全文获取类型
收费全文 | 706968篇 |
免费 | 7141篇 |
国内免费 | 2518篇 |
专业分类
化学 | 353138篇 |
晶体学 | 8463篇 |
力学 | 36328篇 |
综合类 | 78篇 |
数学 | 102654篇 |
物理学 | 215966篇 |
出版年
2021年 | 5801篇 |
2020年 | 6463篇 |
2019年 | 7179篇 |
2018年 | 13665篇 |
2017年 | 14028篇 |
2016年 | 15591篇 |
2015年 | 8029篇 |
2014年 | 12513篇 |
2013年 | 29184篇 |
2012年 | 25232篇 |
2011年 | 33991篇 |
2010年 | 24007篇 |
2009年 | 23861篇 |
2008年 | 31335篇 |
2007年 | 33166篇 |
2006年 | 23931篇 |
2005年 | 24285篇 |
2004年 | 21124篇 |
2003年 | 19391篇 |
2002年 | 18290篇 |
2001年 | 18672篇 |
2000年 | 14590篇 |
1999年 | 11059篇 |
1998年 | 9510篇 |
1997年 | 9338篇 |
1996年 | 8969篇 |
1995年 | 7837篇 |
1994年 | 7900篇 |
1993年 | 7533篇 |
1992年 | 8067篇 |
1991年 | 8513篇 |
1990年 | 8054篇 |
1989年 | 7929篇 |
1988年 | 7755篇 |
1987年 | 7477篇 |
1986年 | 7229篇 |
1985年 | 9439篇 |
1984年 | 9821篇 |
1983年 | 8248篇 |
1982年 | 8661篇 |
1981年 | 8071篇 |
1980年 | 7654篇 |
1979年 | 8227篇 |
1978年 | 8615篇 |
1977年 | 8486篇 |
1976年 | 8490篇 |
1975年 | 8049篇 |
1974年 | 7948篇 |
1973年 | 8334篇 |
1972年 | 6142篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献
982.
For Hermitian adjoint differential operators, we consider the structure of Darboux–Bäcklund-type transformations in the class of parametrically dependent Hilbert spaces. By using the proposed new method, we obtain the corresponding integro-differential symbols of the operators of transformations in explicit form and consider the problem of their application to the construction of two-dimensional Lax-integrable nonlinear evolution equations and their Darboux–Bäcklund-type transformations. 相似文献
983.
Bogdanovskaya V. A. Grinberg V. A. Krishtalik L. I. Kuznetsov A. M. Pleskov Yu. V. Skundin A. M. Tarasevich M. R. Tsyrlina G. A. 《Russian Journal of Electrochemistry》2003,39(4):441-444
Russian Journal of Electrochemistry - 相似文献
984.
985.
A nonlinear (in the cubic approximation) relaxation equation of state is derived for a rod containing cracks partially filled with an incompressible viscous liquid. The nonlinear effects of the self-action and interaction of low-and high-frequency longitudinal elastic waves propagating in such a rod are studied for the cases of identical and size-varied cracks. Linear and nonlinear acoustic parameters characterizing the self-action and interaction of elastic waves in a cracked rod are determined. 相似文献
986.
H. G. Bohlen W. von Oertzen R. Kalpakchieva B. Gebauer S. M. Grimes A. Lenz T. N. Massey M. Milin Ch. Schulz Tz. Kokalova S. Torilov S. Thummerer 《Physics of Atomic Nuclei》2003,66(8):1494-1500
The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2?, and 3/2?, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C. 相似文献
987.
B.I. Sturman A.S. Gorkunova K.H. Ringhofer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):291-297
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic
states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency
of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to
the periodic states and their apparent characteristics are strongly different for the two limiting cases above.
Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003 相似文献
988.
The paper considers the application of factorized-sparse-approximate-inverse (FSAI) preconditionings to linear algebraic systems with nonsingular unsymmetric coefficient matrices. Special attention is paid to methods for optimizing the sparsity pattern of such preconditioners. It is numerically demonstrated that the efficiency of FSAI preconditionings can be substantially improved by applying the so-called postfiltering and prefiltering in order to sparsify preconditioning matrices. Bibliography: 20 titles. 相似文献
989.
We study nonlinear dynamics of optical pulse propagation in the spectral region inside the polariton gap. It is shown that the Kerr nonlinearity can lead to formation of solitary waves in this region of frequencies. 相似文献
990.
I.A. Khotina L.S. Lepnev N.S. Burenkova P.M. Valetsky A.G. Vitukhnovsky 《Journal of luminescence》2004,110(4):232-238
New materials based on low-generation polyphenylene dendrimers with the light emission in the blue spectrum range were synthesized and examined for an efficient organic light emitting diodes (OLED) application. It has been shown that the ratio of p-phenylene groups with high fluorescence parameters to 1,3,5-triphenylbenzene groups with low fluorescent parameters may be the possible reason for the experimental variations of relative quantum yield of photoluminescence in the compounds explored. The quantum yield value is increased with a number of dendrimer generations up to 50–70%. The role of bromine atoms as the luminescence quenchers have been demonstrated, which is important for synthesis route choice. 相似文献