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11.
Ohne Zusammenfassung 相似文献
12.
N. S. Sivakumaran R. F. Dressler B. Brosowski 《Mathematical Methods in the Applied Sciences》1986,8(1):492-501
The customary procedure for including resistive effects in turbulent hydraulic and stratified atmospheric flows is to integrate the empirically-known boundary shears over the entire wetted boundary of a thin fluid slab. A resistive body-force is then assumed to exist everywhere in each slab to replace the boundary shearing force. For the classical Saint-Venant model, this body-force can be shown to have a constant distribution in the vertical direction, and therefore can be evaluated for use in the momentum differential equation. In the newer Dressler theory, however, for unsteady flow over curved beds, it is proved here that a constant body-force distribution is not possible. We determine its variable distribution and its magnitude for use in the curved-flow equations. This vasriable distribution acts to produce an equal resultant in every thin layer of fluid parallel to the bed in an angular wedge over the curved channel bed. The new curved-flow equations are therefore extended to include resistive effects. 相似文献
13.
N. M. Chiera N. V. Aksenov Y. V. Albin G. A. Bozhikov V. I. Chepigin S. N. Dmitriev R. Dressler R. Eichler V. Ya. Lebedev A. Madumarov O. N. Malyshev D. Piguet Y. A. Popov A. V. Sabelnikov P. Steinegger A. I. Svirikhin A. Türler G. K. Vostokin A. Vögele A. V. Yeremin 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):99-108
The adsorption behavior of 197Hg and 183–185Hg on red amorphous selenium (red a-Se) and trigonal selenium (t-Se) was investigated experimentally by off-line and on-line gas chromatographic methods, in preparation of a sensitive chemical separation and characterization of the transactinides copernicium (Cn, Z = 112) and flerovium (Fl, Z = 114). Monte-Carlo simulations of a diffusion controlled deposition were in good agreement with the experimental results, assuming as interaction limits ?ΔH ads red a-Se (Hg) > 85 kJ/mol, and ?ΔH ads t-Se (Hg) < 60 kJ/mol. Both Se allotropes can be used as stationary surfaces in comparative gas-chromatographic chemical investigations of Cn and Fl. 相似文献
14.
We show how to formulate two-point boundary-value problems in order to compute fully-developed laminar channel and tube flow profiles for viscoelastic fluid models. The formulation is applied to Couette and pressure-driven flows separately, or a combination of both. The application of this methodology is illustrated analytically for the Upper-Convected Maxwell Model, and it is applied computationally for the Phan-Thien/Tanner and Giesekus Models. Numerical solutions exist for the last two models [J.Y. Yoo, H.C. Choi, On the steady simple shear flows of the one-mode Giesekus fluid, Rheol. Acta 28 (1989) 13–24; P.J. Oliveira, F.T. Pinho, Analytical solution for fully developed channel and pipe flow of Phan-Thien–Tanner fluids, J. Fluid Mech. 387 (1999) 271–280; M.A. Alves, F.T. Pinho, P.J. Oliveira, Study of steady pipe and channel flows of a single-mode Phan-Thien–Tanner fluid, J. Non-Newtonian Fluid Mech. 101 (2001) 55–76], allowing verification of the computational technique. Subsequently, the computational algorithm is applied to the constant-volume polymer blend models of Maffettone and Minale [P.L. Maffettone, M. Minale, Equation of change for ellipsoidal drops in viscous flow, J. Non-Newtonian Fluid Mech. 84 (1999) 105–106 (Erratum), J. Non-Newtonian Fluid Mech. 78 (1998) 227–241] and Dressler and Edwards [M. Dressler, B.J. Edwards, The influence of matrix viscoelasticity on the rheology of polymer blends, Rheol. Acta 43 (2004) 257–282; M. Dressler, B.J. Edwards, Rheology of polymer blends with matrix-phase viscoelasticity and a narrow droplet size distribution, J. Non-Newtonian Fluid Mech. 120 (2004) 189–205]. Rheological and morphological properties of the model blends are thus obtained as functions of the spatial position within the channel, applied pressure drop, and shear rate at the wall. 相似文献
15.
