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41.
42.
The physical and chemical changes that occur on the polymer surfaces during the reaction between concentrated sulphuric acid and films of low density polyethylene, high density polyethylene and isotactic polypropylene at 75–125°C have been studied. Sulphonation-desulphonation reactions, leading to olefinic conjugation and, ultimately, carbonisation, are the most significant chemical changes. These, together with the disruption of the polymer surface, explain the autocatalytic evolution of SO2 noted previously. 相似文献
43.
Vickery L. Arcus Lyndsay Main Brian K. Nicholson 《Journal of organometallic chemistry》1993,460(2):139-147
4-Ethyl-1-hydroxy-3-(4-hydroxyphenyl)-2-oxa-1-boranaphthalene (4) is formed in 78% yield from the reaction of 1-(4-methoxyphenyl)-2-phenylbutan-1-one with an of excess boron tribromide in dichloromethane followed by treatment with water. Reaction of 4 with iodine in aqueous sodium hydroxide gives a second oxaboracycle, 3-ethyl-1-hydroxy-3-(4-hydroxybenzoyl)-2,1-benzoxaborolane (5). The X-ray crystal structure determinations of both boron heterocycles are reported. Other new compounds reported are 1-(4-hydroxyphenyl)-2-(1-hydroxyphenyl)-butan-1-one (6), formed by reaction of 4 with alkaline hydrogen peroxide, and 1-(4-hydroxyphenyl)-2-(2-biphenyl)-butan-1-one (8), formed by coupling of 4 with bromobenzene in the presence of Pd(PPh3) 4. 相似文献
44.
K. Weibert J. Main G. Wunner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(3):381-401
Harmonic inversion has already been proven to be a powerful tool for the analysis of quantum spectra and the periodic orbit
orbit quantization of chaotic systems. The harmonic inversion technique circumvents the convergence problems of the periodic
orbit sum and the uncertainty principle of the usual Fourier analysis, thus yielding results of high resolution and high precision.
Based on the close analogy between periodic orbit trace formulae for regular and chaotic systems the technique is generalized
in this paper for the semiclassical quantization of integrable systems. Thus, harmonic inversion is shown to be a universal
tool which can be applied to a wide range of physical systems. The method is further generalized in two directions: firstly,
the periodic orbit quantization will be extended to include higher order corrections to the periodic orbit sum. Secondly, the use of cross-correlated periodic orbit sums allows us to significantly
reduce the required number of orbits for semiclassical quantization, i.e., to improve the efficiency of the semiclassical method. As a representative of regular systems, we choose the circle billiard,
whose periodic orbits and quantum eigenvalues can easily be obtained.
Received 24 February 2000 and Received in final form 22 May 2000 相似文献
45.
Main W.T. Garate E. Weatherall J.C. Cherry R. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1992,20(3):281-287
A high-power frequency-locked dielectric Cerenkov maser oscillator is presented. The device consists of an annular electron beam traveling down a dielectric-lined waveguide (wall radius 1.74 cm, liner thickness 2-3 mm, linear ∈=10). A 100 kW input signal is injected into the drift tube between the diode and liner, through a rectangular TE10 to cylindrical TM01 mode converter. When operated with a beam current of 500 A and a total output power of 13 MW, the device displays no RF quenching through the full width of the 100 ns beam pulse. Two higher current cases with power as high as 280 MW but severe RF quenching are presented. The results are compared with linear theory, and quenching mechanisms are discussed 相似文献
46.
47.
A new pinoresinol-type lignan from Ligularia kanaitizensis 总被引:1,自引:0,他引:1
A new pinoresinol-type Lignan, 9alpha-angloyloxypinoresinol (1), was isolated from the roots and rhizomes of Ligularia kanaitizensis (Franch.) Hand.-Mazz, in addition to a known compound, 9alpha-hydroxypinoresinol (2). The structure of this new lignan (1) was established on the basis of 1D and 2D NMR experiments. Anti-HIV-1 RT biological assay showed that 1 was inhibitory to HIV-1 RT. 相似文献
48.
49.
D. Yu. Ivanov E. Takhtamirov Yu. V. Dubrovskii V. A. Volkov L. Eaves P. C. Main M. Henini D. K. Maude J. -C. Portal J. C. Maan G. Hill 《JETP Letters》2000,72(9):476-479
Tunnel current measurements between strongly disordered two-dimensional electron systems in a perpendicular magnetic field are presented. Two-dimensional electron accumulation layers are formed by an extremely narrow layer of Si donors (Si delta doping) in GaAs on either side of an AlGaAs tunnel barrier. Strong interaction between Landau levels of the two-dimensional subbands in each accumulation layer is observed as an anticrossing of the related peak positions in the tunnel current vs. voltage curves as a function of magnetic field. The splitting of the interacting Landau levels is about 10 meV, which cannot be explained by nonparabolicity of the conduction band in GaAs. A possible reason for the observed interaction connected with the collective excitations in the 2DES is discussed. 相似文献
50.
A robust, accurate, and computationally efficient interface tracking algorithm is a key component of an embedded computational framework for the solution of fluid–structure interaction problems with complex and deformable geometries. To a large extent, the design of such an algorithm has focused on the case of a closed embedded interface and a Cartesian computational fluid dynamics grid. Here, two robust and efficient interface tracking computational algorithms capable of operating on structured as well as unstructured three‐dimensional computational fluid dynamics grids are presented. The first one is based on a projection approach, whereas the second one is based on a collision approach. The first algorithm is faster. However, it is restricted to closed interfaces and resolved enclosed volumes. The second algorithm is therefore slower. However, it can handle open shell surfaces and underresolved enclosed volumes. Both computational algorithms exploit the bounding box hierarchy technique and its parallel distributed implementation to efficiently store and retrieve the elements of the discretized embedded interface. They are illustrated, and their respective performances are assessed and contrasted, with the solution of three‐dimensional, nonlinear, dynamic fluid–structure interaction problems pertaining to aeroelastic and underwater implosion applications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献