全文获取类型
收费全文 | 327897篇 |
免费 | 10137篇 |
国内免费 | 4560篇 |
专业分类
电工技术 | 9668篇 |
技术理论 | 5篇 |
综合类 | 5923篇 |
化学工业 | 49463篇 |
金属工艺 | 16020篇 |
机械仪表 | 12468篇 |
建筑科学 | 13763篇 |
矿业工程 | 3013篇 |
能源动力 | 8596篇 |
轻工业 | 29040篇 |
水利工程 | 3372篇 |
石油天然气 | 6475篇 |
武器工业 | 686篇 |
无线电 | 40101篇 |
一般工业技术 | 54850篇 |
冶金工业 | 54269篇 |
原子能技术 | 4906篇 |
自动化技术 | 29976篇 |
出版年
2023年 | 1791篇 |
2022年 | 2623篇 |
2021年 | 4737篇 |
2020年 | 3587篇 |
2019年 | 3526篇 |
2018年 | 4767篇 |
2017年 | 4996篇 |
2016年 | 4812篇 |
2015年 | 5112篇 |
2014年 | 7203篇 |
2013年 | 15737篇 |
2012年 | 10919篇 |
2011年 | 13602篇 |
2010年 | 11232篇 |
2009年 | 11818篇 |
2008年 | 12215篇 |
2007年 | 12168篇 |
2006年 | 11835篇 |
2005年 | 10801篇 |
2004年 | 9079篇 |
2003年 | 8703篇 |
2002年 | 8472篇 |
2001年 | 8349篇 |
2000年 | 8046篇 |
1999年 | 9048篇 |
1998年 | 18666篇 |
1997年 | 13314篇 |
1996年 | 10719篇 |
1995年 | 8128篇 |
1994年 | 7075篇 |
1993年 | 6558篇 |
1992年 | 4729篇 |
1991年 | 4530篇 |
1990年 | 3966篇 |
1989年 | 3820篇 |
1988年 | 3607篇 |
1987年 | 2975篇 |
1986年 | 2886篇 |
1985年 | 3428篇 |
1984年 | 3012篇 |
1983年 | 2690篇 |
1982年 | 2507篇 |
1981年 | 2511篇 |
1980年 | 2381篇 |
1979年 | 2197篇 |
1978年 | 2157篇 |
1977年 | 2730篇 |
1976年 | 4094篇 |
1975年 | 1830篇 |
1974年 | 1733篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
In this work was investigated the effect of the addition of barium titanate (BaTiO3) on electrical properties of two chemically recyclable thermosets, polyhemiaminal (PHA) and polyhexahydro‐s‐triazine (PHT), both fabricated from 4,4′‐oxydianiline (ODA), an ether derivative of aniline and paraformaldehyde. Thermal and mechanical properties as well as chemical recyclability of the two polymers and their nanocomposites/nanodielectrics were also investigated. In addition, a quantitative analysis was conducted of the nanoparticle dispersion in the PHA‐/PHT‐based BaTiO3‐containing nanocomposites using transmission electron microscopy imaging and the nearest‐neighbor distance index and this index was used to analyze the investigated properties in connection with the proper mechanisms. Regarding the electrical properties for both neat polymers, conductivity values of the order of 10?8 S m?1 at 100 Hz were observed and dielectric constant values close to 2.80 for both polymers at 1 kHz. The addition of 0.5 wt% of BaTiO3 ferroelectric nanoparticles increased by about 44% the dielectric constant (1 kHz) and conductivity (102 Hz) of the PHA‐based nanocomposite. PHA and PHT exhibited glass transition temperature (Tg) values in the range 125–180 °C. An increase of 7 °C in Tg was observed after the incorporation of 0.5 wt% of BaTiO3 into PHA. Concerning the mechanical properties, values in the range 4.00–4.45 GPa for reduced modulus and 0.30–0.43 GPa for nanohardness for PHA and PHT polymers were observed. Independently of filler content or polymer matrix, both mechanical properties were enhanced after the addition of BaTiO3. The chemical recycling of PHA/PHT and all nanocomposites in the initial ODA reagent after sulfuric acid treatment was successfully characterized using the NMR and Fourier transform infrared spectroscopic techniques. © 2018 Society of Chemical Industry 相似文献
73.
Zhongyu Qiu Xiaowen Ge Naibao Huang Shixian Zhou Junjie Zhang Jiaping Xuan 《International Journal of Hydrogen Energy》2021,46(3):2952-2959
Polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide block copolymer having different molecular weights are used as precursors of carbon materials to prepare Hollow -Derivatives carbon material as an electrocatalyst through block copolymer self-assembly. The composition and microstructure of the prepared catalysts are shown by Raman spectroscopy, X-ray diffraction (XRD), Test of nitrogen adsorption and desorption curves, High resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy (HR-SEM). Oxygen was passed into alkaline electrolyte solution until the solution reached saturation state. With molecular weight increasing, the obtained sample gradually changed from block to hollow and spherical. When the molecular weight was 12600 g mol?1, the evenly hollow carbon nanocages was acquired (C-12600). In O2 saturated alkaline electrolyte (0.1 M KOH solution), C-12600's limited current density,half-wave potential and initial potential are 5.23 mA cm?2@0.4 V, 0.72 V and 0.81 V, respectively. And most important is that half-wave potential and onset potential have barely change after 2000 cycles of cyclic voltammetry. As a result, the porous carbon materials exhibited excellent electrocatalytic activity while maintaining high stability in alkaline KOH solution. 相似文献
74.
Madhu H. C. Edachery Vimal Lijesh K. P. Perugu Chandra Shekhar Kailas Satish V. 《Metallurgical and Materials Transactions A》2020,51(8):4086-4099
Metallurgical and Materials Transactions A - Hybrid nanocomposites have potential as wear-resistant materials. However, synthesizing these nanocomposites by conventional molten state methods result... 相似文献
75.
76.
Yu-Jiao Liu Xiao-Yang Fan Dr. Dong-Dong Zhang Yin-Zheng Xia Dr. Yan-Jun Hu Feng-Lei Jiang Prof. Fu-Ling Zhou Prof. Yi Liu 《ChemMedChem》2020,15(6):552-558
Based on the potential therapeutic value in targeting mitochondria and the fluorophore tracing ability, a fluorescent mitochondria-targeted organic arsenical PDT-PAO-F16 was fabricated, which not only visualized the cellular distribution, but also exerted anti-cancer activity in vitro and in vivo via targeting pyruvate dehydrogenase complex (PDHC) and respiratory chain complexes in mitochondria. In details, PDT-PAO-F16 mainly accumulated into mitochondria within hours and suppressed the activity of PDHC resulting in the inhibition of ATP synthesis and thermogenesis disorder. Moreover, the suppression of respiratory chain complex I and IV accelerated the mitochondrial dysfunction leading to caspase family-dependent apoptosis. In vivo, the acute promyelocytic leukemia was greatly alleviated in the PDT-PAO-F16 treated group in APL mice model. Our results demonstrated the organic arsenical precursor with fluorescence imaging and target-anticancer efficacy is a promising anticancer drug. 相似文献
77.
78.
79.
80.