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   18604篇
  免费   2136篇
  国内免费   999篇
电工技术   1747篇
技术理论   3篇
综合类   2019篇
化学工业   1018篇
金属工艺   302篇
机械仪表   599篇
建筑科学   2765篇
矿业工程   766篇
能源动力   1100篇
轻工业   1622篇
水利工程   1603篇
石油天然气   715篇
武器工业   342篇
无线电   1028篇
一般工业技术   1560篇
冶金工业   1195篇
原子能技术   347篇
自动化技术   3008篇
  2024年   127篇
  2023年   353篇
  2022年   622篇
  2021年   773篇
  2020年   773篇
  2019年   644篇
  2018年   678篇
  2017年   670篇
  2016年   960篇
  2015年   833篇
  2014年   1351篇
  2013年   1636篇
  2012年   1356篇
  2011年   1573篇
  2010年   1206篇
  2009年   1151篇
  2008年   1045篇
  2007年   1141篇
  2006年   1025篇
  2005年   816篇
  2004年   610篇
  2003年   514篇
  2002年   408篇
  2001年   292篇
  2000年   212篇
  1999年   162篇
  1998年   147篇
  1997年   95篇
  1996年   97篇
  1995年   66篇
  1994年   67篇
  1993年   46篇
  1992年   27篇
  1991年   27篇
  1990年   26篇
  1989年   27篇
  1988年   29篇
  1987年   20篇
  1986年   18篇
  1985年   10篇
  1984年   14篇
  1983年   9篇
  1982年   9篇
  1981年   6篇
  1980年   9篇
  1979年   4篇
  1965年   14篇
  1959年   5篇
  1957年   3篇
  1955年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
张红才 《大氮肥》2003,26(2):97-99
对尿素合成塔上封头腐蚀凹坑采用中国SAPV-95和美国API579规范分别进行安全评定,给出安全裕度,简略分析安全评定的结果。  相似文献   
52.
In order to maximize systems average availability during a given period of time, it has recently been developed a non-periodic surveillance test optimization methodology based on genetic algorithms (GA). The fact of allowing non-periodic tests turns the solution space much more flexible and schedules can be better adjusted, providing gains in the overall system average availability, when compared to those obtained by an optimized periodic test scheme. This approach, however, turns the optimization problem more complex. Hence, the use of a powerful optimization technique, such as GA, is required.Considering that some particular features of certain systems can turn it advisable to introduce other specific constraints in the optimization problem, this work investigates the application of seasonal constraints for the set of the Emergency Diesel Generation of a typical four-loop pressurized water reactor in order to planning and optimizing its surveillance test policy. In this analysis, the growth of the blackout accident probability during summer, due to electrical power demand increases, was considered. Here, the used model penalizes surveillance test interventions when the blackout probability is higher.Results demonstrate the ability of the method in adapting the surveillance test policy to seasonal constraints. The knowledge acquired by the GA during the searching process has lead to test schedules that drastically minimize test interventions at periods of high blackout probability. It is compensated by more frequent redistributed tests through the periods of low blackout probability in order to improve on the overall average availability at the system level.  相似文献   
53.
The environmental and socio‐economic impacts of biomass utilization by co‐firing with brown coal in an existing thermoelectric unit in Greece or through its pure combustion in a new plant were studied and evaluated in this work. The 125 MWe lignite‐fired power plant in Ptolemais Power Station (Western Macedonia) was used as reference system. The environmental benefits of the alternative biomass exploitation options were quantified based on the life cycle assessment methodology, as established by SETAC, while the BIOSEM technique was used to carry out socio‐economic calculations. The obtained results showed clear environmental benefits of both biomass utilization alternatives in comparison with the reference system. In addition, co‐firing biomass with lignite in an existing unit outperforms the combustion of biomass exclusively in a new plant, since it exhibits a better environmental performance and it is a low risk investment with immediate benefits. A biomass combustion unit requires a considerably higher capital investment and its benefits are more evident in the long run. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
54.
A model for building integrated photovoltaic systems has been developed and implemented in a dynamic simulation tool. This tool takes into account the thermal interactions between the PV collector and the building. The influence of the type of integration upon the PV collector efficiency has been evaluated and hybrid PV/air collectors have been studied. An overall efficiency is defined, including the production of electricity and heat. A case study has been performed on two different typical buildings. In the case of a multi-crystalline silicon PV collector integrated on the roof of a single family house located in Paris, the efficiency of unventilated PV modules fixed on the roof is 14%. If the PV collector is used to preheat the ventilation air, the efficiency reaches 20%. A proper building integration also improves the environmental balance of PV technologies over their life cycle.  相似文献   
55.
