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   228933篇
  免费   17463篇
  国内免费   9143篇
电工技术   12470篇
技术理论   24篇
综合类   14159篇
化学工业   38790篇
金属工艺   13146篇
机械仪表   14520篇
建筑科学   17583篇
矿业工程   7509篇
能源动力   6420篇
轻工业   13449篇
水利工程   3589篇
石油天然气   16641篇
武器工业   1648篇
无线电   25130篇
一般工业技术   27333篇
冶金工业   12806篇
原子能技术   2247篇
自动化技术   28075篇
  2024年   994篇
  2023年   3800篇
  2022年   6484篇
  2021年   9110篇
  2020年   7083篇
  2019年   6017篇
  2018年   6731篇
  2017年   7537篇
  2016年   6747篇
  2015年   8865篇
  2014年   11249篇
  2013年   13273篇
  2012年   14216篇
  2011年   15449篇
  2010年   13418篇
  2009年   12684篇
  2008年   12352篇
  2007年   11846篇
  2006年   12342篇
  2005年   10749篇
  2004年   7262篇
  2003年   6224篇
  2002年   5465篇
  2001年   4887篇
  2000年   5433篇
  1999年   6437篇
  1998年   5434篇
  1997年   4454篇
  1996年   4193篇
  1995年   3501篇
  1994年   2813篇
  1993年   1970篇
  1992年   1537篇
  1991年   1227篇
  1990年   934篇
  1989年   740篇
  1988年   537篇
  1987年   336篇
  1986年   278篇
  1985年   197篇
  1984年   139篇
  1983年   114篇
  1982年   124篇
  1981年   98篇
  1980年   70篇
  1979年   36篇
  1978年   26篇
  1977年   20篇
  1976年   36篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Bayesian analysis is used to show that Wald's sequential probability ratio test with varying thresholds is optimal for the nonstationary situation, where the observed samples are independent but not identically distributed. Some important properties useful for the design of the test thresholds are discussed. Wald's lower bound, generalized to the nonstationary situation, is also presented. The results have important applications in situations where the observed signal is time-varying. such as in radar signal processing, image processing, and spread spectrum communications  相似文献   
52.
Methods of optimizing the design of electrical machines are discussed. The augmented Lagrangian multiplier method is described, and an algorithm for this method is introduced. The method is compared with the more familiar exterior penalty function method using, as an example, the cost optimization of permanent magnetic variable-speed drive motors. The improved method is shown to be superior, both in its ability to reach an optimum consistently and in the number of required iterations  相似文献   
53.
This paper examines bidding strategies in a bilateral market in which generating companies submit bids to loads. A load accepts electricity delivery from the generator with the lowest bid at its bid price as long as this price is not higher than the load's willingness to pay. Necessary and sufficient conditions of Nash equilibrium (NE) bidding strategy are derived based on a generic generating cost matrix and the loads' willingness to pay vector. The study shows that in any NE, efficient allocation is achieved. Furthermore, all Nash equilibria are revenue equivalent for the generators. Based on the necessary and sufficient conditions, this problem is formulated as an optimal assignment problem. Network optimization techniques are applied to calculate NE bid prices for the generators  相似文献   
54.
HHD型核子秤电离室已成功地使用于HCS型核子秤.对它的各种物理性能指标进行了检测,各项性能指标都达到了设计要求。  相似文献   
55.
56.
57.
58.
59.
本文详细叙述了DFB激光器的设计要点和新的工艺。采用一级全息光栅和二步液相外延法批量研制出高稳定单纵模工作的1.55μm分布反馈激光器(DFB—LD)。外延片成品率>40%。器件特性:25℃时阈值电流20mA,单面光功率>10mw,主边模抑制比SMSR达43dB(λ/4相移光栅),谱线宽度△ν-20dB=0.3nm,调制速率>1.8GHz。可靠性测试显示:高温监测光谱稳定,25°C时阈值退化率△Ith/t<0.3mA/kh,对应器件预估寿命将超过10万h。  相似文献   
60.
Several soil- and atmospheric-correcting variants of the normalized difference vegetation index (NDVI) have been proposed to improve the accuracy in estimating biophysical plant parameters. In this study, a sensitivity analysis, utilizing simulated model data, was conducted on the NDVI and variants by analyzing the atmospheric- and soil-perturbed responses as a continuous function of leaf area index. Percent relative error and vegetation equivalent “noise” (VEN) were calculated for soil and atmospheric influences, separately and combined. The NDVI variants included the soil-adjusted vegetation index (SAVI), the atmospherically resistant vegetation index (ARVI), the soil-adjusted and atmospherically resistant vegetation index (SARVI), the modified SAVI (MSAVI), and modified SARVI (MSARVI). Soil and atmospheric error were of similar magnitudes, but varied with the vegetation index. All new variants outperformed the NDVI. The atmospherically resistant versions minimized atmospheric noise, but enhanced soil noise, while the soil adjusted variants minimized soil noise, but remained sensitive to the atmosphere. The SARVI, which had both a soil and atmosphere calibration term, performed the best with a relative error of 10 percent and VEN of ±0.33 LAI. By contrast, the NDM had a relative error of 20 percent and VEN of ±0.97 LAI  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