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   4683篇
  免费   140篇
  国内免费   10篇
电工技术   52篇
综合类   5篇
化学工业   1110篇
金属工艺   85篇
机械仪表   100篇
建筑科学   314篇
矿业工程   6篇
能源动力   113篇
轻工业   463篇
水利工程   37篇
石油天然气   23篇
无线电   263篇
一般工业技术   745篇
冶金工业   923篇
原子能技术   61篇
自动化技术   533篇
  2022年   55篇
  2021年   53篇
  2020年   47篇
  2019年   57篇
  2018年   60篇
  2017年   84篇
  2016年   103篇
  2015年   59篇
  2014年   112篇
  2013年   301篇
  2012年   155篇
  2011年   224篇
  2010年   199篇
  2009年   176篇
  2008年   199篇
  2007年   200篇
  2006年   193篇
  2005年   166篇
  2004年   150篇
  2003年   133篇
  2002年   108篇
  2001年   92篇
  2000年   79篇
  1999年   81篇
  1998年   130篇
  1997年   112篇
  1996年   73篇
  1995年   72篇
  1994年   81篇
  1993年   61篇
  1992年   54篇
  1991年   55篇
  1990年   61篇
  1989年   67篇
  1988年   63篇
  1987年   37篇
  1986年   59篇
  1985年   60篇
  1984年   64篇
  1983年   52篇
  1982年   54篇
  1981年   55篇
  1980年   46篇
  1979年   57篇
  1978年   60篇
  1977年   50篇
  1976年   47篇
  1975年   33篇
  1974年   31篇
  1973年   37篇
排序方式: 共有4833条查询结果,搜索用时 0 毫秒
1.
Remanufacturing facilities usually face a trade-off between limited information about remanufacturing yields and potentially long supplier lead times. To improve production performance, these firms may attempt to acquire more timely and accurate information about remanufacturing yields or alternatively, to reduce the lead times of purchased parts. We develop four decision-making models to evaluate the impact of yield information and supplier lead time on manufacturing costs. We identify the operating conditions under which these capabilities are valuable, along with their relative impact on facility performance. Each model is formulated as an infinite horizon, stochastic dynamic program (Markov decision process). Our results indicate that the yield information is generally quite valuable, while investments in supplier responsiveness provide trivial returns to products with few parts. However, as product complexity increases with large number of target parts, the value of short lead times increases.  相似文献   
2.
Area- and time-specific marginal capacity costs of electricity distribution   总被引:2,自引:0,他引:2  
Marginal costs of electricity vary by time and location. In the past, researchers attributed the variations to factors related to electricity generation and transmission. These authors, however, have not analyzed possible variations in marginal distribution capacity costs (MDCC). The objectives of this paper are:
1. (i) to show that large MDCC variations are due to the dispersion in distribution capital expenditures by time and space,
2. (ii) to propose a method for quantifying the area- and time-specific MDCC in the presence of lumpy investments, and
3. (iii) to compare our MDCC estimates to those commonly used in the electric utility industry.
Our proposed method and its results were adopted by the California Public Utilities Commission (CPUC) in 1992 for Pacific Gas and Electric Company (PG&E), the largest privately owned electric utility in the U.S.  相似文献   
3.
4.
5.
6.
7.
This paper presents a numerical study of the Lorentz force and fluid flow induced by a rotating magnetic field in a medium with a nonhomogeneous electric conductivity placed in a cylindrical vessel with insulated walls. The nonhomogeneity is modeled by the presence of a solid and a liquid phase of different electrical conductivity. The solid phase is located orthogonally to the axis of rotation, which corresponds to the case of unidirectional solidification. The simulations were performed for different locations of the solid front and different ratios of the electrical conductivity, σ s /σ l =0.2... 10. Here σ s and σ l are the electric conductivity of the solid and liquid phases, respectively. The results showed that the difference between electrical conductivity of solid and liquid phases has a noticeable effect on the mean-time Lorentz force and the velocity: namely, the presence of the solid phase (σ s >σ l ) leads to an increase of the Lorentz force and fluid flow in the cylinder.  相似文献   
8.
Roger L. Kemp 《Cities》1985,2(3):252-255
Since the early 1970s, local governments in the USA have faced limited tax income combined with double-digit inflation. As a result, every local service from fire prevention to recreation has had to be closely scrutinized. Local administrators and politicians have evolved new and innovative retrenchment management policies to respond to both the demands of citizens and the fewer dollars available. A combination of denial of new programmes and public sector pay austerity, with public education and use of community organizations is providing ways to stretch limited funds. The reality in many communities across the USA is that local government and its services will not be growing in the future.  相似文献   
9.
This paper describes the synthesis of photoisomerizable derivatives of isosorbide. These derivatives contain a stilbene or cinnamate moiety and can therefore be used as photoisomerizable chiral compounds in cholesteric liquid‐crystalline mixtures. The reflection wavelength of cholesteric layers made from these mixtures is increased by UV irradiation due to the fact that the Z‐isomers of these derivatives exhibit a lower helical twisting power than the corresponding E‐isomers. The cinnamate derivatives are very suitable for use in cholesteric color filters that find application in liquid‐crystal displays.  相似文献   
10.
Develops 3 hypotheses to explain the role of construal processes in conformity behavior. According to the preconformity change of meaning hypothesis, social influence leads to changes in situational construal that precede and mediate conformity behavior; according to the postconformity change of meaning hypothesis, construal change follows and justifies conformity; and according to the construal-consistency hypothesis, preexisting situational construal distinguishes those who conform from those who dissent. Four experimental studies with varying methodology and involving a total of 361 undergraduate students were performed to test these hypotheses. The results of all studies provide strong evidence for postconformity change of meaning effects. Discussion centers on possible domains in which the different construal mechanisms might operate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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