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   176600篇
  免费   16464篇
  国内免费   9493篇
电工技术   13930篇
技术理论   8篇
综合类   18057篇
化学工业   17567篇
金属工艺   7203篇
机械仪表   15836篇
建筑科学   20388篇
矿业工程   6758篇
能源动力   7862篇
轻工业   13562篇
水利工程   7514篇
石油天然气   8320篇
武器工业   2007篇
无线电   10188篇
一般工业技术   17331篇
冶金工业   7046篇
原子能技术   2531篇
自动化技术   26449篇
  2024年   731篇
  2023年   2169篇
  2022年   4416篇
  2021年   5181篇
  2020年   5437篇
  2019年   4557篇
  2018年   4490篇
  2017年   5467篇
  2016年   6615篇
  2015年   6950篇
  2014年   11320篇
  2013年   11373篇
  2012年   13143篇
  2011年   14464篇
  2010年   10372篇
  2009年   10547篇
  2008年   9915篇
  2007年   11875篇
  2006年   10307篇
  2005年   8657篇
  2004年   7326篇
  2003年   6244篇
  2002年   5062篇
  2001年   4157篇
  2000年   3550篇
  1999年   2969篇
  1998年   2544篇
  1997年   2143篇
  1996年   1764篇
  1995年   1456篇
  1994年   1316篇
  1993年   977篇
  1992年   902篇
  1991年   664篇
  1990年   558篇
  1989年   476篇
  1988年   397篇
  1987年   275篇
  1986年   237篇
  1985年   218篇
  1984年   252篇
  1983年   240篇
  1982年   197篇
  1981年   97篇
  1980年   95篇
  1979年   65篇
  1978年   53篇
  1977年   46篇
  1976年   44篇
  1959年   30篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
This paper discusses a new application of data mining, quantifying the importance of responding to trigger events with reactive contacts. Trigger events happen during a customer’s lifecycle and indicate some change in the relationship with the company. If detected early, the company can respond to the problem and retain the customer; otherwise the customer may switch to another company. It is usually easy to identify many potential trigger events. What is needed is a way of prioritizing which events demand interventions. We conceptualize the trigger event problem and show how survival analysis can be used to quantify the importance of addressing various trigger events. The method is illustrated on four real data sets from different industries and countries.  相似文献   
32.
This paper describes an effective analysis of magnetic shielding based on homogenization. The analyses become time‐consuming if the problems include the magnetic substances having fine structure. The homogenization of the structure makes it possible to analyze effectively the magnetic fields. The authors introduce a method to estimate the effective permeability of the homogenized substance. This method can be applied to any periodic structure made of magnetic substance. The magnetic shielding effects by the structures against direct‐current (DC) fields generated by electric railways are analyzed by using the present method. As a result, it is found that the overhead way and the protective fence near the railway work as a magnetic shield, whose effects can be improved by appropriate arrangement of those constructions. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 7–15, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20310  相似文献   
33.
34.
用宏观断口分析、化学检验、力学性能测定、低倍检查、金相组织及夹杂物评定鉴别、受力分析及强度寿命定量估算的方法,对人字轮被动齿轴端断裂失效原因进行分析,并提出改进措施。  相似文献   
35.
结合本钢的生产实际,对炼焦煤的最佳配比作了比较具体的分析,同时对资源,质量、成本也作了比较详细的调查,并提出了本钢焦化厂最佳配煤比方案,由此可看出,最大限度地降低采购成本,继续开发合理的配煤比例,具有广阔的前景。  相似文献   
36.
Recently, a demand for small-capacity generators has been increasing as electric sources in small ships and automobiles or as portable electric sources driven by engines. It is desired that the structure of small-capacity generators be simple and robust, and that the generators be highly reliable, easily maintained and controlled. This paper describes an analysis of the original brushless synchronous generator without exciter. The output voltage can be adjusted in the wide range by controlling the stator dc current. To analyze the characteristics of this generator, the finite element method is applied. It is found that the results of theoretical analysis agree well with the experimental results.  相似文献   
37.
Poly(ethylene aspartate) [PEA] was synthesized by the melt condensation of D,L-aspartic acid and ethylene glycol. PEA containing pendent amino and carbonyl groups in its repeating chain was used as the polymeric ligand for complexation with transition metal ions, viz. Co(II), Ni(II), Cu(II), Mn(II), Zn(II), Cd(II), Ca(II), Mg(II), Pb(II) and Hg(II). Complexation was found to be most effective in DMSO. The resulting polyester-metal complexes were solid coloured materials which have been characterized by IR spectroscopy, elemental analysis and magnetic susceptibility measurements. The thermal stability of the polyester-metal complexes was investigated by thermogravimetric analysis (TGA). On the basis of the physico-chemical studies, an oxygen and nitrogen coordinated structure for the polyester-metal complexes is proposed.  相似文献   
38.
Market segmentation has commonly applied cluster analysis. This study intends to make the comparison of conventional two-stage method with proposed two-stage method through the simulated data. The proposed two-stage method is the combination of self-organizing feature maps and K-means method. The simulation results show that the proposed scheme is better than the conventional two-stage method based on the rate of misclassification.  相似文献   
39.
本文评述了近年来苯基荧光酮类试剂在金属及合金光度分析中应用的发展状况,显色反应的条件,以及相应光度分析方法的检测限和测定范围等。参考文献87篇。  相似文献   
40.
Solid-waste management, and in particular the disposal of used packaging, is currently the subject of much topical debate. This is driven by both consumer and legislative pressures. Consumers see used packaging as a highly visible element of municipal solid waste, complaining of excessive packaging and low levels of recycling. Legislators, perhaps in pandering to the views expressed by consumer bodies, have been active within the CEC and individual Member States by introducing (or proposing) legislation or similar regulatory tools and targets to facilitate a greater diversion of used packaging from disposal by landfill to alternative solid-waste management practices, in particular recycling, which are widely accepted to have a lower impact on the environment. In this paper the relative environmental profiles of pursuing alternative solid-waste management practices to disposal by landfill are explored, focusing not just on solid waste per se but also on associated considerations of energy consumption and emissions, which are invariably overlooked as factors contributing to the environmental impact of solid-waste management practices.  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