全文获取类型
收费全文 | 12568篇 |
免费 | 1203篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 167篇 |
综合类 | 17篇 |
化学工业 | 3149篇 |
金属工艺 | 484篇 |
机械仪表 | 719篇 |
建筑科学 | 188篇 |
矿业工程 | 6篇 |
能源动力 | 517篇 |
轻工业 | 1224篇 |
水利工程 | 41篇 |
石油天然气 | 9篇 |
武器工业 | 1篇 |
无线电 | 2197篇 |
一般工业技术 | 3005篇 |
冶金工业 | 675篇 |
原子能技术 | 132篇 |
自动化技术 | 1259篇 |
出版年
2024年 | 7篇 |
2023年 | 160篇 |
2022年 | 130篇 |
2021年 | 440篇 |
2020年 | 345篇 |
2019年 | 383篇 |
2018年 | 446篇 |
2017年 | 495篇 |
2016年 | 570篇 |
2015年 | 512篇 |
2014年 | 665篇 |
2013年 | 914篇 |
2012年 | 987篇 |
2011年 | 1178篇 |
2010年 | 829篇 |
2009年 | 806篇 |
2008年 | 675篇 |
2007年 | 547篇 |
2006年 | 473篇 |
2005年 | 391篇 |
2004年 | 379篇 |
2003年 | 356篇 |
2002年 | 264篇 |
2001年 | 229篇 |
2000年 | 215篇 |
1999年 | 205篇 |
1998年 | 280篇 |
1997年 | 169篇 |
1996年 | 143篇 |
1995年 | 89篇 |
1994年 | 81篇 |
1993年 | 60篇 |
1992年 | 51篇 |
1991年 | 34篇 |
1990年 | 40篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 6篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Seungmun Jung Jeonghyeon Do Dong-Geun Lee Byeong-Joo Lee Gil-up Cha Sunghak Lee 《Metals and Materials International》2014,20(4):577-583
In this study, new cost-effective Fe-based amorphous coating alloys having high amorphous forming ability were developed by varying the Fe content, while their microstructure, hardness, and corrosion resistance were also evaluated. Chemical compositions that have the lowest driving force of formation of crystalline phases such as Fe3P, Fe3C, and α-Fe were obtained from thermodynamically calculated phase diagrams of the representative FexAl2(P10.83C7.47B1.7)98-x alloy system at a crystallization temperature of 443 °C. Considering the intersections of driving force curves of Fe3P and Fe3C, Fe3P and α-Fe, and Fe3C and α-Fe, the Fe contents were found to be 77.8, 76.2, and 75.8 at.%, respectively. The microstructural analysis results of 1.5-mm-diameter suction-cast Fe-based alloys indicated that the Fe76.5Al2(P10.83C7.47B1.7)21.5 alloy had a fully amorphous microstructure, whereas crystalline phases were formed in other alloys. This alloy showed a better hardness and corrosion resistance than conventional thermal spray coating alloys, and its production cost could also be reduced by using less expensive alloying elements, which could provide a good way to practically apply this alloy to Fe-based amorphous thermal spray coatings. 相似文献
992.
Hyun CHO Seok Min HWANG Jae Bin LEE Dong Hyun KA Tae Wan KIM Bo Seul LEE Ji Young LEE Jung-Il LEE Jeong Ho RYU 《中国有色金属学会会刊》2014,(Z1):134-140
采用微波辐射辅助柠檬酸络合法制备Ho3+/Tm3+/Yb3+共掺杂CaWO4纳米晶升频转换荧光粉。将柠檬酸络合物前驱体在300~700°C热处理3 h。Ho3+/Tm3+/Yb3+共掺杂CaWO4C在400°C时开始结晶,在600°C时结晶完成。经600°C热处理的Ho3+/Tm3+/Yb3+共掺杂CaWO4主要呈球形,且形态均匀。在980 nm的激光激发下,Ho3+/Tm3+/Yb3+共掺杂CaWO4纳米晶出现肉眼可见的明亮的白色升频转换发射,这种现象来自Tm3+的475 nm蓝光发射以及Ho3+的543 nm绿光和651 nm红光发射。通过调整Tm3+和Ho3+的浓度可以控制Ho3+/Tm3+/Yb3+共掺杂CaWO4的CIE色度图从冷到暖白色之间变化。讨论了Tm3+和Ho3+浓度对升频转换光性能的影响以及与激光泵功率相关的影响机制。 相似文献
993.
