全文获取类型
收费全文 | 4193篇 |
免费 | 59篇 |
国内免费 | 5篇 |
专业分类
化学 | 3028篇 |
晶体学 | 30篇 |
力学 | 45篇 |
数学 | 668篇 |
物理学 | 486篇 |
出版年
2020年 | 35篇 |
2019年 | 34篇 |
2017年 | 26篇 |
2016年 | 74篇 |
2015年 | 53篇 |
2014年 | 66篇 |
2013年 | 158篇 |
2012年 | 158篇 |
2011年 | 157篇 |
2010年 | 111篇 |
2009年 | 97篇 |
2008年 | 178篇 |
2007年 | 136篇 |
2006年 | 162篇 |
2005年 | 137篇 |
2004年 | 141篇 |
2003年 | 101篇 |
2002年 | 117篇 |
2001年 | 90篇 |
2000年 | 72篇 |
1999年 | 86篇 |
1998年 | 73篇 |
1997年 | 63篇 |
1996年 | 86篇 |
1995年 | 75篇 |
1994年 | 65篇 |
1993年 | 66篇 |
1992年 | 70篇 |
1991年 | 71篇 |
1990年 | 61篇 |
1989年 | 64篇 |
1988年 | 76篇 |
1987年 | 69篇 |
1986年 | 66篇 |
1985年 | 83篇 |
1984年 | 83篇 |
1983年 | 73篇 |
1982年 | 82篇 |
1981年 | 70篇 |
1980年 | 61篇 |
1979年 | 58篇 |
1978年 | 64篇 |
1977年 | 65篇 |
1976年 | 49篇 |
1975年 | 61篇 |
1974年 | 46篇 |
1973年 | 32篇 |
1972年 | 37篇 |
1971年 | 30篇 |
1970年 | 32篇 |
排序方式: 共有4257条查询结果,搜索用时 0 毫秒
1.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献
2.
3.
4.
Rolf Dittmann Heinz-Jürgen Feld Wolfgang Samenfink Sigmar Wittig 《Particle & Particle Systems Characterization》1994,11(5):379-384
In utilizing the advantages of extinction measurements in micron and especially submicron particle characterization, the properties of a multiple wavelength extinction technique have been the subject of extended theoretical studies. Furthermore, an experimental set-up was designed which provides high flexibility owing to its modular design. The performance of the technique described is demonstrated by a large variety of applications in aerosol and combustion research and in large-scale industrial systems. It was found to be a reliable tool in characterizing dense particulate systems. 相似文献
5.
Optimal explicit Runge–Kutta methods consider more stages in order to include a particular spectrum in their stability domain
and thus reduce time-step restrictions. This idea, so far used mostly for real-line spectra, is generalized to more general
spectra in the form of a thin region. In thin regions the eigenvalues may extend away from the real axis into the imaginary
plane. We give a direct characterization of optimal stability polynomials containing a maximal thin region and calculate these
polynomials for various cases. Semi-discretizations of hyperbolic–parabolic equations are a relevant application which exhibit
a thin region spectrum. As a model, linear, scalar advection–diffusion is investigated. The second-order-stabilized explicit
Runge–Kutta methods derived from the stability polynomials are applied to advection–diffusion and compressible, viscous fluid
dynamics in numerical experiments. Due to the stabilization the time step can be controlled solely from the hyperbolic CFL
condition even in the presence of viscous fluxes. 相似文献
6.
7.
Michael Höft Jochen Weinzierl Rolf Judaschke 《International Journal of Infrared and Millimeter Waves》2002,23(7):1127-1146
Holography is a promising technique for power combining applications in the frequency range of short millimeter and submillimeter waves. In this paper, quasi-optical holographic power combining circuits are investigated. An equivalent network is utilized which rigorously models horn arrays and biperiodic dielectric structures in order to design computer-generated holograms. We apply the network model to a 5-element quasi-optical power combiner and demonstrate its capability. The hologram is designed for 150 GHz and has an efficiency of 92.5 % with a 90 % bandwidth of 5.3 %. With the aid of a broadband waveguide power divider and a vector field measurement system, the circuit is analyzed. 相似文献
8.
9.
Synthesis and Structure of K3N Two phases in the binary system K/N have been obtained via co‐deposition of potassium and nitrogen onto polished sapphire at 77 K and subsequent heating to room temperature. The powder diffraction pattern of one of these phases can be satisfactorily interpreted by assuming the composition K3N, and the anti‐TiI3 structure‐type, which is also adopted by Cs3O. The resulting hexagonal lattice constants are: a = 779.8(2), c = 759.2(9) pm, Z = 2, P63/mcm. Comparison with possible structures of K3N generated by computational methods and refined at Hartree‐Fock‐ and DFT level, reveals that the energetically most favoured structure has not formed (presumable Li3P‐type), but instead one of those with very low density. In this respect, the findings for K3N are analogous to the results on Na3N. The thermal evolution of the deposited starting mixture has been investigated. Hexagonal K3N transforms to another K/N phase at 233 K. Its XRD can be fully indexed resulting in an orthorhombic cell a = 1163, b = 596, c = 718 pm. Decomposition leaving elemental potassium as the only residue occurs at 263 K. 相似文献
10.
Rolf Vonhoff 《Mathematische Nachrichten》1998,193(1):199-210
In the paper, a new method of constructing asymptotic solutions of differential equations on manifolds with singularities is presented. This method allows not only to widen essentially the space of asymptotics but also to obtain explicit formulas for asymptotic expansions, in particular, in the case when in a neighborhood of a singular point there exist strata of different dimensions. 相似文献