全文获取类型
收费全文 | 6857篇 |
免费 | 585篇 |
国内免费 | 145篇 |
专业分类
电工技术 | 182篇 |
综合类 | 392篇 |
化学工业 | 1234篇 |
金属工艺 | 204篇 |
机械仪表 | 328篇 |
建筑科学 | 984篇 |
矿业工程 | 95篇 |
能源动力 | 252篇 |
轻工业 | 1164篇 |
水利工程 | 109篇 |
石油天然气 | 123篇 |
武器工业 | 14篇 |
无线电 | 559篇 |
一般工业技术 | 976篇 |
冶金工业 | 229篇 |
原子能技术 | 167篇 |
自动化技术 | 575篇 |
出版年
2024年 | 19篇 |
2023年 | 61篇 |
2022年 | 160篇 |
2021年 | 192篇 |
2020年 | 174篇 |
2019年 | 152篇 |
2018年 | 121篇 |
2017年 | 191篇 |
2016年 | 241篇 |
2015年 | 283篇 |
2014年 | 385篇 |
2013年 | 367篇 |
2012年 | 409篇 |
2011年 | 516篇 |
2010年 | 322篇 |
2009年 | 407篇 |
2008年 | 337篇 |
2007年 | 463篇 |
2006年 | 437篇 |
2005年 | 370篇 |
2004年 | 298篇 |
2003年 | 278篇 |
2002年 | 285篇 |
2001年 | 229篇 |
2000年 | 189篇 |
1999年 | 178篇 |
1998年 | 64篇 |
1997年 | 83篇 |
1996年 | 67篇 |
1995年 | 43篇 |
1994年 | 43篇 |
1993年 | 35篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 22篇 |
1989年 | 25篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 3篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有7587条查询结果,搜索用时 31 毫秒
11.
This paper presents a comparative study of the condensation heat transfer coefficients in a smooth tube when operating with pure refrigerant R134a and its mixture with lubricant Castrol “icematic sw”. The lubricant is synthetic polyol ester based oil commonly used in lubricating the compressors. Two concentrations of R134a-oil mixtures of 2% and 5% oil (by mass) were analysed for a range of saturation temperatures of refrigerant R134a between 35 °C and 45 °C. The mass flow rate of the refrigerant and the mixtures was carefully maintained at 1 g/s, with a vapour quality varying between 1.0 and 0. The effects of vapour quality, flow rate, saturation temperature and temperature difference between saturation and tube wall on the heat transfer coefficient are investigated by analysing the experimental data. The experimental results were then compared with predictions from earlier models [Int J Heat Mass Transfer (1979), 185; 6th Int Heat Transfer Congress 3 (1974) 309; Int J Refrig 18 (1995) 524; Trans ASME 120 (1998) 193]. Finally two new empirical models were developed to predict the two-phase condensation heat transfer coefficient for pure refrigerant R134a and a mixture of refrigerant R134a with Castrol “icematic sw”. 相似文献
12.
13.
Frédéric Gaschet 《Papers in Regional Science》2002,81(1):63-81
This article examines the relationships between the employment suburbanisation from central cities towards their suburbs,
and the process of intra-urban specialisation that occurred simultaneously in the fifty largest French metropolitan areas.
A methodology is proposed to identify urban subcentres and to analyse the effects of the intra-urban specialisations on suburbanisation
patterns. We conclude that the specialisation of both subcentres and central cities has a significant effect on suburbanisation
rates. Lastly, an intra-metropolitan shift/share analysis provides additional insights into the employment dynamics of central
cities and suburbs during the last twenty years.
Received: 25 July 2000 / Accepted: 29 May 2001 相似文献
14.
15.
数据包络分析模型及其应用研究 总被引:1,自引:1,他引:0
郑明贵 《南方冶金学院学报》2004,25(4):62-66
通过对传统的C^2R模型进行研究并加以改进,建立了C2RHZ模型,利用有色金属矿采选业1993-2001年科技创新的相关数据进行了计算分析。说明了C^2RHZ模型的应用价值. 相似文献
16.
No authorship indicated 《Canadian Metallurgical Quarterly》2007,62(8):788
Presents the citation, biography, and selected bibliography for R. Chris Fraley, one of the 2007 recipients of the American Psychological Association's Award for Distinguished Scientific Early Career Contributions to Psychology (individual differences). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
H. Hou J. C. Holste
B. E. Gammon
K. N. Marsh 《International Journal of Refrigeration》1992,15(6):365-371This paper reports densities of compressed R134a (1,1,1,2-tetrafluoroethane) determined by using a contiuously weighed pycnometer at 20 K intervals between 180 and 380 K at pressures from slightly greater than the vapour pressure to 70 MPa. The results are accurate to within ±0.1%. Saturated liquid densities derived by extrapolation from the experimental values agree with other reported values to within ±0.3%. 相似文献
18.
An equation of state for 1,1-difluoroethane (HFC 152a, CH3CHF2) has been developed on the basis of reliable experimental data including PVT, liquid Cp, and saturated-liquid-density data measured by our group. It is a non-dimensionalized virial equation whose functional form is the same as that originally developed for 1,1,1,2-tetrafluoroethane (HFC 134a) in our group. The effective range is for pressures up to 15 MPa, temperatures from 230 to 450 K, and densities to 1000 kg m−3. The equation represents reliable PVT measurements within ± 1% in pressure for the superheated vapour and supercritical fluid, while within ±0.5% in density for the compressed liquid. In addition, it should be noted that the equation represents the other essential thermodynamic properties including vapour pressures, saturated-liquid/ vapour densities, isobaric/isochoric specific heats and sound velocity in both the liquid and gaseous phase of HFC 152a. 相似文献
19.
Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles 总被引:1,自引:0,他引:1
Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. 相似文献
20.
Support vector clustering involves three steps—solving an optimization problem, identification of clusters and tuning of hyper-parameters. In this paper, we introduce a pre-processing step that eliminates data points from the training data that are not crucial for clustering. Pre-processing is efficiently implemented using the R*-tree data structure. Experiments on real-world and synthetic datasets show that pre-processing drastically decreases the run-time of the clustering algorithm. Also, in many cases reduction in the number of support vectors is achieved. Further, we suggest an improvement for the step of identification of clusters. 相似文献