Coatings on Mg alloys were prepared using NaOH + Na2SiO3 as basic electrolyte containing electrolyte of Na2SiF6 or NaF. EPP treatment was carried out on AZ31 Mg alloys matrix under a hybrid voltage of AC of 200 V combined with DC of 260 V for 30 min. Structural and morphological analyses of ceramic coatings were analyzed by XRD and SEM. Wear and hardness of coatings were measured by pin-on disk test and Vickers hardness test. The coatings formed in Na2SiF6 and NaF electrolytes were mainly composed of MgO and Mg2SiO4. The measured micro-hardness of coating formed in Na2SiF6 electrolyte was found to be over HV 1100, while, coating formed in NaF electrolyte possessed micro-hardness of HV ~900. These results show that the mechanical properties of AZ31B Mg alloys can be enhanced by the proper selection of electrolyte agent. 相似文献
994.
Jaedeuk Park Jae Hyun Cho Heon Jung Kwang-Deog Jung Il Moon 《International Journal of Hydrogen Energy》2014
This article details comprehensive energy and exergy analyses of the sulfuric acid decomposition process of the sulfur–iodine (SI) thermochemical cycle for hydrogen production. Energy and exergy efficiencies of the proposed process were evaluated over a variety of reaction temperatures and pressures. At an atmospheric temperature of 25 °C, the calculated values of exergy destruction of the H2SO4 decomposer ranged between 157 kJ/mol and 360 kJ/mol over reaction temperatures of 800–1000 °C and pressures between 1 and 50 atm. It was shown that the exergy efficiency of the H2SO4 decomposer improved with an increase in reaction temperature, while reaction pressure had a negative effect on exergy efficiency. 相似文献
995.
Hong Jae Yim Jae Hong Kim Sun-Jong Park Hyo-Gyoung Kwak 《Cement and Concrete Research》2012,42(11):1438-1446
Thermal damage in concrete usually induces contact-type defects, which result in degradation of the concrete's performance. This paper attempts to visualize the thermal damage in a multiscale, and characterizes the thermally damaged concrete using a nonlinear ultrasonic method. An impact-modulation method is used to obtain nonlinearity parameters, as a quantitative measure of contact-type defects, and shows better sensitivity than phase velocity variation as a linear ultrasonic method for thermally damaged concrete. The measured nonlinearity parameter is compared with the permeable pores, which reflect the occurrence of opening and pores in thermally damaged concrete. Degradation of concrete strength due to thermal damage is also assessed via the measurement. 相似文献
996.
Man Jae Han Shishir Kumar Behera Hung‐Suck Park 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(11):1541-1550
BACKGROUND: Anaerobic co‐digestion of refractory liquid organic wastes is an alternative environmental management strategy with economic benefits arising out of biogas production. Laboratory‐scale experimental investigations were carried out on the anaerobic co‐digestion of two liquid organic wastes, food waste leachate (FWL) and piggery wastewater (PWW). Three important parameters affecting methane yield were chosen for this study, namely, mixing ratio, alkalinity and salinity, which were optimized using response surface methodology. RESULTS: The results were analyzed statistically and the optimum conditions identified as: mixing ratio (FWL: PWW) 33 (in terms of volatile solid, w/w) (2 on v/v), alkalinity 2850 mg CaCO3 L?1, and salinity 3.4 g NaCl L?1. Under the optimum conditions, a cumulative methane yield (CMY) of 310 mL CH4 g?1 VSadded and VS reduction (VSR) of 54% were predicted. Mixing ratio and alkalinity showed the greatest individual and interactive effects on CMY and VSR (P < 0.05). A confirmation experiment under optimum conditions showed a CMY and VSR of 323 mL CH4 g?1 VSadded and 50%, respectively. This was only 1.04% and 1.1%, respectively, different from the predicted values. CONCLUSION: Anaerobic co‐digestion of FWL and PWW carried out under the optimum condition may be a feasible and efficient treatment option for methane production. Copyright © 2012 Society of Chemical Industry 相似文献
997.
