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   219156篇
  免费   17657篇
  国内免费   12686篇
电工技术   34572篇
技术理论   22篇
综合类   24954篇
化学工业   10482篇
金属工艺   7544篇
机械仪表   18505篇
建筑科学   18595篇
矿业工程   8938篇
能源动力   8246篇
轻工业   4761篇
水利工程   6461篇
石油天然气   6644篇
武器工业   3818篇
无线电   21731篇
一般工业技术   11428篇
冶金工业   6894篇
原子能技术   2296篇
自动化技术   53608篇
  2024年   740篇
  2023年   1947篇
  2022年   3907篇
  2021年   4945篇
  2020年   5357篇
  2019年   3879篇
  2018年   3552篇
  2017年   5075篇
  2016年   6039篇
  2015年   7106篇
  2014年   13659篇
  2013年   11598篇
  2012年   16124篇
  2011年   17125篇
  2010年   12985篇
  2009年   13042篇
  2008年   13392篇
  2007年   17145篇
  2006年   15427篇
  2005年   13817篇
  2004年   11318篇
  2003年   10230篇
  2002年   7755篇
  2001年   6516篇
  2000年   5379篇
  1999年   4366篇
  1998年   3269篇
  1997年   2665篇
  1996年   2352篇
  1995年   1995篇
  1994年   1660篇
  1993年   1118篇
  1992年   948篇
  1991年   683篇
  1990年   554篇
  1989年   457篇
  1988年   326篇
  1987年   186篇
  1986年   114篇
  1985年   120篇
  1984年   102篇
  1983年   91篇
  1982年   71篇
  1981年   64篇
  1980年   51篇
  1979年   45篇
  1978年   34篇
  1977年   28篇
  1976年   23篇
  1959年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
大学在办学资源、办学过程、办学质量、办学形象的竞争中出现大量的不良倾向。大学的不良竞争是由于政府主导资源配置、资源和制度供给不足、大学系统重构等因素导致。必须通过控制主体、控制手段的转变和控制对象的发展形成新的控制机制,以保证大学竞争的秩序化和规范化。  相似文献   
12.
提出一种配电网电容电流测量的新方法,在零序电压互感器的开口三角侧串联一个可调电感,通过注入一个变频恒流信号寻找配电网的谐振频率,改变可调电感的数值后寻找另一谐振频率,联立2个谐振方程求解电容电流,该方法消除了电压互感器漏抗对测量的影响。开发了配电网电容电流测量仪,经模拟试验和现场测试表明,该方法具有安全、快捷、准确等特点,适用于中性点不接地或经随调式消弧线圈接地配电网。  相似文献   
13.
Some 100 years before Albert Munsell developed his color order system, French silk merchant and inventor of a technology for producing works of art in silk velours, Gaspard Grégoire, introduced a color order system based on the color attributes hue, (relative) chroma, and lightness. Conceived in the mid‐1780s, an atlas with 1350 samples was produced before 1813 and found use in French Royal manufacturing operations and educational institutions. It was followed a few years later by one with 343 samples. Grégoire's work was subsequently overshadowed by Michel‐Eugene Chevreul's more complicated and less intuitive hemispherical system of 1839. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 5–9, 2008  相似文献   
14.
The breakdown processes of oil films under quasi-static loading have been investigated by using a newly developed steel-oil-mercury system. The relationship between the thickness and breakdown ratio of a hexadecane film is represented by a single master curve independently of the indentation speed, indentation load, and temperature. The master curve shows that the breakdown process of hexadecane includes two stages; one is the decrement of the thickness without breakdown and the other is the decrement of the thickness with a drastic progress of breakdown. By solving a small amount of fatty acid in hexadecane, the thickness increases and the breakdown ratio decreases noticeably; a multilayer residual film supporting normal load is formed between two metal surfaces. Experiments at different temperatures reveal a negative relationship between the temperature and thickness of residual film, which indicates that the residual film is organized by physical interaction rather than chemical interaction. At least under a lower concentration, the residual film appears to consist of not only fatty acid molecules but also hexadecane molecules.  相似文献   
15.
