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   3913篇
  免费   60篇
  国内免费   6篇
电工技术   28篇
化学工业   422篇
金属工艺   114篇
机械仪表   69篇
建筑科学   100篇
矿业工程   4篇
能源动力   67篇
轻工业   277篇
水利工程   18篇
石油天然气   7篇
无线电   238篇
一般工业技术   433篇
冶金工业   1847篇
原子能技术   36篇
自动化技术   319篇
  2021年   18篇
  2019年   26篇
  2018年   28篇
  2017年   24篇
  2016年   27篇
  2015年   25篇
  2014年   36篇
  2013年   140篇
  2012年   49篇
  2011年   92篇
  2010年   76篇
  2009年   76篇
  2008年   86篇
  2007年   79篇
  2006年   66篇
  2005年   49篇
  2004年   67篇
  2003年   65篇
  2002年   57篇
  2001年   55篇
  2000年   54篇
  1999年   89篇
  1998年   522篇
  1997年   314篇
  1996年   218篇
  1995年   144篇
  1994年   132篇
  1993年   155篇
  1992年   47篇
  1991年   51篇
  1990年   52篇
  1989年   32篇
  1988年   38篇
  1987年   41篇
  1986年   49篇
  1985年   56篇
  1984年   46篇
  1983年   46篇
  1982年   51篇
  1981年   56篇
  1980年   77篇
  1979年   58篇
  1978年   50篇
  1977年   89篇
  1976年   129篇
  1975年   44篇
  1974年   27篇
  1973年   22篇
  1972年   18篇
  1970年   17篇
排序方式: 共有3979条查询结果,搜索用时 15 毫秒
1.
2.
3.
We present a new approach to analyse the deformation of the left ventricle of the heart based on a parametric model that gives a compact representation of a set of points in a 3-D image. We present a strategy for tracking surfaces in a sequence of 3-D cardiac images. Following tracking, we then infer quantitative parameters which characterize: left ventricle motion, volume of left ventricle, ejection fraction, amplitude and twist component of cardiac motion. We explain the computation of these parameters using our model. Experimental results are shown in time sequences of two modalities of medical images, nuclear medicine and X-ray computed tomography (CT). Video sequences presenting these results are on the CD-ROM.  相似文献   
4.
MACHYDR0'90 was an experiment conducted in Pennsylvania in 1990 to study the synergistic use of remote sensors in multitemporal hydrologic studies. As part of this mission the pushbroom microwave radiometer was flown and used to produce brightness temperature maps. Verification studies and vegetation algorithms for mixed land cover areas are described  相似文献   
5.
6.
BACKGROUND: X-linked severe combined immunodeficiency (SCIDXI) is an inherited immune defect which leads to death in infancy from severe infections. The defect is caused by mutations of the IL-2RG gene that encodes for the common gamma chain shared by several cytokine receptors. The disease is characterised by lack of T and NK cells with normal numbers of B cells. SCIDXI can be cured by bone marrow transplantation (BMT) or prevented by abortion after prenatal diagnosis. METHODS: A male fetus was diagnosed as having SCIDXI by molecular, immunophenotypic, and functional analyses. The fetus was injected intraperitoneally under ultrasound guidance with CD34 haematopoietic progenitor cells purified from paternal bone marrow and T-cell depleted by E rosetting. Chimerism analysis was by HLA-DQ alpha typing and gamma-chain staining on cord blood. FINDINGS: A healthy 3.6 kg boy was delivered by caesarean section at 38 weeks of gestation with no clinical or laboratory signs of graft-versus-host disease. Engraftment of donor-derived CD2 cells was found at birth. At 3.5 months of age the infant is well and his T-cell counts and function are normal. INTERPRETATION: In-utero transplantation of haematopoietic progenitor cells allowed immune reconstitution of a fetus with SCIDXI and may be an alternative to elective abortion. Our report should encourage applications of this method to other inherited disorders curable by BMT.  相似文献   
7.
BACKGROUND AND PURPOSE: Norway has the highest reported incidence of hip fractures in western Europe. Little is known about the epidemiology of falls in Norway where the winter season is long and dark. The objective of this work was to study reported falls and their consequences among elderly Norwegians living at home. METHODS: A cross-sectional design was used for the study. Interviews were performed in the homes of 431 subjects, aged 67-97 years, living at home. Information on falling was gathered through six questions: whether the subject had fallen during the last six months, and if so, how many falls they had, where the last fall occurred, its perceived reason, the activity the subject had been engaged in when the fall occurred, and the resulting injury. RESULTS: In all, 24.1% of subjects reported falling during the last six months, and 9.5% had suffered more than one fall. Falls were most frequently linked to external events (63.1%). Outdoor falls were more frequent (59.0%; 95% CI = 51.2-82.0) than indoor falls. Older subjects were associated with more frequent indoor falls (p < 0.05), but gender was not significant. Fifty-one per cent of subjects had fallen while walking and 53% had suffered an injury from the last fall. In 13.4% of the women and 16.2% of the men, the last fall had resulted in a fracture. CONCLUSIONS: Compared to the results of other studies from industrialized Western countries, a similar crude fall rate, similar frequency and similar type of injury were found. However, in contrast to other studies, no gender difference was observed with regard to falling, place of falling and fracture rate.  相似文献   
8.
Terminal composition control of a pilot scale binary distillation column operated under the control of an IBM 1800 digital computer has been studied for disturbances in feed flow rate. Conventional two point control, whereby the overhead composition is controlled by reflux flow rate and bottom composition by means of steam rate, was demonstrated to be unsatisfactory. Two alternate control systems, namely a noninteracting control system and a ratio control system were evaluated. The noninteracting control system was constructed from a transfer function representation of the distillation column dynamics, determined from a series of on-line pulse tests. The results show that a very significant improvement in the control of both compositions is achieved by using noninteracting control or the ratio control scheme suggested by Rijnsdorp compared to the behavior that results using conventional two point feedback control. However, the control performance obtained using noninteracting control was only marginally better than that using the ratio control scheme.  相似文献   
9.
10.
Electronic systems used within the home and in public places are increasingly sophisticated. Simplifying the interface between people and these complex systems is a major design challenge. User trials which highlight the needs of older people can result in interface design which performs well for a wide range of users. Three case studies are outlined as illustrations.  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