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   110601篇
  免费   8354篇
  国内免费   4093篇
电工技术   5807篇
技术理论   11篇
综合类   6628篇
化学工业   18235篇
金属工艺   5803篇
机械仪表   6727篇
建筑科学   8608篇
矿业工程   3071篇
能源动力   3094篇
轻工业   6731篇
水利工程   1713篇
石油天然气   6225篇
武器工业   697篇
无线电   13912篇
一般工业技术   14102篇
冶金工业   5725篇
原子能技术   1258篇
自动化技术   14701篇
  2024年   182篇
  2023年   1659篇
  2022年   2221篇
  2021年   3770篇
  2020年   3011篇
  2019年   2547篇
  2018年   2964篇
  2017年   3347篇
  2016年   2916篇
  2015年   3875篇
  2014年   4917篇
  2013年   6280篇
  2012年   6624篇
  2011年   7279篇
  2010年   6311篇
  2009年   6223篇
  2008年   6226篇
  2007年   5794篇
  2006年   6099篇
  2005年   5442篇
  2004年   3729篇
  2003年   3221篇
  2002年   2854篇
  2001年   2742篇
  2000年   2830篇
  1999年   3344篇
  1998年   2884篇
  1997年   2510篇
  1996年   2247篇
  1995年   1905篇
  1994年   1529篇
  1993年   1214篇
  1992年   962篇
  1991年   728篇
  1990年   587篇
  1989年   491篇
  1988年   381篇
  1987年   284篇
  1986年   194篇
  1985年   166篇
  1984年   94篇
  1983年   76篇
  1982年   86篇
  1981年   56篇
  1980年   44篇
  1979年   32篇
  1978年   24篇
  1977年   25篇
  1976年   40篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
71.
Wu  Huiling  Weng  Chengguo  Zeng  Yan 《OR Spectrum》2018,40(2):541-582
OR Spectrum - This paper studies a multi-period investment–consumption optimization problem with a stochastic discount rate and a time-varying utility function, which are governed by a...  相似文献   
72.
In this study, we used a combination of graphene oxide-based porous carbon (GC) and titanium chloride (TiCl3) to improve the reversible dehydrogenation properties of magnesium hydride (MgH2). Examining the effects of GC and TiCl3 on the hydrogen storage properties of MgH2, the study found GC was a useful additive as confinement medium for promoting the reversible dehydrogenation of MgH2. And TiCl3 was an efficient catalytic dopant. A series of controlled experiments were carried out to optimize the sample preparation method and the addition amount of GC and TiCl3. In comparison with the neat MgH2 system, the MgH2/GC-TiCl3 composite prepared under optimized conditions exhibited enhanced dehydrogenation kinetics and lower dehydrogenation temperature. A combination of phase/microstructure/chemical state analyses has been conducted to gain insight into the promoting effects of GC and TiCl3 on the reversible dehydrogenation of MgH2. Our study found that GC was a useful scaffold material for tailoring the nanophase structure of MgH2. And TiCl3 played an efficient catalytic effect. Therefore, the remarkably improved dehydrogenation properties of MgH2 should be attributed to the synergetic effects of nanoconfinement and catalysis.  相似文献   
73.
Against a background of deepened globalization, the socio-spatial distribution characteristics of the employed population are one of the important perspectives that reflect the impact of globalization on urban social space. Based on data of the population census of Shanghai in 2000 and 2010, using location quotient and index of dissimilarity, this paper analyzes the residential differentiation evolution in Shanghai from 2000 to 2010. The results show that except the high-end service industry, the residential differentiation of the employees in the other three types of industries has intensified but is not serious. In addition, the proportion of employees in high-end service industry within the Middle Ring has increased, while that of employees in the middle-and low-end service industry beyond the Middle Ring has increased, which further proves that globalization has an increasingly obvious impact on the socio-spatial differentiation in Shanghai. However, the adjustment in spatial development made by the Shanghai municipal government in response to globalization makes the socio-spatial evolution of Shanghai greatly different from the suburbanization of social elites in the West.  相似文献   
74.
75.
Lei  Yuan  Shi  Yiyuan  Jiang  Liang  Lei  Jingxin  Wu  Bo 《Iranian Polymer Journal》2020,29(8):669-677
Iranian Polymer Journal - A novel class of photochromic copolymer based on spironaphthoxazine (SO) moieties was smoothly prepared through the copolymerization of methyl methacrylate (MMA), butyl...  相似文献   
76.
李强  吴文斌  张贵虎 《机械制造》2020,58(4):84-86,100
生产系统复杂多变,在生产管理过程中存在多变性和不均衡性。对此,实际生产中需要实现生产工艺多方案并行与快速转换。分析了生产过程变化因素,介绍了主工艺+子工艺这一生产工艺多方案并行与快速转换方法,并通过实例验证了这一方法的有效性。  相似文献   
77.
78.
79.
In this study, the ultrasound was fixed in the pulp zone of flotation cell and its effect on the true flotation of lignite was analyzed. Flotation results indicated that the simultaneous ultrasound treatment increased the concentrate yield and decreased the concentrate ash content. Screening analysis of flotation products revealed that the ultrasound could crush coarse coal to fine coal and scanning electron microscopy (SEM) tests indicated that the ultrasound could reduce the coverage of high-ash coal fines on the coarse particle surface. Thus, the flotation recovery of coarse lignite particle was increased. In addition, the true flotation and entrainment of ?0.074 mm fine particles were studied by the sink-float test and the method of Trahar. It was found the ultrasound significantly enhanced the true flotation of fine particles and improved the overall water recovery in lignite flotation.  相似文献   
80.
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