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   330740篇
  免费   2593篇
  国内免费   671篇
电工技术   4788篇
综合类   2406篇
化学工业   51369篇
金属工艺   19826篇
机械仪表   13034篇
建筑科学   6305篇
矿业工程   4317篇
能源动力   4963篇
轻工业   13255篇
水利工程   5320篇
石油天然气   13334篇
武器工业   32篇
无线电   29220篇
一般工业技术   78373篇
冶金工业   34644篇
原子能技术   11382篇
自动化技术   41436篇
  2021年   2755篇
  2019年   2733篇
  2018年   19571篇
  2017年   18762篇
  2016年   15814篇
  2015年   3645篇
  2014年   5533篇
  2013年   10317篇
  2012年   10352篇
  2011年   18102篇
  2010年   15388篇
  2009年   13527篇
  2008年   14773篇
  2007年   15467篇
  2006年   6459篇
  2005年   6722篇
  2004年   6558篇
  2003年   6427篇
  2002年   5650篇
  2001年   5040篇
  2000年   5109篇
  1999年   4307篇
  1998年   7221篇
  1997年   5865篇
  1996年   4467篇
  1995年   3661篇
  1994年   3434篇
  1993年   3633篇
  1992年   3225篇
  1991年   3385篇
  1990年   3482篇
  1989年   3370篇
  1988年   3279篇
  1987年   3262篇
  1986年   3159篇
  1985年   3315篇
  1984年   3253篇
  1983年   3148篇
  1982年   2997篇
  1981年   3049篇
  1980年   3078篇
  1979年   3257篇
  1978年   3491篇
  1977年   3462篇
  1976年   3911篇
  1975年   3210篇
  1974年   3293篇
  1973年   3342篇
  1972年   2987篇
  1971年   2754篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Wastewater treatment plant operators encounter complex operational problems related to the activated sludge process and usually respond to these by applying their own intuition and by taking advantage of what they have learnt from past experiences of similar problems. However, previous process experiences are not easy to integrate in numerical control, and new tools must be developed to enable re-use of plant operating experience. The aim of this paper is to investigate the usefulness of a case-based reasoning (CBR) approach to apply learning and re-use of knowledge gained during past incidents to confront actual complex problems through the IWA/COST Benchmark protocol. A case study shows that the proposed CBR system achieves a significant improvement of the benchmark plant performance when facing a high-flow event disturbance.  相似文献   
2.
In this paper, implementation of the Benchmark Simulation Model No 2 (BSM2) within Matlab-Simulink is presented. The BSM2 is developed for plant-wide WWTP control strategy evaluation on a long-term basis. It consists of a pre-treatment process, an activated sludge process and sludge treatment processes. Extended evaluation criteria are proposed for plant-wide control strategy assessment. Default open-loop and closed-loop strategies are also proposed to be used as references with which to compare other control strategies. Simulations indicate that the BM2 is an appropriate tool for plant-wide control strategy evaluation.  相似文献   
3.
Intensive use of the benchmark simulation model No. 1 (BSM1), a protocol for objective comparison of the effectiveness of control strategies in biological nitrogen removal activated sludge plants, has also revealed a number of limitations. Preliminary definitions of the long-term benchmark simulation model No. 1 (BSM1_LT) and the benchmark simulation model No. 2 (BSM2) have been made to extend BSM1 for evaluation of process monitoring methods and plant-wide control strategies, respectively. Influent-related disturbances for BSM1_LT/BSM2 are to be generated with a model, and this paper provides a general overview of the modelling methods used. Typical influent dynamic phenomena generated with the BSM1_LT/BSM2 influent disturbance model, including diurnal, weekend, seasonal and holiday effects, as well as rainfall, are illustrated with simulation results. As a result of the work described in this paper, a proposed influent model/file has been released to the benchmark developers for evaluation purposes. Pending this evaluation, a final BSM1_LT/BSM2 influent disturbance model definition is foreseen. Preliminary simulations with dynamic influent data generated by the influent disturbance model indicate that default BSM1 activated sludge plant control strategies will need extensions for BSM1_LT/BSM2 to efficiently handle 1 year of influent dynamics.  相似文献   
4.
The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit.  相似文献   
5.
This paper describes a novel planar antenna sensor created for the purpose of noninvasive temperature measurements using microwave radiometry. In order to improve radiometric measurements in industrial applications, a new generation of sensors is introduced, composed of a metallic sheet. Simulations based upon the method of moments is used both to design and to determine their electromagnetic performances. This paper also describes a radiometric device using these sensors to measure and control the temperature of food products during deep freezing processes. The results and discussions are presented.  相似文献   
6.
7.
为了分析多水库系统中两座水库之间灌溉用水的分配问题,建立了基到动态规划的神经网络模型。为了研究从一座上游水库取水在下游两座之库之间进行水量分配的问题,提出了3个状态变量和4个决策变量的改进的动态规划算法。采用神经网络模型,用3个状态变量动态规划算法得出调度原则,就所研究的多水库系统实例来说,新的动态规划神经网络模型的性能很好,将该模型的性能与临时凑合的标准调度原则和以前推荐使用的约束动态规划神经网络模型进行了比较。  相似文献   
8.
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals.  相似文献   
9.
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working defects on the behavior of structures under standard and emergency conditions. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006.  相似文献   
10.
Relations for determining a motive force in a complex model of mass transfer as applied to concurrent, countercurrent, and cross motion of the vapor and liquid phases have been introduced. These forces have been compared for different forms of organization of the flow, and their comparison with similar quantities from the known Murphree and Hausen models is presented.  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