values in soft tissue were low and did not differ materially among treatments. The decreases in radioactive calcium absorption and bone deposition with higher dietary calcium indicated that variable absorption was a major factor in calcium homeostasis. Added fat did not materially effect calcium metabolism with either low or high dietary calcium.  相似文献   
94.
95.
96.
97.
98.
OBJECTIVE: Previous research has suggested that support services supplementing methadone maintenance programs vary in their cost-effectiveness. This study examined the cost-effectiveness of varying levels of supplementary support services to determine whether the relative cost-effectiveness of alternative levels of support is sustained over time. METHOD: A group of 100 methadone-maintained opiate users were randomly assigned to three treatment groups receiving different levels of support services during a 24-week clinical trial. One group received methadone treatment with a minimum of counseling, the second received methadone plus more intensive counseling, and the third received methadone plus enhanced counseling, medical, and psychosocial services. The results at the end of the trial period have been published elsewhere. This article reports the results of an analysis at a 6-month follow-up. RESULTS: The follow-up analysis reaffirmed the preliminary findings that the methadone plus counseling level provided the most cost-effective implementation of the treatment program. At 12 months, the annual cost per abstinent client was $16,485, $9,804, and $11,818 for the low, intermediate, and high levels of support, respectively. Abstinence rates were highest, but modestly so, for the group receiving the high-intensity, high-cost methadone with enhanced services intervention. CONCLUSIONS: This study suggests that large amounts of support to methadone-maintained clients are not cost-effective, but it also demonstrates that moderate amounts of support are better than minimal amounts. As funding for these programs is reduced, these findings suggest a floor below which supplementary support should not fall.  相似文献   
99.
100.
This article examines the determinants of first-time use durations of the injectable contraceptive Depo Medroxy Progesterone Acetate (DMPA) for rural Bangladeshi women. The method's side effects were defined by 200 first-time users in Matlab district during lengthy, open-ended interviews. Women with many children used the method longer than did women of low parity. Those who experienced side effects had shorter use durations than those who did not, and those who cited heavy bleeding as their main problem discontinued use soonest. Women whose husbands approved of family planning had significantly longer use durations than those whose husbands disapproved. Respondents who adopted DMPA because of perceived positive aspects of the drug used it longer than those who chose it for other reasons. Results of the study underscore the importance of viewing side effects in a specific social and cultural context. Expanded side-effects counseling for women and their husbands is needed.  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