全文获取类型
收费全文 | 1767篇 |
免费 | 54篇 |
国内免费 | 35篇 |
专业分类
化学 | 1100篇 |
晶体学 | 15篇 |
力学 | 29篇 |
综合类 | 1篇 |
数学 | 177篇 |
物理学 | 534篇 |
出版年
2022年 | 14篇 |
2019年 | 13篇 |
2017年 | 13篇 |
2016年 | 26篇 |
2015年 | 33篇 |
2014年 | 30篇 |
2013年 | 46篇 |
2012年 | 55篇 |
2011年 | 46篇 |
2010年 | 60篇 |
2009年 | 44篇 |
2008年 | 61篇 |
2007年 | 59篇 |
2006年 | 53篇 |
2005年 | 54篇 |
2004年 | 69篇 |
2003年 | 60篇 |
2002年 | 63篇 |
2001年 | 72篇 |
2000年 | 61篇 |
1999年 | 41篇 |
1998年 | 35篇 |
1997年 | 32篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 34篇 |
1993年 | 45篇 |
1992年 | 41篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 25篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 20篇 |
1974年 | 22篇 |
1973年 | 17篇 |
1972年 | 17篇 |
1971年 | 13篇 |
1970年 | 15篇 |
排序方式: 共有1856条查询结果,搜索用时 15 毫秒
111.
Andrea D. Beck David G. Flad Claudia Tonhäuser Gregor Gassner Claus-Dieter Munz 《Flow, Turbulence and Combustion》2016,97(2):475-511
In this work we investigate the interplay of polynomial de-aliasing and sub-grid scale models for large eddy simulations based on discontinuous Galerkin discretizations. It is known that stability is a major concern when simulating underresolved turbulent flows with high order nodal collocation type discretizations. By changing the interpolatory character of the nodal collocation type discretization to a projection based discretization by increasing the number of quadrature points (polynomial de-aliasing), one is able to remove the aliasing induced stability problems. We focus on this effect and on the consequence for large eddy simulations with explicit subgrid scale models. Often, subgrid scale models have to achieve two possibly conflicting tasks in a single simulation: firstly stabilizing the numerics and secondly modeling the physical effect of the missing scales. Within a discontinuous Galerkin approach, it is possible to use either a fast (but potentially aliasing afflicted) nodal collocation discretization or a projection-based (but computationally costly) variant in combination with an explicit subgrid scale model. We use this framework to investigate the effect on the appropriate model parameter of a standard Smagorinsky subgrid scale model and of a Variational Multiscale Smagorinsky formulation. For this we first consider the 3-D viscous Taylor-Green vortex example to investigate the impact on the stability of the method and second the turbulent flow past a circular cylinder to investigate and compare the accuracy of the results. We show that the aliasing instabilities of collocative discretizations severely limit the choice of the model constant, in particular for high order schemes, while for de-aliased DG schemes, the closure model parameters can be chosen independently from the numerical scheme. For the cylinder flow, we also find that for the same model settings, the projection-based results are in better agreement with the reference DNS than those of the collocative scheme. 相似文献
112.
Synthesis and characterisation of the SrxBa1−xFeO3−y-system and the fluorinated phases SrxBa1−xFeO2F
Oliver Clemens Robert Haberkorn Peter R. Slater Horst Philipp Beck 《Solid State Sciences》2010,12(8):1455-1463
Compounds in the system SrxBa1?xFeO3?y have been prepared under different partial pressures of oxygen. In this system, different perovskite-type structures are found depending highly on the values of x and y. Fluorination using polyvinylidenedifluoride (PVDF) gives oxyfluoride materials of composition SrxBa1?xFeO2F, which normally crystallize in the cubic perovskite structure. Rietveld refinement results provide information about the packing density for oxide and oxyfluoride samples and allow a general comparison between these two different types of materials. Furthermore, the determination of the average iron oxidation state also showed that the oxygen deficiency, y, depends significantly on the value of x and the structure determined by the Sr/Ba ratio. 相似文献
113.
114.
115.
