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   671709篇
  免费   9445篇
  国内免费   1930篇
电工技术   11626篇
综合类   2861篇
化学工业   98909篇
金属工艺   28947篇
机械仪表   22725篇
建筑科学   17108篇
矿业工程   3410篇
能源动力   16828篇
轻工业   52696篇
水利工程   7266篇
石油天然气   10692篇
武器工业   41篇
无线电   74097篇
一般工业技术   131807篇
冶金工业   114617篇
原子能技术   11629篇
自动化技术   77825篇
  2022年   3519篇
  2021年   5452篇
  2020年   3868篇
  2019年   5081篇
  2018年   25665篇
  2017年   24944篇
  2016年   19802篇
  2015年   7016篇
  2014年   10338篇
  2013年   26315篇
  2012年   20145篇
  2011年   34867篇
  2010年   29010篇
  2009年   28234篇
  2008年   29302篇
  2007年   31173篇
  2006年   16985篇
  2005年   18883篇
  2004年   16818篇
  2003年   16408篇
  2002年   14411篇
  2001年   13572篇
  2000年   12580篇
  1999年   13164篇
  1998年   33347篇
  1997年   23423篇
  1996年   17982篇
  1995年   13532篇
  1994年   11768篇
  1993年   11434篇
  1992年   8347篇
  1991年   7715篇
  1990年   7624篇
  1989年   7343篇
  1988年   6755篇
  1987年   6058篇
  1986年   5908篇
  1985年   6633篇
  1984年   6259篇
  1983年   5446篇
  1982年   5160篇
  1981年   5217篇
  1980年   4946篇
  1979年   4847篇
  1978年   4611篇
  1977年   5528篇
  1976年   7149篇
  1975年   3975篇
  1974年   3704篇
  1973年   3809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