全文获取类型
收费全文 | 2796篇 |
免费 | 331篇 |
国内免费 | 179篇 |
专业分类
电工技术 | 75篇 |
综合类 | 139篇 |
化学工业 | 862篇 |
金属工艺 | 191篇 |
机械仪表 | 26篇 |
建筑科学 | 15篇 |
矿业工程 | 16篇 |
能源动力 | 305篇 |
轻工业 | 17篇 |
水利工程 | 1篇 |
石油天然气 | 23篇 |
武器工业 | 5篇 |
无线电 | 643篇 |
一般工业技术 | 774篇 |
冶金工业 | 159篇 |
原子能技术 | 20篇 |
自动化技术 | 35篇 |
出版年
2024年 | 1篇 |
2023年 | 56篇 |
2022年 | 70篇 |
2021年 | 77篇 |
2020年 | 112篇 |
2019年 | 166篇 |
2018年 | 170篇 |
2017年 | 139篇 |
2016年 | 102篇 |
2015年 | 117篇 |
2014年 | 145篇 |
2013年 | 132篇 |
2012年 | 164篇 |
2011年 | 221篇 |
2010年 | 160篇 |
2009年 | 172篇 |
2008年 | 132篇 |
2007年 | 159篇 |
2006年 | 161篇 |
2005年 | 132篇 |
2004年 | 113篇 |
2003年 | 95篇 |
2002年 | 83篇 |
2001年 | 67篇 |
2000年 | 58篇 |
1999年 | 44篇 |
1998年 | 41篇 |
1997年 | 34篇 |
1996年 | 26篇 |
1995年 | 28篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有3306条查询结果,搜索用时 15 毫秒
1.
《Ceramics International》2022,48(14):20000-20009
Zinc oxide (ZnO) offers a major disadvantage of asymmetry doping in terms of reliability, stability, and reproducibility of p-type doping, which is the main hindrance in realization of optoelectronic devices. The problem is even more complicated due to formation of various native defects in unintentionally doped n-type ZnO. The realization of p-type conductivity in doped ZnO requires an in-depth understanding of the formation of an effective shallow acceptor, as well as donor-acceptor compensation. Photophysical properties such as photoconductivity along with photoluminescence (PL) studies have unprecedentedly and effectively been utilized in this work to monitor the evolution of various in-gap defects. Phosphorus (P) doped ZnO thin films have been grown by RF magnetron sputtering under various Ar to O2 gas ratios to investigate the effect of O2 on the donor-acceptor compensation by comprehensive photoconductivity measurements supported by the PL studies. Initial elemental analyses indicate presence of abundant zinc vacancies (VZn) in O-rich ambience. The results predict that P sits in the zinc (Zn) site rather than the oxygen (O) site causing the formation of PZn–2VZn acceptor-like defects, which compensates the donor defects in P doped ZnO films. Photocurrent spectra uniquely reveal presence of more oxygen vacancies (VO) defects states in lower O2 flow, which gets compensated with an increase in the O2 flow. Successive photocurrent transients indicate probable presence of more VO in the films grown with lower O2 flow and more VZn in higher O2 flow. Overall the photosensitivity measurements clearly present that O-rich ambience expedites the formation of acceptor defects which are compensated, thereby lowering the dark current and enhancing the ultraviolet photosensitivity. 相似文献
2.
《International Journal of Hydrogen Energy》2022,47(70):30172-30177
Sulfured doped carbon electrocatalysts is synthesized from the waste biomass Sargassum spp. Two doping procedures are examined to determine which is better for Oxygen Reduction Reaction (ORR); one by doping biocarbon obtained from the pyrolysis of the biomass and the second through a process of in situ doping in autoclave. The electrocatalyst are obtained from pyrolysis of the sample at 700 °C, which is finally characterized as a metal free electrocatalyst for the ORR. The electrocatalyst are characterized by BET surface area analysis, Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and the electrochemical characterization is determined in 0.1 M KOH. The sample SSKPT-1 exhibits a promising electrocatalytic activity with an onset potential of 0.896 V vs RHE and a current density of 5 mA cm?2 (at 0.2 V vs. RHE) which could be partly attributed to its high BET surface area of 2755 m2 g?1. 相似文献
3.
《Ceramics International》2020,46(3):2969-2978
Tin doped nanomagnetites, SnxFe3-xO4, were synthesized with various concentrations of Sn2+ ion (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) by co-precipitation method. XRD, VSM, TG-DTA, SEM-EDX and UV–Vis were used to characterize and study the structural, magnetic, thermal, and optical properties of SnxFe3-xO4 nanoparticles. XRD confirmed the presence of cubic structure and spinel phase of tin doped magnetites. The d-spacing, lattice parameter, density, crystallite size and cation distribution were derived from the XRD analysis. The M − H curves exhibited changes in saturation magnetization (Ms), coercive field (Hc), remanent magnetization (Mr) and susceptibility (χ), with increasing concentration of non-magnetic Sn2+ ions. Differential thermal analysis was used to study the thermal stability of SnxFe3-xO4 nanoparticles. The SEM images revealed the surface morphology of the nanoparticles and the EDX spectra showed an increase in the Sn content and a corresponding decrease in the Fe content for the tin doped samples. The optical bandgap was found to be centered at 3.9 eV for the synthesized materials. This systematic study may be the first comprehensive report on synthesis and characterization of tin doped magnetites. 相似文献
4.
