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   544245篇
  免费   9148篇
  国内免费   1563篇
电工技术   9927篇
综合类   743篇
化学工业   81900篇
金属工艺   20531篇
机械仪表   15632篇
建筑科学   13387篇
矿业工程   2403篇
能源动力   14891篇
轻工业   49740篇
水利工程   5381篇
石油天然气   9455篇
武器工业   47篇
无线电   60990篇
一般工业技术   105428篇
冶金工业   107851篇
原子能技术   10666篇
自动化技术   45984篇
  2021年   5387篇
  2020年   3894篇
  2019年   4905篇
  2018年   8478篇
  2017年   8207篇
  2016年   8633篇
  2015年   6191篇
  2014年   9940篇
  2013年   25399篇
  2012年   15630篇
  2011年   21115篇
  2010年   16650篇
  2009年   18521篇
  2008年   19002篇
  2007年   18629篇
  2006年   16172篇
  2005年   14726篇
  2004年   13966篇
  2003年   13725篇
  2002年   12967篇
  2001年   13051篇
  2000年   12079篇
  1999年   12870篇
  1998年   34038篇
  1997年   23674篇
  1996年   18008篇
  1995年   13378篇
  1994年   11571篇
  1993年   11243篇
  1992年   8029篇
  1991年   7544篇
  1990年   7356篇
  1989年   7128篇
  1988年   6568篇
  1987年   5874篇
  1986年   5749篇
  1985年   6419篇
  1984年   6049篇
  1983年   5299篇
  1982年   4998篇
  1981年   5091篇
  1980年   4829篇
  1979年   4703篇
  1978年   4487篇
  1977年   5476篇
  1976年   7331篇
  1975年   3862篇
  1974年   3618篇
  1973年   3744篇
  1972年   3009篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
71.
72.
73.
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   
74.
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   
75.
Wu  Li  Li  Jing  Fu  Caixia  Kühn  Bernd  Wang  Xiaolin 《Magma (New York, N.Y.)》2019,32(4):501-509
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the...  相似文献   
76.
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   
77.
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   
78.
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   
79.
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   
80.
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   
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