全文获取类型
收费全文 | 57篇 |
免费 | 4篇 |
国内免费 | 12篇 |
专业分类
化学 | 53篇 |
晶体学 | 2篇 |
力学 | 2篇 |
综合类 | 2篇 |
数学 | 2篇 |
物理学 | 12篇 |
出版年
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有73条查询结果,搜索用时 15 毫秒
21.
A clear and reliable theoretical investigation on dibromomethane (CH(2)Br(2)) photodissociation is desired. The calculation must consider: (i) relativistic effects; (ii) the potential energy curves (PECs) of spin-orbit coupling states; (iii) geometry optimization by the method with both static and dynamic electron correlations; (iv) solvent effects on the photodissociation in the solution. All these have been considered in this study by state-of-the-art quantum chemical calculations. The experimentally observed photodissociation in the gas phase with products of spin-orbit-coupled states, Br((2)P(3/2)) and Br*((2)P(1/2)), was assigned by multi-state second order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space state interaction (MS-CASPT2/CASSI-SO) PECs. The mechanisms of the experimentally observed photodissociation and photoisomerization in solvent were elucidated by the MS-CASPT2/CASSI-SO method combined with polarized continuum model of the solvent. 相似文献
22.
The l-proline-based dipeptide has been discovered and developed as an efficient catalyst for the direct asymmetric aldol reactions of unmodified ketones with various aldehydes including aromatic, aliphatic, heteroaromatic, and unsaturated aldehydes in the presence of water at 0 °C. The resulted methodology and optimal conditions led to the corresponding aldol products with high yields (up to 94%) and good enantioselectivities (up to 97% ee). 相似文献
23.
One of the fundamental photoreactions for ketones is Norrish type I reaction, which has been extensively studied both experimentally and theoretically. Its α bond-cleavage mechanisms are usually explained in an adiabatic picture based on the involved excited-state potential energy surfaces, but scarcely investigated in terms of a nonadiabatic picture. In this work, the S(1) α bond-cleavage reactions of CH(3)OC(O)Cl have been investigated by using the CASSCF and MRCI-SD calculations, and the ab initio based time-dependent quantum wavepacket simulation. The numerical results indicate that the photoinduced dissociation dynamics of CH(3)OC(O)Cl could exhibit strong nonadiabatic bond-fission characteristics for the S(1) α C-Cl bond cleavage, while the dynamics of the S(1) α C-O bond cleavage is mainly of adiabatic characteristics. This nonadiabatic mechanism for Norrish type I reaction of CH(3)OC(O)Cl is uncovered for the first time. The quantum wavepacket dynamics, based on the reduced-dimensional coupled potential energy surfaces, to some extent illustrates the significance of the nonadiabatic effect in the transition-state region on the dynamics of Norrish type I reaction. 相似文献
24.
Alkoxy radicals are important intermediates in the formation of tropospheric ozone. The spectroscopic identification and characterization of these species are important for understanding their chemistry in the atmosphere. In this work, we report the observation of the laser induced fluorescence (LIF) excitation spectrum of cycloheptoxy radical. The spectrum was assigned preliminary to the lowest energy twist-chair conformer (TC-i) of cycloheptoxy. The whole picture of the interconversions at ground state between different conformers of cycloheptoxy radicals was described by density functional theory calculations. The results revealed that despite the ring strain, the seven-membered ring alkoxy radical could exist in the supersonic jet-cooled condition. The decomposition and the low energy barrier pseudorotation between twist-chair conformers might be the reason of the much quieter spectrum of cycloheptoxy compared with the LIF spectrum of cyclohexoxy. 相似文献
25.
Mingwei Wan Junjie Song Wenli Li Lianghui Gao Weihai Fang 《Journal of computational chemistry》2020,41(8):814-829
A fast, reasonable, and transferable coarse-grained (CG) molecular dynamics force field (FF) is essential to combine experimental and simulation data. However, the parameterization of CG FF usually requires massive computation, which hinders its rapid development. Here, we presented an efficient optimization protocol by combining multilinear interpolation technique with simplex algorithm. In this preliminary work, taking the experimental properties as the benchmark, we constructed a new set of CG FF for water and n-alkanes by adopting piecewise Morse function to describe the nonbonded interactions. This CG FF has a delicate balance between efficiency, accuracy, and transferability and well reproduced the correct structural and thermodynamics properties of pure water and alkane liquids. More importantly, optimized Morse potential was also successfully applied to describe the interactions between water and n-alkanes. It nicely predicted the phase separation, interface tension, hydration free energy, and formation of microemulsions of water/oil mixtures. © 2019 Wiley Periodicals, Inc. 相似文献
26.
