全文获取类型
收费全文 | 12686篇 |
免费 | 1472篇 |
国内免费 | 594篇 |
专业分类
电工技术 | 1484篇 |
综合类 | 1221篇 |
化学工业 | 1308篇 |
金属工艺 | 699篇 |
机械仪表 | 725篇 |
建筑科学 | 1360篇 |
矿业工程 | 241篇 |
能源动力 | 2278篇 |
轻工业 | 438篇 |
水利工程 | 359篇 |
石油天然气 | 524篇 |
武器工业 | 83篇 |
无线电 | 602篇 |
一般工业技术 | 1714篇 |
冶金工业 | 372篇 |
原子能技术 | 361篇 |
自动化技术 | 983篇 |
出版年
2024年 | 20篇 |
2023年 | 188篇 |
2022年 | 389篇 |
2021年 | 539篇 |
2020年 | 507篇 |
2019年 | 450篇 |
2018年 | 419篇 |
2017年 | 490篇 |
2016年 | 569篇 |
2015年 | 536篇 |
2014年 | 832篇 |
2013年 | 866篇 |
2012年 | 851篇 |
2011年 | 1098篇 |
2010年 | 721篇 |
2009年 | 728篇 |
2008年 | 644篇 |
2007年 | 740篇 |
2006年 | 666篇 |
2005年 | 590篇 |
2004年 | 504篇 |
2003年 | 422篇 |
2002年 | 374篇 |
2001年 | 295篇 |
2000年 | 210篇 |
1999年 | 207篇 |
1998年 | 146篇 |
1997年 | 124篇 |
1996年 | 111篇 |
1995年 | 93篇 |
1994年 | 79篇 |
1993年 | 56篇 |
1992年 | 53篇 |
1991年 | 42篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1974年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 59 毫秒
41.
Alexander Döß Markus Schubert Michael Wiezorek Uwe Hampel Felix Flegiel Christoph Windmeier Eckhard Schleicher Christoph Schunk 《化学,工程师,技术》2021,93(7):1126-1133
Tailored conditioning and control of flashing feeds in industrial applications requires knowledge of the evolving flow morphology and phase fractions along the feed pipe. Design methods obtained from reference systems (e.g. water-air) are hardly applicable for commercial scales and critical fluid properties (e.g. high vapor densities, low surface tension). In this study, the flow morphology of flashing feeds in a novel refrigerant test rig at critical fluid properties was analyzed using wire-mesh sensors at two locations along the feed pipe and experimental data from the water-air system. 相似文献
42.
Bulin Boonrod Paweena Prapainainar Viganda Varabuntoonvit Kandis Sudsakorn Chaiwat Prapainainar 《International Journal of Hydrogen Energy》2021,46(17):10570-10585
Bio-hydrogenated diesel (BHD) is a second generation biofuel that can be produced from vegetable oil and hydrogen via hydroprocessing. BHD is considered as one of alternative and renewable energy. This work presents evaluation of environmental impacts of BHD produced from palm fatty acid distillate (PFAD) compared to fatty acid methyl ester (FAME). Greenhouse gas emission, energy consumption, and overall environmental impacts are assessed. System boundary is from palm oil cultivation to BHD production. The functional unit is defined as 1 kg of fuel produced at the plant. The results indicate that energy consumption of BHD-PFAD is 1.18 times higher than that of BHD-FAME, while giving GHG emission 13.56 times lower than that of BHD-FAME. The results of overall environmental impacts indicated that BHD-PFAD was 3.58 greater than that of BHD-FAME. 相似文献
43.
Li-Jane Shih Jia-Yu Wang Jing-Yao Jheng An-Ci Siao Yen-Yue Lin Yi-Wei Tsuei Yow-Chii Kuo Chih-Pin Chuu Yung-Hsi Kao 《International journal of molecular sciences》2020,21(23)
Prostate cancer (PCa) is a reproductive system cancer in elderly men. We investigated the effects of betel nut arecoline on the growth of normal and cancerous prostate cells. Normal RWPE-1 prostate epithelial cells, androgen-independent PC-3 PCa cells, and androgen-dependent LNCaP PCa cells were used. Arecoline inhibited their growth in dose- and time-dependent manners. Arecoline caused RWPE-1 and PC-3 cell cycle arrest in the G2/M phase and LNCaP cell arrest in the G0/G1 phase. In RWPE-1 cells, arecoline increased the expression of cyclin-dependent kinase (CDK)-1, p21, and cyclins B1 and D3, decreased the expression of CDK2, and had no effects on CDK4 and cyclin D1 expression. In PC-3 cells, arecoline decreased CDK1, CDK2, CDK4, p21, p27, and cyclin D1 and D3 protein expression and increased cyclin B1 protein expression. In LNCaP cells, arecoline decreased CDK2, CDK4, and cyclin D1 expression; increased p21, p27, and cyclin D3 expression; had no effects on CDK1 and cyclin B1 expression. The antioxidant N-acetylcysteine blocked the arecoline-induced increase in reactive oxygen species production, decreased cell viability, altered the cell cycle, and changed the cell cycle regulatory protein levels. Thus, arecoline oxidant exerts differential effects on the cell cycle through modulations of regulatory proteins. 相似文献
44.
45.
46.
