全文获取类型
收费全文 | 848067篇 |
免费 | 65373篇 |
国内免费 | 35502篇 |
专业分类
电工技术 | 50987篇 |
技术理论 | 110篇 |
综合类 | 58594篇 |
化学工业 | 135943篇 |
金属工艺 | 46465篇 |
机械仪表 | 54073篇 |
建筑科学 | 69214篇 |
矿业工程 | 27462篇 |
能源动力 | 23245篇 |
轻工业 | 56768篇 |
水利工程 | 16184篇 |
石油天然气 | 52150篇 |
武器工业 | 7092篇 |
无线电 | 92873篇 |
一般工业技术 | 92176篇 |
冶金工业 | 44513篇 |
原子能技术 | 8734篇 |
自动化技术 | 112359篇 |
出版年
2024年 | 3238篇 |
2023年 | 11659篇 |
2022年 | 22241篇 |
2021年 | 30746篇 |
2020年 | 23636篇 |
2019年 | 18879篇 |
2018年 | 21984篇 |
2017年 | 25123篇 |
2016年 | 22861篇 |
2015年 | 31437篇 |
2014年 | 40957篇 |
2013年 | 49386篇 |
2012年 | 53436篇 |
2011年 | 59083篇 |
2010年 | 52430篇 |
2009年 | 49835篇 |
2008年 | 49369篇 |
2007年 | 47340篇 |
2006年 | 48401篇 |
2005年 | 42532篇 |
2004年 | 28284篇 |
2003年 | 25205篇 |
2002年 | 23603篇 |
2001年 | 21301篇 |
2000年 | 20948篇 |
1999年 | 22920篇 |
1998年 | 18531篇 |
1997年 | 15569篇 |
1996年 | 14556篇 |
1995年 | 11993篇 |
1994年 | 9948篇 |
1993年 | 6963篇 |
1992年 | 5575篇 |
1991年 | 4321篇 |
1990年 | 3345篇 |
1989年 | 2781篇 |
1988年 | 2311篇 |
1987年 | 1488篇 |
1986年 | 1152篇 |
1985年 | 771篇 |
1984年 | 589篇 |
1983年 | 452篇 |
1982年 | 406篇 |
1981年 | 286篇 |
1980年 | 287篇 |
1979年 | 162篇 |
1978年 | 68篇 |
1977年 | 102篇 |
1976年 | 112篇 |
1975年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Feng Wenran Li Zhen Chen Yingying Chen Jinyang Lang Haoze Wan Jianghong Gao Yan Dong Haitao 《Journal of Materials Science》2022,57(3):1881-1889
Journal of Materials Science - Although chalcogenide materials continue to generate considerable interest due to great potentials for various optoelectronic devices, annealing for a long time in... 相似文献
2.
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
3.
Zhao Jiandong Lei Wei Li Zijian Zhao Dongfeng Han Mingmin Hou Xiaoqing 《Multimedia Tools and Applications》2022,81(4):4753-4780
Multimedia Tools and Applications - The crowding in bus is an important factor affecting passenger satisfaction and bus dispatching level. However, how to use video images to detect crowding... 相似文献
4.
Wireless Networks - Geolocation is important for many emerging applications such as disaster management and recommendation system. In this paper, we propose a multilayer recognition model (MRM) to... 相似文献
5.
7.
8.
了解我国儿童家长的家庭食品安全知识知晓情况及其影响因素,对开展精准食品安全宣教,减少家庭食源性疾病具有积极意义。本研究在7个城市的13 923名3~12岁儿童家长中开展问卷调查,收集基本信息、家庭食品安全知识知晓情况及需求。家长家庭食品安全知识平均得分为18.6分(总分29分),及格率为68.7%。易错知识点包括熟食室温存储时间、食品保质期、易引起中毒的食物以及食品贮存环境等。多因素logistics回归分析显示:家长家庭食品安全知识及格率受地区、文化程度、职业、家长类型、是否关注食品安全、孩子是否讲过食品安全知识以及是否阅读孩子带回来资料的影响。家长最关心的前三位内容为滥用食品添加剂(84.9%)、卫生状况不合格(82.9%)、农药/药物残留(82.7%)。受家长信任的信息来源主要为电视/广播/广告(76.1%)、书籍/报纸/期刊(70.4%)、微博/微信等新媒体(57.7%)。家长的家庭食品安全知识仍存在短板,需利用传统媒体和新媒体结合的方式以及小手牵大手形式开展精准专题宣传,并特别关注文化程度低,从事食品行业的家长以及孩子父亲和保姆。 相似文献
9.
Kelin Hu Feipeng Wang Yuyang Yan Hongcheng Liu Zijia Shen 《Ceramics International》2021,47(11):15228-15236
In this paper, a novel hybrid structure of Pd doped ZnO/SnO2 heterojunction nanofibers with hexagonal ZnO columns was one step synthesized from electrospun precursor nanofibers. Due to the synergistic effect of hexagonal ZnO, SnO2 and Pd, the structure exhibited excellent hydrogen (H2) gas sensing properties. At low-temperature of 120 °C, the response (Ra/Rg) to 100 ppm H2 gas exceeded 160, the response/recovery time was only 20 s and 6 s respectively and the limit of detection was only 0.5 ppm. Meanwhile, it also had good selectivity for H2 gas and excellent linearity. In addition, the materials were characterized by XRD, FESEM, HRTEM, XPS, and the synthesis mechanism and gas sensing mechanism were proposed. 相似文献
10.
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