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   27243篇
  免费   689篇
  国内免费   36篇
电工技术   337篇
综合类   14篇
化学工业   5954篇
金属工艺   520篇
机械仪表   474篇
建筑科学   1172篇
矿业工程   332篇
能源动力   660篇
轻工业   1768篇
水利工程   229篇
石油天然气   247篇
无线电   1768篇
一般工业技术   4117篇
冶金工业   6359篇
原子能技术   267篇
自动化技术   3750篇
  2022年   249篇
  2021年   416篇
  2020年   266篇
  2019年   348篇
  2018年   427篇
  2017年   371篇
  2016年   488篇
  2015年   392篇
  2014年   623篇
  2013年   1658篇
  2012年   956篇
  2011年   1213篇
  2010年   935篇
  2009年   983篇
  2008年   1165篇
  2007年   1080篇
  2006年   985篇
  2005年   893篇
  2004年   749篇
  2003年   717篇
  2002年   711篇
  2001年   493篇
  2000年   398篇
  1999年   456篇
  1998年   498篇
  1997年   458篇
  1996年   499篇
  1995年   458篇
  1994年   463篇
  1993年   448篇
  1992年   435篇
  1991年   275篇
  1990年   417篇
  1989年   394篇
  1988年   345篇
  1987年   406篇
  1986年   353篇
  1985年   444篇
  1984年   470篇
  1983年   404篇
  1982年   379篇
  1981年   309篇
  1980年   302篇
  1979年   363篇
  1978年   304篇
  1977年   244篇
  1976年   224篇
  1975年   248篇
  1974年   221篇
  1973年   230篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
The seasonal performance of space cooling systems generally depends on indoor and outdoor temperatures and humidities and on the ratio between actual cooling loads and cooling equipment size. In principle, any given weather condition and desired indoor dry-bulb temperature calls for an interactive application of psychrometrics and equipment performance curves until satisfactory indoor conditions are derived for which both sensible and latent cooling loads equal sensible and latent heat removal rates. This paper presents a simplified approach that derives the indoor wet-bulb temperature in close form for both cases when the cooling system condenses water from the space and when it does not. This approach relies on a local linearization of the psychrometric chart in the region of interest for indoor comfort conditions. Performance curves for total and sensible capacity and for the electric power input were derived for several different residential air-to-air reciprocating compressive cooling systems. The performance curves are empirical fits to manufacturer's data or to laboratory results. The predictions of the simplified method were compared with DOE-2 when calculating space cooling consumption for a residence in both a hot arid and in a hot humid climate. The comparison showed excellent agreement both for hour-by-hour calculations and for monthly calculation of this method are sufficiently simple to be applicable to micro-computers and pocket calculators.  相似文献   
22.
Six measures of divergent thinking were administered to 825 men ranging in age from 17 to 101 over the period from 1959 to 1972; repeat administrations were given to a subset of 278 men after a 6-year interval. Cross-sectional analyses showed curvilinear trends, with an increase in scores for men under 40 and a decline thereafter. Repeated measures analyses on subjects initially aged 33 to 74 generally replicated this finding, whereas cross-sequential analyses suggested a decline for all cohorts tested at a later time. Additional analyses suggested that not all of the decline could be attributed to reduced speed of response production. These longitudinal findings confirm earlier cross-sectional reports of decline in divergent thinking abilities with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
23.
24.
25.
An account of the use of landscape as subject-matter as a basis for the exploration of personal concerns and the search for self by various 20th Century photographers. Particular reference is made to the landscape photography of Eugene Atget, Edward Weston and Bill Brandt.  相似文献   
26.
27.
28.
29.
The NRC's Research Program on Core-Debris/Cavity Interactions comprises two principal elements: (1) an analytical effort focused primarily on development of computer codes needed to predict the potential consequences of risk-significant severe-accident scenarios; and (2) an experimental component to provide insights into the relevant phenomenological processes and to develop the experimental data base necessary for validation of the codes. The analytical activities at Sandia National Laboratories (SNL) focus primarily on refinement and validation of the CORCON and VANESA codes. Two major experimental activities are also based at SNL: (1) the large-scale SURC tests address the thermal-hydraulic phenomena in the cavity as well as aerosol release associated with prototypical core-melt materials in various types of concrete crucibles, while (2) the WITCH and GHOST experiments are concerned with aerosol generation and radionuclide release phenomena. A program of small-scale special-effects tests at Brookhaven National Laboratory (BNL) is coupled to a concomitant model-development and code-validation activity. In addition, measurements are being made at Battelle Columbus Laboratory (BCL) to augment the thermochemical data base needed in the VANESA code to permit refined radiological source-term predictions. The current scope and status of this research is reviewed.  相似文献   
30.
Utility conservation programmes are designed to benefit both participants and non-participants. This article outlines the issues involved in designing conservation programmes for utilities and determining the appropriate amount of incentives that can be provided to participants without harming non-participants. More importantly, the article discusses the issue of access to the programmes by utility customers. It concludes that it is the existing restrictions to participation, and not the level of compensation, that are of greatest concern to non-participants. A number of utility programmes designed to eliminate the problem of non-participation are reviewed.  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