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   241659篇
  免费   2633篇
  国内免费   427篇
电工技术   4294篇
综合类   259篇
化学工业   39451篇
金属工艺   9379篇
机械仪表   7406篇
建筑科学   5481篇
矿业工程   1391篇
能源动力   5159篇
轻工业   24964篇
水利工程   2478篇
石油天然气   5093篇
武器工业   32篇
无线电   25051篇
一般工业技术   44812篇
冶金工业   45367篇
原子能技术   5950篇
自动化技术   18152篇
  2021年   2107篇
  2019年   2018篇
  2018年   3489篇
  2017年   3424篇
  2016年   3691篇
  2015年   2237篇
  2014年   3900篇
  2013年   10283篇
  2012年   6148篇
  2011年   8298篇
  2010年   6550篇
  2009年   7233篇
  2008年   7587篇
  2007年   7722篇
  2006年   6899篇
  2005年   6051篇
  2004年   5821篇
  2003年   5602篇
  2002年   5675篇
  2001年   5561篇
  2000年   5385篇
  1999年   5308篇
  1998年   12577篇
  1997年   8905篇
  1996年   6864篇
  1995年   5340篇
  1994年   4747篇
  1993年   4629篇
  1992年   3674篇
  1991年   3391篇
  1990年   3597篇
  1989年   3478篇
  1988年   3314篇
  1987年   2910篇
  1986年   2945篇
  1985年   3379篇
  1984年   3221篇
  1983年   2899篇
  1982年   2744篇
  1981年   2826篇
  1980年   2720篇
  1979年   2626篇
  1978年   2691篇
  1977年   2954篇
  1976年   3813篇
  1975年   2373篇
  1974年   2246篇
  1973年   2381篇
  1972年   1975篇
  1971年   1863篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Abstract: This paper describes a shell for cooperating expert systems that has been developed at the University of Porto. The main goal of this shell is two-fold: to generate a community of cooperative knowledge-based systems and to develop several special reasoning techniques which can be used under a distributed and cooperative paradigm. UPShell is able to convert a set of generated intelligent systems (ISs) into a community of cooperative ISs. In this first version it is already possible to generate different intelligent systems which are able to run 'simultaneously' as separate Unix processes and, using a message-passing mechanism, to communicate among themselves. They can be set to pursue an overall goal in a cooperative way. Moreover, several tasks can be given to each IS to be solved simultaneously, and the IS can switch from task to task according to dynamic priorities reflecting the urgency attached to the specific sub-tasks that emerge. The shell described here may also be used to test, within a distributed environment, some time-bounded reasoning techniques that are presently being developed. The paper has three main parts: a general overview of the UPShell (Section 1); a tutorial explaining, by means of examples, how to use the package (Section 2); and, finally, some considerations on the reasoning techniques used and future improvements (Sections 3–5).  相似文献   
82.
83.
84.
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.  相似文献   
85.
86.
87.
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV  相似文献   
88.
This work investigates the impact of nine new product development (NPD) acceleration approaches (supplier involvement, lead user involvement, speeding up activities and tasks, reduction of parts and components, training and rewarding of employees, implementation of support systems and techniques, stimulating interfunctional cooperation, emphasis on the customer, and simplification of organizational structure) on development speed and new product profitability. Our findings from 233 manufacturing firms show that lead user involvement and training/rewarding of employees increase both development speed and profitability. Supplier involvement, speeding up activities and tasks, and a simplification of the organizational structure also enhance development speed, while an emphasis on the customer has an additional positive impact on new product profitability. Both new product speed and profitability increase firm financial performance. Our results further show that pioneers and fast followers should not select the same NPD acceleration approaches as the speed and profitability impact of the majority of the acceleration approaches depends on the new product strategy of the firm. These results are important as they provide guidance for pioneers and fast followers regarding which NPD acceleration approaches to select in order to enhance speed and profitability and, hence, firm financial performance.  相似文献   
89.
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem.  相似文献   
90.
The electrochemical faceting of polycrystalline (pc) platinum yielding a (100)-preferred oriented electrode surface was accomplished in HF solutions by applying to the pc platinum electrode a square wave potential perturbation at 1 kHz in the 0.2 to 1.3 V range (vs rhe). SEM patterns of the resulting surfaces were also obtained. For HF concentrations up to 2 M no appreciable influence of the electrolyte concentration on the electrochemical faceting was noticed. Otherwise, the voltammetric response of the (100)-type preferred oriented platinum surface in the H-adatom potential range when compared to previously reported data resulted remarkably sensitive to the electrolyte composition. The discussion of results was based on the non-equilibrium adsorption conditions for anions under the periodic perturbation.  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