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   45723篇
  免费   734篇
  国内免费   793篇
电工技术   763篇
综合类   56篇
化学工业   7181篇
金属工艺   3155篇
机械仪表   1483篇
建筑科学   1013篇
矿业工程   168篇
能源动力   1492篇
轻工业   2591篇
水利工程   384篇
石油天然气   1399篇
无线电   4267篇
一般工业技术   11278篇
冶金工业   7907篇
原子能技术   809篇
自动化技术   3304篇
  2021年   413篇
  2020年   339篇
  2019年   421篇
  2018年   733篇
  2017年   721篇
  2016年   838篇
  2015年   604篇
  2014年   908篇
  2013年   2623篇
  2012年   1592篇
  2011年   2109篇
  2010年   1636篇
  2009年   1930篇
  2008年   1776篇
  2007年   1927篇
  2006年   1517篇
  2005年   1311篇
  2004年   1268篇
  2003年   1176篇
  2002年   1156篇
  2001年   1176篇
  2000年   1004篇
  1999年   1064篇
  1998年   2226篇
  1997年   1724篇
  1996年   1487篇
  1995年   1034篇
  1994年   797篇
  1993年   823篇
  1992年   626篇
  1991年   599篇
  1990年   563篇
  1989年   526篇
  1988年   395篇
  1987年   431篇
  1986年   388篇
  1985年   422篇
  1984年   330篇
  1983年   335篇
  1982年   331篇
  1981年   329篇
  1980年   381篇
  1979年   374篇
  1978年   328篇
  1977年   450篇
  1976年   664篇
  1975年   350篇
  1974年   316篇
  1973年   332篇
  1972年   289篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Recent research suggests that social interactions in video games may lead to the development of community bonding and prosocial attitudes. Building on this line of research, a national survey of U.S. adults finds that gamers who develop ties with a community of fellow gamers possess gaming social capital, a new gaming‐related community construct that is shown to be a positive antecedent in predicting both face‐to‐face social capital and civic participation.  相似文献   
992.
The human‐machine interface design is not a new problem; however, existing knowledge appears to be focused either on interface conceptual design, which determines what information at what time needs to be displayed, or on interface detailed design, which determines the form of display elements. This article presents a study on interface layout design. Three interface layout designs were proposed based on the proximity compatibility priniciple, which were on the same interface conceptual design. In particular, the first interface layout design is with the highest degree of proximity cognition and the second and third with a reduced degree of proximity cognition. They are called sophisticated, semisophisticated, and nonsophisticated interfaces, respectively. An experiment with a simple process plant was conducted to understand user behaviors on the three interfaces. It is noted that in order to provide an unbiased comparative evaluation of these interfaces the same application problem and similar look‐and‐feel forms of interfaces were designed. In the experiment, three general classes of tasks were considered, namely, normal control operation, fault detection (or monitoring), and fault diagnosis. Two categories of measures were used: the performance measure and the subjective measure. The major results obtained from the experiment are 1) the nonsophisticated interface is the best for fault detections in terms of performance measure; besides, this interface has the lowest mental workload for fault detection; 2) the sophisticated interface is the best for normal operation in terms of performance measure; 3) there appears no significant difference for fault diagnosis in terms of performance measures for all these three interfaces; 4) for normal operation and fault diagnosis, the mental workloads for the three interfaces have no significant difference. Overall, the experiment suggests that the nonsophisticated interface be used in practice with additional two reasons: 1) most of time in the chemical process plant today is the fault detection or operation monitoring task, and 2) it is relatively easier for the nonsophisticated interface to adapt to changes in the chemical process plant design, which are common in today's manufacturing environments.  相似文献   
993.
Active disturbance rejection control (ADRC), as proposed by Prof. Jingqing Han, reduces first the plant dynamics to its canonical form, normally in the form of cascade integrators, for which the standard controller can be employed to meet the design specifications. This paper concerns with the selection of the canonical form for non-minimum phase systems. In particular, it is shown that, by employing the well known controllable canonical form, the uncertainties of such systems can be divided into two terms in the state space model, one in the control channel and the other in the output channel. The necessary and sufficient condition is obtained for the stability of the closed-loop system with the proposed canonical form and ADRC. Also, by showing the necessity of the detectability of the extended system as well as certain information of the systemˉs “zeros”, we present the fundamental guidelines of design ADRC for non-minimum phase uncertain systems.  相似文献   
994.
With the rapid deployments of the active disturbance rejection control (ADRC) as a bonafide industrial technology in the background, this paper summarizes some recent results in the analysis of linear ADRC and offers explanations in the frequency response language with which practicing engineers are familiar. Critical to this endeavor is the concept of bandwidth, which has been used in a more general sense. It is this concept that can serve as the link between the otherwise opaque state space formulation of the ADRC and the command design considerations and concerns shared by practicing engineers. The remarkable characteristics of a simple linear ADRC was first shown in the frequency domain, followed by the corresponding analysis in time domain, where the relationship between the tracking error and the ADRC bandwidth is established. It is shown that such insight is only possible by using the method of solving linear differential equations, instead of the more traditional techniques such as the Lyapunov methods, which tend to be more conservative and difficult to grasp by engineers. The insight obtained from such analysis is further demonstrated in the simulation validation.  相似文献   
995.
996.
997.
This paper proposes a novel method to quantify the error of a nominal normalized right graph symbol (NRGS) for an errors-in-variables (EIV) system corrupted with bounded noise. Following an identification framework for estimation of a perturbation model set, a worst-case v-gap error bound for the estimated nominal NRGS can be first determined from \textit{a priori} and \textit{a posteriori} information on the underlying EIV system. Then, an NRGS perturbation model set can be derived from a close relation between the v-gap metric of two models and ${\rm H}_\infty$-norm of their NRGSs' difference. The obtained NRGS perturbation model set paves the way for robust controller design using an ${\rm H}_\infty$ loop-shaping method because it is a standard form of the well-known NCF (normalized coprime factor) perturbation model set. Finally, a numerical simulation is used to demonstrate the effectiveness of the proposed identification method.  相似文献   
998.
以碳纳米管材料作为场致发射电子源的 X 射线源是近几年国际上的研究前沿。相比传统热电子发射 X 射线源而 言,碳纳米管 X 射线源具有结构紧凑、高时间分辨、可编程发射等优势。面向静态扫描成像系统的多光束 X 射线源是 碳纳米管 X 射线源的重要发展方向之一。文章将介绍基于碳纳米管阴极的多光束 X 射线源技术。  相似文献   
999.
The heat treatment of Nb(3)Sn coil with the glass fabric insulation is one of the key and critical processes for the outsert solenoids of the 40 T hybrid magnet, which could be wound with cable-in-conduit conductors using the insulation-wind-and-react technique. The manufacturing of the large vertical type vacuum/Ar atmosphere-protection heat treatment system has been completed and recently installed in the High Magnetic Filed Laboratory, Chinese Academy of Sciences. The heat treatment system composed mainly the furnace, the purging gas supply system, the control system, the gas impurities monitoring system, and so on. At present, the regulation and testing of the heat treatment system has been successfully finished, and all of technical parameters meet or exceed specifications.  相似文献   
1000.
A thermodiffusion cell is developed for performing Soret experiments on binary mixtures at high pressure and in the presence of a porous medium. The cell is validated by performing experiments at atmospheric pressure. The experiments are performed by applying different temperature gradients to binary mixtures in order to determine their thermal contrast factor. These measurements provide a first demonstration of the good reproducibility of this kind of measurements upon calibration.  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