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   24229篇
  免费   2271篇
  国内免费   1235篇
电工技术   2379篇
综合类   1299篇
化学工业   4250篇
金属工艺   747篇
机械仪表   845篇
建筑科学   532篇
矿业工程   215篇
能源动力   8531篇
轻工业   352篇
水利工程   119篇
石油天然气   1437篇
武器工业   266篇
无线电   1353篇
一般工业技术   1484篇
冶金工业   876篇
原子能技术   1494篇
自动化技术   1556篇
  2024年   106篇
  2023年   593篇
  2022年   912篇
  2021年   1028篇
  2020年   1141篇
  2019年   1092篇
  2018年   870篇
  2017年   927篇
  2016年   862篇
  2015年   742篇
  2014年   1452篇
  2013年   1828篇
  2012年   1528篇
  2011年   2200篇
  2010年   1699篇
  2009年   1543篇
  2008年   1440篇
  2007年   1485篇
  2006年   1174篇
  2005年   876篇
  2004年   783篇
  2003年   631篇
  2002年   572篇
  2001年   524篇
  2000年   379篇
  1999年   260篇
  1998年   209篇
  1997年   173篇
  1996年   134篇
  1995年   110篇
  1994年   96篇
  1993年   69篇
  1992年   69篇
  1991年   33篇
  1990年   30篇
  1989年   30篇
  1988年   19篇
  1987年   9篇
  1986年   11篇
  1985年   14篇
  1984年   17篇
  1983年   7篇
  1982年   16篇
  1981年   3篇
  1980年   8篇
  1979年   5篇
  1978年   2篇
  1959年   11篇
  1956年   1篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
GTL 工艺技术评述   总被引:7,自引:0,他引:7  
介绍了1990年以来GTL工艺技术开发的进展情况,其中以Sasol-SSPD和Syntruleum两种工艺最受关注,从现有数据分析。Syntruleum虽采用含氮合成气生产工艺,但并未使装置的单位投资明显改善,因此,近10年来GTL工艺技术开发虽取得了长足的进步,但其装置投资仍偏高,从而又严重影响了产品成本,按南非Sasol公司的经验。开展资源综合利用是降低液体燃料生产成本的有效途径,目前国外GTL工艺技术的开发仍很活跃,我国也已形成大量实验室成果。建议尽快组织力量完成工业性试验。  相似文献   
42.
介绍了船用堆燃料元件破损监测中较常用的两种方法.通过分析其缺陷,提出了用NaI多道脉冲幅度分析系统测量特征核素(131I、137Cs)的方法,有效避免了监测中的干扰因素的影响,降低了定量监测中的误报率,提高了燃料元件破损监测的效率和置信度.  相似文献   
43.
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing.  相似文献   
44.
A three-dimensional (3D), two-phase, isothermal model of direct methanol fuel cells (DMFCs) was employed to investigate effects of electron transport through the backing layer and the land in bipolar plates. It was found that the electronic resistance of the backing layer, affected by backing layer electronic conductivity, backing layer thickness and flow channel width, played a relatively important role in determining the current density distribution and cell performance. In order to ignore the electron transport effect on the average current density, the minimum electronic conductivity of the backing layer has to be 1000 S m−1, with the relative error in the average current density less than 5%, under the given conditions.  相似文献   
45.
The feasibility of a new alloy design concept utilizing the principle of ‘tungsten bronze effect’ is critically evaluated for the development of metallic bipolar plates for proton exchange membrane fuel cell (PEMFC). An austenitic stainless steel (ASS) is modified with W and La to improve the stability of the passive film in an acidic environment as well as to reduce the contact resistance by the tungsten bronze effect. The experimental ASS containing W and La was evaluated in a simulated PEMFC environment of H3PO4 and H2SO4 solutions at 80 °C, and the electrical property was evaluated by performing a contact resistance test. The test results show that the ASS modified with W and La has good passive film stability for corrosion resistance and low contact resistance. The X-ray photoelectron spectroscopy (XPS) analysis clearly suggests the possibility of the tungsten bronze effect from the change in valency state of W6+ to W5+ in the passive film formed on the modified ASS. The feasibility of a new alloy design concept utilizing the ‘tungsten bronze effect’ is well demonstrated; however, more study is highly required for the development of metallic bipolar plates of PEMFC.  相似文献   
46.
