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   2187篇
  免费   20篇
  国内免费   1篇
电工技术   20篇
化学工业   116篇
金属工艺   21篇
机械仪表   21篇
建筑科学   26篇
矿业工程   3篇
能源动力   18篇
轻工业   78篇
水利工程   5篇
石油天然气   5篇
无线电   145篇
一般工业技术   203篇
冶金工业   1449篇
原子能技术   15篇
自动化技术   83篇
  2021年   11篇
  2019年   6篇
  2018年   15篇
  2017年   11篇
  2016年   7篇
  2015年   9篇
  2014年   12篇
  2013年   42篇
  2012年   24篇
  2011年   40篇
  2010年   23篇
  2009年   21篇
  2008年   30篇
  2007年   47篇
  2006年   28篇
  2005年   23篇
  2004年   24篇
  2003年   28篇
  2002年   24篇
  2001年   27篇
  2000年   12篇
  1999年   61篇
  1998年   399篇
  1997年   252篇
  1996年   165篇
  1995年   102篇
  1994年   80篇
  1993年   114篇
  1992年   22篇
  1991年   32篇
  1990年   32篇
  1989年   28篇
  1988年   25篇
  1987年   22篇
  1986年   32篇
  1985年   28篇
  1984年   7篇
  1983年   23篇
  1982年   18篇
  1981年   21篇
  1980年   25篇
  1979年   16篇
  1978年   13篇
  1977年   55篇
  1976年   99篇
  1975年   13篇
  1974年   9篇
  1973年   6篇
  1970年   6篇
  1969年   5篇
排序方式: 共有2208条查询结果,搜索用时 15 毫秒
11.
12.
A review of 35 patients > 60 years of age with odontoid fractures showed that a type II injury (Anderson and D'Alonso) was the most common fracture pattern (82% of cases). On the basis of mechanism of injury and sex incidence, we deduced that osteopenia is a contributory factor in the occurrence of odontoid fractures. A fall in a domestic setting was the cause in 53%. The peg was posteriorly displaced in 88% of type II fractures, and primary union occurred in 23%. The incidence of concomitant spinal cord injury with type II fractures was higher in older patients than it was in those < 60 years of age. The outcome for these patients was largely determined by their neurological status at presentation. Myelopathy as a late complication of nonunion was not observed in nine patients with an average follow-up of 21 months. The data suggest that vigorous attempts to secure both primary union and a sound arthrodesis for non-union are questionable in the elderly except in unusual circumstances.  相似文献   
13.
We give a parametrized family of rational interval maps of degree two, each ergodic, exact and preserving a measure equivalent to a Lebesgue measure. The family includes the unique quadratic Chebyshev polynomial as its only polynomial map. We extend the family to other settings on the circle and real line. We also give numerical approximations to the entropy of the equivalent invariant measure and the Hausdorff dimension of the singular measure of maximal entropy.  相似文献   
14.
15.
A retrospective cross-sectional cephalometric investigation was undertaken to examine the facial form of a group of Finnish children with juvenile chronic arthritis (JCA). Following digitization, the radiographs were divided into three age groups, and according to whether or not 'bird-face' deformity was present. From a total of 67 cases (39 females and 28 males) 19 per cent were judged to be 'affected'. Analyses were carried out and the groups compared using t-tests. The mandible was found to be smaller both in ramal height and body length in the affected sample, with reduction in posterior face height being only partly compensated by increase in bony apposition at the angle producing antegonial notching. There was posterior rotation of the mandible with a reduction in angles S-N-B and S-N-Pog, and an increase in the gonial angle, the angle between the mandibular plane and S-N, maxillary, and occlusal planes. The changes in the maxilla were less marked. Although S-N-A was reduced in all three age groups, it was not significantly so. Maxillary length (ANS-PNS) was significantly smaller in the two younger age groups. In the vertical plane maxillary dimensions were reduced in the two younger age groups. A highly significant increase in the occlusal to maxillary planes angle was observed in all groups. There was, however, no difference in S-N to maxillary planes angle, indicating a more steeply inclined occlusal plane due to subnormally erupted maxillary molars. Although the inter-incisal angle was reduced there was no significant difference in the incisor inclinations in relation to the jaws and despite the posterior rotation of the mandible there was no significant increase in size of overjet or in the frequency of anterior open bite.  相似文献   
16.
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   
17.
18.
Electrical, electrooptical, mechanical, and microstructural characterizations explain why the leakage currents in advanced Cu/ultralow-interconnects can change from bulk (3-D) to mostly interfacial (2-D) above 150degC. A physical model consistent with all these results is proposed.  相似文献   
19.
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