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   18329篇
  免费   1011篇
  国内免费   468篇
电工技术   634篇
技术理论   1篇
综合类   1666篇
化学工业   2538篇
金属工艺   441篇
机械仪表   732篇
建筑科学   1817篇
矿业工程   415篇
能源动力   364篇
轻工业   1812篇
水利工程   267篇
石油天然气   317篇
武器工业   71篇
无线电   794篇
一般工业技术   2774篇
冶金工业   954篇
原子能技术   137篇
自动化技术   4074篇
  2024年   61篇
  2023年   200篇
  2022年   280篇
  2021年   370篇
  2020年   425篇
  2019年   436篇
  2018年   397篇
  2017年   506篇
  2016年   570篇
  2015年   586篇
  2014年   1064篇
  2013年   1091篇
  2012年   1256篇
  2011年   1483篇
  2010年   1115篇
  2009年   1124篇
  2008年   935篇
  2007年   1135篇
  2006年   959篇
  2005年   808篇
  2004年   717篇
  2003年   632篇
  2002年   539篇
  2001年   412篇
  2000年   337篇
  1999年   318篇
  1998年   276篇
  1997年   229篇
  1996年   170篇
  1995年   183篇
  1994年   125篇
  1993年   112篇
  1992年   86篇
  1991年   65篇
  1990年   67篇
  1989年   76篇
  1988年   78篇
  1987年   46篇
  1986年   43篇
  1985年   58篇
  1984年   73篇
  1983年   89篇
  1982年   90篇
  1981年   29篇
  1980年   30篇
  1979年   21篇
  1978年   19篇
  1977年   17篇
  1959年   5篇
  1955年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
The knowledge of turbo code's minimum Hamming distance (dmin) and its corresponding codeword multiplicity (Amin) is of a great importance because the error correction capability of a code is strongly tied to the values of dmin and Amin. Unfortunately, the computational complexity associated with the search for dmin and Amin can be very high, especially for a turbo code that has high dmin value. This paper introduces some useful properties of turbo codes that use structured interleavers together with circular encoding. These properties allow for a significant reduction of search space and thus reduce significantly the computational complexity associated with the determination of dmin and Amin values. © 2014 The Authors. International Journal of Communication Systems published by John Wiley & Sons, Ltd.  相似文献   
3.
We present a distribution‐free tabular cumulative sum chart for monitoring the variability of an autocorrelated process. A quantity known as the asymptotic variance parameter is employed as a measure of the variability, and a distribution‐free tabular cumulative sum chart is applied to variance estimates calculated from batches of nonoverlapping samples. The proposed chart is applicable to a stationary process with a general marginal distribution and a general autocorrelation structure. It also determines control limits analytically without trial‐and‐error simulations. The performance of the proposed chart is tested on stationary processes with both normal and nonnormal marginals with various autocorrelation structures. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
4.
Numerical dissipation acts as artificial viscosity to make smoke viscous. Reducing numerical dissipation is able to recover visual details smeared out by the numerical dissipation. Great efforts have been devoted to suppress the numerical dissipation in smoke simulation in the past few years. In this paper we investigate methods of combating the numerical dissipation. We describe visual consequences of the numerical dissipation and explore sources that introduce the numerical dissipation into course of smoke simulation. Methods are investigated from various aspects including grid variation, high-order advection, sub-grid compensation, invariant conservation, and particle-based improvement, followed by discussion and comparison in terms of visual quality, computational overhead, ease of implementation, adaptivity, and scalability, which leads to their different applicability to various application scenarios.  相似文献   
5.
This study addresses the problem of choosing the most suitable probabilistic model selection criterion for unsupervised learning of visual context of a dynamic scene using mixture models. A rectified Bayesian Information Criterion (BICr) and a Completed Likelihood Akaike’s Information Criterion (CL-AIC) are formulated to estimate the optimal model order (complexity) for a given visual scene. Both criteria are designed to overcome poor model selection by existing popular criteria when the data sample size varies from small to large and the true mixture distribution kernel functions differ from the assumed ones. Extensive experiments on learning visual context for dynamic scene modelling are carried out to demonstrate the effectiveness of BICr and CL-AIC, compared to that of existing popular model selection criteria including BIC, AIC and Integrated Completed Likelihood (ICL). Our study suggests that for learning visual context using a mixture model, BICr is the most appropriate criterion given sparse data, while CL-AIC should be chosen given moderate or large data sample sizes.  相似文献   
6.
The focus of this paper lies in the practical aspects of voice over IP communication. VoIP configurations in the H.323 standard will be presented briefly. Following that, the fundamental protocol procedure of H.323 communication will be briefly explained. A further part of the paper will address the subject QoS (quality of service), and present the common measurement methods used in QoS. Results gained from experiments conducted in a VoIP environment will then follow. The investigations concentrate primarily on the load behavior of voice packets in relation to important parameters of this service. The results obtained are presented and evaluated in diagrams. The paper concludes with a summary.  相似文献   
7.
In this paper we present a numerical method for estimating the current state of a nonlinear control system. We use finite differences to discretize a modified version of the finite-time observer equations in James. The discretized equations are simple and easily programmed. The convergence and accuracy of the scheme is proved, and the scheme enjoys a number of important properties: availability of rate of convergence estimates, good robustness characteristics, and the ability to handle certain types of discontinuities in the observations. The major disadvantage is that the number of grid points required increases exponentially with the number of state dimensions.  相似文献   
8.
Work system improvements are implemented in various manufacturing processes to prevent problems caused by human errors. However, they are almost always applied to problems which have already occurred. This paper examines a method of identifying latent human errors existing within the work systems beforehand. A procedure for applying failure mode and effect analysis to this identification problem was defined based on over 1000 empirical errors: a work system decomposition criterion and fundamental error modes for listing latent human errors, and then applied to three practical manufacturing processes in order to evaluate its effectiveness.  相似文献   
9.
This work aims to compare numerical results obtained by using the Monte Carlo composition-PDF method and a presumed-β-PDF in order to reveal their effects on the prediction of flow and scalar fields in swirling confined methane diffusion flame. Using the intrinsic low dimensional manifolds method for modelling the chemistry and a second moment closure for the turbulence, it is shown that both PDF-methods provide a similar accuracy level of the prediction of mean quantities. While the presumed-β-PDF performs using reasonable computational efforts, the Monte Carlo-PDF allows to capture well the turbulence-chemistry interaction and strong finite-chemistry effects such as local extinction.  相似文献   
10.
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