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   1178篇
  免费   4篇
  国内免费   6篇
电工技术   2篇
综合类   9篇
化学工业   11篇
金属工艺   4篇
机械仪表   4篇
建筑科学   3篇
矿业工程   2篇
能源动力   1篇
轻工业   16篇
水利工程   2篇
无线电   16篇
一般工业技术   7篇
冶金工业   1099篇
原子能技术   1篇
自动化技术   11篇
  2021年   1篇
  2014年   2篇
  2013年   5篇
  2012年   2篇
  2011年   9篇
  2010年   8篇
  2009年   19篇
  2008年   21篇
  2007年   2篇
  2006年   3篇
  2005年   2篇
  2003年   2篇
  2002年   5篇
  2001年   4篇
  2000年   1篇
  1999年   34篇
  1998年   257篇
  1997年   163篇
  1996年   113篇
  1995年   72篇
  1994年   62篇
  1993年   78篇
  1992年   15篇
  1991年   22篇
  1990年   18篇
  1989年   24篇
  1988年   23篇
  1987年   18篇
  1986年   18篇
  1985年   12篇
  1983年   3篇
  1982年   8篇
  1981年   16篇
  1980年   9篇
  1978年   3篇
  1977年   38篇
  1976年   93篇
  1975年   1篇
  1972年   1篇
  1965年   1篇
排序方式: 共有1188条查询结果,搜索用时 15 毫秒
71.
72.
73.
OBJECTIVE: To examine noradrenergic (NA) function in children with attention-deficit hyperactivity disorder (ADHD) by replicating and expanding upon a previous finding that ADHD children with and without reading disabilities (RD) differ in plasma levels of the NA metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG). METHOD: Plasma levels of MHPG were compared in ADHD children who were subdivided on the basis of the presence or absence of RD. Subsequently, this replication sample was combined with a previously studied sample to further explore the relationship between plasma MHPG levels and measures of cognitive function in children with ADHD. RESULTS: Plasma levels of MHPG were significantly lower in ADHD children without RD, compared with those with RD, replicating a published finding. Analyses in the combined sample indicated that, among children with ADHD, plasma MHPG levels were inversely associated with measures of academic achievement and verbal processing, but not parent or teacher ratings of behavior or continuous performance test measures of attention and impulsivity. CONCLUSIONS: These data indicate that children with ADHD are not homogeneous with regard to NA function and that neurochemical variation is closely associated with differences in clinical characteristics of the children.  相似文献   
74.
BACKGROUND: Duodenal gastric metaplasia (DGM) is commonly found in association with Helicobacter pylori (Hp)-associated gastritis in adults. DGM is also considered a risk factor for duodenal ulcer development. The prevalence of DGM in children and its association with gastritis, duodenitis, or the presence of Hp organisms is not clear. We investigated the prevalence of DGM in children and explore its association with several possible risk factors, including age, gender, gastritis, duodenitis, or Hp presence in the gastric antrum. METHODS: A retrospective analysis of 173 upper endoscopy procedures performed between 1993 and 1995 at Cabell Huntington Hospital, Huntington, WV, was done. Gastric and duodenal biopsies were stained with Giemsa for Hp detection, periodic acid-Schiff for DGM, and hematoxylin and eosin for histologic assessment. Gastric mucosal inflammation was graded according to Sydney criteria. RESULTS: Duodenal gastric metaplasia was identified in 23 of 173 (13%) patients. Duodenitis but not age, gender, gastritis, or the presence of Hp in the gastric antrum was associated with DGM development. In 4 of 23 DGM foci, Hp was identified. CONCLUSIONS: In children, DGM is not the consequence of Hp infection.  相似文献   
75.
76.
Our aim was to identify new genes involved in the cellular aspects of defense mechanism of Drosophila, as well as in melanotic tumor formation processes that are linked to blood cell disregulation. We have screened 1341 enhancer detector fly lines for expression of the lacZ reporter gene in larval hemocytes at the end of the third instar. We have selected 21 lines in which we observed a reproducible lacZ expression in blood cells. These lines were classified according to the subsets of hemocytes in which lacZ was expressed, and we identified five lines that can be used as lamellocyte markers. Three lines were selected for further analysis. The first exhibited strong lacZ expression in all lamellocytes. The second expressed lacZ in plasmatocytes and lamellocytes, and exhibited a melanotic tumor phenotype in larvae homozygous for the insertion. A third line showed a striking insertion-linked phenotype of melanized lymph glands (the hematopoietic organ), which resulted in the total absence of circulating hemocytes in the mutant larvae. We anticipate that this mutation, which we named domino, will prove a useful tool in the analysis of the role of hemocytes during the various aspects of immune response and melanotic tumor formation.  相似文献   
77.
78.
79.
80.
构皮滩水电站观景供水系统大型长轴深井泵站设计   总被引:1,自引:0,他引:1  
乌江构皮滩水电站大坝上游的观景供水系统,为满足上游水位变化的需要,设计成分阶段分级竖井供水的方式。供水设备选用高工效、低能耗的RJC型大型长轴深井泵,运行方式为开敞式串联运行,单机单台生产能力为1010m3/h,最大扬程96.51m,最大井下安装深度89.475m,经安装调试运行效果良好。大型长轴深井泵在乌江构皮滩水电站供水系统中的成功应用为中国类似工程泵站设计提供了很好的借鉴,也将促进中国大型长轴深井泵的进一步发展。  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