In this study, we have developed a new numerical approach to solve differential-type viscoelastic fluid models for a commonly used benchmark problem, namely, the steady Taylor—Couette flow between eccentric cylinders. The proposed numerical approach is special in that the nonlinear system of discretized algebraic flow equations is solved iteratively using a Newton–Krylov method along with an inverse-based incomplete lower-upper preconditioner. The numerical approach has been validated by solving the benchmark problem for the upper-convected Maxwell model at a large Deborah number. Excellent agreement with the numerical data reported in the literature has been found. In addition, a parameter study was performed for an extended White–Metzner model. A large eccentricity ratio was chosen for the cylinder system in order to allow flow recirculation to occur. We detected several interesting phenomena caused by the large eccentricity ratio of the cylinder system and by the viscoelastic nature of the fluid. Encouraged by the results of this study, we intend to investigate other polymeric fluids having a more complex microstructure in an eccentric annular flow field. 相似文献
16.
Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry 总被引:1,自引:0,他引:1
rico Marlon de Moraes Flores Jos Neri Gottfried Paniz Ayrton Figueiredo Martins Valderi L. Dressler Edson Irineu Müller Adilson Ben da Costa 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2187-2193
A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing. 相似文献
17.
Heinrich R. Karfunkel Thomas Dressler Andreas Hirsch 《Journal of computer-aided molecular design》1992,6(5):521-535
Summary Substituting carbon atoms of fullerenes by heteroatoms and vacancies will lead to new and yet unknown spherical-shaped molecules termed hereafter as heterofullerenes. The enormous structural diversity of these molecules is investigated and their structural, electronic and thermochemical properties are predicted using semiempirical computations. Computational results for complexes with ions lead to the hypothesis that these molecules behave like microscopic Faraday cages in which the electrons concentrate on the outer side of the sphere. It is predicted that some of these heterofullerenes are structurally and electronically similar to phthalocyanines and related molecules but offer many additional advantages. Potential uses such as adding heterofullerenes to fullerene materials, as superior starting materials for the fabrication of diamonds, as catalysts in hydrogenation reactions, as components of materials dominated until now by phthalocyanines, etc., are discussed. Simple synthetic routes to these compounds that are based on minor alternations of existing methods for fullerene production are proposed. On the basis of the thermochemical calculations, we believe that the most promising possibility consists of using metal cyanide/graphite composite target rods instead of pure graphite rods as in a conventional fullerene synthesis. 相似文献
18.
Rheological models of complex fluids with a physically restricted microstructure are analyzed to obtain general classes of
dynamical evolution equations for these materials. These classes insure that the appropriate mathematical constraints, associated
with each type of physical restriction, are consistently incorporated into the corresponding model development. Describing
the microstructure of the complex fluid with a second-rank tensor variable, a general class of dynamical evolution equations
is derived for three physically meaningful constraints associated with constancy of the invariants of this microstructural
tensor. The physical rationale for each of these constraints is discussed, and a corresponding set of constrained dynamical
evolution equations is derived in general terms.
Abdellatif Ait-Kadi passed away suddenly during the course of this research. The surviving authors express their gratitude
to Abdellatif for our many hours of productive work and companionship. 相似文献
19.
20.
The surprisingly large “pair” term corrections to threshold radiative neutron capture, previously calculated by Riska and Brown, and Gari and Huffman, are calculated in a new way in which they appear as relativistic corrections to the impulse approximation arising from the small negative energy components of the wave functions of the two nucleon system. Looking at these corrections from this point of view suggests not only that these small negative energy components are observable in non-relativistic processes, but also that the size of these corrections may ultimately depend on, or give information about, a consistent relativistic treatment of the nuclear force problem. 相似文献