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   238915篇
  免费   15133篇
  国内免费   7540篇
电工技术   10983篇
技术理论   9篇
综合类   13055篇
化学工业   37416篇
金属工艺   13416篇
机械仪表   12850篇
建筑科学   14951篇
矿业工程   5140篇
能源动力   5693篇
轻工业   14619篇
水利工程   4149篇
石油天然气   9607篇
武器工业   1351篇
无线电   27075篇
一般工业技术   33986篇
冶金工业   9578篇
原子能技术   2326篇
自动化技术   45384篇
  2024年   629篇
  2023年   2622篇
  2022年   4824篇
  2021年   6856篇
  2020年   5223篇
  2019年   4316篇
  2018年   18477篇
  2017年   18112篇
  2016年   14099篇
  2015年   6980篇
  2014年   8124篇
  2013年   9383篇
  2012年   13259篇
  2011年   20018篇
  2010年   17650篇
  2009年   14549篇
  2008年   15577篇
  2007年   16042篇
  2006年   8765篇
  2005年   8666篇
  2004年   6204篇
  2003年   5703篇
  2002年   4978篇
  2001年   4130篇
  2000年   4074篇
  1999年   3980篇
  1998年   3180篇
  1997年   2744篇
  1996年   2561篇
  1995年   2104篇
  1994年   1734篇
  1993年   1251篇
  1992年   1047篇
  1991年   787篇
  1990年   566篇
  1989年   505篇
  1988年   410篇
  1987年   270篇
  1986年   173篇
  1985年   101篇
  1984年   71篇
  1983年   51篇
  1982年   72篇
  1981年   46篇
  1968年   43篇
  1966年   42篇
  1965年   47篇
  1959年   45篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
81.
Ji  Chengang  Yang  Chenying  Shen  Weidong  Lee  Kyu-Tae  Zhang  Yueguang  Liu  Xu  Guo  L. Jay 《Nano Research》2019,12(3):543-548

We present a new scheme for visibly-opaque but near-infrared-transmitting filters involving 7 layers based on one-dimensional ternary photonic crystals, with capabilities in reaching nearly 100% transmission efficiency in the near-infrared region. Different decorative reflection colors can be created by adding additional three layers while maintaining the near-infrared transmission performance. In addition, our proposed structural colors show great angular insensitivity up to ±60° for both transverse electric and transverse magnetic polarizations, which are highly desired in various fields. The facile strategy described here involves a simple deposition method for the fabrication, thereby having great potential in diverse applications such as image sensors, anti-counterfeit tag, and optical measurement systems.

  相似文献   
82.
In this paper, we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme, which was found insecure under two kinds of attacks, fake entangled particles attack and disentanglement attack. Then, by changing the party of the preparation of cluster states and using unitary operations, we present an improved protocol which can avoid these two kinds of attacks. Moreover, the protocol is proposed using the three-qubit partially entangled set of states. It is more efficient by only using three particles rather than four or even more to transmit one bit secret information. Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource, it makes this protocol more convenient from an applied point of view.  相似文献   
83.
The design of an efficient non-noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo2C/CeO2 catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low-valent Mo species, as well as high concentration of Ce3+ and surface oxygen species. The presence of Mo2C and CeO2 overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO2 catalyst prepared without carbonization, the Mo2C/CeO2 catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo-based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis.  相似文献   
84.
设计了Matlab语言程序,并用于"乙酸乙酯皂化反应速率常数测定"的物理化学实验的数据处理与图形绘制,处理结果与所作的图形均符合实验要求。与手工作图相比,具有简洁、快捷与直观等特点,而且可避免人为因素的误差。  相似文献   
85.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms.  相似文献   
86.
对码头吊桥液压设备进行了设计,包括液压缸的结构、液压动力站结构、管路安装、现地电气控制以及液压原理,该设计在轮渡码头方面得到了广泛地应用。  相似文献   
87.
88.
89.
Journal of Mechanical Science and Technology - To coordinate the contradiction between artillery launching performance indexes under parameter uncertainty, this paper proposes an artillery...  相似文献   
90.
徐瑞岗 《机械管理开发》2021,36(2):51-52,66
针对顶梁部件焊接过程中的变形,采用ANSYS有限元分析的方式对焊接过程中的温度场及变形进行仿真分析,结果显示,温度应力及残余应力的影响是产生变形的主要原因.针对顶梁的焊接变形,提出了相应的控制措施,以减小顶梁的焊接变形,提高液压支架的生产效率及性能,为煤矿的开采提供有效的理论支撑.  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