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   536730篇
  免费   7432篇
  国内免费   1481篇
电工技术   9718篇
综合类   535篇
化学工业   81096篇
金属工艺   20185篇
机械仪表   15388篇
建筑科学   13191篇
矿业工程   2324篇
能源动力   14833篇
轻工业   47755篇
水利工程   5333篇
石油天然气   9407篇
武器工业   37篇
无线电   60735篇
一般工业技术   103507篇
冶金工业   105955篇
原子能技术   10670篇
自动化技术   44974篇
  2022年   3267篇
  2021年   5050篇
  2020年   3591篇
  2019年   4664篇
  2018年   7981篇
  2017年   7771篇
  2016年   8130篇
  2015年   5718篇
  2014年   9494篇
  2013年   24833篇
  2012年   14989篇
  2011年   20636篇
  2010年   16177篇
  2009年   18096篇
  2008年   18550篇
  2007年   18197篇
  2006年   15890篇
  2005年   14552篇
  2004年   13912篇
  2003年   13653篇
  2002年   12893篇
  2001年   13035篇
  2000年   12065篇
  1999年   12791篇
  1998年   33237篇
  1997年   23191篇
  1996年   17697篇
  1995年   13254篇
  1994年   11491篇
  1993年   11171篇
  1992年   8064篇
  1991年   7547篇
  1990年   7401篇
  1989年   7177篇
  1988年   6589篇
  1987年   5914篇
  1986年   5807篇
  1985年   6426篇
  1984年   6066篇
  1983年   5302篇
  1982年   5027篇
  1981年   5086篇
  1980年   4820篇
  1979年   4722篇
  1978年   4492篇
  1977年   5462篇
  1976年   7113篇
  1975年   3892篇
  1974年   3647篇
  1973年   3748篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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   
2.
3.
4.
5.
6.
7.
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   
8.
Lobster krill (Munida genus) represents an under‐valued crustacean frequently caught on European fishing banks. In this work, its sensory, microbiological and biochemical qualities were evaluated during chilled storage. Additionally, the effects of a prestorage antimelanosic treatment consisting of soaking in sodium metabisulphite (SMB) solutions at two different concentrations (0.25% and 0.75%) were also studied. SMB prestorage treatment provided lobster specimens that still exhibited acceptable sensory quality after 10 days of storage, while control specimens were unacceptable at that time. SMB treatment also resulted in a significant (P < 0.05) inhibition of microbial growth, mainly of Enterobacteriaceae, psychrotrophes and proteolytic bacteria. Low lipid oxidation levels were observed for all batches; however, a significantly higher (P < 0.05) retention of polyunsaturated fatty acids was found in SMB‐treated lobster, especially in the 0.75% SMB batch. The results presented here open the way to the potential commercialisation of currently under‐utilised lobster krill as a chilled product.  相似文献   
9.
10.
Programming and Computer Software - Image segmentation using a hierarchical sequence of piecewise constant approximations that minimally differ from the original image in terms of the total squared...  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