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   389218篇
  免费   31854篇
  国内免费   19145篇
电工技术   25029篇
技术理论   64篇
综合类   47160篇
化学工业   46357篇
金属工艺   12221篇
机械仪表   18133篇
建筑科学   57860篇
矿业工程   23103篇
能源动力   14451篇
轻工业   23295篇
水利工程   31920篇
石油天然气   23400篇
武器工业   3233篇
无线电   22185篇
一般工业技术   25349篇
冶金工业   19576篇
原子能技术   5432篇
自动化技术   41449篇
  2024年   1098篇
  2023年   3782篇
  2022年   7844篇
  2021年   9525篇
  2020年   10058篇
  2019年   8270篇
  2018年   7779篇
  2017年   9629篇
  2016年   11348篇
  2015年   12387篇
  2014年   23212篇
  2013年   21208篇
  2012年   27502篇
  2011年   28647篇
  2010年   22257篇
  2009年   22877篇
  2008年   21286篇
  2007年   27472篇
  2006年   25729篇
  2005年   22502篇
  2004年   18718篇
  2003年   16980篇
  2002年   14062篇
  2001年   11708篇
  2000年   9784篇
  1999年   7856篇
  1998年   5857篇
  1997年   5104篇
  1996年   4508篇
  1995年   3893篇
  1994年   3334篇
  1993年   2533篇
  1992年   2181篇
  1991年   1632篇
  1990年   1398篇
  1989年   1253篇
  1988年   982篇
  1987年   693篇
  1986年   537篇
  1985年   487篇
  1984年   436篇
  1983年   314篇
  1982年   255篇
  1981年   194篇
  1980年   157篇
  1979年   130篇
  1978年   69篇
  1977年   81篇
  1976年   61篇
  1975年   59篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
This paper presents a fast distance relay for series compensated transmission lines based on the R–L differential-equation algorithm using the theory of equal transfer process of transmission lines. The measuring distances based on the proposed algorithm can fast approach the actual value of fault distance when a fault occurs in front of the series capacitor. When a fault occurs behind of the series capacitor, the fault loop, including the series capacitor, does not match the R–L transmission line model, so the measuring distances fluctuate severely. Based on this, the relative position of the fault with respect to the series capacitor can be judged effectively according to the fluctuation range of the measuring distances, and the accurate fault location can be obtained fast. A variety of PSCAD/EMTDC simulation tests show that the new relay has fast operating speed and high accuracy when applied to the long series compensated transmission lines.  相似文献   
73.
Ni2P nanoparticles and CdS nanorods were grew together on a mesoporous g-C3N4 through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni2P composite displays a high H2 evolution rate with 2905.86 μmol g?1 h?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni2P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni2P. Meanwhile, Ni2P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni2P composite exerts good stability in 12-h cycles.  相似文献   
74.
来水利 《云南化工》2019,(7):180-181
有机化学是化学化工、材料、制药、食品等多个专业的基础课程,在其教学过程中,教师可以根据课程的内容及特点,分别以有机化学发展中的重大历史事件、有机化物的性质及有机反应为引导,开展学生的思想品德教育,加强课程思政建设。  相似文献   
75.
76.
With the ambition of solving the challenges of the shortage of fossil fuels and their associated environmental pollution, visible-light-driven splitting of water into hydrogen and oxygen using semiconductor photocatalysts has emerged as a promising technology to provide environmentally friendly energy vectors. Among the current library of developed photocatalysts, organic conjugated polymers present unique advantages of sufficient light-absorption efficiency, excellent stability, tunable electronic properties, and economic applicability. As a class of rising photocatalysts, organic conjugated polymers offer high flexibility in tuning the framework of the backbone and porosity to fulfill the requirements for photocatalytic applications. In the past decade, significant progress has been made in visible-light-driven water splitting employing organic conjugated polymers. The recent development of the structural design principles of organic conjugated polymers (including linear, crosslinked, and supramolecular self-assembled polymers) toward efficient photocatalytic hydrogen evolution, oxygen evolution, and overall water splitting is described, thus providing a comprehensive reference for the field. Finally, current challenges and perspectives are also discussed.  相似文献   
77.
以电信用户入网协议为切入点,电信用户的携号转网行为应受到《合同法》《消费者权益保护法》等私法规范的保护与限制。该行为引起的格式条款解释、合同终止、违约责任、损失赔偿等问题,不能仅靠《电信条例》等公法规范来调整。应当积极引导广大消费者用户以私法领域相关规定为依据,转变争议解决思维,拓宽纠纷处理途径,合理选择维权手段,以保护自身合法民事权益,与行业监管部门共同推动电信行业有序发展。  相似文献   
78.
In this paper, a new inverse identification method of constitutive parameters is developed from full kinematic and thermal field measurements. It consists in reconstructing the heat source field from two different approaches by using the heat diffusion equation. The first one requires the temperature field measurement and the value of the thermophysical parameters. The second one is based on the kinematic field measurement and the choice of a thermo-hyperelastic model that contains the parameters to be identified. The identification is carried out at the local scale, ie, at any point of the heat source field, without using the boundary conditions. In the present work, the method is applied to the challenging case of hyperelasticity from a heterogeneous test. Due to large deformations undergone by the rubber specimen tested, a motion compensation technique is developed to plot the kinematic and the thermal fields at the same points before reconstructing the heterogeneous heat source field. In the present case, the constitutive parameter of the Neo-Hookean model has been identified, and its distribution has been characterized with respect to the strain state at the surface of a cross-shaped specimen.  相似文献   
79.
80.
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