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181.
S. Mudry T. Lutchyshyn Yu. Plevachuk V. Sklyarchuk 《Journal of Molecular Liquids》2005,120(1-3):99-102
Structure of Cu1−xPbx (x=0, 0.025, 0.05, 0.075, 0.1, 0.125) molten alloys has been studied by means of X-ray diffraction method. Structural parameters obtained from structure factors (SF) and radial distribution functions were analyzed. Partial structure factors were calculated by using Reverse Monte-Carlo method. It is shown that tendency to preferred interaction of atoms of the same kind grows with increasing of lead content. 相似文献
182.
A new finite element technique has been developed for employing integral-type constitutive equations in non-Newtonian flow simulations. The present method uses conventional quadrilateral elements for the interpolation of velocity components, so that it can conveniently handle viscoelastic flows with both open and closed streamlines (recirculating regions). A Picard iteration scheme with either flow rate or elasticity increment is used to treat the non-Newtonian stresses as pseudo-body forces, and an efficient and consistent predictor-corrector scheme is adopted for both the particle-tracking and strain tensor calculations. The new method has been used to simulate entry flows of polymer melts in circular abrupt contractions using the K-BKZ integral constitutive model. Results are in very good agreement with existing numerical data. The important question of mesh refinement and convergence for integral models in complex flow at high flow rate has also been addressed, and satisfactory convergence and mesh-independent results are obtained. In addition, the present method is relatively inexpensive and in the meantime can reach higher elasticity levels without numerical instability, compared with the best available similar calculations in the literature. 相似文献
183.
Linking Phase-Field and Atomistic Simulations to Model Dendritic Solidification in Highly Undercooled Melts 总被引:2,自引:0,他引:2
Even though our theoretical understanding of dendritic solidification is relatively well developed, our current ability to model this process quantitatively remains extremely limited. This is due to the fact that the morphological development of dendrites depends sensitively on the degree of anisotropy of capillary and/or kinetic properties of the solid-liquid interface, which is not precisely known for materials of metallurgical interest. Here we simulate the crystallization of highly undercooled nickel melts using a computationally efficient phase-field model together with anisotropic properties recently predicted by molecular dynamics simulations. The results are compared to experimental data and to the predictions of a linearized solvability theory that includes both capillary and kinetic effects at the interface. 相似文献
184.
In the last years, interest in the use of high-temperature molten fluoride salts as fluid fuels and coolants in nuclear power systems has been increasing. The comprehensive information on the properties of molten fuel and coolant salts is necessary for development of new designs. Experimental data on physical properties of some prospective molten salt mixtures of Li, Na, Be, Zr fluorides containing fertile and fissile materials as well as soluble fission products are unknown. At the first stage of the conceptual development estimation of the required properties from the known experimental data can be useful for selection of suitable molten salt compositions. In this paper the approaches for estimation of the physicochemical properties such as density (ρ), dynamic viscosity (η), isobaric heat capacity (cp), and thermal conductivity (λ) for molten salt fluoride mixtures are proposed. The calculation algorithm was based on the additivity principle for the properties (Px) of multi-component molten salt mixtures, which can be found from the relationship Px = ΣNiPi. Here Ni and Pi denote mole fraction and corresponding property of individual molten salts or their binary mixtures as constituents of the more complex systems. The empirical expressions connecting the property with molar volume and molecular mass of selected fluoride compositions are also derived and tested. Estimated values are compared with each other and available experimental data. 相似文献
185.
In this study, we use optical tweezers to investigate the ionic effects of magnesium salt solutions on the overstretching
transition of single B-DNA molecules. The experimental data are compared with those in sodium salt solutions. The overstretching
transition force increases when the NaCl or MgCl2 salt concentration increases. Magnesium cations have much stronger effects on the overstretching transition force than sodium
cations. For both NaCl and MgCl2 salt solutions, the overstretching transition force is linear with the natural logarithm of salt concentration, which confirms
the theory proposed in previous paper. The modified ZZO model is applied to study the electrostatic contribution of magnesium
salt solutions to the overstretching transition of single B-DNA molecules. The consistency between the experimental data and
analytical results shows that the modified ZZO model can simulate the transition behavior of single B-DNA molecules in different
NaCl and MgCl2 salt solutions. 相似文献
186.
