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   530248篇
  免费   8539篇
  国内免费   1510篇
电工技术   9636篇
综合类   601篇
化学工业   80013篇
金属工艺   20113篇
机械仪表   15350篇
建筑科学   12958篇
矿业工程   2309篇
能源动力   14712篇
轻工业   47912篇
水利工程   5273篇
石油天然气   9368篇
武器工业   37篇
无线电   60388篇
一般工业技术   102928篇
冶金工业   103841篇
原子能技术   10617篇
自动化技术   44241篇
  2022年   3237篇
  2021年   5072篇
  2020年   3645篇
  2019年   4718篇
  2018年   8084篇
  2017年   7912篇
  2016年   8264篇
  2015年   5763篇
  2014年   9507篇
  2013年   24653篇
  2012年   14920篇
  2011年   20558篇
  2010年   16106篇
  2009年   17995篇
  2008年   18362篇
  2007年   18049篇
  2006年   15688篇
  2005年   14360篇
  2004年   13777篇
  2003年   13529篇
  2002年   12842篇
  2001年   12897篇
  2000年   11942篇
  1999年   12662篇
  1998年   32906篇
  1997年   22967篇
  1996年   17506篇
  1995年   13085篇
  1994年   11321篇
  1993年   11006篇
  1992年   7943篇
  1991年   7444篇
  1990年   7284篇
  1989年   7043篇
  1988年   6500篇
  1987年   5791篇
  1986年   5675篇
  1985年   6298篇
  1984年   5915篇
  1983年   5190篇
  1982年   4920篇
  1981年   4990篇
  1980年   4726篇
  1979年   4628篇
  1978年   4431篇
  1977年   5353篇
  1976年   6989篇
  1975年   3805篇
  1974年   3563篇
  1973年   3675篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
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   
63.
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   
64.
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y...  相似文献   
65.
Hussien  O. S.  Elamy  M. I. 《Strength of Materials》2020,52(3):470-479
Strength of Materials - The use of a damping system is one of the seismic protection systems that improve the seismic response of structures. The proposed methodology estimates the location (which...  相似文献   
66.
Powder Metallurgy and Metal Ceramics - The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was...  相似文献   
67.
Measurement Techniques - A method is proposed for transferring the unit of mean power of laser radiation by means of measuring high-intensity power (kilowatts), with the possibility of constant...  相似文献   
68.
Sustainable and efficient food supply chain has become an essential component of one’s life. The model proposed in this paper is deeply linked to people's quality of life as a result of which there is a large incentive to fulfil customer demands through it. This proposed model can enhance food quality by making the best possible food quality accessible to customers, construct a sustainable logistics system considering its environmental impact and ensure the customer demand to be fulfilled as fast as possible. In this paper, an extended model is examined that builds a unified planning problem for efficient food logistics operations where four important objectives are viewed: minimising the total expense of the system, maximising the average food quality along with the minimisation of the amount of CO2 emissions in transportation along with production and total weighted delivery lead time minimisation. A four objective mixed integer linear programming model for intelligent food logistics system is developed in the paper. The optimisation of the formulated mathematical model is proposed using a modified multi-objective particle swarm optimisation algorithm with multiple social structures: MO-GLNPSO (Multi-Objective Global Local Near-Neighbour Particle Swarm Optimisation). Computational results of a case study on a given dataset as well as on multiple small, medium and large-scale datasets followed by sensitivity analysis show the potency and effectiveness of the introduced method. Lastly, there has been a scope for future study displayed which would lead to the further progress of these types of models.  相似文献   
69.
70.
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