全文获取类型
收费全文 | 179885篇 |
免费 | 776篇 |
国内免费 | 262篇 |
专业分类
化学 | 89810篇 |
晶体学 | 2638篇 |
力学 | 9381篇 |
综合类 | 7篇 |
数学 | 20917篇 |
物理学 | 58170篇 |
出版年
2020年 | 1849篇 |
2019年 | 2290篇 |
2018年 | 3398篇 |
2017年 | 3525篇 |
2016年 | 4160篇 |
2015年 | 1853篇 |
2014年 | 3589篇 |
2013年 | 7057篇 |
2012年 | 5544篇 |
2011年 | 6599篇 |
2010年 | 5521篇 |
2009年 | 5641篇 |
2008年 | 6376篇 |
2007年 | 6339篇 |
2006年 | 5628篇 |
2005年 | 4993篇 |
2004年 | 4829篇 |
2003年 | 4372篇 |
2002年 | 4531篇 |
2001年 | 5003篇 |
2000年 | 3695篇 |
1999年 | 2827篇 |
1998年 | 2608篇 |
1997年 | 2460篇 |
1996年 | 2256篇 |
1995年 | 2049篇 |
1994年 | 2006篇 |
1993年 | 2039篇 |
1992年 | 2075篇 |
1991年 | 2384篇 |
1990年 | 2317篇 |
1989年 | 2386篇 |
1988年 | 2267篇 |
1987年 | 2297篇 |
1986年 | 2125篇 |
1985年 | 2660篇 |
1984年 | 2670篇 |
1983年 | 2318篇 |
1982年 | 2371篇 |
1981年 | 2275篇 |
1980年 | 2079篇 |
1979年 | 2395篇 |
1978年 | 2548篇 |
1977年 | 2639篇 |
1976年 | 2731篇 |
1975年 | 2540篇 |
1974年 | 2467篇 |
1973年 | 2637篇 |
1972年 | 2153篇 |
1971年 | 1974篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
It is experimentally demonstrated that second-order polarizability gratings preliminarily recorded using bichromatic light in a phosphate glass can be amplified under the action of monochromatic radiation. The amplification effect takes place irrespective of the polarization and direction of propagation of the amplifying radiation and is achieved at various wavelengths. The phenomenon is related to the asymmetry of optical transitions between local centers in an isotropic medium in the presence of electric field. It is theoretically shown that this system may feature the formation of alternating electric field domains with dimensions depending on the grating amplitude. 相似文献
262.
A fractal-like structure of the domain boundaries was revealed in “overcritical” uniaxial Permalloy magnetic films. The fractal dimension of domain boundaries at the film surfaces was determined as a function of the film thickness. It is shown that the phase transition between the two possible types of fractal-like structures is accompanied by a jump in fractal dimension.
相似文献263.
The influence of the parameter of amplitude-phase coupling for nonlinear amplification on the phase-frequency characteristics of an injection laser in the regime of pumping current modulation has been investigated theoretically. The parameter is defined as the coefficient of proportionality between changes in the real and imaginary parts of the refractive index during variation of the density of photons in the cavity. The substantial dependence of the coefficient of phase modulation on the parameter of the amplitude-phase coupling for nonlinear amplification at small modulation frequencies is shown. A technique to determine the indicated parameter based on the frequency dependence of the ratio between the coefficients of phase and amplitude modulation is suggested. 相似文献
264.
N. S. Kazak E. G. Katranji I. A. Utkin A. A. Ryzhevich A. N. Khilo 《Journal of Applied Spectroscopy》2004,71(5):697-701
The phenomenon of self-diffraction of Bessel light beams (BLB) in a nonlinear liquid medium has been studied experimentally and theoretically for the first time. Diffraction maxima which do not correspond to integer orders for an induced periodic structure have been registered. It has been shown that the appearance of these maxima is due to the initial BLB modulation, which can be caused by the departure of the axicon refracting surface from the ideal conical surface, as well as by the imperfection of the form of the Gaussian beam incident on the axicon. 相似文献
265.
V. G. Domelunksen I. R. Krylov G. A. Polyanskaya M. A. Tsygankov 《Optics and Spectroscopy》2004,97(1):136-140
An interference method for measuring certain parameters of a substance in the vicinity of the critical state is proposed. The essence of the method is to decipher the interference pattern arising upon grazing incidence of a laser beam on a curved liquid-vapor interface. The deciphering allows one to determine the difference between the refractive indices of the two phases and the scaling factor of the wetting meniscus shape. This, in turn, makes it possible to calculate the critical exponents for the temperature dependences of the surface tension and the difference in the densities of the two phases. The ratio of these critical exponents for xenon, measured in the paper, is 3.81±0.03. 相似文献
266.
O. I. Reinov 《Journal of Mathematical Sciences》2003,115(2):2243-2250
We investigate Banach spaces possessing (or not possessing) the approximation properties AP s, 0 < s ≤ 1, in connection with the following known question in the geometric theory of operators: under which conditions on Banach spaces X and Y and on positive numbers r and p does the p-nuclearity of the second adjoint of a continuous operator T from X to Y imply the p-nuclearity of T? Actually, we give necessary and sufficient conditions under which this question is answered affirmatively. In addition, the corresponding counterexamples are obtained in the maximally strong form. For instance, it is shown (and this statement is a significant strengthening of the previous results of that sort) that there exists a pair of separable Banach spaces Z and W such that the spaces Z ** and W have Schauder bases, while for every p, 1 ≤ p < 2, there is a non-p-nuclear operator from W to Z with a p-nuclear second adjoint. Earlier, in similar examples, the corresponding spaces did not possess even the Grothendieck approximation property. The technique developed in this paper does not allow us to treat the case p > 2. That case will be studied in a forthcoming paper of the author. Bibliography: 11 titles. 相似文献
267.
For an arbitrary finite time interval, the unique solvability of a linear half-space problem is obtained in Hölder classes of functions. The problem arises as the result of the linearization of a free boundary problem for the Navier--Stokes system governing the unsteady motion of a finite mass of a compressible fluid. The boundary conditions in the linear problem are noncoercive because of the surface tension acting on the free boundary. This fact presents the main difficulty in the problem, while the differential system in itself is parabolic in the sense of Petrovskii. The principal idea of the investigation is to reduce the noncoercive problem to a coercive one with zero coefficient of the surface tension. Bibliography: 6 titles. 相似文献
268.
269.
270.
We prove new theorems on the justification of the averaging method for multifrequency oscillation systems with pulse influence at fixed times. 相似文献