全文获取类型
收费全文 | 207篇 |
免费 | 13篇 |
国内免费 | 84篇 |
专业分类
化学 | 286篇 |
晶体学 | 1篇 |
力学 | 1篇 |
物理学 | 16篇 |
出版年
2024年 | 6篇 |
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 40篇 |
2020年 | 42篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 5篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 13篇 |
2008年 | 8篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 1篇 |
排序方式: 共有304条查询结果,搜索用时 296 毫秒
101.
制备过程中缓冲溶液对Pt-Ru/C电催化剂性能的影响 总被引:8,自引:0,他引:8
采用浸渍还原法制备了Pt-Ru/C直接甲醇燃料电池阳极催化剂. 为了提高催化剂的活性,使用乙酸钠和氢氧化钠缓冲溶液来调节反应溶液的pH值,考察了缓冲溶液对催化剂性能的影响; 通过XRD和TEM技术对催化剂的晶体结构及微观形貌进行了分析; 并利用玻碳电极测试了催化剂在0.5 mol/L CH3OH和0.5 mol/L H2SO4混合溶液中的循环伏安曲线和阶跃电位曲线,考察了催化剂对甲醇阳极催化氧化活性的影响. 结果表明,用乙酸钠和氢氧化钠缓冲溶液调节反应溶液pH值所得催化剂的性能优于用NaOH调节反应溶液pH值所得的催化剂. 缓冲溶液pH值对催化剂性能有较大影响,使用pH值为12的缓冲溶液所制备的催化剂性能最佳, Pt-Ru颗粒在碳载体上分散均匀,其最小粒径为4.2 nm. 还原温度对缓冲溶液作用的发挥有一定影响,还原温度升高会使溶液的pH值下降,不利于缓冲溶液作用的发挥. 相似文献
102.
103.
Ke‐Qiang Ding 《中国化学会会志》2009,56(5):891-897
The composite of manganese dioxide‐polyaniline (MnO2‐PANI) was successfully prepared by cyclic voltammetry (CV) from a 0.5 M H2SO4 solution containing 0.2 M aniline and 0.5 M MnSO4. Scanning electron microscopy (SEM) images revealed that cauliflower like manganese dioxides entangled with PANI were generated. The spectra obtained from UV‐vis spectrophotometry (UV‐vis) and Fourier transform infrared spectrometry (FTIR) strongly demonstrated that this novel composite was composed by MnO2 and PANI, and also there was an interaction between MnO2 and PANI. Then, for the first time, this resultant composite was modified on a graphite electrode and employed in the oxygen reduction reaction (ORR), subsequently, the obtained cyclic voltammograms (CVs) verified that ORR could proceed on this resultant composite of MnO2‐PANI. Lastly, the possible catalysis mechanism of MnO2‐PANI towards ORR was proposed based on the results we acquired. Developing a novel substrate on which ORR could proceed is the main contribution of this work. 相似文献
104.
DFT study of difference caused by catalyst supports in Pt and Pd catalysis of oxygen reduction reaction 总被引:1,自引:0,他引:1
Li Li ZiDong Wei Yi Zhang XueQiang Qi MeiRong Xia Jie Zhang ZhiGang Shao CaiXin Sun 《中国科学B辑(英文版)》2009,52(5):571-578
Based on an experimental phenomenon that catalytic activity of Pt and Pd for oxygen reduction reaction (ORR) changes with
catalyst supports from C to TiO2, density function theory (DFT) was used to elucidate the cause behind the difference in catalysis caused by catalyst supports.
First, factors closely associated with the first electron transfer of the ORR were assessed in the light of quantum chemistry.
Then intermediate (atomic oxygen, O) adsorption strength on the catalyst surface was calculated. The results show that, in
terms of minimum energy difference, the best orbital symmetry match, and the maximum orbital overlap, TiO2 does bring about a very positive effect on catalysts Pd/TiO2 for the first electron transfer of the ORR. Especially, TiO2 remarkably expands the space size of Pd/TiO2 HOMO orbital and improves orbital overlap of Pd/TiO2 HOMO and O2 LUMO. The analysis of deformation density and partial density of state shows that the strong interaction between Pt and Ti
leads to a strong adsorption of intermediate O on Pt/TiO2, but the strong interaction between Pd and surface O causes positive net charge of Pd and a weak adsorption of intermediate
O on Pd/TiO2. Thus, the ORR can proceed more smoothly on Pd/TiO2 than Pt/TiO2 in every respect of maximum orbital overlap and rate delay by intermediate O. The research also discloses that several factors
lead to less activity of TiO2-supported Pt and Pd catalysts than the C-supported ones for the ORR. These factors include the poor dispersion of Pt and
Pd particles on TiO2, poor electric conduction of TiO2 carrier itself, and bigger energy difference between HOMO of TiO2-carried metallic catalysts and LUMO of O2 molecule due to electrons deeply embedded in the semiconductor TiO2 carrier.
Supported by the National Natural Science Foundation of China (Grant No. 20676156), the Chinese Ministry of Education (Grant
No. 307021), the National 863 Program (Grant Nos. 2006AA11A141 and 2007AA05Z124), and the Chongqing Sci &Tech Key Project
(Grant No. CSTC2007AB6012) 相似文献
105.
