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   282171篇
  免费   5375篇
  国内免费   2075篇
电工技术   6435篇
综合类   2486篇
化学工业   41297篇
金属工艺   10896篇
机械仪表   9250篇
建筑科学   8126篇
矿业工程   1604篇
能源动力   7971篇
轻工业   23783篇
水利工程   2834篇
石油天然气   5008篇
武器工业   228篇
无线电   37526篇
一般工业技术   53319篇
冶金工业   49749篇
原子能技术   5417篇
自动化技术   23692篇
  2022年   2201篇
  2021年   3269篇
  2020年   2422篇
  2019年   2623篇
  2018年   4047篇
  2017年   4244篇
  2016年   4215篇
  2015年   3372篇
  2014年   5437篇
  2013年   13306篇
  2012年   8269篇
  2011年   10787篇
  2010年   8944篇
  2009年   9821篇
  2008年   10326篇
  2007年   10118篇
  2006年   9147篇
  2005年   8016篇
  2004年   7348篇
  2003年   7366篇
  2002年   6774篇
  2001年   7097篇
  2000年   6573篇
  1999年   6977篇
  1998年   16941篇
  1997年   11803篇
  1996年   9172篇
  1995年   6909篇
  1994年   6136篇
  1993年   6028篇
  1992年   4279篇
  1991年   4134篇
  1990年   3916篇
  1989年   3713篇
  1988年   3621篇
  1987年   3042篇
  1986年   2965篇
  1985年   3224篇
  1984年   2937篇
  1983年   2836篇
  1982年   2645篇
  1981年   2544篇
  1980年   2466篇
  1979年   2307篇
  1978年   2107篇
  1977年   2604篇
  1976年   3562篇
  1975年   1764篇
  1974年   1729篇
  1973年   1665篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
With the emergence of large-scale knowledge base, how to use triple information to generate natural questions is a key technology in question answering systems. The traditional way of generating questions require a lot of manual intervention and produce lots of noise. To solve these problems, we propose a joint model based on semi-automated model and End-to-End neural network to automatically generate questions. The semi-automated model can generate question templates and real questions combining the knowledge base and center graph. The End-to-End neural network directly sends the knowledge base and real questions to BiLSTM network. Meanwhile, the attention mechanism is utilized in the decoding layer, which makes the triples and generated questions more relevant. Finally, the experimental results on SimpleQuestions demonstrate the effectiveness of the proposed approach.  相似文献   
2.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
3.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
4.
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   
5.
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   
6.
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype.  相似文献   
7.
8.
9.
10.
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