全文获取类型
收费全文 | 313580篇 |
免费 | 30015篇 |
国内免费 | 17464篇 |
专业分类
电工技术 | 75264篇 |
技术理论 | 24篇 |
综合类 | 32407篇 |
化学工业 | 13954篇 |
金属工艺 | 9446篇 |
机械仪表 | 22818篇 |
建筑科学 | 23041篇 |
矿业工程 | 10809篇 |
能源动力 | 18618篇 |
轻工业 | 5967篇 |
水利工程 | 9055篇 |
石油天然气 | 8102篇 |
武器工业 | 4485篇 |
无线电 | 34879篇 |
一般工业技术 | 15874篇 |
冶金工业 | 8742篇 |
原子能技术 | 4203篇 |
自动化技术 | 63371篇 |
出版年
2024年 | 1271篇 |
2023年 | 3447篇 |
2022年 | 6662篇 |
2021年 | 8011篇 |
2020年 | 8866篇 |
2019年 | 6738篇 |
2018年 | 6111篇 |
2017年 | 8613篇 |
2016年 | 9925篇 |
2015年 | 11378篇 |
2014年 | 20626篇 |
2013年 | 17400篇 |
2012年 | 23897篇 |
2011年 | 25518篇 |
2010年 | 19070篇 |
2009年 | 19103篇 |
2008年 | 19267篇 |
2007年 | 23751篇 |
2006年 | 21112篇 |
2005年 | 18500篇 |
2004年 | 15145篇 |
2003年 | 13274篇 |
2002年 | 10173篇 |
2001年 | 8606篇 |
2000年 | 7134篇 |
1999年 | 5628篇 |
1998年 | 4148篇 |
1997年 | 3374篇 |
1996年 | 2975篇 |
1995年 | 2489篇 |
1994年 | 2093篇 |
1993年 | 1432篇 |
1992年 | 1212篇 |
1991年 | 870篇 |
1990年 | 698篇 |
1989年 | 587篇 |
1988年 | 409篇 |
1987年 | 248篇 |
1986年 | 155篇 |
1985年 | 170篇 |
1984年 | 188篇 |
1983年 | 145篇 |
1982年 | 128篇 |
1981年 | 89篇 |
1980年 | 77篇 |
1979年 | 63篇 |
1978年 | 49篇 |
1977年 | 38篇 |
1976年 | 27篇 |
1959年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Chris Harty 《Building Research & Information》2005,33(6):512-522
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
22.
Average consensus in networks of dynamic agents with switching topologies and multiple time-varying delays 总被引:5,自引:0,他引:5
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
23.
Shu‐Li Sun Jing Ma Nan Lv 《International Journal of Adaptive Control and Signal Processing》2008,22(10):932-948
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
24.
Porous carbon nanofibers are synthesized by CVD method from acetylene with use of iron-containing catalysts. Activation of the nanofibers in melted potassium hydroxide results in increasing surface area from initial 300–400 m2 g−1 to 1700 m2 g−1. As follows from XRD data, activated nanofibers do not contain regular packages of graphene layers, but retain high electric conductivity. Deposition of copper improves electrochemical hydrogen storing characteristics of carbon nanofibers. Carbon nanomaterials obtained can be used as hydrogen storing materials in batteries instead of hydride forming metals. 相似文献
25.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
26.
Enhancement of islanding-detection of distributed generation systems via wavelet transform-based approaches 总被引:1,自引:1,他引:0
Cheng-Tao Hsieh Jeu-Min Lin Shyh-Jier Huang 《International Journal of Electrical Power & Energy Systems》2008,30(10):575-580
In this paper, a wavelet transform-based approach is proposed to detect the occurrence of islanding events in distributed generation systems. Thanks to time–frequency localization capabilities exhibited by wavelet transform, the approach embedded with this transform technique has grasped the appearance of the islanding event in a highly effective manner. Moreover, for those regions which are in need of a better visualization, the proposed approach would serve as an efficient aid such that the mains power disconnection can be better distinguished. To validate the feasibility of this approach, the method has been validated through several scenarios. Test results supported the effectiveness of the method for the application considered. 相似文献
27.
28.
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
29.
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
30.