全文获取类型
收费全文 | 304746篇 |
免费 | 1791篇 |
国内免费 | 648篇 |
专业分类
化学 | 146366篇 |
晶体学 | 4470篇 |
力学 | 15078篇 |
综合类 | 6篇 |
数学 | 46481篇 |
物理学 | 94784篇 |
出版年
2020年 | 1971篇 |
2019年 | 2265篇 |
2018年 | 10953篇 |
2017年 | 11674篇 |
2016年 | 7997篇 |
2015年 | 3113篇 |
2014年 | 3931篇 |
2013年 | 9369篇 |
2012年 | 10876篇 |
2011年 | 19880篇 |
2010年 | 12515篇 |
2009年 | 12559篇 |
2008年 | 17832篇 |
2007年 | 21218篇 |
2006年 | 7821篇 |
2005年 | 12974篇 |
2004年 | 9268篇 |
2003年 | 8885篇 |
2002年 | 6852篇 |
2001年 | 6097篇 |
2000年 | 4994篇 |
1999年 | 3508篇 |
1998年 | 3054篇 |
1997年 | 3052篇 |
1996年 | 2992篇 |
1995年 | 2426篇 |
1994年 | 2503篇 |
1993年 | 2530篇 |
1992年 | 2666篇 |
1991年 | 2730篇 |
1990年 | 2634篇 |
1989年 | 2617篇 |
1988年 | 2556篇 |
1987年 | 2524篇 |
1986年 | 2436篇 |
1985年 | 3123篇 |
1984年 | 3298篇 |
1983年 | 2652篇 |
1982年 | 2917篇 |
1981年 | 2796篇 |
1980年 | 2592篇 |
1979年 | 2825篇 |
1978年 | 2953篇 |
1977年 | 2889篇 |
1976年 | 2897篇 |
1975年 | 2739篇 |
1974年 | 2714篇 |
1973年 | 2900篇 |
1972年 | 1912篇 |
1967年 | 1868篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A tight-binding (TB) hamiltonian for calcium is built with a high precision parametrization technique based on density functional calculations of the energy bands and the total energy at various lattice volumes. The new set of TB parameters is appropriate to study phenomena under pressures as high as 20 GPa. Specifically, both the metal to nonmetal transition at 4 GPa and the structural transition fcc to bcc at 19 GPa are well reproduced. These transitions and several static properties are in excellent agreement with experiments. Phonon frequencies, plasmon energy, melting temperature and the coefficient of thermal expansion were calculated with a molecular dynamics scheme of this TB hamiltonian. 相似文献
992.
Yu. Kh. Vekilov E. I. Isaev A. V. Godoniuk 《Journal of Experimental and Theoretical Physics》2003,97(5):1005-1009
The electronic spectrum of the three-dimensional Penrose lattice with “central” decoration by atoms is investigated using the tight binding model with nearest-neighbor interaction. Inverse participation ratios, higher moments of density probabilities, and fractal dimensions of the system are determined. The WFs are critical (they have a power-law dependence on the distance) at all energies in the band and are multifractal measures leading to the entire spectrum of the exponents. The results show that the system is in the critical state of the metal-insulator transition. On critical WFs, the cubic root temperature dependence of the conductivity is obtained. 相似文献
993.
Synchronized whistlers recorded at Varanasi 总被引:1,自引:0,他引:1
Some interesting events of synchronized whistlers recorded at low latitude station Varanasi during magnetic storm period of
the year 1977 are presented. The dynamic spectrum analysis shows that the component whistlers are Eckersley whistlers having
dispersion 10 s1/2 and 30 s1/2. An attempt has been made to explain the dynamic spectra using lightning discharge generated from magnetospheric sources 相似文献
994.
B. G. Tagiev U. F. Kasumov N. N. Musaeva R. B. Dzhabbarov 《Physics of the Solid State》2003,45(3):426-432
The current-voltage characteristics of Ca4Ga2S7: Eu3+ single crystals are measured for the first time, and the processes affecting these characteristics are analyzed theoretically. It is demonstrated that Ca4Ga2S7: Eu3+ single crystals are high-resistance semiconductors with a resistivity of ~109 Ω cm and a relative permittivity of 10.55. The electrical properties of the studied materials are governed by traps with activation energies of 0.13 and 0.19 eV and a density ranging from 9.5×1014 to 2.7×1015 cm?3. The one-carrier injection is observed in weak electric fields. In electric fields with a strength of more than 4×103 V/cm, traps undergo thermal field ionization according to the Pool-Frenkel mechanism. At low temperatures and strong fields (160 K and 5×104 V/cm), the electric current is most likely due to hopping conduction by charge carriers over local levels in the band gap in the vicinity of the Fermi level. 相似文献
995.
996.
997.
998.
E. Yu. Daniyarova I. V. Kazatchkov V. N. Remeslennikov 《Journal of Mathematical Sciences》2005,131(6):6015-6022
This article is the fourth part of the series of papers whose aim is the construction of algebraic geometry over metabelian
Lie algebras.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 14, Algebra,
2004. 相似文献
999.
1000.
The load-carrying capacity of circular plates made of a fiber-reinforced composite and loaded with axisymmetric transverse forces under axisymmetric boundary conditions is investigated. The plates can be freely supported or clamped along their contour. To the known yield condition used, in the plane of main bending moments, there correspond irregular hexagons, which depend on the mechanical properties of composite constituents and some characteristic geometrical parameters. It is shown that, depending on the ratio of ultimate radial and circumferential bending moments, in the plastic state, the circular plates (the central part of the clamped plates) take the form of a cone or a frustum of cone. For each of the cases, the limit load is found, which is a function of the above-mentioned mechanical parameters. The statically allowable fields of bending moments and the corresponding allowable fields of deflection rates are determined. The solutions found are exact. Special cases for the freely supported plates are analyzed, and the results obtained are presented in the form of graphs.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 177–192, March–April, 2005. 相似文献