The present focus of the CBELSA/TAPS experiment is on meson-photoproduction off the nucleon using polarized photons and polarized targets. Here first preliminary results on the reactions γp → pπ and γp → pπ for both circularly and linearly polarized photons and a longitudinally polarized target are presented. Preliminary results for the beam asymmetry ∑ and the double polarization observable G have been extracted for both reactions using the linear polarization data. From the circular polarization data the observable E has been determined. Due to the near 4π angular coverage of the detector system these results cover almost the full solid angle. 相似文献
116.
M. Mukherjee D. Beck K. Blaum G. Bollen J. Dilling S. George F. Herfurth A. Herlert A. Kellerbauer H. -J. Kluge S. Schwarz L. Schweikhard C. Yazidjian 《The European Physical Journal A - Hadrons and Nuclei》2008,35(1):1-29
ISOLTRAP is a Penning trap mass spectrometer for high-precision mass measurements on short-lived nuclides installed at the
on-line isotope separator ISOLDE at CERN. The masses of close to 300 radionuclides have been determined up to now. The applicability
of Penning trap mass spectrometry to mass measurements of exotic nuclei has been extended considerably at ISOLTRAP by improving
and developing this double Penning trap mass spectrometer over the past two decades. The accurate determination of nuclear
binding energies far from stability includes nuclei that are produced at rates less than 100 ions/s and with half-lives well
below 100ms. The mass-resolving power reaches 107 corresponding to 10keV for medium heavy nuclei and the uncertainty of the resulting mass values has been pushed down to below
10-8. The article describes technical developments achieved since 1996 and the present performance of ISOLTRAP. 相似文献
117.
D. A. Konevetz I. E. Beck G. V. Shishkin V. V. Vlassov V. N. Silnikov 《Russian Chemical Bulletin》2002,51(7):1100-1111
The review surveys the results of our studies devoted to the design of highly efficient catalysts of hydrolysis of the phosphodiester bonds in RNA. These catalysts contain the imidazole residue in the catalytic domain, one or several bis-quaternized rings of 1,4-diazabicyclo[2.2.2]octane as a polycationic RNA-binding domain, and a lipophilic radical. A versatile approach to artificial ribonucleases of this type was proposed, which allows one to vary not only the number of positive charges in the RNA-binding domain, the structure of the catalytic site, and their mutual arrangement but also the domain structure of the molecule as a whole. Analysis of the catalytic properties of the synthesized constructs makes it possible to optimize the domain structure and the geometry of the molecule ensuring its maximum ribonuclease activity. 相似文献
118.
We consider the crystal structure of the level zero extremal weight modules V() using the crystal base of the quantum affine algebra constructed in Duke Math. J.
99 (1999), 455–487. This approach yields an explicit form for extremal weight vectors in the U
– part of each connected component of the crystal, which are given as Schur functions in the imaginary root vectors. We show the map
induces a correspondence between the global crystal base of V() and elements
. 相似文献
119.
Formation of Compounds in the Quasi-binary Systems AcX4? MX2 (Ac = Th, U; M = Ca, Sr, Ba, Eu, Ge, Sn, Pb; X = Br, I) T,x-phase diagrams of the systems ThI4? SnI2, ThI4? PbI2, ThI4? CaI2, and ThI4? SrI2 were established using thermoanalysis and x-ray methods. The only ternary compounds have a 1:1 composition. Further AcMX6 compounds (Ac: Th, U; M: Ca, Sr, Ba, Eu, Ge, Sn, Pb; X: Br, I) were synthesized and their structures investigated. Four structure types are found depending on the temperature and the Ac/M combinations. The structures of γ-ThSnI6 and β-ThSnI6 were determined with single crystal methods as representatives of a whole series of isotypic compounds. 相似文献
120.
The results of high pressure experiments with ternary iodides of the general formula ABI6 with A = Ca, Dy, Ge, Sn, Pb and B = Th, U are described. These compounds transform from a β- to a γ-SnThI6-type structure, both variants of known trihalide structures (BiI3- and PuBr3-type). Trends and pecularities in the values for the minimal transformation pressures and in the velocities of transition are pointed out, and they are discussed in terms of geometric and electronic factors. 相似文献