全文获取类型
收费全文 | 198627篇 |
免费 | 22403篇 |
国内免费 | 14885篇 |
专业分类
电工技术 | 17175篇 |
技术理论 | 4篇 |
综合类 | 21842篇 |
化学工业 | 25393篇 |
金属工艺 | 13895篇 |
机械仪表 | 14332篇 |
建筑科学 | 14679篇 |
矿业工程 | 8424篇 |
能源动力 | 5016篇 |
轻工业 | 23104篇 |
水利工程 | 6183篇 |
石油天然气 | 7754篇 |
武器工业 | 3002篇 |
无线电 | 20206篇 |
一般工业技术 | 16402篇 |
冶金工业 | 8316篇 |
原子能技术 | 3146篇 |
自动化技术 | 27042篇 |
出版年
2024年 | 1182篇 |
2023年 | 3031篇 |
2022年 | 7313篇 |
2021年 | 9357篇 |
2020年 | 6928篇 |
2019年 | 4745篇 |
2018年 | 5251篇 |
2017年 | 6321篇 |
2016年 | 5438篇 |
2015年 | 8852篇 |
2014年 | 11107篇 |
2013年 | 13017篇 |
2012年 | 16080篇 |
2011年 | 16833篇 |
2010年 | 16195篇 |
2009年 | 15790篇 |
2008年 | 16256篇 |
2007年 | 15526篇 |
2006年 | 13578篇 |
2005年 | 10907篇 |
2004年 | 8124篇 |
2003年 | 5457篇 |
2002年 | 5042篇 |
2001年 | 4497篇 |
2000年 | 3653篇 |
1999年 | 1553篇 |
1998年 | 705篇 |
1997年 | 583篇 |
1996年 | 473篇 |
1995年 | 410篇 |
1994年 | 367篇 |
1993年 | 259篇 |
1992年 | 205篇 |
1991年 | 145篇 |
1990年 | 131篇 |
1989年 | 134篇 |
1988年 | 83篇 |
1987年 | 72篇 |
1986年 | 50篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 29篇 |
1980年 | 44篇 |
1979年 | 32篇 |
1975年 | 3篇 |
1967年 | 1篇 |
1959年 | 32篇 |
1951年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
51.
ZHAO Pengfei TIAN Yuming LIU Aiping KONG Xiangchen CHAI Yuesheng LI Zhangang BAI Pinbo 《中国耐火材料》2015,(2):36-41
Based on the needs of the market,a new 52 MPa medium-density and high-strength ceramic proppant was prepared by adopting third grade bauxite and clay as raw materials and using the solid phase sintering method,and the effect of the firing temperature on the microstructure,phase composition and mechanical properties of the ceramic proppant was studied. The broken resistance mechanism of this ceramic proppant was also discussed. The results show that the main phases of the prepared ceramic proppant are mullite and corundum; the broken rates are 3. 92% and 7. 21% under 52 MPa and69 MPa,respectively. 相似文献
52.
探讨了采用Hazelett生产线,从原料到合格铝液各道工序的操作要求;特别是采用电解铝液,对每道工序操作时间和铝液质量控制提出严格要求。通过实际生产,对现有熔炼炉配置、设备台数、精炼设备配置作了详细阐述,对每道工序要达到的铝液净化参数提出严格要求,经过6次净化提纯,基本满足Hazelett铸机要求,并对熔炼设备配置的不足提出合理化建议。 相似文献
53.
通过文献计量方法从样本选取、研究动态分析、主题分布三方面对健康人力资本发展现状及热点问题进行总结.研究结果表明,自2004年开始该领域所属学科种类和期刊源日益丰富,并形成合著度较高的核心作者群体,健康人力资本研究成为人力资本领域的研究热点,健康人力资本与经济增长或收入的关系、健康人力资本指标体系的构建和居民健康人力资本收入效应的测算等问题都成为当前和未来的研究重点. 相似文献
54.
55.
