全文获取类型
收费全文 | 32020篇 |
免费 | 1448篇 |
国内免费 | 865篇 |
专业分类
电工技术 | 714篇 |
技术理论 | 1篇 |
综合类 | 1479篇 |
化学工业 | 7446篇 |
金属工艺 | 1065篇 |
机械仪表 | 1195篇 |
建筑科学 | 1168篇 |
矿业工程 | 1395篇 |
能源动力 | 4415篇 |
轻工业 | 4029篇 |
水利工程 | 380篇 |
石油天然气 | 4185篇 |
武器工业 | 64篇 |
无线电 | 528篇 |
一般工业技术 | 1813篇 |
冶金工业 | 2556篇 |
原子能技术 | 238篇 |
自动化技术 | 1662篇 |
出版年
2024年 | 52篇 |
2023年 | 417篇 |
2022年 | 847篇 |
2021年 | 967篇 |
2020年 | 1121篇 |
2019年 | 832篇 |
2018年 | 665篇 |
2017年 | 760篇 |
2016年 | 707篇 |
2015年 | 708篇 |
2014年 | 1813篇 |
2013年 | 1979篇 |
2012年 | 2271篇 |
2011年 | 2292篇 |
2010年 | 1866篇 |
2009年 | 1702篇 |
2008年 | 1424篇 |
2007年 | 1869篇 |
2006年 | 1900篇 |
2005年 | 1652篇 |
2004年 | 1436篇 |
2003年 | 1327篇 |
2002年 | 1179篇 |
2001年 | 943篇 |
2000年 | 813篇 |
1999年 | 653篇 |
1998年 | 473篇 |
1997年 | 344篇 |
1996年 | 303篇 |
1995年 | 230篇 |
1994年 | 197篇 |
1993年 | 106篇 |
1992年 | 114篇 |
1991年 | 75篇 |
1990年 | 53篇 |
1989年 | 54篇 |
1988年 | 37篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 9篇 |
1983年 | 17篇 |
1982年 | 4篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1955年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
《Oil and Energy Trends》2020,45(11):26-28
Current data on natural gas production, as well as a breakdown of production by country. Updated on a monthly basis. 相似文献
992.
《International Journal of Hydrogen Energy》2021,46(63):32017-32035
A comprehensive study was conducted on the performance of M-promoted (M = 1%Ru, 1%Rh, 5%Ni) upgraded slag oxide metallurgical waste catalysts (M-UGSO) for hydrogen production by glycerol steam reforming (GSR). The results confirmed that the tendency of the incorporated metal to interact with Mg/Fe containing species within UGSO plays a key role in the surface availability of the corresponding metal, structural changes after reduction, and catalyst stability. Aside its best stability, 5% Ni-UGSO showed a performance (glycerol conversion to gaseous products of 100% and H2 yield of 74%) comparable with 1% Rh-UGSO (100% and 78%, respectively) or even surpassing that of 1% Ru-UGSO (94% and 71%, respectively), as noble metal-based catalysts. Synergistic cooperation was achieved by incorporated metals (M) and Fe/Mg containing species within UGSO, resulting in enhanced glycerol and water activation. The weakest results of Ru-UGSO could be justified by lack of propensity for MgO–RuO2 interaction on UGSO surface. 相似文献
993.
Wei-Je Huang Ching-Tsung Yu Wen-Jenn Sheu Yen-Cho Chen 《International Journal of Hydrogen Energy》2021,46(31):16522-16533
The effect of non-uniform temperature on the sorption-enhanced steam methane reforming (SE-SMR) in a tubular fixed-bed reactor with a constant wall temperature of 600 °C is investigated numerically by an experimentally verified unsteady two-dimensional model. The reactor uses Ni/Al2O3 as the reforming catalyst and CaO as the sorbent. The reaction of SMR is enhanced by removing the CO2 through the reaction of CaO + CO2 → CaCO3 based on the Le Chatelier's principle. A non-uniform temperature distribution instead of a uniform temperature in the reactor appears due to the rapid endothermic reaction of SMR followed by an exothermic reaction of CO2 sorption. For a small weight hourly space velocity (WHSV) of 0.67 h?1 before the CO2 breakthrough, both a low and a high temperature regions exist simultaneously in the catalyst/sorbent bed, and their sizes are enlarged and the temperature distribution is more non-uniform for a larger tube diameter (D). Both the CH4 conversion and the H2 molar fraction are slightly increased with the increase of D. Based on the parameters adopted in this work, the CH4 conversion, the H2 and CO molar fractions at D = 60 mm are 84.6%, 94.4%, and 0.63%, respectively. After CO2 breakthrough, the reaction of SMR dominates, and the reactor performance is remarkably reduced due to low reactor temperature.For a higher value of WHSV (4.03 h?1) before CO2 breakthrough, both the reaction times for SMR and CO2 sorption become much shorter. The size of low temperature region becomes larger, and the high temperature region inside the catalyst/sorbent bed doesn't exist for D ≥ 30 mm. The maximum temperature difference inside the catalyst/sorbent bed is greater than 67 °C. Both the CH4 conversion and H2 molar fraction are slightly decreased with the increase of D. However, this phenomenon is qualitatively opposite to that for small WHSV of 0.67 h?1. The CH4 conversion and H2 molar fraction at D = 60 mm are 52.6% and 78.7%, respectively, which are much lower than those for WHSV = 0.67 h?1. 相似文献
994.