Abstract Research has demonstrated girls to outperform boys on conventional literacy tests. The present studies concern gender differences on computerised educational tests. Seventy-one children were tested using LASS Secondary and a set of seven conventional measures. No significant gender differences were found on any of the LASS Secondary modules, although females did outperform males on a conventional spelling test. A further 126 pupils were tested on computerised and paper versions of the LASS Secondary reading, spelling and reasoning modules. No gender differences were found on the computerised versions, but there were significant differences on the paper versions of the reading and spelling modules favouring females. In a third study, 45 children were administered computerised and paper versions of the LASS Junior reading and spelling modules. There were no significant differences on the computerised modules, but girls performed significantly higher than boys on the paper version of the spelling module. It is possible that computerised assessment does not detect the established gender effect due to differences between males and females in motivation, computer experience and competitiveness. Further large-scale studies are necessary to confirm these findings.  相似文献   
56.
诚信:中国企业亟待解决的问题   总被引:1,自引:0,他引:1  
刘畅 《天津冶金》2003,(6):47-49
分析论述了诚信的重要性,指出了在维系市场秩序中诚信处于十分重要的地位。分析了中国企业诚信的现状,提出了企业重塑诚信的措施。  相似文献   
57.
Ecological momentary assessment (EMA) consists of assessing phenomena in real time in the natural environment. EMA allows for more fine-grained analyses of addictive behavior and minimizes threats to internal validity, such as recall biases and errors. However, because of the intensive monitoring involved in EMA, measurement reactivity is a concern. To test whether EMA with palmtop personal computers induces reactivity, the authors compared smoking-related outcomes between smokers using EMA and those not using EMA during a quit attempt. The use of no-EMA control groups has been rare in reactivity investigations to date. The EMA protocol included event-contingent assessments (smoking episodes, urge episodes) and random assessments. Outcomes included biologically confirmed abstinence and self-report measures of withdrawal, self-efficacy, motivation, affect, and temptations. Participants were smokers motivated to quit (N = 96). They were randomized to 1 of 3 groups: EMA for the week preceding a planned quit date, EMA for the week following the quit date, and no EMA. Abstinence rates did not differ between the groups at Day 7 or at Day 28 postcessation. For the 20 subscales assessed at each of 3 assessment times, there were significant differences between participants with and without EMA experience for 3 subscales at the 1st of 3 assessment times, and significant differences for 3 different subscales at the 3rd assessment time. These differences suggest some reactivity to EMA, although the inconsistent pattern across time indicates that further research is needed to definitively conclude that EMA induces reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
58.
Working collaboratively, psychologist educators and trainers at the doctoral, internship, and postdoctoral levels; credentialers; practitioners; and students offer 8 proposals for psychologists to consider in recognizing, assessing, and intervening with problems of professional competence in students and practicing professionals. In the proposals, the authors address the following topics: definitions and categories; preparing the system; self-assessment; remediation; diversity; communication across various levels of the system; confidentiality; and ethical, regulatory, and legal underpinnings. They also propose future directions for the assessment of problems in professional competence in both students and practicing psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
59.
企业诚信经营浅议   总被引:3,自引:0,他引:3  
以大量史实分析了国内外企业经营的诚信问题,诚信经营在企业发展中的重要性以及如何健全企业诚信机制等相关问题,并呼吁各商家企业严格遵守企业诚信经营准则。  相似文献   
60.
Samples of chicken meat from spent laying hens were obtained by four different methods: (1) manual deboning of whole carcasses; (2) manual deboning of skinned carcasses; (3) mechanical deboning of whole carcasses; and (4) mechanical deboning of skinned carcasses. The meat was packaged, frozen and stored at ?18 °C for up to 3 months. Functional properties studied were pH, emulsifying capacity (EC) and water‐holding capacity (WHC) and, in addition, pigment concentration was investigated. Sensory properties included aroma, colour, texture and overall acceptability, as judged by a trained panel using a nine‐point hedonic scale. Removal of the skin prior to deboning by either method gave significantly higher values (P < 0.05) for EC, while WHC values were not significantly different among the experimental treatments, despite higher pH values for mechanically‐deboned meat, with and without skin. Pigment concentrations were highest in meat from Treatment 4 and lowest for Treatment 1, but values for both methods of deboning were affected by the presence of skin. There were no significant differences between treatments for any of the sensory properties studied. Changes occurring in the meat during frozen storage are described.  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