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   37809篇
  免费   4173篇
  国内免费   2777篇
电工技术   2923篇
技术理论   8篇
综合类   5612篇
化学工业   2798篇
金属工艺   912篇
机械仪表   2387篇
建筑科学   3651篇
矿业工程   1294篇
能源动力   1294篇
轻工业   529篇
水利工程   1057篇
石油天然气   884篇
武器工业   636篇
无线电   3444篇
一般工业技术   4450篇
冶金工业   2168篇
原子能技术   326篇
自动化技术   10386篇
  2024年   151篇
  2023年   641篇
  2022年   866篇
  2021年   1112篇
  2020年   1269篇
  2019年   1144篇
  2018年   1156篇
  2017年   1300篇
  2016年   1412篇
  2015年   1454篇
  2014年   2226篇
  2013年   2625篇
  2012年   2446篇
  2011年   2756篇
  2010年   2208篇
  2009年   2325篇
  2008年   2394篇
  2007年   2502篇
  2006年   2314篇
  2005年   1983篇
  2004年   1590篇
  2003年   1310篇
  2002年   1131篇
  2001年   903篇
  2000年   778篇
  1999年   680篇
  1998年   536篇
  1997年   478篇
  1996年   407篇
  1995年   386篇
  1994年   316篇
  1993年   278篇
  1992年   254篇
  1991年   180篇
  1990年   147篇
  1989年   166篇
  1988年   127篇
  1987年   68篇
  1986年   90篇
  1985年   67篇
  1984年   67篇
  1983年   48篇
  1982年   54篇
  1981年   42篇
  1980年   33篇
  1979年   31篇
  1978年   29篇
  1977年   26篇
  1964年   28篇
  1955年   35篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
161.
有形波束的散射问题在粒度分析测量仪器的研究中有着特殊重要的意义,本文介绍了处理均匀球形粒子对有形波束散射的广义米理论,并应用该理论研究了双柱形激光波束粒子测量系统的散射问题,与未理论和几何光学相比,其结果与实验吻合很好。  相似文献   
162.
本文在弱闪烁条件下,利用广泛适用于星际闪烁、行星际闪烁和电离层闪烁的薄相屏理论,以行星际闪烁为算例,对薄相屏闪烁进行了数值分析。结果表明:垂直于介质运动方向上的不规则结构的大小对闪烁有着重要的影响,直接表现在频谱的变化趋势和振荡幅度的不同。尤其是当小于Fresnel尺度时,数值计算表明此时没有闪烁发生。  相似文献   
163.
天线方向图的复射线仿真   总被引:1,自引:0,他引:1  
阮颖铮 《通信学报》1994,15(1):92-96
根据复射线理论,利用复源点高斯波束场来模拟天线的远场方向图。本文提出三种模拟方法,即主瓣匹配法,峰值匹配法和逐点匹配法,给出了多种方向图的仿真结果。数值分析和优化结果表明,复射线峰值匹配法是一种精确实用的天线方向图仿真技术。  相似文献   
164.
Energy minimization and design for testability   总被引:6,自引:0,他引:6  
The problem of fault detection in general combinational circuits is NP-complete. The only previous result on identifying easily testable circuits is due to Fujiwara who gave a polynomial time algorithm for detecting any single stuck fault inK-bounded circuits. Such circuits may only contain logic blocks with no more thanK input lines and the blocks are so connected that there is no reconvergent fanout among them. We introduce a new class of combinational circuits called the (k, K)-circuits and present a polynomial time algorithm to detect any single or multiple stuck fault in such circuits. We represent the circuit as an undirected graphG with a vertex for each gate and an edge between a pair of vertices whenever the corresponding gates have a connection. For a (k, K)-circuit,G is a subgraph of ak-tree, which, by definition, cannot have a clique of size greater thank+1. Basically, this is a restriction on gate interconnections rather than on the function of gates comprising the circuit. The (k, K)-circuits are a generalization of Fujiwara'sK-bounded circuits. Using the bidirectional neural network model of the circuit and the energy function minimization formulation of the fault detection problem, we present a test generation algorithm for single and multiple faults in (k, K)-circuits. This polynomial time aggorithm minimizes the energy function by recursively eliminating the variables.  相似文献   
165.