This research analyzes the source of the power consumption in an optical disk drive (ODD) of a laptop computer. It shows that approximately 70?% of electrical input power is dissipated through the windage loss in the ODD. The windage loss is calculated by simulating the air flow around the rotating disk, and the simulated windage loss is verified by comparing with the measured one. It investigates the windage loss according to the variation of the upper and lower gaps between the rotating disk and case, and the optimal upper and lower gaps are determined by using the response surface methodology to reduce the windage loss. Finally, it shows experimentally that the proposed optimal model reduces total power consumption by 6.5?%. 相似文献
998.
Jae-Hyun Jung Byung-Dong Hahn Woon-Ha Yoon Dong-Soo Park Jong-Jin Choi Jungho Ryu Jong-Woo Kim Cheolwoo Ahn Kie-Moon Song 《Journal of the European Ceramic Society》2012,32(10):2451-2457
Dense yttria, erbia and dysprosia films with thicknesses of 44.8 ± 1.7, 51.6 ± 0.9 and 36.8 ± 3.1 μm, respectively, were deposited on plasma sprayed alumina coating by aerosol deposition (AD). The rare earth oxide films remarkably enhanced the erosion resistance of the plasma sprayed alumina coating upon exposure to the halogen gas plasma. The enhanced plasma erosion resistances were related to their low surface porosity as well as the low vapor pressures of the rare earth fluorides and chlorides compared with those of corresponding aluminum halogenides. Electrical breakdown voltages of the samples with yttria, erbia and dysprosia films on the plasma sprayed alumina coating were 5.5, 6.2 and 5.3 kV, respectively, at room temperature and 4.0, 4.2 and 3.9 kV, respectively, at 573 K. The breakdown voltages at RT and 573 K were more than double that of the plasma sprayed alumina coating without the AD films. 相似文献
999.
1000.
Manish Shrivastava Ashok Gidwani Heejung S. Jung 《Aerosol science and technology》2013,47(12):1218-1229
This work examines the measurement of surface specific soot oxidation rates with the High Temperature Oxidation-Tandem Differential Mobility Analyzer (HTO-TDMA) method. The Computational Fluid Dynamics package CFD-ACE+ is used to understand particle flow, oxidation and size dependent particle losses in the laminar aerosol flow reactor using an Eulerian-Lagrangian framework. Decrease of DMA selected mono-disperse particle size distribution due to oxidation within the aerosol tube is modeled using fitted kinetic soot oxidation parameters. The effects of Brownian diffusion and thermophoresis on particle flow and loss to the reactor walls are evaluated. The position of peak particle diameter, which is used as an indicator to determine oxidation rate, is found to be independent of diffusion, thermophoresis and secondary flow effects, thus validating its use in deriving kinetic soot oxidation parameters. Diffusion does not affect the evolution of particle size distribution within the reactor. However, thermophoresis is found to be the dominant mechanism influencing both shape of particle size distribution and particle loss to the walls of the aerosol reactor. Simulations show reduced effects of secondary recirculating flows on the particle flow trajectories in a vertical furnace as compared to horizontal furnace orientation. This work highlights the importance of making accurate measurements of temperature within the modeling domain. Since gas temperature within the flow tube could not be measured with high radial resolution using radiation shielded thermocouple, the derived soot oxidation rate may be uncertain by a factor of 2. Importantly, CFD simulations suggest that a distribution of temperature and size-dependent particle reactivities may be present in the reactor, requiring further theoretical and experimental investigation. 相似文献