An alternative approach to understanding innovation is made using two intersecting ideas. The first is that successful innovation requires consideration of the social and organizational contexts in which it is located. The complex context of construction work is characterized by inter-organizational collaboration, a project-based approach and power distributed amongst collaborating organizations. The second is that innovations can be divided into two modes: 'bounded', where the implications of innovation are restricted within a single, coherent sphere of influence, and 'unbounded', where the effects of implementation spill over beyond this. Bounded innovations are adequately explained within the construction literature. However, less discussed are unbounded innovations, where many firms' collaboration is required for successful implementation, even though many innovations can be considered unbounded within construction's inter-organizational context. It is argued that unbounded innovations require an approach to understand and facilitate the interactions both within a range of actors and between the actors and technological artefacts. The insights from a sociology of technology approach can be applied to the multiplicity of negotiations and alignments that constitute the implementation of unbounded innovation. The utility of concepts from the sociology of technology, including 'system building' and 'heterogeneous engineering', is demonstrated by applying them to an empirical study of an unbounded innovation on a major construction project (the new terminal at Heathrow Airport, London, UK). This study suggests that 'system building' contains outcomes that are not only transformations of practices, processes and systems, but also the potential transformation of technologies themselves.  相似文献   
16.
In this paper, we discuss average consensus problem in undirected networks of dynamic agents with fixed and switching topologies as well as multiple time-varying communication delays. By employing a linear matrix inequality method, we prove that all the nodes in the network achieve average consensus asymptotically for appropriate communication delays if the network topology is connected. Particularly, several feasible linear matrix inequalities are established to determine the maximal allowable upper bound of time-varying communication delays. Numerical examples are given to demonstrate the effectiveness and the sharpness of the theoretical results.  相似文献   
17.
Based on the optimal fusion estimation algorithm weighted by scalars in the linear minimum variance sense, a distributed optimal fusion Kalman filter weighted by scalars is presented for discrete‐time stochastic singular systems with multiple sensors and correlated noises. A cross‐covariance matrix of filtering errors between any two sensors is derived. When the noise statistical information is unknown, a distributed identification approach is presented based on correlation functions and the weighted average method. Further, a distributed self‐tuning fusion filter is given, which includes two stage fusions where the first‐stage fusion is used to identify the noise covariance and the second‐stage fusion is used to obtain the fusion state filter. A simulation verifies the effectiveness of the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
18.
李海峰 《河北冶金》1997,(3):43-47,62
主要介绍了承钢棒材连轧线计算机控制系统,其中包括了系统的硬件配置,控制功能及控制说明。  相似文献   
19.
ETRⅠ-30调速器是瑞士爱舍维斯工厂生产的具有PID调节规律的电液调速器。本文对其液压控制系统作了较详细的介绍,供有关人员参考。  相似文献   
20.
New technologies such as power electronics have made it possible to change continuously the impedance of a power system not only to control power flow but also to enhance stability. A power system incorporating a variable impedance apparatus such as a variable series capacitor (VSrC) and high-speed phase shifter (HSPS) is called VIPS (Variable Impedance Power System) by the authors. This paper proposes a novel control method of VIPS apparatus such as VSrC and HSPS installed at an interconnecting point for stabilizing inter-area unstable and/or oscillatory modes. The proposed design method of the control system is a kind of hierarchical decentralized control method of a large-scale power system based on a Lyapunov function. Under the proposed control scheme, each subsystem can be stabilized independently by local controllers such as AVR, speed governor and PSS, and then the whole interconnected system can be stabilized by VIPS apparatus taking into account interactions between subsystems. The effectiveness and robustness of the VIPS apparatus control are shown by numerical examples with model systems including a large-scale power system.  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