Guohua Wu Tonggang Zhao Jianhua Ren Junyi Zhang Xiaolei Zhang Weihai Li 《Optics & Laser Technology》2011,43(7):1225-21173
Based on extended Huygens-Fresnel principle, an analytical expression of M2 factor for partially coherent Hermite-Gaussian (PCHG) beams through non-Kolmogorov turbulence is obtained. Our results show that M2 factor of PCHG beams depends on coherence length, beam order m, wavelength, exponent value α, outer scale L0 and inner scale l0. The impact of the exponent's variation on the M2 factor is analyzed in detail. When the propagation distance fixed, the M2 factor of PCHG beams has a maximum for alpha values lower than 11/3. 相似文献
27.
28.
Grzelczak M Mezzasalma SA Ni W Herasimenka Y Feruglio L Montini T Pérez-Juste J Fornasiero P Prato M Liz-Marzán LM 《Langmuir : the ACS journal of surfaces and colloids》2012,28(24):8826-8833
The optical response of nanoplasmonic colloids in disperse phase is strictly related to their shape. However, upon self-assembly, new optical features, for example, bonding or antibonding modes, emerge as a result of the mutual orientations of nanoparticles. The geometry of the final assemblies often determines which mode is dominating in the overall optical response. These new plasmon modes, however, are mostly observed in silico, as self-assembly in the liquid phase leads to cluster formation with a broad range of particle units. Here we show that low-symmetry clustering of gold nanorods (AuNRs) in solution can also reveal antibonding modes. We found that UV-light irradiation of colloidal dispersions of AuNRs in N-methyl-2-pyrrolidone (NMP), stabilized by poly(vinylpyrrolidone) (PVP) results in the creation of AuNRs clusters with ladderlike morphology, where antibonding modes can be identified. We propose that UV irradiation induces formation of radicals in solvent molecules, which then promote cross-linking of PVP chains on the surface of adjacent particles. This picture opens up a number of relevant questions in nanoscience and is expected to find application in light induced self-assembly of particles with various compositions and morphologies. 相似文献
29.
Leixiaomeng Fu Tingting Chen Gaiqing Xue Lily Zu Weihai Fang 《Journal of mass spectrometry : JMS》2013,48(1):128-134
Selective cleavage is of great interest in mass spectrometry studies as it can help sequence identification by promoting simple fragmentation pattern of peptides and proteins. In this work, the collision‐induced dissociation of peptides containing internal lysine and acetylated lysine residues were studied. The experimental and computational results revealed that multiple fragmentation pathways coexisted when the lysine residue was two amino acid residues away from N‐terminal of the peptide. After acetylation of the lysine side‐chain, ions were the most abundant primary fragment products and the Lys(Ac)–Gly amide bond became the dominant cleavage site via an oxazolone pathway. Acetylating the side‐chain of lysine promoted the selective cleavage of Lys–Xxx amide bond and generated much more information of the peptide backbone sequence. The results re‐evaluate the selective cleavage due to the lysine basic side‐chain and provide information for studying the post‐translational modification of proteins and other bio‐molecules containing Lys residues. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
30.
Weihai Fang Shanjia Xu 《International Journal of Infrared and Millimeter Waves》2006,27(12):1683-1694
The effects of left-handed materials (LHM) on frequency selective reflection and transmission characteristics of dielectric
periodic structures are carefully investigated using a method which combines the multimode network theory with the rigorous
mode matching method. In addition, the effects of LHM dielectric loss on the selective properties are also given. It has been
shown that the selective behavior of periodic structures can be modified by adding LHM layers above and below the periodic
layer.
Supported by the National Natural Science Foundation of China (No. 60171037) (No. 60371010) and (No. 63531020) 相似文献