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   340262篇
  免费   25673篇
  国内免费   13042篇
电工技术   18582篇
技术理论   57篇
综合类   20692篇
化学工业   57516篇
金属工艺   18939篇
机械仪表   21892篇
建筑科学   26357篇
矿业工程   11064篇
能源动力   10017篇
轻工业   19839篇
水利工程   5464篇
石油天然气   23348篇
武器工业   2695篇
无线电   37490篇
一般工业技术   40515篇
冶金工业   18353篇
原子能技术   3390篇
自动化技术   42767篇
  2024年   1026篇
  2023年   5104篇
  2022年   8330篇
  2021年   12728篇
  2020年   9944篇
  2019年   8042篇
  2018年   9313篇
  2017年   10589篇
  2016年   9475篇
  2015年   12666篇
  2014年   16417篇
  2013年   19869篇
  2012年   21025篇
  2011年   23262篇
  2010年   19927篇
  2009年   19072篇
  2008年   18660篇
  2007年   18020篇
  2006年   18877篇
  2005年   16671篇
  2004年   10715篇
  2003年   9480篇
  2002年   8509篇
  2001年   7814篇
  2000年   8277篇
  1999年   9840篇
  1998年   8269篇
  1997年   6850篇
  1996年   6432篇
  1995年   5385篇
  1994年   4403篇
  1993年   3105篇
  1992年   2504篇
  1991年   1962篇
  1990年   1508篇
  1989年   1235篇
  1988年   1009篇
  1987年   649篇
  1986年   517篇
  1985年   326篇
  1984年   229篇
  1983年   191篇
  1982年   194篇
  1981年   126篇
  1980年   126篇
  1979年   69篇
  1978年   36篇
  1977年   39篇
  1976年   56篇
  1975年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
为了综合回收现有南非铜尾矿中的有价铁元素,在试验室对该铜尾矿进行了回收铁的可选性试验研究。研究结果表明:该铜尾矿铁品位为59.36%,磁性铁含量为57.99%,当原矿磨矿细度为-0.074 mm 58%时,经两次磁选后,可获得产率为88.95%,铁品位为65.69%,铁回收率为98.43%的铁精矿。  相似文献   
83.
84.
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   
85.
86.
In this article, an adaptive fuzzy output feedback control method is presented for nonlinear time-delay systems with time-varying full state constraints and input saturation. To overcome the problem of time-varying constraints, the integral barrier Lyapunov functions (IBLFs) integrating with dynamic surface control (DSC) are applied for the first time to keep the state from violating constraints. The effects of unknown time delays can be removed by using designed Lyapunov-Krasovskii functions (LKFs). An auxiliary design system is introduced to solve the problem of input saturation. The unknown nonlinear functions are approximated by the fuzzy logic systems (FLS), and the unmeasured states are estimated by a designed fuzzy observer. The novel controller can guarantee that all signals remain semiglobally uniformly ultimately bounded and satisfactory tracking performance is achieved. Finally, two simulation examples illustrate the effectiveness of the presented control methods.  相似文献   
87.
Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic–inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc.  相似文献   
88.
徐浩  吴炜  陈浩  王子康 《电子测试》2020,(10):117-118,27
无人机技术目前的快速发展使得我们国家输电线路自身的巡检能力得到了持续的提升,基于此本文在对无人机技术给予认识的情况下,在了解了输电线路巡检过程中的使用优势之后,还总结了无人机技术在当前我国线路巡检过程中的应用路径以及应用方法;之后使用案例分析的方式分析了无人机技术在当前输电线路巡检过程中的应用方法。  相似文献   
89.
90.
Wang  Lijing  Chen  Jiangzhuo  Marathe  Achla 《World Wide Web》2019,22(6):2997-3020
World Wide Web - Infectious diseases such as Influenza and Ebola pose a serious threat to everyone but certain demographics and cohorts face a higher risk of infection than others. This research...  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