全文获取类型
收费全文 | 670篇 |
免费 | 4篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 3篇 |
综合类 | 5篇 |
化学工业 | 258篇 |
金属工艺 | 8篇 |
机械仪表 | 4篇 |
建筑科学 | 8篇 |
矿业工程 | 4篇 |
能源动力 | 220篇 |
轻工业 | 2篇 |
水利工程 | 2篇 |
石油天然气 | 6篇 |
无线电 | 28篇 |
一般工业技术 | 129篇 |
冶金工业 | 7篇 |
自动化技术 | 2篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 59篇 |
2021年 | 45篇 |
2020年 | 46篇 |
2019年 | 49篇 |
2018年 | 30篇 |
2017年 | 29篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 48篇 |
2013年 | 38篇 |
2012年 | 22篇 |
2011年 | 42篇 |
2010年 | 30篇 |
2009年 | 37篇 |
2008年 | 36篇 |
2007年 | 26篇 |
2006年 | 25篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 14篇 |
2002年 | 6篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1990年 | 1篇 |
排序方式: 共有686条查询结果,搜索用时 15 毫秒
81.
We report, for the first time, binary ZnO/MnWO4 nanocomposites with p-n heterojunction fabricated by a simple ultrasonic-calcination route. The phase structure, morphology, and optical along with textural properties were comprehensively characterized. The photocatalytic performance was studied via degradations of rhodamine B, methyl blue and methyl orange (RhB, MB, MO), and fuchsine pollutants under visible-light illumination. The ZnO/MnWO4 nanocomposites exhibited better photocatalytic performance than their single components and the nanocomposite with 30?wt% MnWO4 showed the highest activity. Photocatalytic performance of this nanocomposite is 22.5, 17.7, 26.8, and 23.9 times higher than that of the ZnO sample in degradations of RhB, MB, MO, and fuchsine dyes, respectively. The improved photocatalytic performance was ascribed to the formation of p-n heterojunction between ZnO and MnWO4 with high charge separation efficiency as well as strong visible-light absorption ability. The possible mechanism for the improved photocatalytic performance was proposed. This study revealed that the novel ZnO/MnWO4p-n heterojunction can act as a promising visible-light-active photocatalyst for environmental applications. 相似文献
82.
L. Vimala Devi S. Sellaiyan T. Selvalakshmi H.J. Zhang A. Uedono K. Sivaji S. Sankar 《Advanced Powder Technology》2017,28(11):3026-3038
Monoclinic undoped and Tb doped CuO are prepared by solution combustion method and annealed at different temperatures. The effect of annealing and doping on their structural and optical properties of CuO are examined using XRD, FTIR and DRS. The surface and lattice defects in CuO and Tb doped CuO is analyzed qualitatively and quantitatively using positron lifetime and Doppler broadening spectroscopy. The average positron lifetime and electron momentum (energy) S parameter increases owing to the number of vacancies in the CuO lattice upon doping and decreases with increasing temperature. The migration of vacancies from grain to grain boundary region is observed at 600 °C annealed samples. At 800 °C, the overall behavior of lifetime value denotes that the vacancy type defect is recovered, cluster vacancy and microvoids exists with reducing size. The photocatalytic performance of undoped and Tb doped CuO on degradation of methylene blue (MB) and methyl orange (MO) is investigated under visible light for two different lamp power and dye concentration. The influence of annealing temperature and dopant ion on the efficiency is also elaborated. Enhanced photocatalytic efficiency in Tb doped CuO is observed upon annealing. X-ray photoelectron spectroscopy (XPS) result indicates that the valence states of Cu, O and Tb ions exist at the surface of the particles. Brunauer–Emmett–Teller N2 adsorption–desorption analyses were employed to characterize specific surface area and porosity of Tb doped CuO. The doped CuO with pore size of about ~34 nm have a surface area of 16–28 m2/g. The surface area effect plays an important role in the enhanced catalytic performance on Tb doped catalysts. 相似文献
83.
Applying photocatalysts for utilizing solar energy is attractive because of its clean and limitless characteristics, but they have giant obstacles such as wide bandgaps, photocorrosion, and rapid charge recombinations to overcome for applications. In this study, the TiO2/CuxO composite films are investigated as photoactive materials for the photodegradation ofmethylene blue (MB) pollutant molecules under standard sun light illumination. The TiO2 layer is firstly fabricated on the FTO substrate by a doctor blade method, and then the second copper component is introduced by a spin-coating. Then, the composite films are thermally sintered to form cuprous and cupric oxides. This additional copper oxide phases plays a crucial role in achieving high photodegradation performance of MB under light irradiation. The best MB photodegradability from the TiO2/CuxO composite films was achieved with the 3.6 wt% CuxO content case, and it is probably due to the effective charge separations with reduced recombinations in the copper oxide phases by the Z-scheme band arrangements between Cu2O and CuO components. The composite films were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy for the film surface and cross-sectional morphology, crystalline structure, atomic binding energy, and light absorbance, respectively. 相似文献
84.
Kyeong Taek Jung Yong Gun Shul Masakazu Anpo Hiromi Yamashita 《Korean Journal of Chemical Engineering》1997,14(3):213-215
TS-1 zeolite film has been prepared by using nano sized TS-1 zeolite particles for the photocatalytic isomerization of cis-2-butene.
TS-1 zeolite film showed optical transparent property and the thickness of film was 0.7 μm. UV irradiation of TS-1 zeolite
film in the presence ofcis-2-butene leads to the photocatalytic isomerization ofcis-2-butene intotrans-2-butene at the temperature of 275 K. The yield oftrans- 2-butene was linearly increased with UV-irradiation time. 相似文献
85.
