全文获取类型
收费全文 | 747篇 |
免费 | 14篇 |
国内免费 | 14篇 |
专业分类
化学 | 105篇 |
晶体学 | 2篇 |
力学 | 361篇 |
数学 | 61篇 |
物理学 | 246篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 16篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 14篇 |
2016年 | 18篇 |
2015年 | 15篇 |
2014年 | 37篇 |
2013年 | 56篇 |
2012年 | 17篇 |
2011年 | 21篇 |
2010年 | 17篇 |
2009年 | 23篇 |
2008年 | 57篇 |
2007年 | 57篇 |
2006年 | 42篇 |
2005年 | 49篇 |
2004年 | 38篇 |
2003年 | 44篇 |
2002年 | 26篇 |
2001年 | 26篇 |
2000年 | 22篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 23篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 3篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有775条查询结果,搜索用时 31 毫秒
161.
Free across-the-thickness vibrations of a closed spherical shell consisting of three rigidly connected layers with arbitrary
physical constants and thicknesses are studied. A closed-form solution in displacements to a one-dimensional (along the radius)
vibration problem for a homogeneous spherical shell is derived and then used in posing a boundary-value problem on free vibrations
of a heterogeneous sphere. Based on the degeneration of the sixth-order determinant of a system of homogeneous equations satisfying
the corresponding boundary conditions, a transcendental equation for eigenfrequencies is found. Transformation variants for
the equation of eigenfrequencies in the cases of degeneration of physical and geometric parameters of the compound shell are
considered. The main attention in investigating the lowest frequency is given to its dependence on the structure of shell
wall, whose parameters greatly affect the calculated values of the high-frequency vibration spectrum of the shell.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 6, pp. 839–852, November–December, 2008. 相似文献
162.
V. I. Sardyko 《Journal of Applied Spectroscopy》1998,65(6):923-929
From the condition of generation (of the reproducibility of opposite waves for a pass around a resonator) it follows that
in addition to amplitude-phase changes an active medium must also compensate for backscatter in the resonator. The most probable
mechanism involved in this compensation is nonlinear backscatter. In the process of generation, nonlinear scattering compensates
for resonator scattering as a result of self-regulation. Amplitude-frequency characteristics are determined by the types of
vibrations of a resonator, whereas nonlinear effects specify these characteristics.
Higher College of Communication, 8/2 Staroborisovskii Trakt, 220114, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 65, No. 6, pp. 881–887, November–December, 1998. 相似文献
163.
L. O. Grigor’eva 《International Applied Mechanics》2006,42(12):1371-1379
The paper proposes and analyzes different approaches to constructing numerical schemes to solve the nonstationary vibration
problem for a radially polarized piezoelectric hollow cylinder with different electric boundary conditions under mechanical
loading. It is established that when the cylinder is subjected to internal pressure, the radial displacements are similar
and the longitudinal displacements substantially different in cylinders with electroded and nonelectroded surfaces
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 12, pp. 67–75, December, 2006. 相似文献
164.
L. N. Znamenskaya 《Computational Mathematics and Mathematical Physics》2007,47(6):900-914
The boundary observation problems (initial state reconstruction) of vibrations in objects with distributed and lumped parameters are solved. The vibrations in an object with distributed parameters are described by boundary value problems with boundary conditions of various types. An object with lumped parameters is described by a second-order ordinary differential equation. 相似文献
165.
Summary We present a detailed study of the lattice dynamics of thep(3×1)O-Ag(110) surface to determine the structural changes of the substrate upon oxygen chemisorption. The lattice dynamical
calculations are carried out using central forces with nearest-neighbour interactions and assuming different surface structures.
The limits of the models are discussed. A comparison with the dispersion curves measured along two azimuthal directions by
means of energy-resolved He-atom scattering unambiguously shows the reconstruction of the silver substrate.
In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching. 相似文献
166.
M. Amabili 《Flow, Turbulence and Combustion》1998,61(1-4):21-30
The linear study of free vibrations of structures coupled to incompressible and inviscid fluids are studied by using the Rayleigh-Ritz
method. The system is modelled by using different components. The artificial spring method is used to synthesise these components.
The advantage is that admissible functions are defined in each component and the continuity condition of translational and
rotational displacements between the rigid joints of the structure is no longer required. The fluid-structure interaction
can be accurately described by using this method, including the effect of the free surface waves and the dynamic interaction
among structural components via the fluid medium. An application of the method to a vertical circular tank partially filled
with water is also presented in order to show the potential of the method.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
167.
Yoshitaka Takezawa Noriaki Taketani Seikichi Tanno Shuichi Ohara 《Journal of Polymer Science.Polymer Physics》1992,30(8):879-885
We have studied simple empirical equations to estimate light absorption loss αv due to harmonics of molecular vibrations of transparent amorphous polymers used in plastic optical fibers (POFs). In the visible region, absorption involves two losses. One is αv, and the other is the electronic transition absorption loss, αe. Of the two, αv is considerably larger than αe in the wavelength region used for optical communication with POFs. We have clarified relationships between chemical structure of repeat units of polymers and αv. We find that αv is proportional to the concentration of specific chemical bonds (C? H, N? H, and Obond;H bonds) in the polymer solid, and we propose empirical equations to estimate αv from the polymer density and the chemical structure of the repeat unit. These equations are used to estimate αv of several polymers [i.e., poly(methyl methacrylate), polystyrene, and polycarbonate]. The estimated values are nearly equal to the experimental or reference values. Furthermore, to minimize the attenuation in the POF, we conclude that the POF core polymer should have no N? H, O? H, or aliphatic C? H bonds in its repeat unit. 相似文献
168.
The dependence of the quality of calculation of the geometric parameters and frequencies of normal vibrations on the choice of the theoretical method and the basis set of Gaussian functions has been investigated within the framework of four approximations (DFT/B3LYP, HF, MP2, MP3), using benzene and s-triazine molecules as an example. It has been shown that the molecular parameters calculated using the basis set without polarization functions within the framework of any of the above theoretical methods agree poorly with the experimental data. It has been concluded that the use of the basis set 6-31G(d) within the framework of these methods with allowance for the electron correlation for calculating the geometric parameters and frequencies of normal vibrations of polyatomic cyclic compounds is most optimum in terms of the relation between the expenditure of time and the quality of the calculation. The coefficients of linear scaling of frequencies have been obtained by the DFT/B3LYP method for 22 basis sets that were tested on porphin, pyrrole, indene, and pyridine molecules. Atypically large errors in determining the frequencies of some benzene and s-triazine vibrations have been obtained in a number of quantum-mechanical calculations with large basis sets. The changes in the force field for these cases have been investigated with the example of the benzene molecule. 相似文献
169.
A calculation of the frequencies and forms of the normal vibrations of the 31-atom molecule 2,3-di-O-nitromethyl-β-D-glucopyranoside
has been performed. Particular emphasis has been placed on the interpretation of the strongest bands in the spectrum of 2,3-di-O-nitro-methyl-β-D-glucopyranoside,
which are due to vibrations of the nitrate groups.
The present work has been reported at the IV International Congress of theoretically competent chemists, Jerusalem (Israel),
July 7–12, 1996.
B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 724–728, November–December, 1997. 相似文献
170.
Summary Taking into consideration nuclear motion in non-separable potentials, we have probed the solution of the Schrödinger equation by random walk sampling in imaginary time on a two-dimensional example. Evaluation of the many-dimensional Franck-Condon overlap and the chemical species conversion rate is outlined. 相似文献