Debojyoti Das Vaneet Bhatia Jayarethanam Pillai Aviral Kumar Tiwari 《Energy Sources, Part B: Economics, Planning, and Policy》2018,13(1):37-45
The authors revisit the relationship between US economic growth and crude oil prices considering Industrial Production Index and West Texas Intermediate crude oil spot prices as respective proxies for a period spanning over January 1986 to June 2017. To capture the asymmetric and time-varying relationship, the authors employ maximum overlap discrete wavelet transform (MODWT)-based quantile regression (QR) analysis. Interestingly, MODWT-based QR analysis provides evidence of supply-driven link between crude oil prices and economic growth in the short run. However, in the medium to long run a demand-driven link is dominant. In addition, the QR results without MODWT also advocate a demand-driven link. Overall, the result of this study adds a new dimension to the literature on the relationship between crude oil prices and economic growth by focusing upon the time-frequency varying business cycle fluctuations. 相似文献
47.
Ashish Nadar Atindra Mohan Banerjee M.R. Pai R.V. Pai Sher Singh Meena R. Tewari A.K. Tripathi 《International Journal of Hydrogen Energy》2018,43(1):37-52
Supported iron oxides have been established as an important class of catalyst for high temperature sulfuric acid decomposition. With an objective to elucidate the role of support in modifying the overall catalytic properties of dispersed iron oxide catalysts, a series of supported iron oxide based catalysts, Fe2O3 (15 wt%)/MO2 (M = Zr, Ce, Ti and Si), synthesized by adsorption-equilibrium method, is investigated for sulfuric acid decomposition reaction. The structure of dispersed iron oxide phases largely depended on the nature of the support oxide as revealed by the XRD and Mössbauer studies. α-Fe2O3 is found to be present as a major phase on ZrO2 and CeO2 support while ε-Fe2O3 was the major phase on silica supported iron oxide. On the other hand, presence of mixed oxide Fe2TiO5 was revealed over TiO2 support. Strong dispersed metal oxide-support interactions inhibited the total reduction of the dispersed phase on SiO2 and TiO2 as compared to complete reduction of dispersed iron oxide on CeO2 and ZrO2 supports during temperature programmed reduction upto 1000 °C. The order of catalytic activity at a temperature of ~750 °C is observed as Fe2O3/SiO2 > Fe2TiO5/TiO2 > Fe2O3/ZrO2 > Fe2O3/CeO2, while at higher temperatures of ~900 °C the SO2 yield is found to be comparable for all catalysts. A relationship between the rate of sulfate decomposition and catalytic activity is established through detailed TG-DTA investigations of sulfated catalyst and support. Considerable influence of the support oxide on the composition, structure, redox properties, morphology and catalytic activities of the active iron oxide dispersed phase has been observed. Thus, the support oxides operate as a critical component in the complex supported metal oxide catalysts and these findings might influence the design and development of future high temperature sulfuric acid decomposition catalysts. 相似文献
48.
Martia Shahsavan Mohammadrasool Morovatiyan J.Hunter Mack 《International Journal of Hydrogen Energy》2018,43(29):13575-13582
The thermodynamic efficiency of internal combustion engines is primarily dependent on the compression ratio and specific heat ratio of the working fluid. Due to a higher specific heat ratio, using a noble gas and oxygen instead of air can increase the thermal efficiency. The lack of nitrogen in the working fluid also eliminates NOx formation. In this study, the three-dimensional turbulent injection of hydrogen into a constant volume combustion chamber has been modeled and compared to mixtures of oxygen with nitrogen, argon, and xenon at different injection velocities. The results indicate that the hydrogen jet has a longer penetration length in nitrogen compared to argon and xenon. However, smaller penetration lengths lead to more complex jet shapes and larger cone angles. Combustion in a noble gas environment results in higher temperatures and OH radical concentrations, due in part to lower specific heats and the jet characteristics. Furthermore, mixedness is investigated using mean spatial variation and mean scalar dissipation. Hydrogen in argon shows a better mixing rate compared to nitrogen and xenon due to the higher diffusivity. The results indicate that reduction in mean spatial variation can lead to a shorter ignition delay. 相似文献
49.
Experimental and optimization of material synthesis process parameters for improving capacity of lithium‐ion battery 下载免费PDF全文
Yuhao Huang Binh Thanh Tran Saeed Asghari Hoang‐do Nguyen Xiongbin Peng Akhil Garg My Loan Phung LE 《国际能源研究杂志》2018,42(10):3400-3409
New methods for synthesis of active materials have been developed to improve capacity and cycle life performance of lithium‐ion batteries. Past studies have focused on routes of development of materials and new processes, which might not be economical for large‐scale production. In this regard, this study examines a widely employed carbothermal reduction technology for the synthesis of lithium‐iron phosphate (LiFePO4/C) and investigates effects of process conditions during this synthesis on final battery performance. An experimental combined genetic programming approach is used to model the effects of crucial process conditions (sintering time, the carbon content, and the sintering temperature) on the discharge capacity of the assembled battery. Experiments are conducted to collect the discharge capacity data based on varying LiFePO4/C synthesis conditions, and genetic programming is employed to develop a suitable functional relationship between them. The results show that the battery discharge capacity is controlled significantly by adjusting sintering temperature and carbon content, while the effect of sintering time is found to be insignificant. Further, the interaction effect of the sintering time and carbon content is much more obvious than that of the sintering time and the sintering temperature. The findings from the study pave the way for the optimum design of the synthesis process of LiFePO4/C for a higher battery performance. 相似文献
50.
《中国有色金属学会会刊》2020,30(5):1249-1266
The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31B alloy and AZ31B/1.5vol.%Al2O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 °C and then an open-die forging at 450 °C. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain; however, a degradation was observed in the high applied strain region. Unlike AZ31B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging. 相似文献