全文获取类型
收费全文 | 402589篇 |
免费 | 31945篇 |
国内免费 | 18959篇 |
专业分类
电工技术 | 24609篇 |
技术理论 | 59篇 |
综合类 | 48549篇 |
化学工业 | 46728篇 |
金属工艺 | 13045篇 |
机械仪表 | 19039篇 |
建筑科学 | 59088篇 |
矿业工程 | 20923篇 |
能源动力 | 13281篇 |
轻工业 | 32189篇 |
水利工程 | 30631篇 |
石油天然气 | 21353篇 |
武器工业 | 3027篇 |
无线电 | 24763篇 |
一般工业技术 | 25557篇 |
冶金工业 | 21105篇 |
原子能技术 | 3818篇 |
自动化技术 | 45729篇 |
出版年
2024年 | 1446篇 |
2023年 | 4460篇 |
2022年 | 8180篇 |
2021年 | 9970篇 |
2020年 | 10600篇 |
2019年 | 8866篇 |
2018年 | 8409篇 |
2017年 | 10255篇 |
2016年 | 11728篇 |
2015年 | 12744篇 |
2014年 | 24002篇 |
2013年 | 21813篇 |
2012年 | 27865篇 |
2011年 | 29250篇 |
2010年 | 22750篇 |
2009年 | 23638篇 |
2008年 | 21747篇 |
2007年 | 27880篇 |
2006年 | 26221篇 |
2005年 | 22911篇 |
2004年 | 19307篇 |
2003年 | 17469篇 |
2002年 | 14563篇 |
2001年 | 11994篇 |
2000年 | 10118篇 |
1999年 | 8126篇 |
1998年 | 6073篇 |
1997年 | 5141篇 |
1996年 | 4620篇 |
1995年 | 3940篇 |
1994年 | 3374篇 |
1993年 | 2528篇 |
1992年 | 2238篇 |
1991年 | 1644篇 |
1990年 | 1385篇 |
1989年 | 1244篇 |
1988年 | 979篇 |
1987年 | 714篇 |
1986年 | 572篇 |
1985年 | 465篇 |
1984年 | 422篇 |
1983年 | 309篇 |
1982年 | 252篇 |
1981年 | 184篇 |
1980年 | 162篇 |
1979年 | 126篇 |
1978年 | 68篇 |
1977年 | 87篇 |
1976年 | 61篇 |
1975年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Two types of conventional kiln-drying schedules (mild and harsh) based on moisture content (MC) were compared with regard to time, drying quality, and energy cost. The results were evaluated according to the classification of the European Drying Group. Proper drying periods of mild and harsh schedules were found to be 550 and 514 h, respectively. Evaluations in terms of drying quality indicated that better results were achieved with the mild schedule, especially when comparing drying defects and final MC. From an energy efficiency point of view, the harsh schedule, by saving 36 h of drying time, reduced electricity by 594 KWh and was therefore found to be $65 more profitable in this trial. 相似文献
103.
Diana Hurdowar-Castro Ioannis Tsanis Ilmar Simanovskis 《Journal of Great Lakes research》2007,33(1):232-252
A 3D transport model is used to perform a comparative analysis of several potential drinking water intakes located along the northwest shore of Lake Ontario between Toronto and Oshawa. The model is specifically used to assess each intake under both long- and short-term transport of a potential pollutant release from the Pickering Nuclear Generating Station and potential and actual pollutant releases from local land sources respectively. A model based on a 500 m grid resolution is calibrated using data collected in the aftermath of the 1992 tritium spill at the Pickering Nuclear Generation Station and subsequently used to simulate long-term transport. A model based on a 100 m grid resolution is verified using drogue studies and used to simulate short-term transport events. Both models are used to assess pollutant levels at each of nine potential intake locations under different wind scenarios and pollutant releases. Field data for the study included water quality and flow measurements from local sewers and rivers, and estimates of pollutant levels from the local waste water treatment plants. This paper describes the model setup for both the long-term and short-term transport models, calibration using field data, long-term transport modeling, short-term transport modeling, and the comprehensive analysis approach used to evaluate the nine potential intake locations proposed. Results indicated that four intakes in particular outperformed other intake locations by maintaining bottom pollutant levels within governmental standards and warning times that exceeded 20 hours. 相似文献
104.
我们于1985年对我院1984年开展肝单光子发射计算机断层以来的52例肝病人进行了分析总结。结果表明,肝单光子发射断层在诊断肝内占位性病变方面比普通肝静态γ照相有许多优点。需要指出的是,肝单光予发射断层的若干优点及诊断的准确性是与物理条件的正确选择和应用密切相关的。本文根据至今积累的近100例断层经验,从技术方面介绍了影响单 相似文献
105.
We analyze the wear resistance of plasma coatings for a constant work of friction. The dependences of the wear resistance
of the coatings are obtained for a broad range of loading conditions. It is shown that the minimum sensitivity to loading
conditions is exhibited by the molybdenum coatings. It is also established that the wear resistance of the coatings decreases
as the amplitude of displacements increases and the cyclic frequency of the tests decreases due to the intensification of
fatigue processes on the surfaces. The comparative characteristics of coatings are presented.
__________
Translated from Problemy Prochnosti, No. 5, pp. 94–100, September–October, 2007. 相似文献
106.
107.
《Drying Technology》2007,25(10):1621-1632
A study was performed to determine the drying characteristics and quality of barley grain dried in a laboratory scale spouted-bed dryer at 30, 35, 40, and 45°C and an inlet air velocity of 23 m/s-1, and in an IR-convection dryer under an infrared radiation intensity of 0.048, 0.061, 0.073, and 0.107 W cm-2 at an air velocity of 0.5 m/s-1. The results show that the first, relatively short, phase of a sharp decrease in the drying rate was followed by the phase of a slow decrease. The time of barley drying depended on temperature of inlet air in a spouted-bed dryer and on radiation intensities in an IR-convection dryer. Barley drying at 45°C in a spouted-bed dryer was accompanied by the lowest total energy consumption. The average specific energy consumption was lower and the average efficiency of drying was higher for drying in a spouted-bed dryer. The effective diffusivities were in the range 2.20-4.52 × 10-11 m2 s-1 and 3.04-4.79 × 10-11 m2/s-1 for barley dried in a spouted-bed and in an IR-convection dryer, respectively. There were no significant differences in kernel germination energy and capacity between the two drying methods tested. 相似文献
108.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024 相似文献
109.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals. 相似文献
110.
Distilled fractions of a coal-derived liquid from the H-Coal process were upgraded to diesel fuel by catalytic hydrotreatment. The total hydrotreated products were distilled into naphtha (<180°C) and diesel fuel fractions (>180°C) and the diesel fractions were analysed for hydrocarbon-type composition, hydrogen content and some diesel fuel properties. GC—MS-analyses were carried out on the hydrocarbon-type fractions to identify individual chemical compounds. To investigate the effect of different distillation cut points on diesel fuel yield and properties, cut points for one hydrotreated product were varied. The diesel fuel cetane numbers were correlated with percentage hydrogen, total aromatics and saturates. Cetane numbers above 40 were obtained for diesel fuels containing (i) more than 75% saturates, (ii) less than 15% total aromatics and (iii) a hydrogen content above 12.8%. Compounds identified by GC—MS-analyses (in the diesel fractions) were typical aromatic and cycloparaffin compounds. Normal-and iso-paraffin compounds were not detected. By varying the distillation cut point from 135 to 180°C, the cetane number of the residual diesel fraction improved from 37 to 44. This increase is ascribed to the removal of aromatic compounds in the 135–180°C boiling point range. 相似文献