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   4056篇
  免费   143篇
  国内免费   1篇
电工技术   31篇
综合类   5篇
化学工业   882篇
金属工艺   53篇
机械仪表   73篇
建筑科学   116篇
矿业工程   9篇
能源动力   93篇
轻工业   295篇
水利工程   23篇
石油天然气   20篇
无线电   272篇
一般工业技术   586篇
冶金工业   1254篇
原子能技术   27篇
自动化技术   461篇
  2023年   34篇
  2022年   65篇
  2021年   134篇
  2020年   73篇
  2019年   76篇
  2018年   67篇
  2017年   74篇
  2016年   57篇
  2015年   79篇
  2014年   86篇
  2013年   149篇
  2012年   145篇
  2011年   165篇
  2010年   138篇
  2009年   130篇
  2008年   161篇
  2007年   146篇
  2006年   126篇
  2005年   93篇
  2004年   96篇
  2003年   101篇
  2002年   73篇
  2001年   83篇
  2000年   68篇
  1999年   74篇
  1998年   275篇
  1997年   169篇
  1996年   155篇
  1995年   105篇
  1994年   96篇
  1993年   75篇
  1992年   37篇
  1991年   48篇
  1990年   43篇
  1989年   45篇
  1988年   54篇
  1987年   39篇
  1986年   29篇
  1985年   57篇
  1984年   36篇
  1983年   27篇
  1982年   36篇
  1981年   32篇
  1980年   20篇
  1979年   24篇
  1978年   24篇
  1977年   42篇
  1976年   55篇
  1974年   22篇
  1973年   19篇
排序方式: 共有4200条查询结果,搜索用时 15 毫秒
41.
Three experiments, with 98 undergraduates, investigated the effects of increasing task difficulty and noise intensity on postnoise persistence on the Feather tolerance for frustration puzzles. In Exp I, greater persistence occurred both after exposure to moderate noise levels (55 db [A]) and an easy perceptual-motor task and after high noise levels (90 db [A]) and a more difficult task. The same pattern of persistence was obtained in Exp II, with more attempts to solve the Feather puzzles occurring after moderate noise and an easy cognitive task and after loud noise and a more difficult cognitive task. In Exp III, a modified Feather task was presented with instructions to determine solvability. A similar U-shaped relationship was obtained, with longer correct response times to unsolvable puzzles following low noise and high noise. Such aftereffect patterns are more easily explained as the result of residual arousal than of frustration tolerance. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
42.
Results of simulations, designed to illustrate the influence of power system stabilizers (PSS) on inter-area and local oscillations in interconnected power systems, are reported. It is shown that the PSS location and the voltage characteristics of the system loads are significant factors in the ability of a PSS to increase the damping of interarea oscillations. It is also shown that an interaction between modes in two distinct parts of a power system is possible, due to resonance, and that this might cause distortions in mode shape and participation factors  相似文献   
43.
44.
We investigate the transverse modal properties of cylindrical subwavelength metal-clad nanowire and micropost lasers via rigorous theoretical waveguide analysis, including the effects of finite thickness metal cladding and gain in the core. The results of this analysis show that air-metal surface guided TM01 and some hybrid surface guided modes suffer less loss but are less confined to the core, while core-metal surface guided modes are better confined to the core but suffer greater loss. An increase in the thickness of the metal cladding reduces the loss of the core-metal surface guided modes. The modal gain and confinement of the metal-clad cavity are compared to an unclad cavity.  相似文献   
45.
The complexity of many chemical and refining reaction systems and the thus-derived tedious and time-consuming process of building the associated kinetic models have been major obstacles in the use of fundamental kinetics in the solution of chemical engineering problems. This review summarizes work aimed at removing theses obstacles. Our recent work that has led to the enhancement of the Kinetic Modeler's Toolbox (KMT) and the development of the Kinetic Model Editor (KME) presents an end-to-end solution to the kinetic modeling process, including automated feedstock modeling, reaction network construction, kinetic rate estimation, model programming, process system configurations, model customizations, compilations, model execution and results analysis.  相似文献   
46.
Molecular electrostatic potential (MEP) maps of certain 3-methoxy flavone derivatives having different anti-picornavirus activities have been studied. Geometries of the molecules were optimised and charge distributions computed using the AM1 molecular orbital method. Hybridization displacement charges (HDC) were combined with the L?wdin charge distributions to compute the MEP maps. Reliability of the method of computing MEP maps was tested by studying certain other molecules for which ab initio MEP results are available. The anti-picornavirus activities of the flavones have been shown to be related with negative MEP values in two regions, one near the 3-methoxy group and another in a diagonally opposite region near the substituent attached to the C7 atom of the molecules.  相似文献   
47.
Ross.  AH Gilh.  KS 《电信科学》1996,12(3):6-17
本文主要讨论数字移动通信中扩频码分多址技术,阐明了CDMA体制的优越之外,分析了CDMA的关键技术,全面介绍了CDMA系统设计的基本原则和IS-95-A空中接口标准的含义。  相似文献   
48.
49.
A new self-tuning regulator for control of mean arterial blood pressure using sodium nitroprusside is presented. In addition to adapting to various patient response gains and time constants, the controller can accommodate variations in pure time delays, a problem that has not been addressed fully in previously proposed controllers. The control algorithm derivation is based on incorporating a self-turning controller with an adaptive discrete time delay compensator. The derivation, however, is general and can potentially be applied to other pharmacological agents in addition to sodium nitroprusside. The a priori information required for implementation of the controller is the estimate of the order of the patient response transfer function and the range of the pure time delay. An attractive feature of the controller is its capability to optimize the level of the infused drug during the transient phase of the control without creating an output offset. This feature tends to reduce the overall level of the infused drug. Hence, it may be useful when the cost of a drug or its long-term administration side effects is of concern, such as in the case of sodium nitroprusside  相似文献   
50.
The paper presents a case study of the development of an expert decision support system which uses simple heuristic methods for fast determination of routes for simultaneous signals in a transmission network of limited capacity. It illustrates how heuristic solutions can be embodied in a model-based DSS and how the standard decision support literature, although intuitively appealing, provides little practical assistance in system construction or classification  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