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   23740篇
  免费   2164篇
  国内免费   1141篇
电工技术   1364篇
技术理论   2篇
综合类   1546篇
化学工业   3931篇
金属工艺   1443篇
机械仪表   1535篇
建筑科学   2162篇
矿业工程   855篇
能源动力   639篇
轻工业   1302篇
水利工程   436篇
石油天然气   1697篇
武器工业   161篇
无线电   2416篇
一般工业技术   2968篇
冶金工业   1122篇
原子能技术   275篇
自动化技术   3191篇
  2024年   53篇
  2023年   448篇
  2022年   641篇
  2021年   1014篇
  2020年   834篇
  2019年   696篇
  2018年   779篇
  2017年   870篇
  2016年   733篇
  2015年   977篇
  2014年   1274篇
  2013年   1423篇
  2012年   1614篇
  2011年   1674篇
  2010年   1455篇
  2009年   1337篇
  2008年   1278篇
  2007年   1225篇
  2006年   1317篇
  2005年   1208篇
  2004年   723篇
  2003年   631篇
  2002年   563篇
  2001年   531篇
  2000年   490篇
  1999年   644篇
  1998年   503篇
  1997年   420篇
  1996年   368篇
  1995年   330篇
  1994年   252篇
  1993年   148篇
  1992年   137篇
  1991年   119篇
  1990年   91篇
  1989年   73篇
  1988年   53篇
  1987年   33篇
  1986年   31篇
  1985年   10篇
  1984年   10篇
  1983年   6篇
  1982年   10篇
  1981年   5篇
  1980年   4篇
  1979年   6篇
  1978年   2篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 295 毫秒
1.
如何在互联网时代打造一个信息化的管理模式,已经成为广大学校图书管理发展过程中亟待处理的问题。文章就互联网时代下的高职图书管理信息化建设进行了详细探讨,以期能够给广大同仁提供一些借鉴参考,共同为图书管理工作的现代化改革和发展贡献力量。  相似文献   
2.
3.
Developing the thermal stability of metal-based ceramic composites or their films has always been challenging and bottlenecks for the utilization of energy. In this paper, the novel mesh-like functional Al doped-MoO3 nanocomposite film with even distribution and high purity was firstly fabricated by the high-efficiency electrophoretic deposition and surface modification. The optimal suspension turned out to be the mixture of isopropanol and the additives of polyethyleneimine and benzoic acid. The microtopography, crystalline structure, environmental resistance and thermal stability were analyzed by field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX), X-ray diffractometer (XRD), exposure and droplet-impacting test, DSC analysis and ignition test, respectively. The water contact angle and sliding angle of product can reach ~170° and <1°, indicating the excellent anti-wetting property. In addition, the high heat-release (~3180 J/g) of product all kept almost unchangeable after six months exposure experiments, demonstrating the outstanding thermostability. The exquisite design idea here can perfectly match microelectromechanical system (MEMS), providing the valuable reference for fabricating other metal-based high-energy composites with long lifespan for real industrial applications.  相似文献   
4.
Various products, including foods and pharmaceuticals, are sensitive to temperature fluctuations. Thus, temperature monitoring during production, transportation, and storage is critical. Facile indicators are required to monitor temperature conditions via color changes in real time. This study aimed to prepare and apply thiol-functionalized covalent organic frameworks (COFs) as a novel indicator for monitoring thermal history and temperature abuse. The COFs underwent obvious color changes from bright yellow to purple after exposure to different temperatures for varying durations. The reaction kinetics are analyzed under isothermal conditions, which reveal that the order of reaction rates is k−20°C < k4°C < k20°C < k35°C < k55°C. The activation energy (Ea) of the COFs is calculated using the Arrhenius equation as 50.71 kJ moL−1. The COFs are capable of sensitive color changes and offer a broad temperature tracking range, thereby demonstrating their application potential for the monitoring of temperature and time exposure history during production, transportation, and storage. This excellent performance thermal history indicator also shows promise for expanding the application field of COFs.  相似文献   
5.
6.
In the future, hydrogen will be an important energy carrier and industrial raw material. Catalytic steam reforming of bio-oils is a promising and economically viable technology for hydrogen production. However, during the reforming process, the catalysts are rapidly deactivated due to coke formation and sintering. Thus, maintaining the activity and stability of catalysts is the key issue in this process. Optimized operation conditions could extend the catalyst lifetime by affecting the coke morphology or promoting coke gasification. This article summarizes the recent developments in the field of catalytic steam reforming of bio-oils, focusing on the operation conditions, the properties of the catalysts, and the effects of the catalyst supports. The expected insights into the catalytic steam reforming of bio-oils will provide further guidance for hydrogen production from bio-oils.  相似文献   
7.
ABSTRACT

In the lower chamber of pressurized water reactor (PWR), the flow distribution device is the core module to distribute coolant into the core. It has complex structure and numerous design parameters. Therefore, it has important theoretical and practical significance to optimize the device. The mesh independence verification, turbulence model selection, and data processing all can influence the numerical simulation results of the lower chamber, in order to research the influence, a numerical simulation method based on the original model of CNP1000 reactor lower chamber is proposed in this paper. In the method, an optimization design method of flow distribution device is established based on surrogate model. The main design variables and optimization objectives are determined based on the device’s structure and function characteristics. And then it respectively adopts Kriging algorithm and multi-objective genetic algorithm to establish a surrogate model of flow distribution device and optimize it globally. Finally, the optimal design variables are obtained. Compared with the device’s performance before optimization, the after optimization has smaller total pressure loss and more uniform flow. The effectiveness and practicability of proposed optimization design method can be verified.  相似文献   
8.
9.
Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being obtained.Herein Fe3C/C and Fe2N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH4/H2and pure NH3,respectively.By acid leaching of Fe2N/C sample,only single sites of FeN4species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN4in ORR.A correlation was conducted between the concentration of FeN4in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin FeN4 species as highly active sites for the ORR.  相似文献   
10.
为实现固体废弃物的高值化利用,从微晶泡沫玻璃的制备机理、工艺流程及温度制度等方面分析了工业固体废弃物制备微晶泡沫玻璃的可行性,重点论述了金属矿尾矿、赤泥、高炉矿渣、煤矸石、粉煤灰等固体废弃物制备微晶泡沫玻璃的国内外研究进展,并对微晶泡沫玻璃的研究和发展趋势进行了展望。  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