The local structure and the photoactivity of B2O3–SiO2/TiO2 ternary mixed oxides (SiO2 content was fixed as 30 at.% with respect to TiO2) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing Ti---O---Si with Si---O---B or Ti---O---B bonds. Also, paramagnetic species such as O− and Ti3+ defects were formed by the boron incorporation. In SiO2/TiO2 mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B2O3–SiO2/TiO2 samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900 °C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B2O3–SiO2/TiO2 ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (g moles/min l) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (g moles/m2 l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti3+ sites are responsible for the deterioration in the photoactivity of B2O3–SiO2/TiO2 ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase. 相似文献
86.
Krzysztof Brodzik Jerzy Walendziewski Marek Stolarski Luc Van Ginneken Kathy Elst Vera Meynen 《Journal of Porous Materials》2007,14(2):219-226
A series of titania–silica aerogels with different compositions were prepared using four different preparation methods. The
preparation steps were followed by a high temperature supercritical drying (HTSCD). It was found that application of ethanol
and 2-propanol as the solvents for the titania precursor (with or without modification with acetyloacetone) resulted in materials
with BET surface area up to 990 m2/g, total pore volume up to 5.6 cm3/g and density as low as 0.041 g cm−3. Obtained aerogels were mesoporous materials with the average pore diameter in the range 11–27 nm. It was stated that application
of the I method (prehydrolysis) resulted in aerogels with higher average pore diameter than other preparation methods while
aerogels with the lowest average pore diameter were obtained using the so-called IV, impregnation method. Anatase form of
titania was found in all prepared samples. The prepared aerogels were being applied as catalysts in photodegradation of salicylic
acid solution in water. The obtained results suggest a much higher catalytic efficiency of titania, which is present in aerogel
than it is in the case of commercial P25 Degussa titanium dioxide. 相似文献
87.
以钛酸丁酯和硝酸镨为原料,将溶胶-凝胶法制备的纳米Pr-TiO_2颗粒采用Discover聚焦单模微波进行微波处理。采用XRD、SEM、TEM考察了微波辐射温度、时间及功率对其晶型结构、表观形貌及光催化性能的影响。结果表明:当微波辐射温度为120℃,功率为100 W,辐射20 min时得到晶型结构比较完善的锐钛矿纳米Pr-TiO_2,并且在此条件下对甲基橙的降解率最高,光催化性能最强。对其形貌进行分析可知,所制备的纳米Pr-TiO_2为花球状的纳米簇,并且此结构是由片层结构组装而成,所制备的Pr-TiO_2纳米簇为多晶结构。利用聚焦单模微波法拓宽了TiO_2的光响应范围,提高了可见光的利用率。。 相似文献
88.
Nanocrystalline LaTiO2N with a surface area of 27.5 m2/g was synthesized by nitridation of amorphous La2O3/TiO2 composite powder at 900 °C for 8 h using NH3 as the reactant gas. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the as-prepared LaTiO2N nanocrystals had a mean diameter of about 30 nm. It was found that the absorption edge of the oxynitride is significantly red-shifted compared with that of La2Ti2O7 as increasing the nitridation temperature. The UV–vis absorption spectra indicated that the synthesized oxynitrides displayed good light absorption properties not only in the ultraviolet light but also in the visible-light region. 相似文献
89.
Reductive decomposition of nitrate ion to nitrogen in water on a unique hollandite photocatalyst 总被引:2,自引:0,他引:2
Toshiyuki Mori Jun Suzuki Kenjiro Fujimoto Mamoru Watanabe Yoshio Hasegawa 《Applied catalysis. B, Environmental》1999,23(4):113-289
Photocatalysis of a hollandite compound KxGaxSn8−xO16 (x = ca. 1.8) was examined for the reduction of nitrate ion with a reducing agent of methanol in water under UV irradiation. Hollandites have a characteristic one-dimensional tunnel structure. The hollandite powder, which was prepared by the sol–gel method and unloaded with any additives like metals, was used as the photocatalyst and its photocatalytic reaction was analyzed quantitatively by using ion chromatography and on-line mass spectrometry, and its reaction mechanism was analyzed by in-situ FT-IR. The hollandite photocatalyst showed a significant activity for the formation of N2 from NO3−. The nitrate was reduced to N2 and NO2−, while the reducing agent methanol was partly oxidized to change to formic acid. The conversion of NO3−was proportional to the yields of N2, NO2−, and HCOO−. The present photocatalyzed decomposition of NO3− to N2 would be a useful photocatalysis for the environmental protection of water. 相似文献
90.
《International Journal of Hydrogen Energy》2020,45(46):24697-24709
A novel composite has been successfully synthesized in situ via a coprecipitation method about the coupling of Cu2(OH)2CO3 with oxidized carbon nitride (O-g-C3N4) forming Cu2(OH)2CO3/O-g-C3N4 (CuCN) heterojunction structure. The as-prepared composites were characterized by diverse means. The CuCN composite with 3:5 mass ratio of Cu2(OH)2CO3 to O-g-C3N4 (60CuCN) presented an extremely excellent photocatalytic activity. The photocatalytic H2 evolution of 60CuCN was around 23.26 and 44.62 times higher than that of g-C3N4 and Cu2(OH)2CO3, respectively. The photocatalytic degradation malachite green (MG) rate of 60CuCN was up to 91%, which was around 2.2 and 4.8 times as much as that of g-C3N4 and Cu2(OH)2CO3, respectively. These results are mainly attributed to the structure property of O-g-C3N4 and the heterojunction structure of the composite, which could effectively accelerate the separation and transfer rate of photogenerated electrons and holes. The holes (h+) and superoxide radicals (·O2−) played a dominant role in photocatalytic degradation MG reaction. 相似文献