全文获取类型
收费全文 | 288篇 |
免费 | 11篇 |
国内免费 | 13篇 |
专业分类
化学 | 97篇 |
晶体学 | 3篇 |
力学 | 34篇 |
综合类 | 2篇 |
数学 | 72篇 |
物理学 | 104篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 9篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 18篇 |
2012年 | 3篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 14篇 |
2008年 | 10篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1948年 | 1篇 |
排序方式: 共有312条查询结果,搜索用时 15 毫秒
191.
192.
The rotational spectrum of the CO-dimethyl sulfide (DMS) complex was measured in the frequency region from 4.8 up to 25 GHz by Fourier transform microwave spectroscopy. For the normal species 27 a-type and 57 c-type transitions were observed, while 16 and 8 c-type transitions were assigned for the species with 34S and 13C in the DMS moiety, respectively, in natural abundance. In addition, 7 a-type and 48 c-type transitions were assigned for the complex with the 13CO enriched species as a component and 9 a-type and 42 c-type transitions for the complex with enriched C18O. No splitting was observed, which could be ascribed to the tunneling motion of the CO between two possible potential minima around DMS, while many transitions were split by the internal-rotation of the two methyl tops of the DMS unit. In cases where the K-type splitting was close to the methyl internal-rotation splitting, forbidden transitions were observed which apparently followed b-type selection rules. All of the observed transition frequencies for the normal species were analyzed simultaneously using a two-top internal-rotation and rotation Hamiltonian. The potential barrier height V3 to internal rotation of the methyl groups of the DMS was determined to be 745.5 (30) cm−1. The transition frequencies observed for all the isotopomers were analyzed using an asymmetric-rotor rotational Hamiltonian, to determine rotational and centrifugal distortion constants. The rs coordinates calculated from the observed rotational constants led to the conclusion that the CO moiety was located in a plane perpendicular to the skeletal plane of the DMS and bisecting its CSC angle. This structure of the CO-DMS is very much different from that of the CO-DME, in which the CO is located in the DME skeletal plane. The distance between the centers of gravity of the two moieties, Rcm, was calculated to be 3.789 Å for the CO-DMS, which is longer by only 0.11 Å than that in the CO-DME complex: 3.68 Å, in spite of the fact that the van der Waals radius of the S atom is much larger than that of the O atom. The small difference in Rcm is, in part, ascribed to the location of the CO relative to the DMS/DME. The more important reason is that the intermolecular bonding of the CO-DMS is stronger than that of CO-DME; by assuming a Lennard-Jones-type potential, the force constant of the van der Waals stretching mode and the dissociation energy were estimated to be 2.7 Nm−1 and 3.3 kJ mol−1, respectively, which were larger than those of the CO-DME: 1.4 Nm−1 and 1.6 kJ mol−1. 相似文献
193.
Using molecular dynamic simulation (MDS), effects of chirality and Van der Waals interaction on Young's modulus, elastic compressive modulus, bending, tensile, and compressive stiffness, and critical axial force of double-walled carbon nanotube (DWCNT) and its inner and outer tubes are considered. Achieving the highest safety factor, mechanical properties have been investigated under applied load on both inner and outer tubes simultaneously and on each one of them separately. Results indicate that as a compressive element, DWCNT is more beneficial than single-walled carbon nanotube (SWCNT) since it carries two times higher compression before buckling. Except critical axial pressure and tensile stiffness, in other parameters zigzag DWCNT shows higher amounts than armchair type. Outer tube has lower strength than inner tube; therefore, most reliable design of nanostructures can be attained if the mechanical properties of outer tube taken as the properties of DWCNT. 相似文献
194.
195.
An analytical method is presented to solve the influence of surface effect on non-coaxial resonance of multi-walled carbon nanotubes embedded in matrix utilizing laminated structures model. Due to coupled van der Waals forces between adjacent tubes and surface effect exerted carbon nanotubes, the resonance frequencies and amplitude ratios of multi-walled carbon nanotubes under initial stresses show that the resonant characteristics of the multi-walled carbon nanotubes become complex and the numbers of vibrational modes do not keep increase under identical conditions after considering surface effects. The result obtained can be used as a beneficial reference for investigating the electronic and physical behaviors of carbon nanotubes. 相似文献
196.
The melting properties and the heat capacity of the solid state and the melt state 4’-bromomethyl-2-cyanobiphenyl (OTBNBr) were determined. The enthalpy, entropy and Gibbs free energy of fusion were also calculated. The solubility of OTBNBr in eight organic solvents was experimentally measured at temperatures from (283.15 to 323.15) K by using a static method. The reasons for the differences of the solubility of OTBNBr in various solvents are discussed by using the intermolecular interaction. Furthermore, the experimental solubility values were well correlated by the modified Apelblat equation, the λh equation, the Wilson model and the van’t Hoff equation. Finally, the temperature dependence of the activity coefficient and the van’t Hoff enthalpy in the tested solutions was investigated and is discussed. 相似文献
197.
Flemming Jørgensen 《International journal of quantum chemistry》2015,115(24):1691-1708
Bloch's transformation from the zeroth‐order space for a perturbation problem to the corresponding space of exact eigenvectors, was found as a geometrically defined alternative to the algebraically constructed Van Vleck transformation. Klein's theorem of uniqueness transferred some of this geometrical interpretation to its canonical form . Quite recently Kvaal has taken a large step further by writing as a product of commuting planar rotations, obtained by describing and in terms of certain principal vectors and canonical angles. Kvaal's approach is now developed further, using a new commutation relation which simplifies algebraic manipulations substantially. It allows for a simple definition of an operator for the angle between and which has Kvaal's vectors and angles as eigenvectors and eigenvalues. Klein's theorem is refined in various ways. The impact of the approach on a number of previous results is considered. © 2015 Wiley Periodicals, Inc. 相似文献
198.
Haisheng Li Weiguang Chen Xiaoyu Han Liben Li Qiang Sun Zhengxiao Guo Yu Jia 《Journal of computational chemistry》2015,36(25):1919-1927
Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first‐principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Gen (n = 10–50) clusters. In agreement with the injected ion drift tube techniques that “clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge7 and Ge10),” we found these stable fragments are connected by Ge6, Ge9, or Ge10 unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge7 and Ge10 clusters, in accordance with the experiment results that the spectra Ge7 and Ge10 correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc. 相似文献
199.
Sheng XW Mentel L Gritsenko OV Baerends EJ 《Journal of computational chemistry》2011,32(13):2896-2901
This article investigates the errors in supermolecule calculations for the helium dimer. In a full CI calculation, there are two errors. One is the basis set superposition error (BSSE), the other is the basis set convergence error (BSCE). Both of the errors arise from the incompleteness of the basis set. These two errors make opposite contributions to the interaction energies. The BSCE is by far the largest error in the short range and larger than (but much closer to) BSSE around the Van der Waals minimum. Only at the long range, the BSSE becomes the larger error. The BSCE and BSSE largely cancel each other over the Van der Waals well. Accordingly, it may be recommended to not include the BSSE for the calculation of the potential energy curve from short distance till well beyond the Van der Waals minimum, but it may be recommended to include the BSSE correction if an accurate tail behavior is required. Only if the calculation has used a very large basis set, one can refrain from including the counterpoise correction in the full potential range. These results are based on full CI calculations with the aug-cc-pVXZ (X = D, T, Q, 5) basis sets. 相似文献
200.