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   15583篇
  免费   1125篇
  国内免费   22篇
电工技术   146篇
综合类   10篇
化学工业   4011篇
金属工艺   172篇
机械仪表   455篇
建筑科学   681篇
矿业工程   31篇
能源动力   443篇
轻工业   2964篇
水利工程   163篇
石油天然气   43篇
无线电   1121篇
一般工业技术   2778篇
冶金工业   688篇
原子能技术   51篇
自动化技术   2973篇
  2024年   46篇
  2023年   207篇
  2022年   326篇
  2021年   583篇
  2020年   448篇
  2019年   469篇
  2018年   659篇
  2017年   640篇
  2016年   759篇
  2015年   600篇
  2014年   783篇
  2013年   1431篇
  2012年   1310篇
  2011年   1274篇
  2010年   819篇
  2009年   814篇
  2008年   863篇
  2007年   752篇
  2006年   609篇
  2005年   450篇
  2004年   419篇
  2003年   343篇
  2002年   339篇
  2001年   180篇
  2000年   177篇
  1999年   127篇
  1998年   139篇
  1997年   121篇
  1996年   106篇
  1995年   97篇
  1994年   95篇
  1993年   80篇
  1992年   58篇
  1991年   49篇
  1990年   39篇
  1989年   36篇
  1988年   36篇
  1987年   29篇
  1986年   27篇
  1985年   36篇
  1984年   45篇
  1983年   26篇
  1982年   30篇
  1981年   25篇
  1980年   25篇
  1979年   30篇
  1978年   15篇
  1976年   15篇
  1975年   14篇
  1974年   13篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
Interconnect imperfections have become an important issue in modern nanometer technologies. Some of them cause Small Delay Defects (SDDs) which are difficult to detect. Those SDDs not detected during testing may pose a reliability problem. Furthermore, nanometer issues (e.g. process variations, spatial correlations) represent important challenges for traditional delay test methods. In this paper, a methodology to compute the Detection Probability (DP) of resistive open and bridge defects using a statistical timing framework that takes into account process variations and other nanometer issues is proposed. The DP gives the sensitivity of the circuit performance to a given resistance range of the defect. The efficiency issue when analyzing large circuits is alleviated using stratified sampling techniques to reduce the space of possible analyzed defect locations This methodology is applied to some ISCAS benchmark circuits. The obtained results show the feasibility of the proposed methodology. Measures can be taken for those circuits presenting non-acceptable DP in order to improve the test quality.  相似文献   
133.
134.
This paper focuses on the results of the national research of cyberbullying of Czech teachers, which was realized in year 2016 in the entire Czech Republic. The research focused on impact of cyberbullying on teachers – especially in emotional, physiological and behavioural area. The research involved a total of 5136 primary and secondary school teachers from all regions of the Czech Republic. The research has shown that a fifth of respondents (21.73%) has experienced a cyber-attack on their person, however cyberbullying during the last 12 months lasting over 1 week was confirmed only by 3.52% of the total number of respondents.  相似文献   
135.
The Hg0.8Cd0.2Te type-conversion, Hg self-diffusion and interdiffusion processes are analyzed in the context of a first order reaction kinetics approach. Sets of nonlinear, stiffly coupled continuity equations are presented which describe the underlying physics, and their solutions model the observed macroscopic behavior. It is demonstrated that the Frenkel pair mechanism interactions dominated by the cation sublattice, in conjunction with basic diffusive and drift properties of the ionized point defects, comprise the basic processes which effect all macroscopic phenomena discussed. Existing experimental results are reviewed and apparent discrepancies discussed. Use is made of the Stanford University mercury cadmium telluride process simulator to provide quantitative and insightful examples of important results.  相似文献   
136.
The formulation is developed in the frequency domain and the finite difference method is used for the numerical solution of the scalar wave equation, written in terms of the transverse components of the magnetic field. As a result a conventional eigenvalue problem is obtained without the presence of spurious modes due to the implicit inclusion of the divergence of the magnetic field equal to zero. The formulation is developed to include biaxial anisotropic dielectrics with an index profile varying arbitrarily in the cross section of the waveguide under analysis. This formulation is then applied to the analysis of the influence on the dispersion characteristics of the dimensions of asymmetric coupled rectangular uniaxial anisotropic dielectric waveguides. As expected, the reduction of the height or the width of one of the rectangular dielectric waveguides causes the dispersion curves to move towards higher frequencies.  相似文献   
137.
This paper presents a new thermogenerator based on moderate-temperature (up to 175°C) BiTe modules available on the open market. Despite this handicap relative to commercial thermogenerators based on high-temperature proprietary-technology PbBi modules (up to 560°C), this new design may become economically competitive due to its innovative thermal sink. Our thermal sink is based on a free-convection water loop built with standard tubing and household hot-water radiators, leading to a more practical, modular design. So, the specific cost of about 55,000 USD/kW obtained for this 120-W prototype is improved to 33,000 USD/kW for a 1-kW unit, which represents about half the price of commercial thermogenerators. Moreover, considering recently launched BiTe modules (that withstand up to 320°C), our proposition could have an even more favorable outlook.  相似文献   
138.
In high frequency thercs measurement of large target must be done at important distances, so the distance of measurement (Fraunhofer’s distance) R is given by R ≥ 2d2 /λ where d is the tranversal length of the target and λ the radiation wavelength. In this paper we present a method for target that are large relative to the curvature of the spherical wavefront and the curvature of the cylindrical wavefront. A two-dimensional analytical algorithm transforms the spherical wave (near-field) measurement into the desired plane wave (far-field) and a one-dimensionnal analytical algorithm transforms the cylindrical wave (near-field) measurement into the desired plane wave (far-field). We present some results on simulations and measurements. A comparison of one-dimensional and two-dimensional methods demonstrates the efficiency of the two dimensional methods.  相似文献   
139.
Audio-visual and other multimedia services are seen as an important source of traffic for ATM networks. Due to the statistical multiplexing schemes used by ATM networks, cells are exposed to delays, jitters and losses. These phenomena affect the quality of the service provided to the video-based applications. In this paper, we introduce a set of control mechanisms at different levels of the protocol architecture. These mechanisms have been particularly tailored to better support MPEG-2-based video communications applications using ATM networks as their underlying transmission mechanism. We show that the use of errorconcealment mechanisms prove more effective when supplemented by a structured set of protocol mechanisms. We study the impact of cell losses on the quality of MPEG-2 video sequences and provide an evaluation of the quality of the decoded video as perceived by the end user. Our results demonstrate the effectiveness of the proposed protocol architecture in improving the quality of service provided to the video application.  相似文献   
140.
Micro-emboli detection: an ultrasound Doppler signal processing viewpoint   总被引:1,自引:0,他引:1  
Several studies have been carried out in the last twenty years on the characterization and detection of cerebral artery emboli. From the detection point of view, the existing methods are largely based on the classical Fourier analysis of which the well known limitations provide poor accuracy. This paper first recalls existing methods based on Fourier, Wigner-Ville and wavelet approaches. It then presents new emboli detection methods based on parametric signal processing approaches. The basic idea of these parametric methods is to compare the Doppler embolic signal to its autoregressive model. The detection principle consists in constructing a decision information which contains the signature of the micro-embolus being sought. The detection is finally evaluated using receiver operating characteristic (ROC) curves. Comparison between the new methods and classical approaches is performed using a realistic embolic signal simulation. Furthermore, to validate our theoretical study, we tested our new algorithms using in vivo signals. This comparison shows the significant inaccuracy of existing methods to detect micro-emboli.  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