Multiphased mixed crystals of NaCl, KCl and KI were grown by the melt method, for the first time. Densities and refractive indices of all the grown crystals were determined and used for the estimation of the composition in the crystal. Atomic absorption spectroscopic measurements were done to estimate the metal atom contents in the crystal. Lattice parameters and thermal parameters (Debye‐Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency) were determined from the X‐ray powder diffraction data. DC and AC electrical measurements were done at various temperatures ranging from 40 to 150°C. Activation energies were also estimated. The observed lattice parameters showed that the system exhibits three phases each nearly corresponds to NaCl, KCl and KI. The thermal and electrical parameters show a highly nonlinear bulk composition dependence. Results are reported. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
187.
Eddie Rossinsky Konstantin B. Tarmyshov Michael C. Bhm Florian Müller‐Plathe 《Macromolecular theory and simulations》2009,18(9):545-552
MD studies of liquid isopropyl alcohol and melts of short poly(vinyl alcohol) (PVA) oligomers are described. The specific volume was found to depend inversely on the number N of repeat units. If the chain length is enhanced, the viscosity of the PVA melt increases and the peaks in the radial distribution function become sharper. Additional peaks that appear in melts of PVA chains are of pure intramolecular origin. The calculated radius of gyration was found to depend on the number of formula units via . The orientation correlation functions showed that all molecular vectors of PVA melts with chain lengths N = 1, 2, 3 relax completely within a few nanoseconds. The relaxation times for the O H bond vector as obtained via the Kohlrausch‐Williams‐Watts expression showed an exponential dependence on the number of repeat units.
188.
189.
线型聚乙烯及其共聚物的挤出畸变与熔体粘弹性的关系 总被引:7,自引:0,他引:7
采用恒速型双筒毛细管流变仪研究了一类线型聚乙烯熔体的挤出畸变与熔体非线性粘弹性的关系。实验研究了发生畸变时挤出压力的振荡规律,发现线型大分子或带小侧基的大分子熔体,容易发生壁滑和挤出压力振荡;而有较大侧基、或分子量分布宽、或带大量短支链的熔体,挤出畸变现象较轻。挤出畸变与熔体的弹性及熔体.壁面吸附状态紧密相关。容易发生壁滑和挤出压力振荡的熔体,弹性较大(入口压力降大);在壁面的吸附作用强(壁面临界剪切应力大)。稳态剪切粘度大小与挤出畸变和压力振荡的关系不大;而拉伸应力和拉伸粘度大的熔体较易发生壁滑和挤出压力振荡。 相似文献
190.
Greco F 《The European physical journal. E, Soft matter》2008,25(2):175-180
In de Gennes-Doi-Edwards theory for entangled polymeric melts, a length scale r0 is introduced, giving the equilibrium mesh size of the physical network of chains. Each polymer molecule is then represented
as a random walk, with a step size r0 (a “subchain”, made up of n0 Kuhn segments) dictated by the existence of entanglements. Progressing from this simple picture, an issue that has been constantly
overlooked so far, despite its potential relevance, is that of finite-size effects at the de Gennes-Doi-Edwards characteristic
length scale. Actually, since a subchain in a melt is a “small”, nonmacroscopic system, fluctuations of both its length and
its number of Kuhn segments are certainly nonnegligible. An ad hoc theoretical treatment from nonstandard (nano) statistical mechanics and thermodynamics seems then required, to find the anticipated
equilibrium statistical distributions of the subchain population. In this contribution, we carefully discuss this topic. Some
predictions from the nonstandard fluctuation-inclusive approach on the statistics of subchains are here obtained, and compared
with existing simulations, even down to the atomistic level. 相似文献