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   1408篇
  免费   61篇
  国内免费   3篇
电工技术   13篇
综合类   1篇
化学工业   407篇
金属工艺   50篇
机械仪表   41篇
建筑科学   5篇
矿业工程   2篇
能源动力   78篇
轻工业   113篇
水利工程   5篇
石油天然气   10篇
无线电   118篇
一般工业技术   410篇
冶金工业   111篇
原子能技术   8篇
自动化技术   100篇
  2024年   5篇
  2023年   17篇
  2022年   39篇
  2021年   49篇
  2020年   45篇
  2019年   30篇
  2018年   53篇
  2017年   54篇
  2016年   44篇
  2015年   43篇
  2014年   52篇
  2013年   110篇
  2012年   90篇
  2011年   108篇
  2010年   60篇
  2009年   66篇
  2008年   57篇
  2007年   67篇
  2006年   33篇
  2005年   37篇
  2004年   21篇
  2003年   29篇
  2002年   31篇
  2001年   14篇
  2000年   17篇
  1999年   18篇
  1998年   27篇
  1997年   23篇
  1996年   17篇
  1995年   21篇
  1994年   17篇
  1993年   18篇
  1992年   14篇
  1991年   8篇
  1990年   9篇
  1989年   15篇
  1988年   14篇
  1987年   13篇
  1986年   4篇
  1985年   5篇
  1984年   9篇
  1983年   8篇
  1982年   7篇
  1981年   12篇
  1980年   13篇
  1979年   3篇
  1978年   5篇
  1977年   3篇
  1976年   12篇
  1971年   2篇
排序方式: 共有1472条查询结果,搜索用时 15 毫秒
1.
Wireless Personal Communications - The rapid development of Information and Communication Technology and the growing number of devices connected to the Internet make the Internet of Things (IoT) as...  相似文献   
2.
Hydrothermally prepared zinc oxide nanorods are sulphonated (S–ZnO NR) and incorporated into 15% Sulphonated Poly (1,4-Phenylene Ether Ether Sulfone) (SPEES) to improve the hydrophilicity, water uptake and ion transfer capacity. Water uptake and ion transfer capacity increased to 34.6 ± 0.6% and 2.0 ± 0.05 meq g?1 from 29.8 ± 0.3% and 1.4 ± 0.04 meq g?1 by adding 7.5 wt% S–ZnO NR to SPEES. Morphological studies show the prepared S–ZnO NR is well dispersed in the polymer matrix. SPEES +7.5 wt% S–ZnO NR membrane exhibits optimum performance after three-weeks of continual operation in a fabricated microbial fuel cell (MFC) to produce a maximum power density of 142 ± 1.2 mW m?2 with a reduced biofilm compared to plain SPEES (59 ± 0.8 mW m?2), unsulphonated filler incorporated SPEES (SPEES + 7.5 wt% ZnO, 68 ± 1.1 mW m?2) and Nafion (130 ± 1.5 mW m?2) thereby suggesting its suitability as a sustainable and improved cation exchange membrane (CEM) for MFCs.  相似文献   
3.
Hydrogen fuel is a promising alternative to fossil fuels because of its energy content, clean nature, and fuel efficiency. However, it is not readily available. Most current producion processes are very energy intensive and emit carbon dioxide. Therefore, this article reviews technological options for hydrogen production that are eco-friendly and generate clean hydrogen fuel. Biological methods, such different fermentation processes and photolysis are discussed together with the required substrates and the process efficiency.  相似文献   
4.
5.
Jatropha oil is a promising nonedible feedstock for producing renewable diesel. In this work, the hydrotreatment processing of jatropha oil was investigated. Instead of using conventional alumina-supported Co–Mo, Ni–Mo, and Ni–W catalysts that need sulfidation pretreatment, noble metals such as Pd and Ru were chosen. Trials were performed in an isothermal trickle-bed reactor and the reaction conditions were as follows: temperature 603–663?K, weight hourly space velocity (WHSV) 1 to 4/h, pressure 1.5–3?MPa, and H2/oil ratio 200–800 (v/v). Yield of n-C15 to n-C18 hydrocarbons was maximized (70.3 and 43.8% for Pd/Al2O3 and Ru/Al2O3, respectively) at the following conditions: T?=?663 K, WHSV?=?2/h, P?=?3?MPa, and H2/oil ratio?=?600 (v/v). Since Ru favored cracking reactions to a larger extent than Pd, the yield of C15 to C18 hydrocarbons over Ru/Al2O3 was lowered. Using simple first-order plots for oil conversion, activation energies for the hydrotreating process over Pd/Al2O3 and Ru/Al2O3 were found and they were equal to 109 and 121?kJ/mol, correspondingly.  相似文献   
6.
7.
The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO3, RbVO3 and CsVO3, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric state and depends upon sodium concentration.  相似文献   
8.
Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations.  相似文献   
9.
10.
The effect on the interfacial tension of the water toluene system has been studied at 25 °C in the presence of four phase-transfer catalysts i.e. tricaprylmethyl ammonium chloride, hexadecyltrimethyl ammonium chloride, hex-adecytrimethyl ammonium bromide and hexadecyltributyl phosphonium bromide. The interfacial tension of aqueous phenol/resorcinol-toluene in the presence and absence of tricaprylmethyl ammonium chloride has also been reported. Attempt has been made to elucidate the change in volumetric rate of extraction with different catalysts for two phase reactions, on the basis of interfacial tension.  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