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   38197篇
  免费   3690篇
  国内免费   1822篇
电工技术   2726篇
技术理论   1篇
综合类   2398篇
化学工业   6561篇
金属工艺   2265篇
机械仪表   2383篇
建筑科学   2965篇
矿业工程   1107篇
能源动力   1010篇
轻工业   3067篇
水利工程   770篇
石油天然气   2111篇
武器工业   318篇
无线电   4486篇
一般工业技术   4733篇
冶金工业   1559篇
原子能技术   459篇
自动化技术   4790篇
  2024年   211篇
  2023年   762篇
  2022年   1486篇
  2021年   1810篇
  2020年   1432篇
  2019年   1159篇
  2018年   1252篇
  2017年   1437篇
  2016年   1158篇
  2015年   1648篇
  2014年   2050篇
  2013年   2292篇
  2012年   2517篇
  2011年   2591篇
  2010年   2230篇
  2009年   2200篇
  2008年   2115篇
  2007年   1911篇
  2006年   1946篇
  2005年   1608篇
  2004年   1055篇
  2003年   1064篇
  2002年   998篇
  2001年   865篇
  2000年   880篇
  1999年   964篇
  1998年   746篇
  1997年   638篇
  1996年   551篇
  1995年   484篇
  1994年   368篇
  1993年   280篇
  1992年   253篇
  1991年   161篇
  1990年   141篇
  1989年   118篇
  1988年   88篇
  1987年   54篇
  1986年   31篇
  1985年   35篇
  1984年   18篇
  1983年   21篇
  1982年   24篇
  1981年   7篇
  1980年   11篇
  1979年   6篇
  1978年   6篇
  1977年   7篇
  1975年   3篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
We develop the complex scaling method within the relativistic framework by expanding the Dirac spinors in the complete set of eigensolutions of a harmonic oscillator potential, and present the theoretical formalism of describing the discrete bound and resonant states on the same footing. Based on a well established and frequently used model, we demonstrate the utility and applicability of the extended method and examine the stability of the results with respect to the variations of the parameters of the model. Satisfactory agreements are found for all the calculated results in comparison with some other calculations in references. Especially, the present calculation in the nonrelativistic limit gives a consistent result with that in the nonrelativistic calculation.  相似文献   
53.
针对燃气行业人工抄表费时费力等问题,提出一种基于GPRS和无线多跳网络技术的燃气无线抄表系统,在分析传统抄表系统的结构以及传输方式优缺点的基础上介绍了系统的总体结构、工作原理以及各部分组成和功能。采用计算机网络和数据库等技术,使得该系统具有功能强大、使用方便、可扩展性好等特点,可实现对整个燃气输配系统的监控,有效提高燃气公司的管理水平和服务效率。  相似文献   
54.
Segmenting center of interests (COIs) from pictures is an important but highly challenging problem for researchers in computer vision and image processing. The capability of understanding the meanings of pictures by computers can lead to breakthroughs in a wide range of applications including Web image search and online picture-sharing communities. In this paper, a two-level strategy is presented, which consists of a rough segmentation stage and a fine segmentation stage. In the first level, a picture is partitioned into four regions by using a block clustering method based on color and texture features, and the COI within the picture is distinguished from the background according to the principles of photographic composition. This stage aims to determine the approximate region of the target. In the second level, a novel active contour model is established based on shape information and vector method, where the image energy is defined by a hue gradient and the external energy is generated from either a triangular inner force or a supplementary force. This stage tries to extract the boundary of the target accurately. Experimental results on photos downloaded from the Internet show the feasibility and effectiveness of the proposed method.  相似文献   
55.
一种基于组策略的过滤式特征选择算法   总被引:1,自引:0,他引:1  
MRMR算法具有快速、高效等优势,在处理高维数据方面较为流行。基于此,提出一种基于组策略的MRMR改进算法(MRMRE),该算法不仅考虑单个特征属性的相关性与冗余性,同时针对特征组间的相互关系进行研究。算法以MRMR算法为框架,以CCA作为度量基准,选择SVMs作为基分类器,使其特征选择效果提升。在UCI机器学习数据库中图像与基因序列数据集上的大量实验表明:与MRMR算法相比,所提出的算法其特征选择结果具有更高的结果稳定性与分类精度。  相似文献   
56.
Wireless channels comprise various signal characteristics that correspond to different features. This research applies digital signal processing to first excavate and categorize various features found in the channel data. Then, borrowing from graph theory, fast clustering analysis and decision tree modeling are introduced to identify unique “fingerprint” characteristics. Finally, two scenarios were tested using artificial neural networks to identify and verify their applicability in different geographical locations.  相似文献   
57.
International Journal of Control, Automation and Systems - Vibration disturbances with variable instantaneous frequencies can be found in many industrial applications. Therefore, rejecting...  相似文献   
58.
Yang Liu  Yao Zhang 《Information Sciences》2011,181(19):4139-4153
This paper proposes a method for solving the stochastic multiple criteria decision making (SMCDM) problem, where consequences of alternatives with respect to criteria are represented by random variables with probability distributions. Firstly, definitions and related analysis of dominance degree of one probability distribution over another are given. Then, by calculating the dominance degrees, the dominance degree matrix of alternative pairwise comparisons with respect to each criterion is built. Further, using PROMETHEE II method, an overall dominance degree matrix of alternative pairwise comparisons is constructed, and a net flow of each alternative is calculated. Based on the obtained net flows, a ranking of alternatives is determined. Finally, numerical examples for the three cases are given to illustrate the use of the proposed method.  相似文献   
59.
Three-dimensional quantitative structure-activity relationship (3D-QSAR) models were developed using comparative molecular field analysis (CoMFA) and comparative molecular similarity analysis (CoMSIA) on a series of agonists of thyroid hormone receptor beta (TRbeta), which may lead to safe therapies for non-thyroid disorders while avoiding the cardiac side effects. The reasonable q(2) (cross-validated) values 0.600 and 0.616 and non-cross-validated r(2) values of 0.974 and 0.974 were obtained for CoMFA and CoMSIA models for the training set compounds, respectively. The predictive ability of two models was validated using a test set of 12 molecules which gave predictive correlation coefficients (r(pred)(2)) of 0.688 and 0.674, respectively. The Lamarckian Genetic Algorithm (LGA) of AutoDock 4.0 was employed to explore the binding mode of the compound at the active site of TRbeta. The results not only lead to a better understanding of interactions between these agonists and the thyroid hormone receptor beta but also can provide us some useful information about the influence of structures on the activity which will be very useful for designing some new agonist with desired activity.  相似文献   
60.
Mie scattering computations have been performed for light scattered by small particles from a pulsed sheet of laser illumination and collected and imaged by a camera lens. From these computations the smallest particles that can be photographed in various fluid measurement situations, including air and water, have been determined in terms of system parameters such as laser power, light sheet geometry, f/No., and photographic film properties. The particle scattering requirements of the individual particle image mode and the speckle mode are compared.  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