This paper analyses the collaborative design ofa high-technology product, a neuromagnetometerused in the analysis of the activity of thehuman cortex. The producer, Neuromag Company istrying to transform the device from a basicresearch instrument into a means of clinicalpractice. This transition is analyzed as asimultaneous evolution of the product,producer-user network and user activities. Thenetwork is analyzed as a network of activitysystems. Each activity has a historicallyformed object and a motive of its own, as wellas a system of cultural means and expertise. Weuse these to explain and understand theinterests and points of view of the actors inrelation to the product and the contradictionsof the producer-user network. It is suggestedthat the emerging user needs of collectiveactors must be analyzed at three levels. At thefirst level, the use value of the product, itscapacity of solving the vital problems andchallenges of developing user activities, ischaracterized. The second-level analysisconcerns the creation and development of thenecessary complementary tools and services thatmake the implementation and use of the productpossible. This task presupposes collaborationbetween several communities of the innovationnetwork. The third level is the situatedpractical use of the product. In ourexperience, it is advantageous that researcherscontribute with their data to a dialogue inwhich the user needs are articulated.  相似文献   
166.
A finite element based on the efficient higher‐order zig‐zag theory with multiple delaminations is developed. The bending part of the formulation is constructed from the concept of DKQ element. Unlike conventional elements, a developed element has its reference in the bottom surface which simplifies zig‐zag terms on formulation. Exact patch solutions are developed on elements which have the bottom reference system. The present element passes proper bending patch tests in the arbitrary mesh configurations in isotropic materials. Zig‐zag formulation is adopted to model laminated plates with multiple delaminations. To assess the accuracy and efficiency of the present element based on higher‐order zig‐zag theory with multiple delaminations, the linear buckling problem of laminated plates with multiple delaminations has been analysed. The results have been compared with three‐dimensional elasticity solutions. The present element works as an efficient tool for analysing the behaviour of the laminated composites with multiple delaminations. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
167.
éditorial.     
This issue begins with an invited paper by Ronald Melzack, continuing the "Distinguished Contribution Series" begun in 1990 by my predecessor, Gordon Winocur. Professor Melzack is known world-wide for his research on pain. In 1965, together with Patrick Wall, he proposed the gate control theory, an entirely new conception of pain. For the first time, there was an explicit physiological model emphasizing the role played by the brain as well as by the spinal cord, leading to a new integration of psychological and physiological contributions to pain, as well as to new avenues for the control of pain. This theory has been highly influential, as a quick look in virtually any textbook in biology or medicine will confirm. Professor Melzack's continuing development of his ideas is presented with remarkable clarity in his books and in his many journal articles. It is, therefore, especially exciting for CJEP to be the first to publish a sketch of his new neuromatrix theory. When the book developing this theory is published, it too will no doubt have an immediate and major impact. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
168.
Research bearing on several popular conceptions of the major determinants of anger arousal indicates that the particular appraisals often identified as causes of anger frequently only serve to affect the intensity of the anger that is generated. Research into effects of physical pain or other physically unpleasant conditions or involving social stresses suggests that decidedly aversive conditions are a major spur to anger. Experiments are also reviewed showing that anger-related muscular movements can also lead to anger-related feelings, memories, cognitions, and autonomic responses. Alternative explanations for the findings are discussed. The authors urge emotion theorists to widen their methodology and analyses so that they give careful, detailed attention to the many different factors that can influence anger. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
169.
在非AWGN环境下,针对CW,AM,FM,OOK,PSK,QPSK,16QAM,FSK,MSK,SSB十种混合调制信号,对调制类型特征提取方法和自动识别算法进行了分析、综合、设计和计算机仿真。提出了梯层电平分析方法、频率瞬时信号分析、剔除载波的归一化能量分析、平方后信号的频谱分析、四次方后的信号频谱分析等方法。当SNR=10dB时,计算机仿真结果是正确识别率不低于95%,自动识别的平均处理时间为不超过10s。  相似文献   
170.
属性识别理论在黄前水库水质评价中的应用   总被引:6,自引:0,他引:6  
本文根据属性识别理论,探讨了水库水质的综合评价模型,应用此模型对黄前水库的水质进行评价,结果与灰色关联度法基本相同,比较符合实际情况。同时该方法简单、易懂,更适合于有标准的系统质量评价问题。  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