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   74925篇
  免费   9700篇
  国内免费   3797篇
电工技术   9623篇
技术理论   3篇
综合类   6889篇
化学工业   5479篇
金属工艺   2442篇
机械仪表   7026篇
建筑科学   3265篇
矿业工程   2236篇
能源动力   3600篇
轻工业   4698篇
水利工程   1849篇
石油天然气   2841篇
武器工业   973篇
无线电   5901篇
一般工业技术   6495篇
冶金工业   2029篇
原子能技术   391篇
自动化技术   22682篇
  2025年   1043篇
  2024年   2993篇
  2023年   2747篇
  2022年   3282篇
  2021年   3406篇
  2020年   3710篇
  2019年   3230篇
  2018年   2798篇
  2017年   3312篇
  2016年   3665篇
  2015年   3831篇
  2014年   5212篇
  2013年   5118篇
  2012年   5842篇
  2011年   5606篇
  2010年   3923篇
  2009年   4105篇
  2008年   3646篇
  2007年   4031篇
  2006年   3301篇
  2005年   2629篇
  2004年   2102篇
  2003年   1687篇
  2002年   1391篇
  2001年   1110篇
  2000年   927篇
  1999年   614篇
  1998年   594篇
  1997年   497篇
  1996年   391篇
  1995年   343篇
  1994年   271篇
  1993年   204篇
  1992年   183篇
  1991年   154篇
  1990年   129篇
  1989年   107篇
  1988年   69篇
  1987年   25篇
  1986年   29篇
  1985年   17篇
  1984年   19篇
  1983年   20篇
  1982年   19篇
  1981年   10篇
  1980年   22篇
  1979年   15篇
  1978年   6篇
  1977年   7篇
  1951年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
In this paper, we propose a new approach for signal detection in wireless digital communications based on the neural network with transient chaos and time-varying gain (NNTCTG), and give a concrete model of the signal detector after appropriate transformations and mappings. It is well known that the problem of the maximum likelihood signal detection can be described as a complex optimization problem that has so many local optima that conventional Hopfield-type neural networks fail to solve. By refraining from the serious local optima problem of Hopfield-type neural networks, the NNTCTG makes use of the time-varying parameters of the recurrent neural network to control the evolving behavior of the network so that the network undergoes the transition from chaotic behavior to gradient convergence. It has richer and more flexible dynamics rather than conventional neural networks only with point attractors, so that it can be expected to have much ability to search for globally optimal or near-optimal solutions. After going through a transiently inverse-bifurcation process, the NNTCTG can approach the global optimum or the neighborhood of global optimum of our problem. Simulation experiments have been performed to show the effectiveness and validation of the proposed neural network based method for the signal detection in digital communications.  相似文献   
3.
Shear Bombs in Fibre Composites Despite an optimum external shape non‐load adapted internal fibre orientation can lead to the formation of shear cracks where crossing tension‐compression principal stress trajectories create localized shear peaks. Trees are subject to those failure because they cannot re‐arrange their fibres after wood formation. Bones can adjust their micro‐structure to changing load conditions and in this way can better control shear failure. The engineer working with fibre composites should be alert to avoid fibre arrangements not following the force flow. Localized shear zones may also form near notches similar to normal notch stresses, however they are not always situated at the contour line of the notch.  相似文献   
4.
Many organizations, best illustrated by libraries, have access to hundreds of databases possessing varying degrees of complimentary and overlapping records. While users may receive positive marginal benefits from data duplications, all databases and their services cannot be supported because of resource limitations. This paper attempts to conceptualize the problem of database collection in an environment of multiple databases, with differential content and performance characteristics, diverse users, and limited resources. It defines the database collection problem as a constrained zero-one integer programming problem and solves for the optimal combination or union of databases. Several extensions are shown, where special conditions are imposed on the relationships between databases and/or their availability.  相似文献   
5.
6.
A new practical method is proposed which gives a quasi-optimal solution of the dynamic load-dispatching problem formulated by a multiconstraint multiobjective optimization problem. Here, the multiple constraints are rate reserve constraints and power flow ones, and the multiple objectives are fuel cost and CO2 emission. The proposed method is an integration of the following three techniques: (1) “Group Dispatch Scheme,” which is developed by the authors, is used to satisfy a violated constraint easily. This scheme consists of three steps. The first step is to classify all generators into two groups. One is the group which should be more loaded to satisfy the violated constraint, and the other is the should-be less loaded group. The second step is to add some load to the former group, and to subtract the same load from the latter. The third step is to dispatch each group load to each groups generators, respectively; (2) the dynamic load-dispatching algorithm is used which provides, in practical time, quasi-optimal generation trajectories; (3) the conventional weighting parametric method is used to obtain a Pareto optimal solution of multiobjective problems. The effectiveness of the method is clarified by a computer simulation on the actual power system of Kansai Electric Power Company.  相似文献   
7.
本文提出了确定化工用搅拌器搅拌时间的一种简单试验方法,并用正交表安排寻找最佳搅拌参数的试验和整理试验数据,得到了有实用价值的结果。  相似文献   
8.
In the presence of rate constraints in actuator, design of cascade controller based on the primary controller conditional integration can result into closed-loop system oscillations. Stability analysis, performed by the describing function technique and confirmed by simulation, demonstrates that the solution based on the Anti-Reset Windup Cascade Control System (ARW CCS) structure is successful. Design and tuning of the ARW CCS secondary controller is a standard ARW single-input single-output problem. In the present paper tuning is proposed for the ARW CCS primary controller. For the serial process modeling simple rules are derived and confirmed by experimental results, obtained on a drum type boiler of a 210 MWe lignite coal fired unit. General design of the ARW CCS is based on the parallel process modeling and optimization of the primary controller. Optimization is performed in the frequency domain, under constraints on the maximum sensitivity, multiplicative uncertainty bound and sensitivity to measurement noise. Simulation and experimental results on a laboratory thermal plant demonstrate effectiveness of the proposed optimization.  相似文献   
9.
介绍菜钢型钢AV80风机冷风保安控制系统的优化改造,以增加其控制安全性及可靠性.  相似文献   
10.
Based on a simplified 3-DOF model of twin-tower structure linked by a sky-bridge, the frequency response functions, the displacement power spectral density (PSD) functions, and the time-averaged total vibration energy were derived, by assuming the white noise as the earthquake excitation. The effects of connecting parameters, such as linking stiffness ratio and linking damping ratio, on the structural vibration responses were then studied, and the optimal connecting parameters were obtained to minimize the vibration energy of either the independent monomer tower or the integral structure. The influences of sky-bridge elevation position on the optimal connecting parameters were also discussed. Finally, the distribution characteristics of the top displacement PSD and the structural responses, excited by El Centro, Taft and artificial waves, were compared in both frequency and time domain. It is found that the connecting parameters at either end of connection interactively affect the responses of the towers. The optimal connecting parameters can greatly improve the damping connections on their seismic reduction effectiveness, but are unable to reduce the seismic responses of the towers to the best extent simultaneously. It is also indicated that the optimal connecting parameters derived from the simplified 3-DOF model are applicable for two multi-story structures linked by a sky-bridge with dampers. The seismic reduction effectiveness obtained varies from 0.3 to 1.0 with different sky-bridge mass ratio. The displacement responses of the example structures are reduced by approximately 22% with sky-bridge connections.  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