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1.
A gas‐phase approach to form Zn coordination sites on metal–organic frameworks (MOFs) by vapor‐phase infiltration (VPI) was developed. Compared to Zn sites synthesized by the solution‐phase method, VPI samples revealed approximately 2.8 % internal strain. Faradaic efficiency towards conversion of CO2 to CO was enhanced by up to a factor of four, and the initial potential was positively shifted by 200–300 mV. Using element‐specific X‐ray absorption spectroscopy, the local coordination environment of the Zn center was determined to have square‐pyramidal geometry with four Zn?N bonds in the equatorial plane and one Zn‐OH2 bond in the axial plane. The fine‐tuned internal strain was further supported by monitoring changes in XRD and UV/Visible absorption spectra across a range of infiltration cycles. The ability to use internal strain to increase catalytic activity of MOFs suggests that applying this strategy will enhance intrinsic catalytic capabilities of a variety of porous materials.  相似文献   
2.
 采用不同极性的溶剂作为环己酮肟的溶剂,考察了溶剂极性对B2O3/TiO2-ZrO2催化环己酮肟气相Beckmann重排反应性能的影响. 结果表明,除乙醇外,随着溶剂极性的增大,己内酰胺的收率逐渐提高. 在所考察的溶剂范围内,当采用极性最强的乙腈为溶剂时,B2O3/TiO2-ZrO2的催化性能最佳,连续反应9 h,环己酮肟的转化率为100%,己内酰胺的选择性高达98.6%. 极性较强的溶剂可显著改善B2O3/TiO2-ZrO2催化性能的原因主要是其有利于反应所生成的己内酰胺从催化剂表面快速脱附,从而可抑制己内酰胺进一步发生聚合及分解等副反应.  相似文献   
3.
Nanostructured rare-earth hexaborides (REB6) are promising materials for photonic and electronic applications due to their unique characteristic. These include high melting point, hardness, chemical stability, low work function, low volatility at high temperatures, superconductivity, magnetic properties, efficiency, thermionic emission, and narrow band semiconductivity. This article focuses on recent developments regarding the synthesis, characterization, and applications of REB6 nanostructures. We first summarize information regarding the classification and crystal chemistry of REB6. Next, we examine the means by which researchers have successfully synthesized REB6. We consider the structural properties and morphology of REB6, and the growth mechanism involved in their fabrication. Finally, we offer suggestions for the use of REB6 nanostructures in photonic and electronic applications, and identifying four areas for further research.  相似文献   
4.
为提高气相传输法制备微纳结构样品形貌的可控性,进行了生长温度调控下氧化锌晶体生长机制及其变化的实验研究。实验中的样品制备,以高纯度锌粉末为原料,在无模板、无催化条件下,通过加热蒸发-氧化冷却-生长晶体过程实现。其中,蒸发温度固定于750℃,反应区气体氛围保持稳定,生长区温度在450~600℃变化,制备出不同生长温度下样品。对所制备出诸样品,应用扫描电子显微镜、X-射线衍射仪和透射电子显微镜等方法,进行形貌与结构表征。基于表征结果,观察、分析、研究生长温度变化的影响,结合理论分析,得出了生长温度通过对生长过程中锌蒸汽过饱和度的影响,决定着不同生长机制,从而有着不同的形貌结构的样品。  相似文献   
5.
Ni-M(M=Cu,Zn,Ce)/C双金属催化剂上的乙醇气相羰化   总被引:1,自引:0,他引:1       下载免费PDF全文
利用等体积浸渍法制备了NiM0.2(M=Cu, Zn, Ce)/C双金属催化剂及Ni/C催化剂,考察了其乙醇气相羰化制丙酸的活性。结果表明,4种催化剂的活性大小顺序为NiCe0.2/C>Ni/C>NiCu0.2/C>NiZn0.2/C,催化剂NiCe0.2/C的羰化活性最高,乙醇转化率和丙酸的选择性分别为98.0%和95.1%,而催化剂NiZn0.2/C的羰化活性最低,乙醇转  相似文献   
6.
It has been well illustrated that the rapid catalyst deactivation with time is the most serious limitation of vapor phase approach to the production of ε-caprolactam from cyclohexanone oxime (CHO) (Scheme 1), and is a common problem with all catalyst typ…  相似文献   
7.
The crystallographic tilt of the lateral epitaxial overgrown (LEO) GaN on sapphire substrate with SiNx mask is investigated by double crystal X-ray diffraction. Two wing peaks beside the GaN 0002 peak can be observed for the as-grown LEO GaN. During the selective etching of SiNx mask, each wing peak splits into two peaks, one of which disappears as the mask is removed, while the other remains unchanged. This indicates that the crystallographic tilt of the overgrown region is caused not only by the plastic deformation resulted from the bending of threading dislocations, but by the non-uniformity elastic deformation related with the GaN/SiNx interfacial forces. The widths of these two peaks are also studied in this paper.  相似文献   
8.
Characteristic parameters of a single vessel procedure were investigated for Co and Fe determination in biological samples using nitric acid-vapor extraction under atmospheric pressure. A laboratory-made PTFE support vessel suitable for four cups containing the samples was adapted to fit on the microwave glass vessel. Biological samples (30mg) were weighed directly into these PTFE cups and exposed to nitric acid vapor stemming from 15mL concentrated HNO3 placed in the bottom of the glass vessel. Sample cups were positioned at 50, 80, 110, and 140mm from the support base. We evaluated the temperature, acidity, and residual carbon content of each sample cup, i.e. parameters that could influence the efficiency of vapor-phase acid digestion. The influence of sample particle size on digestion efficiency was also considered. It was demonstrated that temperature was the main parameter for efficient recovery of both Co and Fe in biological samples, and higher temperatures allowed lower residual carbon contents.  相似文献   
9.
《中国物理 B》2021,30(10):106803-106803
We present a controlled, stepwise formation of layered semiconductor Bi_2O_2 Se thin films prepared via the vapour process by annealing topological insulator Bi_2Se_3 thin films in low oxygen atmosphere for different reactions. Photodetectors based on Bi_2O_2 Se thin film show a responsivity of 1.7×10~4 A/W at a wavelength of 980 nm. Field-effect transistors based on Bi_2O_2 Se thin film exhibit n-type behavior and present a high electron mobility of 17 cm~2/V·s. In addition, the electrical properties of the devices after 4 months keeping in the air shows little change, implying outstanding air-stability of our Bi_2O_2 Se thin films. From the obtained results, it is evident that low oxygen annealing is a surprisingly effective method to fabricate Bi_2O_2 Se thin films for integrated optoelectronic applications.  相似文献   
10.
甲醇直接气相氧化羰基化合成碳酸二甲酯   总被引:1,自引:0,他引:1  
碳酸二甲酯(DMC)是一种重要的绿色有机合成中间体.合成DMC有多种方法,甲醇直接气相氧化羰基化法对设备腐蚀小,产物易分离,原料易得,有着诱人的工业化前景.本文综述了甲醇直接气相氧化羰基化合成DMC的研究进展,包括反应条件的影响,催化剂的选择,反应机理及动力学的研究.针对反应副产物水会造成催化剂快速失活、设备腐蚀等问题,提出将二甲醚引入反应体系,通过耦合二甲醚水解反应消除水引起的负面效应,改善催化剂的稳定性.  相似文献   
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