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   404276篇
  免费   33670篇
  国内免费   19949篇
电工技术   25995篇
技术理论   45篇
综合类   29953篇
化学工业   64837篇
金属工艺   24201篇
机械仪表   25693篇
建筑科学   31296篇
矿业工程   13118篇
能源动力   10821篇
轻工业   30575篇
水利工程   8333篇
石油天然气   24822篇
武器工业   3255篇
无线电   44031篇
一般工业技术   43293篇
冶金工业   20309篇
原子能技术   4448篇
自动化技术   52870篇
  2024年   1773篇
  2023年   6408篇
  2022年   11761篇
  2021年   16243篇
  2020年   12133篇
  2019年   9688篇
  2018年   10989篇
  2017年   12468篇
  2016年   11471篇
  2015年   15895篇
  2014年   19952篇
  2013年   24020篇
  2012年   26501篇
  2011年   29160篇
  2010年   25984篇
  2009年   24792篇
  2008年   24584篇
  2007年   23545篇
  2006年   23397篇
  2005年   20313篇
  2004年   13971篇
  2003年   12033篇
  2002年   11158篇
  2001年   10042篇
  2000年   9751篇
  1999年   9753篇
  1998年   7295篇
  1997年   6269篇
  1996年   5889篇
  1995年   4855篇
  1994年   3950篇
  1993年   2682篇
  1992年   2114篇
  1991年   1612篇
  1990年   1290篇
  1989年   1024篇
  1988年   864篇
  1987年   575篇
  1986年   436篇
  1985年   274篇
  1984年   216篇
  1983年   174篇
  1982年   133篇
  1981年   89篇
  1980年   114篇
  1979年   52篇
  1978年   19篇
  1977年   27篇
  1976年   31篇
  1959年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
结合兰州市的水泥标准稠度用水量方法测定 (代用法 )的实例 ,分析代用法测定标准稠度用水量的缺点 ,并对此方法提出了一些改进措施  相似文献   
22.
风管摩擦阻力的直接计算方法   总被引:2,自引:1,他引:1  
彭小勇  李惠敏 《暖通空调》2004,34(12):76-77,80
提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明,用该方法计算,计算结果比采用常用工程设计方法更为准确,为应用计算机进行风道设计提供了直接、简便的方法。  相似文献   
23.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection.  相似文献   
24.
偏高岭土的研究现状及展望   总被引:9,自引:0,他引:9  
简要介绍了偏高岭土的反应机理和在国内外的研究现状。同时对偏高岭土的研究进行了展望 ,提出因麦特林水泥原料丰富 ,污染小 ,加工简单 ,性能优越 ,其应用前景广阔 ,应对其加强研究。  相似文献   
25.
A new type of piezoelectric linear motor incorporating a traveling wave has been developed. The linear motor is comprised of a stator and a carriage. The stator design, which consists of a meander-line structure and gear teeth mounted on the meander-line structure, is the focus of this article. The meander-line structure is constructed with bimorph actuators arranged in a line. These actuators are driven by two phased sets of alternating current (ac) in order to generate a traveling wave. The traveling wave is transferred to the gear teeth, by which the carriage is driven. Modeling of the stator is derived by use of a strain energy method. The performance of various materials is evaluated by analytical and experimental methods. The analytical and the experimental results are quite approximate. Modal analysis is investigated using ANSYS. Appropriate modes associated with ultrasonic levels of resonant frequency are selected to obtain desired motion and to enhance the output performance. Surface speed for various applied input voltage are studied and indicate a nearly linear relationship. The stator in combination with the carriage makes up the linear motor.  相似文献   
26.
The term ‘object-oriented database’ has been used to refer to different characteristics and mechanisms supported by semantic databases and (behaviorally) object-oriented ones. While this indicates the current confusion due to the lack of a common model, it also suggests the potential desirability of combining these two kinds of modeling facilities into the same nutshell. This paper summarizes from these two paradigms the features common to both, the features influenced/adopted by each other, and the features which are presented in one paradigm but missing from the other. After a brief analysis and discussion of these features, we conclude this paper by proposing our major theme: a complete object data model should take the union of the facilities offered by these two kinds of models.  相似文献   
27.
李海峰 《河北冶金》1997,(3):43-47,62
主要介绍了承钢棒材连轧线计算机控制系统,其中包括了系统的硬件配置,控制功能及控制说明。  相似文献   
28.
报道了4,4′-硫代双[2-(1,1-二甲基乙基)-5一甲基苯酚]的合成方法及结构鉴定。  相似文献   
29.
30.
Two coupled-mode theories based on individual waveguide modes and compound system modes, respectively, are briefly reviewed with proper modification and new comments. The relation between these two theories is built and it is found that one theory is actually an efficient approximation of the other. Also, the reason why the results obtained with the first more accurate than those obtained with the second is found. The constraint on both approaches is shown  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