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   115789篇
  免费   8159篇
  国内免费   3879篇
电工技术   6081篇
技术理论   15篇
综合类   6615篇
化学工业   19274篇
金属工艺   5910篇
机械仪表   6974篇
建筑科学   8667篇
矿业工程   3094篇
能源动力   3322篇
轻工业   6896篇
水利工程   1719篇
石油天然气   6259篇
武器工业   692篇
无线电   14796篇
一般工业技术   15074篇
冶金工业   5919篇
原子能技术   1354篇
自动化技术   15166篇
  2025年   13篇
  2024年   1994篇
  2023年   2161篇
  2022年   2976篇
  2021年   4217篇
  2020年   3513篇
  2019年   3049篇
  2018年   3081篇
  2017年   3464篇
  2016年   3119篇
  2015年   3914篇
  2014年   4943篇
  2013年   6283篇
  2012年   6553篇
  2011年   7175篇
  2010年   6240篇
  2009年   6161篇
  2008年   6156篇
  2007年   5743篇
  2006年   6032篇
  2005年   5408篇
  2004年   3689篇
  2003年   3190篇
  2002年   2847篇
  2001年   2753篇
  2000年   2868篇
  1999年   3378篇
  1998年   2911篇
  1997年   2549篇
  1996年   2287篇
  1995年   1921篇
  1994年   1551篇
  1993年   1219篇
  1992年   965篇
  1991年   738篇
  1990年   601篇
  1989年   500篇
  1988年   391篇
  1987年   296篇
  1986年   208篇
  1985年   179篇
  1984年   112篇
  1983年   82篇
  1982年   90篇
  1981年   58篇
  1980年   46篇
  1979年   32篇
  1978年   25篇
  1977年   25篇
  1976年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本文简要介绍了玻璃纤维毡增强聚丙烯片材的研制,性能和应用。  相似文献   
82.
介绍了用糠胺与腺嘌呤在催化条件下反应合成细胞激动素kinetin,该法原料易得,反应条件温和,产品收率及纯度都较高。  相似文献   
83.
Behavioral cues to deception are instrumental in detecting deception. As one of the primary sources of deception behavior, text has been analyzed at the level of sub-sentence or message but not the discourse of interaction. Additionally, empirical studies on cues to deception in the case of multiple receivers remain nonexistent. To fill these voids, we propose a discourse framework and six hypotheses about deception behaviors in a multi-receiver environment. The deception behaviors are operationalized by discourse features based on an analysis of real-world data. The results of statistical analysis validate the efficacy of discourse features in discriminating deceivers from truth-tellers.  相似文献   
84.
Partially observable Markov decision process (POMDP) is an ideal framework for sequential decision-making under uncertainty in stochastic domains. However, it is notoriously computationally intractable to solving POMDP in real-time system. In order to address this problem, this paper proposes a point-based online value iteration (PBOVI) algorithm which involves performing value backup at specific reachable belief points, rather than over the entire belief simplex, to speed up computation processes, exploits branch-and-bound pruning approach to prune the AND/OR tree of belief states online, and proposes a novel idea to reuse the belief states that have been searched to avoid repeated computation. The experiment and simulation results show that the proposed algorithm can simultaneously satisfy the requirement of low errors and high timeliness in real-time system.  相似文献   
85.
Collaboration representation-based classification (CRC) was proposed as an alternative approach to the sparse representation method with similar efficiency. The CRC is essentially a competition scheme for the training samples to compete with each other in representing the test sample, and the training class with the minimum representation residual from the test sample wins the competition in the classification. However, the representation error is usually calculated based on the Euclidean distance between a test sample and the weighted sum of all the same-class samples. This paper exploits alternative methods of calculating the representation error in the CRC methods to reduce the representation residual in a more optimal way, so that the sample classes compete with each other in a closer range to represent the test sample. A large number of face recognition experiments on three face image databases show that the CRC methods with optimized presentation residual achieve better performance than the original CRC, and the maximum improvement in classification accuracy is up to 12 %.  相似文献   
86.
ATO包裹硅酸锆的制备与应用   总被引:2,自引:0,他引:2  
采用化学共沉淀技术制备了锑掺杂二氧化锡(ATO)包裹硅酸锆的导电粉体,对比了该导电粉体与ATO在防静电陶瓷中的应用效果。结果表明与掺纯ATO相比较,掺入ATO包裹硅酸锆的防静电陶瓷颜色比较浅,并且能明显减少氧化锡的用量,当陶瓷的表面电阻为107Ω/□量级时,用ATO包裹硅酸锆作为导电填料可以节省25%左右的ATO。  相似文献   
87.
炭分子筛概述   总被引:9,自引:1,他引:9  
阐述了炭分子筛分离的原理,并分别从其制备原料、制备方法、产品用途等方面综述了近年来炭分子筛的新进展。  相似文献   
88.
Gas phase propylene epoxidation on gold catalysts has attracted wide attention from industry and academia due to its high selectivity. However, it suffers from low propylene conversion and rapid catalyst deactivation. Experiments showed that propylene conversion could be increased by raising H2, O2, or C3H6 concentration in the feed, but the feed compositions were within the explosion limit. It was also shown that the activity of the used catalyst could be fully recovered, but the regeneration temperature was 280 °C, much higher than that for reaction. Therefore a microchannel reactor was devised to suppress explosion and was constructed with Fecralloy, to raise the temperature rapidly for catalyst regeneration by electric heating. In two minutes the temperature of the reactor could be raised from 50 to 300 °C. Catalysts were coated on the alloy belt by dip coating, and the performance of the reactor was evaluated under different operating conditions. Results showed that in the microreactor the overall reaction rate was controlled mainly by the intrinsic reaction rate, and also influenced by film diffusion to a certain extent. The deactivated catalyst was regenerated in the microchannel reactor and the activity was fully recovered.  相似文献   
89.
阐述了熔融石英耐火材料的主要性能与应用领域。  相似文献   
90.
Experiment was conducted on the threshold pressure for atmospheric air through unconsolidated narrow size distributed mini sphere and sand particles at low flow rates. The threshold diameter calculated from measured threshold pressure showed that it does not follow the traditional similarity theory. This is consistent with our experiment on accurate permeability measurement, and can be explained as a result of gas slip flow within such micro pore structure. Our current work tend to find the method to predict the permeability-threshold pressure relationship for unconsolidated porous structures.  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