Water hyacinth was the chosen alternative biomass for H2 production in this study. A batch and a continuous pilot plant systems are proposed. A batch system of 500?ml capacity was developed first for finding an appropriate biomass ratio which was found to be 2.5%wt. Results from the batch system was used to construct a kinetic model of water hyacinth hydrolysis. The same biomass and water ratio was used in the continuous system. Besides water hyacinth, glucose and cellulose?+?lignin biomasses were tested. During processing, temperature, pressure, and electric consumption of the system were recorded. The quality and quantity of gas products were analyzed by gas chromatography (GC). The water hyacinth biomass attained the highest rate of H2 production (providing energy of 11.43?kWh/mole of glucose). Comparing the batch and continuous pilot systems, the continuous system achieved 2.7 times more H2 mole% than the batch system did. 相似文献
995.
《International Journal of Hydrogen Energy》2022,47(3):1499-1515
Dark fermentation (DF) is a promising technology for biohydrogen production. Low efficiency of biohydrogen production is a bottleneck of the scale-up prospects for DF. Additives have been extensively studied to improve the biohydrogen production efficiency. Among of them, iron-based additives present a promising application potential due to their demonstrated significant enhancement of DF efficiency and among the low-cost bioactive agents. However, current reviews mainly examined the effects of nano-materials on DF and an in-depth analysis of enhancing mechanisms with addition of iron-based additives in DF is still lacking. To this end, this article comprehensively reviewed and evaluated the effects of iron-based additives on DF. Further, the potential mechanisms, including altering metabolic pathways, improving activities of microbes and enzymes, promoting electron delivery, and enriching hydrogen-producing bacteria, were discussed. Lastly, prospects and challenges of iron-based additives for subsequent research and large-scale application for DF were summarized. 相似文献
996.
Gregory J. Scott 《International Journal of Food Science & Technology》2021,56(3):1093-1114
For many of the developing world's poorest farmers and food-insecure people, roots, tubers, bananas and plantain crops (RTBs) serve as a critical source of food, nutrition and cash income. RTBs have been particularly important in areas where local agri-food systems are under stress. Under such circumstances, growers, processors and traders often see opportunities to improve food security or increase their incomes with those crops due to shifting tastes and preferences for food and non-food products. Since the early 1990s, cassava output surged in sub-Saharan Africa, while potato production expanded rapidly in Asia. RTBs are consumed by over three billion people in developing countries with a market value of US$ 339 billion. This paper analyses the major changes in production, utilisation and trade of RTBs over the last six decades, assesses estimates of their future trajectory and offers recommendations so that they might achieve their full potential. 相似文献
997.
《International Journal of Hydrogen Energy》2022,47(45):19865-19875
Maritime industry has led renewable energy sources for the greener environment and efficient vehicles that effect by increasing population and energy demands. Hydrogen is one of the most popular of these renewable energy sources and one of the most favourable research area, worldwide. In this study, authors reported the usage of hydrogen fuel cells in marine transport as main power forwarder, their advantages and challenges under the lights on state of art and furthermore new technologies perspective. The latest research activities, hydrogen production and storage methods with challenges are analyzed and the developments of fuel cell based marine vehicles are discussed. In detailed, newly approachment of electrolyses from seawater for sustainable fuel necessity is discussed. As a result, this forseen study is important in terms of handling energy from seawater and compiling the latest technology for marine transport. 相似文献
998.
999.
《International Journal of Hydrogen Energy》2022,47(21):11116-11127
An important difficulty associated with alkaline water electrolysis is the rise in anode overpotential attributable to bubble coverage of the electrode surface. For this study, a system with a high-speed video camera was developed, achieving in-situ observation of bubble generation on an electrode surface, monitoring an area of 1.02 mm2 at 6000 frames per second. The relation between polarization curve (current density up to 3.0 A cm?2) and oxygen bubble generation behavior on nickel electrodes having cylindrical wires and rectangular wires of different sizes (100–300 μm) was clarified. The generated bubbles slide upward, contacting the electrode surface and detaching at the top edge. Observations indicate that small electrodes have short bubble residence time and thin bubble covering layer on the electrode. As a result, the small electrode diameter contributes to smaller overpotential at high current density. 相似文献
1000.
《International Journal of Hydrogen Energy》2020,45(1):56-63
Recently, various studies have been conducted on hydrogen energy as a means of replacing conventional fuels. Polymer electrolyte membrane water electrolyzers (PEMWEs) are being studied as a means of producing hydrogen for renewable energy. The PEMWE can be operated over a wider range than other types of water electrolyzers and can be connected to a renewable energy source, such as solar or wind. However, further studies are required because the water accompanying the hydrogen in the cathode presents a problem regarding hydrogen purity and storage. The phenomenon of water transport which is occurred on the PEMWE is analyzed by electro-osmotic drag and diffusion in the membrane. Electro-osmotic drag coefficients which are calculated by mass flow rate of discharged water with hydrogen are compared to the results of previous studies. The results of Electro-osmotic drag coefficient are different from previous studies at each operating condition. This difference is considered to be caused by the capacity of PEMWE such as active area and the number of cell. 相似文献