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   437228篇
  免费   5677篇
  国内免费   1546篇
电工技术   7459篇
综合类   338篇
化学工业   65856篇
金属工艺   17782篇
机械仪表   13641篇
建筑科学   10299篇
矿业工程   2675篇
能源动力   11248篇
轻工业   38971篇
水利工程   4845篇
石油天然气   9481篇
武器工业   27篇
无线电   51687篇
一般工业技术   86896篇
冶金工业   77804篇
原子能技术   9579篇
自动化技术   35863篇
  2021年   3703篇
  2020年   2789篇
  2019年   3502篇
  2018年   6011篇
  2017年   6049篇
  2016年   6630篇
  2015年   4185篇
  2014年   7082篇
  2013年   19710篇
  2012年   11748篇
  2011年   15947篇
  2010年   12618篇
  2009年   14099篇
  2008年   14639篇
  2007年   14570篇
  2006年   13065篇
  2005年   11910篇
  2004年   11211篇
  2003年   11004篇
  2002年   10435篇
  2001年   10865篇
  2000年   9921篇
  1999年   10419篇
  1998年   25194篇
  1997年   17642篇
  1996年   13389篇
  1995年   10192篇
  1994年   8882篇
  1993年   8997篇
  1992年   6658篇
  1991年   6392篇
  1990年   6157篇
  1989年   5979篇
  1988年   5886篇
  1987年   4912篇
  1986年   4889篇
  1985年   5773篇
  1984年   5284篇
  1983年   4910篇
  1982年   4488篇
  1981年   4506篇
  1980年   4376篇
  1979年   4267篇
  1978年   4127篇
  1977年   4531篇
  1976年   5491篇
  1975年   3680篇
  1974年   3452篇
  1973年   3622篇
  1972年   2999篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment.  相似文献   
102.
103.
104.
Consideration was given to the decision making procedures based on the fuzzy messages of experts whose preferences on the set of collective decisions can also be fuzzy.  相似文献   
105.
106.
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems under a plane-strain condition with the principal misfit strain components ε* xx and ε* yy . For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε* yy /ε* xx . We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness; moreover, the transition is also forbidden when the particle stiffness is greater than a critical value.  相似文献   
107.
Fuzzy logic was first suggested as the mechanism by which humans drive cars. This paper addresses the use of fuzzy logic and algorithms towards the intelligent autonomous motion control of land vehicles. To cope with vehicle complexities, internal parametric changes, and with unpredictable environmental effects, the controllers that are presented, whilst heuristic in nature, are self-organizing or self-learning in that they generate automatically by observation an experiential rule base that models the vehicle, and via an appropriate performance index an optimal control rule base that is robust to large parametric changes. The methodology presented is applicable to any complex process which is too difficult to model or control using conventional methods, or which has relied on the experience of a human operator. An overview of fuzzy logic and static fuzzy logic control (akin to expert systems) is provided, together with illustrative examples.  相似文献   
108.
109.
110.
Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989.  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