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   709346篇
  免费   11604篇
  国内免费   3019篇
电工技术   13715篇
技术理论   5篇
综合类   1676篇
化学工业   108923篇
金属工艺   27565篇
机械仪表   20612篇
建筑科学   17677篇
矿业工程   3653篇
能源动力   18444篇
轻工业   63654篇
水利工程   7261篇
石油天然气   13456篇
武器工业   280篇
无线电   79093篇
一般工业技术   135580篇
冶金工业   138567篇
原子能技术   14085篇
自动化技术   59723篇
  2021年   6756篇
  2020年   4796篇
  2019年   6039篇
  2018年   10008篇
  2017年   9796篇
  2016年   10449篇
  2015年   7625篇
  2014年   12338篇
  2013年   32532篇
  2012年   19969篇
  2011年   27317篇
  2010年   21567篇
  2009年   23643篇
  2008年   24742篇
  2007年   24506篇
  2006年   21467篇
  2005年   19281篇
  2004年   18057篇
  2003年   17548篇
  2002年   16976篇
  2001年   17061篇
  2000年   15870篇
  1999年   16616篇
  1998年   41780篇
  1997年   29628篇
  1996年   22566篇
  1995年   16899篇
  1994年   14935篇
  1993年   14580篇
  1992年   10710篇
  1991年   10059篇
  1990年   9961篇
  1989年   9741篇
  1988年   9047篇
  1987年   7965篇
  1986年   7907篇
  1985年   8793篇
  1984年   8347篇
  1983年   7447篇
  1982年   6927篇
  1981年   7151篇
  1980年   6678篇
  1979年   6713篇
  1978年   6437篇
  1977年   7459篇
  1976年   9867篇
  1975年   5682篇
  1974年   5284篇
  1973年   5440篇
  1972年   4466篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The proliferating need for sustainability intervention in food grain transportation planning is anchoring the attention of researchers in the interests of stakeholders and environment at large. Uncertainty associated with food grain supply further intensifies the problem steering the need for designing robust, cost-efficient and sustainable models. In line with this, this paper aims to develop a robust and sustainable intermodal transportation model to facilitate single type of food grain commodity shipments while considering procurement uncertainty, greenhouse gas emissions, and intentional hub disruption. The problem is designed as a mixed integer non-linear robust optimisation model on a hub and spoke network for evaluating near optimal shipment quantity, route selection and hub location decisions. The robust optimisation approach considers minimisation of total relative regret associated with total cost subject to several real-time constraints. A version of Particle Swarm Optimisation with Differential Evolution is proposed to tackle the resulting NP-hard problem. The model is tested with two other state-of the art meta-heuristics for small, medium, and large datasets subject to different procurement scenarios inspired from real time food grain operations in Indian context. Finally, the solution is evaluated with respect to total cost, model and solution robustness for all instances.  相似文献   
82.

Surface integrity characterization of manufactured component is very important as it significantly affects the in-service performance of the component. Till now, surface integrity was evaluated using conventional measurement technique like microhardness tester, X-ray diffraction, optical microscopy and surface roughness tester. But, this technique being laboratory based cannot be used for in-service monitoring of the surface integrity. The present study focuses on the characterization of surface integrity upon electric discharge machined sample using non-destructive magnetic Barkhausen noise technique. Electric discharge machining was performed in die-sinking mode on die steel using copper–tungsten electrode (negative polarity). Experiment was performed by selecting different levels of peak current, gap voltage and pulse on time. Surface integrity characteristics like microhardness change, residual stress, microstructural alteration and surface roughness were analysed using microhardness tester, X-ray diffraction, optical microscopy and surface roughness tester, respectively, and were then correlated with magnetic parameter like root mean square value and peak value obtained from Barkhausen noise signal. The results show a good correlation between magnetic parameter (RMS and Peak value) of Barkhausen noise with the microhardness and surface roughness of the machined sample.

  相似文献   
83.
Russian Journal of Non-Ferrous Metals - Rolling bearing rings comprise a large reserve for expanding powder metallurgy production. This reserve is being incompletely implemented. The hot forging of...  相似文献   
84.
Metallurgical and Materials Transactions B - The process of obtaining titanium tetrachloride (TiCl4) from the quartz-leucoxene concentrate (QLC) from the Yaregskoe oil-titanium field was studied....  相似文献   
85.
86.
87.
88.
89.
90.
A layer-by-layer analysis of the structures, the phase compositions, and the defect substructures of differentially hardened rails has been carried by optical and transmission electron microscopy. It is found that the material volume of the rail head fillet is cooled faster than the volume located along the central axis.  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