全文获取类型
收费全文 | 103篇 |
免费 | 1篇 |
专业分类
化学 | 24篇 |
数学 | 3篇 |
物理学 | 77篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2014年 | 1篇 |
2012年 | 4篇 |
2011年 | 1篇 |
2010年 | 2篇 |
2009年 | 4篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1993年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 4篇 |
排序方式: 共有104条查询结果,搜索用时 15 毫秒
71.
Ammonia adsorbs without dissociation on clean Ag(110) with a binding energy of 11 kcal/mol. Coadsorption of ammonia and atomic oxygen at 105 K produces adsorbed hydroxyl groups and NHx species. Coadsorption of ammonia and molecular oxygen leads to the stabilization of molecular oxygen, as is shown by the increase in the desorption peak temperature of dioxygen from 180 to 210 K. The reaction of ammonia with both forms of adsorbed oxygen produces the same products at the same temperatures. Water desorbs in a series of peaks at 310, 340, and 400 K resulting from hydroxyl recombination and hydrogen transfer from NHx species to adsorbed oxygen atoms. NO and N2 desorb together at 530 K. Oxygen recombination at 590 K only occurs following small ammonia doses such that excess oxygen persists on the surface. No hydrogen was seen to desorb under any reaction conditions. Vibrational spectroscopy shows that NH groups persist on the surface at temperatures well into the water desorption peak at 310 K and possibly to significantly higher temperatures, indicative of the difficulty of N-H bond cleavage by metallic silver. 相似文献
72.
73.
The structural and electronic transport properties of La1−x
Ce
x
MnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献
74.
The reactive scattering of formic acid from Ni(110) was studied over the temperature range of 175–920 K with MBRS in the millisecond time region by employing a modulation frequency of 36.8 Hz. The steady-state carbon and oxygen composition of the surface varied over the range of temperatures studied. For beam fluxes of 1013 molecules/cm2 sec the onset of decomposition on the steady-state surface occurred at 300 K. By 400 K decomposition was essentially complete, and the products CO2, CO, H2 and H2O were detected. All reaction events were prceded by a common step, and the products were then produced by a series/parallel mechanism. The rate constants measured for H2 and H2O formation indicated stringent limitations on the efficiency of second-order collisions on the surface for producing gaseous products. This study illustrates the use of MBRS for surface reaction mechanistic studies in the millisecond time scale. 相似文献
75.
76.
Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100?% in excess methanol. 相似文献
77.
High resolution electron energy loss vibrational spectroscopy was used to study the intermediate formed in the dehydration reaction for formic acid on Ni(110) and Ni(110)(4 × 5)C. On the carbided surface only the formate was observed. The frequencies of the asymmetric and symmetric OCO sketch indicated a monodentate configuration. On the clean surface a mixed adlayer of CO and HCOO formed. No losses expected for formic anhydride were observed. Lateral interactions between CO and HCOO appear to be responsible for the autocatalytic decomposition of the formate. 相似文献
78.
The structure of the surface formate on Ag(110) at 300 K was studied by near-edge X-ray absorption fine structure (NEXAFS) at the carbon K-edge. Interpretation of the NEXAFS spectra of the formate intermediate with a localized bond picture is inconsistent with the findings of previous vibrational studies. Rather, the resonances must be assigned to transitions to delocalized molecular orbitals, whereupon the results agree with the bidentate configuration deduced from the vibrational experiments. A bonding geometry is determined with respect to the surface normal in which the O-O direction lies parallel to the plane of the surface; no azimuthal ordering was detected. The molecular plane appears to be inclined at an angle of 30 ± 15°. This apparent tilt may be due to a dynamical motion of the species about the surface normal in which the molecular plane oscillates and rotates about the surface normal. These results indicate different bonding geometries for formate on Ag(110) and Cu(110). 相似文献
79.
Local chemisorption geometries of formate (HCO2) and methoxy (CH3O) groups on Cu(100) were examined by means of surface extended (SEXAFS) and near-edge X-ray absorption fine structure (NEXAFS) measurements above the O K edge. At 300 K the oxygen of the formate group are equivalent and asymmetrically located near the four-fold hollow site yielding two CuO distances between 2.31 and 2.45 Å. These distances are at least 0.3 Å longer than typical CuO distances of surface and bulk compounds due to a Cu-C steric interaction. The CO bonds and the OCO angle of the formate are estimated to be and 127 ± 7°, respectively. At 200 K the methoxy group has a CuO distance of and the CO axis is tilted with respect to the surface normal. The exact chemisorption site of the methoxy goup could not be determined, but the atop site is ruled-out. 相似文献
80.