Biyun Fang Chuanfeng Zhang Zeliang Qi Chunyan Li Jun Ni Xiuyun Wang Jianxin Lin Chak-Tong Au Bingyu Lin Lilong Jiang 《American Institute of Chemical Engineers》2022,68(11):e17849
The design of an efficient non-noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo2C/CeO2 catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low-valent Mo species, as well as high concentration of Ce3+ and surface oxygen species. The presence of Mo2C and CeO2 overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO2 catalyst prepared without carbonization, the Mo2C/CeO2 catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo-based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis. 相似文献
5.
Nano crystalline pure and Mg doped ceriaparticles were synthesized by simple chemical co-precipitation method using cerium nitrate hexahydrate as a source material and magnesium nitrate as doping precursor at room temperature. The effect of doping were investigated by X-ray diffraction pattern(XRD), FT-Raman,fourier transform infrared spectroscopy(FTIR), Ultraviolet spectroscopy(UV), photoluminescence spectroscopy(PL), field emission scanning electron microscope(FESEM) and high resolution transmission electron microscopy with energy dispersive spectroscopy (HRTEM &EDS). The X-ray diffraction pattern and FT-Raman studies showed that the prepared samples were nano particulates with cubic fluorite structure. The XRD pattern analysis showed that the size of the particles ranged from 13 to 20?nm, however 4?wt% Mg doping results in reduction of particle size compared with other doping concentrations. The effects of Mg concentration on various structural parameters of the prepared samples were also determined. The slight blue shift observed upon doping in UV–Vis absorption region around 330–360nmrecorded for reduction in particle size. The FTIR unveils the presence of Metal oxygen bonds below 700?cm?1in the prepared samples. All samples showed a broad emission band at 430?nm with linearly increasing intensity with respect to dopant concentrations. The Spherical morphology with weak agglomeration was identified through FESEM and HRTEM analysis. The elemental analysis of Ce, O and Mg were confirmed through EDS analysis. 相似文献
6.
《International Journal of Hydrogen Energy》2020,45(49):26238-26253
The demands for high-purity hydrogen required in fuel-cell applications impose new goals and challenges for design of well performing water-gas shift (WGS) catalysts. Gold-based catalysts have exhibited high activity in the WGS reaction at low temperature. Preparation of appropriate and economically viable supports with complex composition by various synthesis procedures is an attractive approach to WGS performance improvement. The effect of two different preparation methods (wet impregnation or mechanical mixing) and ceria content (10, 20 or 30 wt%) on textural, structural, surface and reductive properties and WGS activity of gold catalysts was studied. Additionally, the role of Y2O3 as a promoter of ceria was examined. Long-term stability test was carried out at 260 °C over the most active catalyst. The composition of the best performing sample (composed of about 70 wt% alumina), prepared by mechanical mixing, was considered promising in case of practical applications because of its cost efficiency. The combination of gold nanoparticles and alumina supported Y-doped ceria proved an advantageous approach for developing new catalytic formulations with high effectiveness in clean hydrogen production. 相似文献
7.
LDD方法在提高电路工作电压中的应用研究 总被引:1,自引:0,他引:1
研究了利用轻掺杂漏结构来制作高电源电压器件的工艺方法。分析了LDD结构参数对器件击穿特性的影响,并结合实验结果对N^-区的注入剂量,长度及引入的串联电阻进行了优化设计。 相似文献
8.
Joo-Sin Lee 《Journal of Electroceramics》2006,17(2-4):709-711
The densification behavior and grain growth of Ce0.8Gd0.2O1.9 ceramics were investigated with the strontium gallate concentration ranging from 0 to 5 mol%. Both the sintered density and
grain size were found to increase rapidly up to 0.5 mol% Sr2Ga2O5, and then to decrease with further addition. Dense Ce0.8Gd0.2O1.9 ceramics with 97% of the theoretical density could be obtained for 0.5 mol% Sr2Ga2O5-added specimen sintered at 1250∘C for 5 h, whereas pure Ce0.8Gd0.2O1.9 ceramics needed to be sintered at 1550∘C in order to obtain an equivalent theoretical density. The addition of Sr2Ga2O5 was found to promote the sintering properties of Gd2O3-doped CeO2. 相似文献
9.
10.