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   48571篇
  免费   5625篇
  国内免费   3033篇
电工技术   3692篇
技术理论   3篇
综合类   6472篇
化学工业   3377篇
金属工艺   1005篇
机械仪表   2402篇
建筑科学   5676篇
矿业工程   2405篇
能源动力   1268篇
轻工业   5458篇
水利工程   2582篇
石油天然气   4639篇
武器工业   981篇
无线电   3197篇
一般工业技术   3275篇
冶金工业   1606篇
原子能技术   301篇
自动化技术   8890篇
  2024年   275篇
  2023年   696篇
  2022年   1323篇
  2021年   1632篇
  2020年   1785篇
  2019年   1486篇
  2018年   1492篇
  2017年   1645篇
  2016年   1951篇
  2015年   2033篇
  2014年   3291篇
  2013年   2997篇
  2012年   3925篇
  2011年   3986篇
  2010年   3001篇
  2009年   3063篇
  2008年   2734篇
  2007年   3383篇
  2006年   2913篇
  2005年   2566篇
  2004年   2055篇
  2003年   1738篇
  2002年   1282篇
  2001年   1124篇
  2000年   869篇
  1999年   749篇
  1998年   548篇
  1997年   517篇
  1996年   403篇
  1995年   350篇
  1994年   286篇
  1993年   218篇
  1992年   139篇
  1991年   129篇
  1990年   86篇
  1989年   108篇
  1988年   47篇
  1987年   36篇
  1986年   37篇
  1985年   24篇
  1984年   30篇
  1983年   33篇
  1982年   17篇
  1981年   13篇
  1979年   16篇
  1963年   12篇
  1961年   13篇
  1960年   14篇
  1959年   13篇
  1956年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Visual evaluation experiments of color discrimination threshold and suprathreshold color‐difference comparison were carried out using CRT colors based on the psychophysical methods of interleaved staircase and constant stimuli, respectively. A large set of experimental data was generated ranged from threshold to large suprathreshold color difference at the five CIE color centers. The visual data were analyzed in detail for every observer at each visual scale to show the effect of color‐difference magnitude on the observer precision. The chromaticity ellipses from this study were compared with four previous published data, of CRT colors by Cui and Luo, and of surface colors by RIT‐DuPont, Cheung and Rigg, and Guan and Luo, to report the reproducibility of this kind of experiment using CRT colors and the variations between CRT and surface data, respectively. The present threshold data were also compared against the different suprathreshold data to show the effect of color‐difference scales. The visual results were further used to test the three advance color‐difference formulae, CMC, CIE94, and CIEDE2000, together with the basic CIELAB equation. In their original forms or with optimized KL values, the CIEDE2000 outperformed others, followed by CMC, and with the CIELAB and CIE94 the poorest for predicting the combined dataset of all color centers in the present study. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 198–208, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20106  相似文献   
2.
赵易彬  苗春发 《衡器》2008,37(1):30-31
本文主要介绍了在动态汽车衡的试验过程中不确定度来源,并以动态试验为例重点介绍了计算各分量的标准不确定度、合成标准不确定度以及扩展不确定度的方法.  相似文献   
3.
随着人们对建筑安全的日益重视 ,对建筑抗震要求的提高 ,国内外有关规范都对箍筋末端的设置作了明确规定 ,要求做成 135度弯钩。而在工程实践中 ,由于施工上的技术困难 ,很多工程都只设置成 90度弯钩。笔者提出的箍筋末端 135度弯钩二次就位法在基本不增加 90度弯钩施工难度与费用的基础上实现了 135度弯钩的施工 ,其法是可行的  相似文献   
4.
Meeting time and cost objectives in complex projects involves specific problems and risks. An attempt is made to analyse the components of total cost increase of a project caused by time delay. An outline is given as to how these considerations can be used to estimate cost increases in investors' decision situations as well as to ascertain fair contractual penalties and claims for compensation and for the evaluation of justified project acceleration costs.  相似文献   
5.
微波干燥原理及其应用   总被引:31,自引:1,他引:30  
祝圣远  王国恒 《工业炉》2003,25(3):42-45
介绍了微波干燥的原理和主要特点及其应用的现状,并且给出了微波干燥经济核算的计算方法。  相似文献   
6.
In this paper the performability analysis of fault-tolerant computer systems using a hierarchical decomposition technique is presented. A special class of queueing network (QN) models, the so-called BCMP [4], and generalized stochastic Petri nets (GSPN) [1] which are often used to separately model performance and reliability respectively, have been combined in order to preserve the best modelling features of both.

A conceptual model is decomposed into GSPN and BCMP submodels, which are solved in isolation. Then, the remaining GSPN portion of the model is aggregated with flow-equivalents of BCMP models, in order to compute performability measures. The substitutes of BCMP models are presented by means of simple GSPN constructs, thereby preserving the 1st and 2nd moments of the throughput. A simple example of a data communication system where failed transmissions are corrected, is presented.  相似文献   

7.
We have assessed the antimicrobial, vapor-phase activity of the following natural essential oils (EOs) when used in paraffin-based “active coatings” for paper packaging materials intended to come into contact with foods: clove (Sygzium aromaticum), cinnamon (Cinnamomum zeylanicum), and oregano (Origanum vulgare) EOs, and cinnamaldehyde-enriched cinnamon EO. To our knowledge, this is the first time that such an approach has been presented for consideration by the scientific community.  相似文献   
8.
从f(n,t)曲线的研究出发,得到了求解油田单井平均日产油量经济极限值的数学方程式,介绍了用曲线交汇法求解的过程,分析了油田月递减余率和原油销售价是影响油田单井平均日产油量经济极限的主要因素。该方法在油田开发调整方案的编制和油田开发规划部署工作中将起到一定的作用。  相似文献   
9.
Abstract. Expert systems proliferate. They are now a usable and used tool in a variety of organizations. However, little research has been undertaken on the quantification of success or failure of expert system projects. By and large the only test carried out for expert system validation is one of comparison of the conclusions of the system with those of an expert or team of experts. While questioning the validity, this paper accepts that this method is being used and analyses whether or not the results obtained from this type of test should be a surprise. That is, what sort of results should be expected and to what extent do the reported ones live up to these expectations? Earlier research from the field of human information processing casts doubts on the success claims made for current expert systems. The implications of this research are then analysed in order to explore the possible redeeming features of expert systems which are not taken into account in such comparisons. The use of linear models as comparators for expert systems may prove beneficial.  相似文献   
10.
Biphasic and nth-order models were tested as to their usefulness to fit experimental inactivation data of Bacillus licheniformis α-amylase, immobilized on glass beads, and were discussed with respect to their suitability to characterize the considered enzymic system as a time—temperature integrator (TTI) to evaluate heat processes. Both isothermal and non-isothermal inactivation experiments were carried out. Model (kinetic) parameters (rate constant k, activation energy EA and reaction order n) were estimated using a non-linear regression procedure. The results obtained, especially the activation energy of about 293 kJ mole–1, indicated a potential use of this system as a TTI for heating processes in the temperature range of 96–108°C.  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