介绍了IPv6产生的背景和发展现状,阐述了IPv6应用于矿井工业以太网的发展趋势和研究方向,指出对于所有基于矿井工业以太网的硬件和软件的开发都应带有双协议栈,随着IPv6技术的成熟和普及再研发出只有IPv6协议栈的适用于煤矿的网络设备,如支持IPv6的防爆网络设备、组态软件以及相应的数据采集驱动设备、控制硬件等。  相似文献   
47.
Stationary projectors mainly used in system applications have recently gained a wider application range, including general presentations in halls and large conference rooms and being used, for example, in digital signage and for monitoring purposes. Consequently, they are required to meet new market demands for durability, reliability, and flexibility in installation in addition to their conventional basic performance such as especially high brightness. To achieve especially high brightness, a new optical system with two lamps is proposed; the profile of the cover glass that prevents the glass from scattering is made aspherical, the profile of the beam‐combining mirror is improved with its position optimized, and the size of the incident plane of the integrator rod is made larger (1.1 times). These measures resulted in an optical system of an even higher efficiency with 7000 lm, which is the highest in its class (according to a June 2010 investigation). Also, the arrangement of two parallel lamps completely eliminated the effect of heat passing from one lamp to the other, which helped secure durability, reliability, and flexibility in installation. Furthermore, the combined use of the unique non‐telecentric optical system, adopted from the conventional single‐lamp model, helps maintain the class‐highest contrast ratio.1,2  相似文献   
48.
This work addresses the fabrication of membrane-type solid oxide fuel cells (SOFCs) operating at medium temperatures, where all components are fabricated by plasma spray technology, and the evaluation of the performance of the SOFC single unit in a temperature range of 500 to 800 °C. Single cells composed of LaSrMgO3 cathodes, LaSrGaMgO3 (LSGM) electrolytes, and Ni/yttria-stabilized zirconia anodes were fabricated in successive atmospheric plasma-spraying processes. Plasma-spraying processes have been optimized and tailored to each layer to achieve highly porous cathode and anode layers as well as high-density electrolyte layers. A major effort has been devoted to the production of the LSGM electrolyte that has a high density and is free of cracks. Electrochemical impedance spectroscopy was used to investigate the conductivity of the electrode layers, and particularly the resistance of the electrolyte layer. It revealed that the heat treatment had a great influence on the specific conductivity of the sprayed electrolyte layers and that the specific conductivity of the heat-treated layers was dramatically increased to the same magnitude as is typical for sintered LSGM pellets. The experimental results have demonstrated that the plasma-spraying process has a great potential for the integrated fabrication of medium-temperature SOFC units. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.  相似文献   
49.
为了提高噪音环境下城市音频分类系统的鲁棒性,提出了一种双特征2阶密集卷积神经网络(D-2-DenseNet)噪音鲁棒的城市音频分类模型.首先介绍了噪音添加和噪音鲁棒处理,阐述了一种双特征互补偿的算法;然后结合2阶密集卷积神经网络与自适应机制提出了一种噪音鲁棒音频分类模型:双特征2阶密集卷积神经网络.模型采用双特征互补偿自适应算法,可在特征提取与模型训练中更有针对性地提取有效音频信息,降低噪音干扰,以提高噪音鲁棒性.最后,基于Dcase2016数据集开展噪音环境下城市音频分类测试.实验结果表明,模型分类准确率分别可达77.12%、75.52%,与基线模型相比,平均分类准确率分别提高了8.51%和10.38%,验证了模型良好的噪音鲁棒性.  相似文献   
50.
以现代学徒制为载体,加快构建校企双元育人机制是我国职业教育改革的新要求。基于现代学徒制的发展趋势,保障校企双元育人的有效落实,需要将校企共建命运共同体、共建高水平专业和课程标准、共建育人队伍、共建共享教学资源作为双元育人机制的建设主线。在此基础上提出注重顶层设计、坚持立德树人目标、完善职教师资培养体系、打造高水平实训基地等校企双元育人的实施路径。  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