全文获取类型
收费全文 | 261400篇 |
免费 | 1770篇 |
国内免费 | 538篇 |
专业分类
化学 | 134496篇 |
晶体学 | 4243篇 |
力学 | 13046篇 |
综合类 | 11篇 |
数学 | 28944篇 |
物理学 | 82968篇 |
出版年
2021年 | 2556篇 |
2020年 | 2677篇 |
2019年 | 3274篇 |
2018年 | 4711篇 |
2017年 | 4750篇 |
2016年 | 6264篇 |
2015年 | 3091篇 |
2014年 | 5519篇 |
2013年 | 11058篇 |
2012年 | 8985篇 |
2011年 | 10488篇 |
2010年 | 8347篇 |
2009年 | 8550篇 |
2008年 | 9868篇 |
2007年 | 9721篇 |
2006年 | 8765篇 |
2005年 | 7714篇 |
2004年 | 7311篇 |
2003年 | 6712篇 |
2002年 | 6707篇 |
2001年 | 7273篇 |
2000年 | 5392篇 |
1999年 | 4118篇 |
1998年 | 3612篇 |
1997年 | 3576篇 |
1996年 | 3261篇 |
1995年 | 2863篇 |
1994年 | 2941篇 |
1993年 | 2870篇 |
1992年 | 3182篇 |
1991年 | 3350篇 |
1990年 | 3189篇 |
1989年 | 3320篇 |
1988年 | 3148篇 |
1987年 | 3105篇 |
1986年 | 2973篇 |
1985年 | 3690篇 |
1984年 | 3857篇 |
1983年 | 3223篇 |
1982年 | 3243篇 |
1981年 | 3117篇 |
1980年 | 2900篇 |
1979年 | 3289篇 |
1978年 | 3401篇 |
1977年 | 3580篇 |
1976年 | 3483篇 |
1975年 | 3234篇 |
1974年 | 3216篇 |
1973年 | 3302篇 |
1972年 | 2510篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The long-range sound propagation from a deep ocean to a receiving system located on the shelf is modeled. The waveguide model is constructed on the basis of the data of an acoustic-oceanographic experiment carried out in the northwestern Pacific. The sensitivity and the frequency dependence of the difference in the sound field levels at the crossing of the frontal zone on the geoacoustic characteristics of the bottom of the shelf and the continental slope are investigated. It is shown that the level difference decreases by 8.2 dB as the velocity of longitudinal waves increases by 100 m/s in the range within 1490–1820 m/s. 相似文献
92.
Results of acoustic measurements in skeletal muscle are generalized. It is shown that assessment of the pathologies and functional condition of the muscular system is possible with the use of shear waves. The velocity of these waves in muscles is much smaller than the velocity of sound; therefore, a higher symmetry type is formed for them. In the presence of a preferential direction (along muscle fibers), it is characterized by only two rather than five (as in usual media with the same anisotropy) moduli of elasticity. A covariant form of the corresponding wave equation is presented. It is shown that dissipation properties of skeletal muscles can be controlled by contracting them isometrically. Pulsed loads (shocks) and vibrations are damped differently, depending on their frequency spectrum. Characteristic frequencies on the order of tens and hundreds of hertz are attenuated due to actin-myosin bridges association/dissociation dynamics in the contracted muscle. At higher (kilohertz) frequencies, when the muscle is tensed, viscosity of the tissue increases by a factor of several tens because of the increase in friction experienced by fibrillar structures as they move relative to the surrounding liquid; the tension of the fibers changes the hydrodynamic conditions of the flow around them. Finally, at higher frequencies, the attenuation is associated with the rheological properties of biological molecules, in particular, with their conformational dynamics in the wave field. Models that describe the controlled shock dissipation mechanisms are proposed. Corresponding solutions are found, including those that allow for nonlinear effects. 相似文献
93.
O. A. Pshenitsyna 《Journal of Mathematical Sciences》2006,135(5):3384-3399
We consider the arithmetic properties of the factor-rank and term-rank functions for matrices over semirings. In particular,
we investigate the sets of matrices that satisfy the extremes of inequalities for these rank functions of matrix union. The
classification of the linear transformations that keep these sets invariant is obtained.
__________
Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 9, No. 3, pp. 175–197, 2003. 相似文献
94.
N. O. Maksimova 《Journal of Mathematical Sciences》2006,135(1):2675-2679
In the article, it is proved that any nonnegative solution of an elliptic quasilinear inequality that vanishes on a subset
of positive measure is trivial.
__________
Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 25, pp. 112–118, 2005. 相似文献
95.
96.
Gabriel N. Gatica Ernst P. Stephan 《Numerical Methods for Partial Differential Equations》2002,18(1):105-128
This article deals with an expanded mixed finite element formulation, based on the Hu‐Washizu principle, for a nonlinear incompressible material in the plane. We follow our related previous works and introduce both the stress and the strain tensors as further unknowns, which yields a two‐fold saddle point operator equation as the corresponding variational formulation. A slight generalization of the classical Babu?ka‐Brezzi's theory is applied to prove unique solvability of the continuous and discrete formulations, and to derive the corresponding a priori error analysis. An extension of the well‐known PEERS space is used to define an stable associated Galerkin scheme. Finally, we provide an a posteriori error analysis based on the classical Bank‐Weiser approach. © 2002 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 18: 105–128, 2002 相似文献
97.
N. L. Vekshin 《Journal of Applied Spectroscopy》1991,54(1):17-22
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 1, pp. 26–32, January, 1991. 相似文献
98.
S. V. Ivanov V. V. Trachevskii O. S. Titova L. A. Zozulya 《Russian Journal of Applied Chemistry》2006,79(10):1712-1714
Experimental data demonstrate that a study of accelerated aging can enable prognostication of the working capacity and storage life of polymeric formulations used in aircraft components on the basis of changes in thermogravimetric constants of these polymeric formulations. 相似文献
99.
100.