全文获取类型
收费全文 | 298345篇 |
免费 | 1360篇 |
国内免费 | 326篇 |
专业分类
化学 | 137016篇 |
晶体学 | 4652篇 |
力学 | 16873篇 |
综合类 | 3篇 |
数学 | 42074篇 |
物理学 | 99413篇 |
出版年
2021年 | 3099篇 |
2020年 | 3423篇 |
2019年 | 4193篇 |
2018年 | 6230篇 |
2017年 | 6442篇 |
2016年 | 7942篇 |
2015年 | 3525篇 |
2014年 | 6882篇 |
2013年 | 12107篇 |
2012年 | 10120篇 |
2011年 | 11789篇 |
2010年 | 9979篇 |
2009年 | 10130篇 |
2008年 | 11408篇 |
2007年 | 11194篇 |
2006年 | 9977篇 |
2005年 | 8606篇 |
2004年 | 8359篇 |
2003年 | 7766篇 |
2002年 | 8050篇 |
2001年 | 7672篇 |
2000年 | 6062篇 |
1999年 | 4490篇 |
1998年 | 4262篇 |
1997年 | 4123篇 |
1996年 | 3735篇 |
1995年 | 3300篇 |
1994年 | 3360篇 |
1993年 | 3381篇 |
1992年 | 3380篇 |
1991年 | 3788篇 |
1990年 | 3788篇 |
1989年 | 3795篇 |
1988年 | 3549篇 |
1987年 | 3628篇 |
1986年 | 3323篇 |
1985年 | 3854篇 |
1984年 | 4089篇 |
1983年 | 3489篇 |
1982年 | 3688篇 |
1981年 | 3375篇 |
1980年 | 3132篇 |
1979年 | 3623篇 |
1978年 | 3686篇 |
1977年 | 3857篇 |
1976年 | 3932篇 |
1975年 | 3672篇 |
1974年 | 3529篇 |
1973年 | 3693篇 |
1972年 | 3178篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
The mechanism of transition of a Bose gas to the superfluid state via thermal fluctuations under the condition of external cooling at a temperature above the transition point is considered. The probability of formation of such critical fluctuations (instantons) is calculated; it is found that this probability increases as the system approaches the transition temperature. It is shown that the evolution of an individual instanton is impossible without the formation of vortices in its superfluid part. 相似文献
212.
The dynamic structure factors (DSFs) of several strong glasses (SF6, SF10, BK7, SUPRASIL) measured by Brillouin light scattering spectroscopy are reported. Spectra have been collected, at and above room temperature, at two scattering angles, θ=90° and θ=180° corresponding to exchanged wavevector q values ranging from 0.0256 to 0.0448 nm−1. In particular we find that the isotropic spectral lineshapes are in all cases well described by the simple hydrodynamic theory of an amorphous solid. The width of the Brillouin peaks are found to be consistent with the predicted q2 dependence at both investigated temperatures. This damping is however found to account only partially for the strong asymmetry of the Brillouin line clearly visible on a logarithmic intensity scale. As a matter of fact there is an excess intensity in the very low frequency plateau underlying the central component. The height of this plateau and hence the entire lineshape is well reproduced if a relaxation process is taken into account in the hydrodynamic equations. Owing to the intense elastic scattering we are able to determine unambiguously only the ratio between amplitude and characteristic time of this process which quantifies the sound dispersion to be of the order of a few percent in all samples. The temperature dependence of the parameters indicates that this relaxation cannot be attributed to thermally activated relaxation phenomena. These general findings favorably compare with molecular dynamics simulation results on similar systems. 相似文献
213.
The Clauser–Horne approach used to derive experimentally measurable quantities for performing experiments on EPR paradox based on Type-I Spontaneous Parametric Down Conversion (SPDC) sources is discussed. It is proved that in this case the deduced Bell's type inequality does not correctly express separability and causality. A deeper analysis of the problem shows that the Clauser–Horne hypothesis of factorizability of joint detection probability cannot be considered so general as to describe this physical situation. 相似文献
214.
The spectrum and the spatial distribution of the emission of scattered particles upon bombardment of Be, Ti, Ta, and W with H and He ions were studied. The quantum yield and the velocity and angular distributions of the scattered excited particles were measured. Computer simulation of the scattering of H ions and He ions from the metals under study was performed with the use of the program TRIM-95. Agreement is observed between the calculated and experimentally measured angular distributions of the scattered particles. 相似文献
215.
The numerical prediction of the fields of inelastic strains (the linear invariant of the tensor of inelastic strains) in thermoset polyester/marble filler composite plates is discussed. A uniformly distributed load is applied to the plates, which lie on a steel base. The strain fields are predicted by means of the boundary element method by using creep test data for the composites and the polyester matrix itself. Identical creep tests were performed for two ages of the materials (1 month and 13 years), which allowed evaluating the aging effect. The study is carried out in two stages. At the first stage, the application of the generalized Maxwell-Gurevich equation to the thermoset matrix/mineral filler composite is demonstrated. The model parameters determined from the experimental creep data is used for the second stage, where the state of inelastic strains in the plates is predicted by applying the boundary element method. The influence of composite formulation (filler content) and physical aging of the polyester matrix on the state of inelastic strains in the plates is shown.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 145–156, March–April, 2005. 相似文献
216.
Hybrid numerical—experimental approach for investigation of dynamics of microcantilever relay system
V. Ostasevicius S. Tamulevicius A. Palevicius M. Ragulskis R. Palevicius V. Grigaliunas 《Optics and Lasers in Engineering》2005,43(1):199
The time average holography measurements of the vibrating microelectromechanical switch (MEMS) were performed in this study. Experimental measurement results exhibit good agreement with computer generated holographic interferogram analysis. The validation of experimental investigations versus numerical analysis provides the necessary background to analyze the dynamical characteristics of micromechanical systems in virtual numerical environments. Direct application of fringe counting techniques for reconstruction of motion from time average holograms cannot be straightforward if the analyzed micromechanical systems contain motion limiters. Modifications of a classical time average holographic technique enable qualitative analysis of MEMS and can be applied for investigation of dynamical properties of much broader classes of MEMS systems. 相似文献
217.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989. 相似文献
218.
219.
M. P. Nosov V. A. Smirnova Yu. F. Zabashta A. Ya. Fridman M. P. Mokhnach 《Mechanics of Composite Materials》1989,25(1):8-12
Conclusion A method was proposed which makes it possible to study the low-frequency internal friction of complex fibers. This method was used to study the internal friction of complex composite fibers based on PCA and PE. We observed a relaxation process which is typical of the composite and is absent in the pure materials.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 11–15, January–February, 1989. 相似文献
220.
P. P. Kirpichok N. B. Voronina A. F. Sitnikov V. Ya. Garmash 《Russian Physics Journal》1989,32(1):26-30
The effect of rare-earth oxides on the properties of anisotropic barium ferrites has been studied by x-ray structural and Mössbauer methods. Additions of SrCO3, as well as SrCO3 and La2O3, SrCO3 and Pr6O11, SrCO3 and Nd2O3, SrCO3 and Sm2O3 in amounts of 7.5 mole % Sr and 10 mole % rare-earth element to grade-A barium powder results in the substitution of barium ions by Sr and rare-earth ions; consequently, the energy of magnetic anisotropy changes and the technically important parameters Br and (BH)max increase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–39, January, 1989. 相似文献