全文获取类型
收费全文 | 145813篇 |
免费 | 10635篇 |
国内免费 | 5108篇 |
专业分类
电工技术 | 7322篇 |
技术理论 | 15篇 |
综合类 | 8135篇 |
化学工业 | 24286篇 |
金属工艺 | 7287篇 |
机械仪表 | 8371篇 |
建筑科学 | 10218篇 |
矿业工程 | 3777篇 |
能源动力 | 4343篇 |
轻工业 | 8821篇 |
水利工程 | 2157篇 |
石油天然气 | 7091篇 |
武器工业 | 843篇 |
无线电 | 19511篇 |
一般工业技术 | 19311篇 |
冶金工业 | 8606篇 |
原子能技术 | 1629篇 |
自动化技术 | 19833篇 |
出版年
2024年 | 263篇 |
2023年 | 2061篇 |
2022年 | 2880篇 |
2021年 | 4939篇 |
2020年 | 3880篇 |
2019年 | 3303篇 |
2018年 | 3815篇 |
2017年 | 4235篇 |
2016年 | 3754篇 |
2015年 | 4899篇 |
2014年 | 6337篇 |
2013年 | 8470篇 |
2012年 | 8652篇 |
2011年 | 9557篇 |
2010年 | 8152篇 |
2009年 | 8080篇 |
2008年 | 8127篇 |
2007年 | 7550篇 |
2006年 | 7681篇 |
2005年 | 6687篇 |
2004年 | 4832篇 |
2003年 | 4416篇 |
2002年 | 4275篇 |
2001年 | 3950篇 |
2000年 | 3717篇 |
1999年 | 4110篇 |
1998年 | 3943篇 |
1997年 | 3274篇 |
1996年 | 2832篇 |
1995年 | 2393篇 |
1994年 | 1959篇 |
1993年 | 1569篇 |
1992年 | 1220篇 |
1991年 | 967篇 |
1990年 | 840篇 |
1989年 | 712篇 |
1988年 | 561篇 |
1987年 | 446篇 |
1986年 | 326篇 |
1985年 | 307篇 |
1984年 | 217篇 |
1983年 | 155篇 |
1982年 | 160篇 |
1981年 | 122篇 |
1980年 | 130篇 |
1979年 | 85篇 |
1978年 | 89篇 |
1977年 | 90篇 |
1976年 | 123篇 |
1975年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
1.
Pengfei Liang Jie Zhu Di Wu Hui Peng Xiaolian Chao Zupei Yang 《Journal of the American Ceramic Society》2021,104(6):2702-2710
Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO2-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag+/Nb5+ co-doped (Ag1/4Nb3/4)xTi1−xO2 (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 103 and 1.6 × 104 at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics. 相似文献
2.
Chen Wen-Kuo Chang Jing-Rong Chen Long-Sheng Hsu Rui-Yang 《Multimedia Tools and Applications》2022,81(6):8317-8347
Multimedia Tools and Applications - With the advancement of technology and the spread of the COVID19 epidemic, learning can no longer only be done through face-to-face teaching. Numerous digital... 相似文献
5.
6.
Jincheng Yu Yabin Chang Ewa Jakubczyk Bing Wang Feridoon Azough Robert Dorey Robert Freer 《Journal of the European Ceramic Society》2021,41(9):4859-4869
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control. 相似文献
7.
针对芳香硝基化合物的催化选择性加氢反应,开发可替代贵金属催化剂的低成本、高效非贵金属催化剂,对于芳香胺类化合物的绿色生产具有重要意义。利用简易、可规模化的制备方法,以镍—2,5-吡啶二羧酸金属有机框架为前驱体,热解制备了氮掺杂石墨碳包覆镍纳米催化材料(Ni@CN)。采用X射线衍射、扫描电镜、透射电镜、元素分析、N2吸脱附等检测手段对Ni@CN的物化性质进行了表征,并对其催化性能进行了评价。结果表明,Ni@CN可在温和条件下(85℃,1.0 MPa H2)高效加氢含取代官能团的芳香硝基化合物生成对应的芳香胺类化合物。对比试验表明,镍纳米颗粒是Ni@CN的加氢活性中心,而石墨碳壳的存在有利于优先吸附硝基官能团。此外,进一步考察了Ni@CN的循环使用性能以及抗硫化物中毒的特性。 相似文献
8.
Wang Chen Bao Chun-Hui Wu Wan-Yu Hsu Chia-Hsun Zhao Ming-Jie Zhang Xiao-Ying Lien Shui-Yang Zhu Wen-Zhang 《Journal of Materials Science》2022,57(26):12341-12355
Journal of Materials Science - Molybdenum oxide (MoOx) films had been grown by using plasma-enhanced atomic layer deposition (PEALD) with Mo(CO)6 precursor and O2 plasma reactant in a substrate... 相似文献
9.
Karimi Bayan Chang Yu-Cheng Pekola Jukka P. 《Journal of Low Temperature Physics》2022,207(3-4):220-225
We discuss the temperature dependence of a common low temperature local thermometer, a tunnel junction between a superconductor and a normal metal (NIS junction). Towards the lowest temperatures its characteristics tend to saturate, which is usually attributed to selfheating effects. In this technical note, we reanalyze this saturation and show that the temperature independent subgap current of the junction alone explains in some cases the low temperature behavior quantitatively.
相似文献10.
Scientometrics - The article published on 5 July 2021 is well-written and of interest. However, some improvements could be made, such as ten Tables/Figures can be shortened to highlight the focused... 相似文献