全文获取类型
收费全文 | 27243篇 |
免费 | 689篇 |
国内免费 | 36篇 |
专业分类
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 |
出版年
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.
Robert Greetham 《Landscape Research》1992,17(1):10-19
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.
S.B. Burson D. Bradley J. Brockmann E. Copus D. Powers G. Greene C. Alexander 《Nuclear Engineering and Design》1989,115(2-3)
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.
Robert M. Wirtshafter 《Energy Policy》1985,13(2):143-155
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