With increasing consumption of natural gas (NG), small NG reservoirs, such as coalbed methane and oil field associated gas, have recently drawn significant attention. Owing to their special characteristics (e.g., scattered distribution and small output), small-scale NG liquefiers are highly required. Similarly, the mixed refrigerant cycle (MRC) is suitable for small-scale liquefaction systems due to its moderate complexity and power consumption. In consideration of the above, this paper reviews the development of mobile miniature NG liquefiers in Technical Institute of Physics and Chemistry (TIPC), China. To effectively liquefy the scattered NG and overcome the drawbacks of existing technologies, three main improvements, i.e., low-pressure MRC process driven by oil-lubricated screw compressor, compact cold box with the new designed heat exchangers, and standardized equipment manufacturing and integrated process technology have been made. The development pattern of “rapid cluster application and flexible liquefaction center” has been eventually proposed. The small-scale NG liquefier developed by TIPC has reached a minimum liquefaction power consumption of about 0.35 kW·h/Nm3. It is suitable to exploit small remote gas reserves which can also be used in boil-off gas reliquefaction and distributed peak-shaving of pipe networks. 相似文献
56.
57.
58.
Haliza Abdul Aziz Noor Azeerah Abas Bonnie Tay Yen Ping Zainab Idris 《Journal of surfactants and detergents》2020,23(2):251-262
The technology for transesterification reactions between methyl esters and alcohols is well established by using classical homogeneous alkaline catalysts, which provide high conversion of methyl esters to specialty or nonindigenous esters. However, in certain products where the purity of the esters is of concern, the removal of homogeneous catalysts after the completion of the reaction is a challenge in terms of production cost and water footprint. Therefore, a study to investigate the potential of heterogeneous catalysts was conducted on reactions between methyl palmitate and triethanolamine. The degree of basicity and active surface area of calcium oxide (CaO), zinc oxide (ZnO), and magnesium oxide (MgO) were first characterized by using temperature-programmed desorption (TPD-CO2) and Brunauere–Emmett–Teller (BET), respectively. Among the metal oxides investigated, the CaO catalyst showed the best catalytic activity toward the transesterification process as it gave the highest conversion of methyl palmitate and yielded fatty esteramine compositions similar to the conventional homogeneous catalyst. The optimum transesterification condition by using the CaO catalyst utilized a lower vacuum system of approximately 200 mbar, which could minimize a considerable amount of energy consumption. Furthermore, low CaO dosage of 0.1% was able to give a conversion of 94.5% methyl ester and formed esteramine at 170 °C for 2 h. Therefore, the production of esterquats from esteramine may become more economically feasible through the methyl ester route by using the CaO catalyst, which can be recycled three times. 相似文献
59.
针对电站锅炉回转式空气预热器运行时上下表面不可见的问题,本文提出了一种视频监控与故障分析系统,可直接监测转子表面情况。该系统通过视频监控获取图像,结合改进的Retinex算法对其进行处理,实现了以下2个功能:1)能分析积灰程度以判断转子堵塞 情况;2)与温度场融合实时显示转子表面热点分布以预防二次燃烧。该系统已应用于某600 MW机组,实现了在热态环境下对空气预热器转子积灰程度、热点分布、堵塞程度的估算与可视化,大大提高了空气预热器运行的可靠性。 相似文献
60.
Qiang Wang Lei Shen Tong Xue Gao Cheng Cheng Zhi Huang Hong Jin Fan Yuan Ping Feng 《Advanced functional materials》2021,31(2):2002187
The {100} facet of single-crystalline TiO2(B) is an ideal platform for inserting Li ions, but it is hard to be obtained due to its high surface energy. Here, the single-crystalline TiO2(B) nanobelts from H2Ti3O7 with nearly 70% {100} facets exposed are synthesized, which significantly enhances Li-storage capacity. The first-principle calculations demonstrate an ab in-plane 2D diffusion through the exposed {100} facets. As a consequence, the nanobelts can significantly accommodate Li ions in LiTiO2 formula with specific capacity up to 335 mAh g−1, which is in good agreement with the electrochemical characterizations. Coating with conductive and protective poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), the cut-off discharge voltage is as low as 0.5 V, leading to a capacity of 160.7 mAh g−1 after 1500 cycles with a retention rate of 66% at 1C. This work provides a practical strategy to increase the Li-ion capacity and cycle stability by tailoring the crystal orientation and nanostructures. 相似文献