采用模板聚合物与金属离子配位-碳粉负载-还原方法得到的纳米复合材料P-M-C (P为聚合物, M为Fe, Co, Ni金属纳米颗粒, C为碳粉XC72). 利用红外光谱(IR)对中间产物进行了表征, 结果表明所制物质为目标产物P; 透射电镜(TEM)结果表明Fe, Co, Ni纳米粒子粒径多数为20~30 nm, 部分在10 nm左右, 纳米粒子均匀地分散在聚合物P上; 扫描电镜的能谱(SEM-EDS)分析结果证实了Fe, Co, Ni三种元素的存在. 通过循环伏安和计时电流法研究表明, 碱性介质中P-M-C复合催化剂对乙醇电化学氧化具有高催化活性和稳定性; 反向高效液相色谱(HPLC)结果表明乙醇氧化后的产物部分为乙醛和乙酸的混合物. 相似文献
106.
Jingjie Cui Wen He Hongtao Liu Shijun Liao Yuanzheng Yue 《Colloids and surfaces. B, Biointerfaces》2009,74(1):274-278
A novel approach is proposed to prepare ordered hierarchical mesoporous TiO2 by using yeast cells as the template via biomimetic mineralization. The structure and the mophology were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), Raman spectra, high-resolution transmission electron microscopy (HRTEM), and N2 adsorption–desorption isotherms (NADI). The bio-templated TiO2 has a hierarchical pore structure mainly distributed at 4.7 nm and 11.3 nm. An air electrode fabricated using this hierarchical mesoporous TiO2 exhibited remarkable electrocatalytic activity for oxygen reduction reaction (ORR). Compared to the electrolytic manganese dioxide (EMD) air electrode employed commercially, a 90% higher catalytic reduction current was achieved for this mesoporous TiO2 electrode. It is supposed that the hierarchically mesoporous structure and ordered pore distribution play important roles in significantly reducing electrochemical polarization and improving mass transport of the air diffusion electrode. This simple and efficient approach could spread as a general way to prepare advanced mesoporous materials in mild condition. 相似文献
107.
采用水合肼水热还原法制备了不同比例还原氧化石墨烯(RGO)与n型自掺杂富勒烯铵碘盐(PCBANI)的复合载体RGO-PCBANI, 并在电极上用这些载体负载Pd纳米粒子制备了Pd/RGO-PCBANI电催化剂. 利用扫描电子显微镜(SEM)、 透射电子显微镜(TEM)、 X射线衍射(XRD)及X射线光电子能谱(XPS)对RGO-PCBANI和Pd/RGO-PCBANI的形貌及结构进行了表征. 利用循环伏安和计时电流等电化学方法研究了该催化剂电催化氧化乙醇的性能. 结果表明, 所制备的RGO-PCBANI(6∶1)载体的分散性较好, 用其负载的Pd纳米粒子平均粒径为5.2 nm, 且Pd/RGO-PCBANI(6∶1)催化剂的催化活性最好, 质量电流密度达到1288.8 mA/mg. 相似文献
108.
109.
Prabu Mani Sharat Devadas Tamilselvi Gurusamy Pitchiah Esakki Karthik Balu P. Ratheesh Kothandaraman Ramanujam Sukhendu Mandal 《化学:亚洲杂志》2019,14(24):4814-4818
Inspired by copper‐based oxygen reduction biocatalysts, we have studied the electrocatalytic behavior of a Cu‐based MOF (Cu‐BTT) for oxygen reduction reaction (ORR) in alkaline medium. This catalyst reduces the oxygen at the onset (Eonset) and half‐wave potential (E1/2) of 0. 940 V and 0.778 V, respectively. The high halfway potential supports the good activity of Cu‐BTT MOF. The high ORR catalytic activity can be interpreted by the presence of nitrogen‐rich ligand (tetrazole) and the generation of nascent copper(I) during the reaction. In addition to the excellent activity, Cu‐BTT MOF showed exceptional stability too, which was confirmed through chronoamperometry study, where current was unchanged up to 12 h. Further, the 4‐electrons transfer of ORR kinetics was confirmed by hydrodynamic voltammetry. The oxygen active center namely copper(I) generation during ORR has been understood by the reduction peak in cyclic voltammetry as well in the XPS analysis. 相似文献
110.
A new method is reported for obtaining microspirals of iron‐based compounds by interfacial interaction. A thin film of Fe(OH)3 is obtained as a result of interaction between an aqueous solution of iron salts and gaseous ammonia. Upon drying, it is transformed into Fe(OH)3 microspirals with a diameter of up to 10 µm. These microspirals can be transformed into Fe2O3 microspirals by annealing in air. As a result of hydrogen reduction, Fe microspirals are formed. Both the annealing in air and that in hydrogen allow the retaining of the morphology. The material synthesized is characterized by electronic microscopy methods, X‐ray diffraction, diffuse reflectance Fourier transform infrared, and Mössbauer and photoelectron spectroscopies. The electrocatalytic properties of the electrode based on Fe2O3 microspirals as a catalyst of hydrogen evolution and the magnetic properties of Fe microspirals are tested. A hypothesis is proposed on the formation of microspirals by the gas–solution interface technique. 相似文献