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   105749篇
  免费   10864篇
  国内免费   5668篇
电工技术   3230篇
综合类   7475篇
化学工业   25637篇
金属工艺   8296篇
机械仪表   3872篇
建筑科学   10488篇
矿业工程   1783篇
能源动力   2450篇
轻工业   10105篇
水利工程   1069篇
石油天然气   1526篇
武器工业   1193篇
无线电   12786篇
一般工业技术   25759篇
冶金工业   3454篇
原子能技术   554篇
自动化技术   2604篇
  2024年   519篇
  2023年   1798篇
  2022年   2654篇
  2021年   3403篇
  2020年   3753篇
  2019年   3251篇
  2018年   3061篇
  2017年   3893篇
  2016年   3846篇
  2015年   3957篇
  2014年   5507篇
  2013年   5921篇
  2012年   7140篇
  2011年   7819篇
  2010年   6051篇
  2009年   6483篇
  2008年   5630篇
  2007年   7356篇
  2006年   6869篇
  2005年   5982篇
  2004年   4792篇
  2003年   4177篇
  2002年   3565篇
  2001年   2922篇
  2000年   2475篇
  1999年   1905篇
  1998年   1537篇
  1997年   1226篇
  1996年   982篇
  1995年   820篇
  1994年   737篇
  1993年   596篇
  1992年   431篇
  1991年   376篇
  1990年   254篇
  1989年   182篇
  1988年   93篇
  1987年   63篇
  1986年   37篇
  1985年   32篇
  1984年   47篇
  1983年   23篇
  1982年   33篇
  1981年   7篇
  1980年   29篇
  1979年   11篇
  1977年   3篇
  1976年   3篇
  1955年   4篇
  1951年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
李乐霞  贺岭 《火工品》2002,(1):12-14
介绍了激光起爆与点火系统中光纤连接器的原理、种类、技术特性及损耗,并对激光起爆与点火系统中光纤连接器的研制动向进行了概括,最后得出一些结论。  相似文献   
92.
气敏材料的研究进展   总被引:7,自引:0,他引:7  
从气敏材料种类,制备方法,改善气敏材料缺陷的手段等方面介绍了气敏材料的研究进展,论述了气敏材料研究中的新动向,展望了它的未来发展。  相似文献   
93.
A one–dimensional, transient thermal degradation heat transfer model for the response of composite materials when exposed to fire is presented. The model can handle layers of different materials. Material properties are functions of temperature. The reaction can be specified using Arrhenius‐type parameters or by inputting a density–temperature relationship determined by any experimental technique such as thermogravimetric analysis. The model is validated against the experimental data presented in Boyer's 1984 dissertation. Overall, the model provides excellent agreement with the experimental data. It is shown that very little difference is found between results arrived at by Arrhenius kinetics and results obtained by specifying the easier to measure density–temperature relationship. From this it is concluded that this technique is a viable alternative to Arrhenius‐type models. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
94.
An attempt is made to study the Einstein relation for the diffusivity–mobility ratio (DMR) in quantum wells (QWs) and quantum well wires (QWWs) of tetragonal compounds on the basis of a newly formulated electron energy spectrum taking into account the combined influences of the anisotropies in effective electron mass, the spin–orbit splitting, and the presence of crystal field splitting, respectively. The results for quantum-confined III–V compounds form a special case of our generalized analysis. The DMR has also been studied for QWs and QWWs of II–VI and IV–VI materials. Taking QWs and QWWs of CdGeAs2, InAs, CdS and PbSe as examples, it was found that the DMR increases with increasing carrier statistics and decreasing film thickness respectively in various oscillatory manners emphasizing the influence of dimensional quantizations and the energy band constants in different cases. An experimental method of determining the DMR in nanostructures with arbitrary dispersion laws has also been suggested and the present simplified analysis is in agreement with the suggested relationship. The well-known results for nanostructures with parabolic energy bands have also been obtained as special cases from this generalized analysis under certain limiting conditions.  相似文献   
95.
The present work summarizes the recent activities of our laboratory in the field of solar-aided hydrogen production with structured monolithic solar reactors. This reactor concept, “transferred” from the well-known automobile exhaust catalytic after-treatment systems, employs ceramic supports optimized to absorb effectively solar radiation and develop sufficiently high temperatures, that are coated with active materials capable to perform/catalyze a variety of “solar-aided” reactions for the production of hydrogen such as water splitting or natural gas reforming. Our work evolves in an integrated approach starting from the synthesis of active powders tailored to particular hydrogen production reactions, their deposition upon porous absorbers, testing of relevant properties of merit such as thermomechanical stability and hydrogen yield and finally to the design, operation simulation and performance optimization of structured monolithic solar hydrogen production reactors. This approach, among other things, has culminated to the world's first closed, solar-thermochemical cycle in operation that is capable of continuous hydrogen production employing entirely renewable and abundant energy sources and raw materials – solar energy and water, respectively – without any CO2 emissions and holds, thus, a significant potential for large-scale, emissions-free hydrogen production, particularly for regions of the world that lack indigenous resources but are endowed with ample solar energy.  相似文献   
96.
97.
98.
广东电力特种光缆存在的问题及解决方法   总被引:1,自引:1,他引:0  
分析了广东电力系统特种光缆应用在工程建设、运行维护等方面出现的问题,以及对电网保护等业务的影响,提出了解决办法和方案,特别是从电网安全运行角度去理解ADSS电腐蚀问题,以及近期广电集团的具体措施。  相似文献   
99.
Fresh niobium hydroxide was first precipitated from NbF5 solution using an aqueous ammonium hydroxide under basic conditions. Then a simple procedure of mixing lithium and niobium hydroxides together and heating at a low temperature (400 °C) produced pure ultrafine single phase LiNbO3 (LN). In the literature, this is the lowest temperature so far reported on the formation of LN. The phase content and lattice parameters are determined by X-ray diffraction (XRD). The average particle size and morphology were studied by transmission electron microscopy (TEM).  相似文献   
100.
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