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   5271篇
  免费   177篇
  国内免费   16篇
电工技术   65篇
综合类   5篇
化学工业   1116篇
金属工艺   128篇
机械仪表   120篇
建筑科学   201篇
矿业工程   43篇
能源动力   151篇
轻工业   362篇
水利工程   15篇
石油天然气   13篇
无线电   615篇
一般工业技术   797篇
冶金工业   1103篇
原子能技术   51篇
自动化技术   679篇
  2022年   42篇
  2021年   76篇
  2020年   49篇
  2019年   49篇
  2018年   76篇
  2017年   84篇
  2016年   95篇
  2015年   84篇
  2014年   116篇
  2013年   429篇
  2012年   186篇
  2011年   228篇
  2010年   202篇
  2009年   221篇
  2008年   211篇
  2007年   226篇
  2006年   163篇
  2005年   148篇
  2004年   141篇
  2003年   143篇
  2002年   122篇
  2001年   97篇
  2000年   99篇
  1999年   129篇
  1998年   155篇
  1997年   104篇
  1996年   109篇
  1995年   96篇
  1994年   103篇
  1993年   82篇
  1992年   62篇
  1991年   46篇
  1990年   71篇
  1989年   68篇
  1988年   58篇
  1987年   59篇
  1986年   64篇
  1985年   57篇
  1984年   54篇
  1983年   51篇
  1982年   52篇
  1981年   48篇
  1980年   40篇
  1979年   54篇
  1978年   49篇
  1977年   49篇
  1976年   35篇
  1975年   42篇
  1974年   47篇
  1970年   26篇
排序方式: 共有5464条查询结果,搜索用时 859 毫秒
41.
The water bamboo husk is one of major agricultural wastes in Taiwan. In this study, the powder obtained from the water bamboo husk was added to poly(lactic acid) (PLA) to form novel reinforced biodegradable composites. Morphologies, mechanical properties, and heat resistance of these water bamboo powder reinforced composites were investigated. The results indicate that the char yields were increased as plant powder was incorporated to PLA. In addition, the mechanical properties were also enhanced due to the addition of powders. The increments of storage moduli of PLA were about 50–200%. Moreover, the increments of loss moduli of PLA were about 70–200%. On the other hand, the Tg of PLA was slightly decreased by the addition of powder, and this may improve the brittle characteristics of PLA. Furthermore, this type of reinforced PLA would be more environmental friendly than the artificial additive‐reinforced one. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers  相似文献   
42.
43.
Ross.  AH Gilh.  KS 《电信科学》1996,12(3):6-17
本文主要讨论数字移动通信中扩频码分多址技术,阐明了CDMA体制的优越之外,分析了CDMA的关键技术,全面介绍了CDMA系统设计的基本原则和IS-95-A空中接口标准的含义。  相似文献   
44.
In this paper the application of workflow technology to monitor, control and coordinate business processes and projects is proposed. The conceptual characteristics of processes and projects as well as their management needs in the functions of planning, execution, monitoring and control are compared. The general design of the proposed system is then developed, with an application example. The proposed monitoring and control system provides proactive tracking of the flow of work and information, and of the utilization and commitment of resources. The design supports hierarchical management of the project and/or business process, allowing concerned persons to visualize and to utilize it in different levels of abstraction, as necessary. The application of workflow technology also provides additional benefits in facilitating communication, documentation and re-utilization.  相似文献   
45.
Reduction of optical proximity effects (OPE), at deep uv wavelength of 248nm, caused by the variation of stepper lens operating conditions is investigated. It is shown that many of these effects, which increase as the Rayleigh limit is approached, can be minimised, and in many cases eliminated, by suitable choice of lens numerical aperture (NA) and partial coherence (sigma, σ).

Application of these results should enable the user of advanced wafer steppers to carry out high resolution lithography with a minimum of time consuming optical proximity correction (OPC).  相似文献   

46.
A previous structural model of Walberg's theory of educational productivity (A. J. Reynolds and H. J. Walberg, 1991) was tested with a national probability sample of 2,535 10th graders for science achievement and attitude. Using data from the Longitudinal Study of American Youth, a 3-wave design incorporated information from students, teachers, and parents. Results indicate that a revised mediated-effects model fit the data best and accounted for substantial variance in Grade 11 science achievement (56%) and attitude (44%). The variables prior achievement, home environment, exposure to mass media through reading, and instructional time had the greatest total effects on science achievement. Prior attitude, home environment, motivation, and prior achievement made the greatest total contributions to science attitude. Although there were different weightings of the factors between the present study and Reynolds and Walberg (1991), both studies support a mediated-effects model of educational productivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
47.
48.
Language-level support for object persistence frees programmers from having to confront a broad class of database issues from within their applications. By virtue of its metaobject protocol, CLOS is a language whose semantics can be tailored by individual programmers. We used the metaobject protocol to extend CLOS with support for object persistence. Our goal was to obtain a version of CLOS with persistence to which we could easily port a commercial geometric CAD modeling system. We describe the design and implementation of our persistence extension and highlight the strengths and weaknesses exhibited by the CLOS metaobject protocol during our experiment. For many aspects of the implementation we found that the metaobject protocol was ideal. In other cases we had to choose among paying a large performance penalty, extending the protocol, and bypassing the protocol by modifying the language implementation directly.  相似文献   
49.
In response to a need to match drug users to the most appropriate and cost-effective level of care, it was hypothesized that socially anxious methadone-maintained patients would attain greater benefit from coping skills training provided in the context of a low-intensity enhanced standard methadone maintenance intervention (E-STD) than in the context of a high-intensity, socially demanding day treatment program (DTP). Social anxiety was assessed in 307 methadone-maintained patients using the Social Anxiety and Distress Scale prior to randomization to either E-STD or DTP. The hypothesis was supported: Socially anxious patients were drug free longer during treatment, were more likely to be abstinent at treatment completion, and had greater reductions in HIV risk behaviors if assigned to the lower intensity intervention, which was provided at ? the cost of the DTP. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
50.
This letter presents for the first time, the experimentally determined majority carrier mobilities in the accumulation layer of a MOSFET for both p-type and n-type channel doping for a wide range of doping concentrations. The measured carrier mobility is observed to follow a universal behavior at high transverse fields, similar to that observed for minority carriers in MOS inversion layers. At the higher doping levels, the effective mobility for majority carriers at low to moderate transverse fields is found to be very close to the bulk mobility. This is believed to be due to carrier screening of the ionized impurity scattering which dominates at the higher doping concentrations  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