全文获取类型
收费全文 | 56篇 |
免费 | 4篇 |
专业分类
化学 | 49篇 |
力学 | 1篇 |
物理学 | 10篇 |
出版年
2023年 | 2篇 |
2018年 | 2篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 4篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有60条查询结果,搜索用时 15 毫秒
1.
The adiabatic ionization energies and COOH+ appearance energies for a series of carboxylic acids have been measured by dissociative photoionization mass Spectrometry. Using the stationary electron convention, a heat of formation of 143.5 ± 0.7 kcal mol?1 (1 kcal = 4.184 kJ) at 298 K is derived for the carboxyl cation in the gas phase, which corresponds to an absolute proton affinity for carbon dioxide of 128.1 ± 0.7 kcal mol?1. 相似文献
2.
3.
Phillip T. Mead John C. Traeger John R. Christie Peter. J. Derrick 《Journal of mass spectrometry : JMS》1978,13(7):386-388
The internal energies of [C3H7]+ ions contributing to the metastable peak [C3H7]+ → [C3H5]+ + H2 are higher (by perhaps > 100 kJ mol?1) than those of the ion contributing to the threshold current in appearance energy measurements on [C3H5]+. The measured appearance energy may lead to an underestimation of the activation energy, i.e. negative ‘kinetic shift’, due to quantum, mechanical tunnelling. The distribution of energy released in the decomposition can be explained on the basis that much of the reverse activation energy and a statistical proportion of the excess energy is released as translation. 相似文献
4.
John C. Traeger Charles E. Hudson David J. McAdoo 《Journal of the American Society for Mass Spectrometry》1992,3(3):183-187
Formation of the 3-pentanone ion (3) from ionized propyl propanoate through the complex [C2H5CO+ ?OC3H7] is proposed based on data obtained by photoionization. The threshold and energy dependence for forming 3 relative to those for related processes support this proposal. The threshold for forming 3 coincides with that predicted for forming [CH3CH2CO+ ?CH2CH3], suggesting that that complex is also an intermediate in the pathway to 3. 3-Pentanone ion formation is important much further above threshold than is alkane elimination through [RCO+ ?R] complexes. This adds to evidence that reactions between the partners in ion-dipole complexes take place over a wider energy range than do such reactions in complexes containing nonpolar neutral partners. 相似文献
5.
John C. Traeger 《Journal of mass spectrometry : JMS》1984,19(10):514-516
Photoionization mass spectrometry has been used to measure the appearance energies for [C2H5]+ from ethanethiol, [C3H7]+ from 2-propanethiol and [C3H5]+ from 2-methylthiirane. From the known thermochemistry of these cations and their precursor molecules, a 298 K heat of formation of 138.6±0.4 kJ mol?1 for the SH radical has been derived. 相似文献
6.
7.
The 298 K heat of formation for the propionyl cation (C2H5CO+) has been measured previously by dissociative photoionization mass spectrometry. However, recent theoretical and experimental studies involving methylketene suggest that this may be significantly underestimated, resulting in a methylketene proton affinity that is too high by ∼30 kJ mol−1. In this study, the previous m/z 57 appearance energies were carefully re-evaluated, with various possible sources of error being investigated. These include factors such as sample purity, carbon-13 contamination from lower energy m/z 56 processes, kinetic and/or competitive shifts, reverse activation energies, ionizing energy calibration errors and the availability of accurate supplementary thermochemical data. In addition, high-level ab initio calculations are used to model the relevant unimolecular fragmentation processes for each of the ionized precursor molecules. As a result, it is found that only the 2-butanone appearance energy can be used to provide a reliable value for the propionyl cation heat of formation. From the 298 K m/z 57 appearance energy of 10.199 ± 0.003 eV for 2-butanone measured here, a value of 617.8 ± 0.9 kJ mol−1 is derived for , which corresponds to 845.4 ± 4.8 kJ mol−1 for the proton affinity of methylketene. This is in good agreement with previous theoretical calculations and thermokinetic proton affinity measurements, indicating that a significant upward revision to the propionyl cation heat of formation is warranted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
8.
Hudson CE McAdoo DJ Griffin LL Traeger JC 《Journal of the American Society for Mass Spectrometry》2003,14(2):136-142
How formation of CH3CH3+* competes with H* loss from C3H6O+* isomers with the CCCO framework has been a puzzle of gas phase ion chemistry because the first reaction has a substantially higher threshold and a supposedly tighter transition state. These together should make CH3CH3+* formation much the slower of the two reactions at all internal energies. However, the rates of the two reactions become comparable at about 20 kJ x mol(-1) above the threshold for CH3CH3+* formation. It was recently shown that losses of atomic fragments increase in rate much more slowly with increasing internal energy than do the rates of competing dissociations to two polyatomic fragments. This occurs because fewer frequencies are substantially lowered in transition states for the former type of reaction than for the latter. The resulting lower transition state sums of states cause the rates of dissociations producing atoms as fragments to increase much more slowly than competing processes with increasing energy. Here we show that this is why CH3CH3+* formation competes with H* loss from CH3CH2CHO+*. These results further establish that the dependence on energy of the rate of a simple unimolecular dissociation is usually directly related to the number of rotational degrees of freedom in the products, a newly recognized factor in determining the dependence of unimolecular reaction rates on internal energy. 相似文献
9.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
10.