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   2484篇
  免费   2篇
电工技术   1篇
化学工业   8篇
金属工艺   1篇
轻工业   4篇
石油天然气   1篇
无线电   2篇
一般工业技术   2篇
冶金工业   2460篇
自动化技术   7篇
  2023年   1篇
  2020年   1篇
  2016年   2篇
  2015年   1篇
  2014年   1篇
  2013年   1篇
  2012年   1篇
  2009年   1篇
  2006年   3篇
  2004年   3篇
  2003年   6篇
  1999年   76篇
  1998年   810篇
  1997年   408篇
  1996年   289篇
  1995年   160篇
  1994年   121篇
  1993年   175篇
  1992年   30篇
  1991年   24篇
  1990年   29篇
  1989年   20篇
  1988年   30篇
  1987年   29篇
  1986年   22篇
  1985年   25篇
  1983年   1篇
  1982年   12篇
  1981年   10篇
  1980年   26篇
  1978年   4篇
  1977年   52篇
  1976年   108篇
  1974年   1篇
  1955年   3篇
排序方式: 共有2486条查询结果,搜索用时 0 毫秒
11.
We report a fetus of 35 weeks gestation in which a continuous flow was detected in the lower portion of the right atrium with a peak velocity of 0.8 m/s. After delivery the echo-doppler study showed a dilated coronary sinus in the long axis parasternal view, and a bilateral superior vena cava in the short axis suprasternal notch view. Comments about the cause of this anomalous continuous flow are discussed.  相似文献   
12.
13.
14.
15.
16.
The origin of the nonconservative nature of the circular dichroism (CD) spectrum of bacteriochlorophyll dimers is investigated. It is shown that coupling between the Qy and Qx transitions can, under rather restricting circumstances, lead to an asymmetrical CD spectrum: only for a limited set of relative orientations of the monomers within the dimer is the spectrum found to be asymmetrical. The relation between intensity and asymmetry of the CD spectrum is elucidated. The results are applied to the B820 subunit of the LH1 antenna system and subsequently to the antenna system LH1 itself. Differences in the geometry of the BChls in LH1 versus the LH2 structure are discussed.  相似文献   
17.
18.
19.
Analyses tested the following contrasting hypotheses: a) The occurrence of a new symptom in the presence of ongoing life stress increases the attribution of symptoms to illness and increases the use of health care; b) new symptoms occurring in the presence of ongoing life stress are attributed to stressors if they are ambiguous indicators of illness, and they are unlikely to motivate care-seeking if the stressor, i.e., the perceived cause, is of recent onset. The 43-to-92-year old subjects in this longitudinal study were less likely to seek care for the ambiguous symptoms they experienced during the previous week if there was a concurrent life stressor that began during the previous 3 weeks; these symptoms were attributed to stress rather than to illness, and subjects tolerated the emotional distress caused by the combination of a stressor and an ambiguous symptom. Subjects were less willing to tolerate the combined distress of an ambiguous symptom and a concurrent life stressor if the stressor onset was not recent; under such conditions, subjects were more likely to seek health care. Current life stressors did not affect care-seeking for symptoms that were clear signs of disease; these symptoms were readily identified as health threats in need of medical attention. The findings contribute to a better theoretical understanding of how individuals perceive their physical states and how they cope with stress. Practical implications of these findings for increasing efficient use of health care services are also discussed.  相似文献   
20.
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