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61.
Precise resistivity ρ (Ω cm) and viscosity η (10−2 P) measurements for isobutyric acid–water (IBAW) critical mixtures with added K+ and Cl− ions have been performed in the Arrhenius temperature domain of the electrolyte. From the activation energy, the resistivity–viscosity relation reveals a fraction power character over the whole range of parameters investigated. To analyze our data we have used an exponential formula derived from the equivalent Arrhenius law: ρ/T is proportional to (η/T)R, where R = Eρ/Eη is the ratio between the resistivity and viscosity activation energies. In the case of the pure system (IBAW), the value of R is in vicinity of 1, but when the salt is added, the ratio R shows dependence on the (K+, Cl−) concentrations: 0.6 < R < 1. The domain of the validity of R is in conformity with the theoretical prediction. The Coulombic interaction is the origin of the deviation. 相似文献
62.
We construct a Poincaré operator for the system
where λ is a real parameter, x
3, x = (x1, x2, x3), [formula], and ƒ is an odd C2 function such that ƒ′(0) = 1, xƒ(x) > 0, for x ≠ 0. We also consider the case where ƒ is C1. We will express F in linearized form, that is, F(x) = Ax + G(x), where A is the linearized part of F around zero and G(x) = o(|x|) near zero. Fixed points of the Poincaré operator correspond to periodic solutions of the functional differential equation
where T is the period of x. 相似文献
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63.
Donnan Dialysis of Ag+ and Zn2+ was investigated through a cation exchange membrane (CMS Neosepta) when a proton concentration difference was maintained between the two sides of the membrane. Developed for the production of brine from sea water, CMS Neosepta showed a higher permeability to monovalent than to bivalent cations. Several physico-chemical parameters have been determined (electrical resistance, membrane potential, sorption of electrolytes, Zn2+ and Ag+ diffusion coefficients). The flux of Ag+ and the diffusion potential in the membrane increase with HNO3 concentrations. Ag+ and Zn2+ can be separated because of the preferential membrane transfer for Ag+. 相似文献
64.
A series of tungsten‐doped Titania photocatalysts were synthesized using a low‐temperature method. The effects of dopant concentration and annealing temperature on the phase transitions, crystallinity, electronic, optical, and photocatalytic properties of the resulting material were studied. The X‐ray patterns revealed that the doping delays the transition of anatase to rutile to a high temperature. A new phase WyTi1‐yO2 appeared for 5.00 wt% W‐TiO2 annealed at 900 °C. Raman and diffuse reflectance UV–Vis spectroscopy showed that band gap values decreased slightly up to 700 °C. X‐ray photoelectron spectroscopy showed that surface species viz. Ti3+, Ti4+, O2?, oxygen‐vacancies, and adsorbed OH groups vary depending on the preparation conditions. The photocatalytic activity was evaluated via the degradation of methylene blue using LED white light. The degradation rate was affected by the percentage of dopants. The best photocatalytic activity was achieved with the sample labeled 5.00 wt% W‐TiO2 annealed at 700 °C. 相似文献
65.
Structural and magnetic properties of manganites series La0.57Nd0.1Sr0.33Mn1?x Sn x O3 with (0.05 ≤ x ≤ 0.30) have been investigated, and the critical exponents and magnetocaloric effect are studied around the room temperature, to shed light on Sn substitution influence. A solid-state reaction method was used in the preparation. A structural study using Rietveld refinement of XRD patterns indicates rhombohedral structure with R \( \overline{3} \) c space group for (0.05 ≤ x ≤ 0.20) and shows the existence of a secondary phase attributed to the neodymium tin oxide (Nd2Sn2O7) pyrochlore for x = 0.3. The variation of the magnetization (M) vs. temperature (T), under an applied magnetic field of 0.05 T, reveals a ferromagnetic–paramagnetic transition at the Curie temperature T C. In addition, it was discovered that increasing the tin content leads to a reduction in magnetization and a lowering of T C from 282 K (x = 0.05) to 158 K (x = 0.20) with increasing Sn substitution. The samples exhibit the characteristics of spin/cluster-glass state which is evident from (zero-field-cooled and field-cooled) magnetization vs. temperature curves. Indeed, the thermal evolution of magnetization in the ferromagnetic phase at low temperature varies as T 3/2, in accordance with Bloch’s law. The spin-stiffness constant D obtained from the Bloch constant was determined. A large magnetocaloric effect has been observed in both samples (x = 0.05 and x = 0.10): the maximum entropy change, \( \left| {\varDelta S_{\text{M} }^{\text{peak}} } \right| \) , reaches the highest value of 3.22 J/kg K under a magnetic field change of 5 T with a RCP value of 56 J/kg for x = 0.10 composition. This opens an interesting opportunity to this compound to compete with materials which work as magnetic refrigerants near room temperature. Besides, we show that the samples follow the conventional behavior of a second-order ferromagnetic transition. This was possible by investigating the critical behavior at the transition region by adopting the modified Arrott plot method. The values of the critical exponents (β, γ, δ and n) are determined and they are between those predicted by the three-dimensional Heisenberg model. 相似文献
66.
Mohamed Amine Cherif Toufic El Arwadi Hassan Emamirad Jean-Marc Sac-épée 《Semigroup Forum》2014,88(3):753-767
The first aim of this paper is to illustrate numerically that the Dirichlet-to-Neumann semigroup represented by P. Lax acts as a magnifying glass. In this perspective, we used the finite element method for discretizing of the correspondent boundary dynamical system using the implicit and explicit Euler schemes. We prove by using the Chernoff’s Theorem that the implicit and explicit Euler methods converge to the exact solution and we use the (P1)-finite elements to illustrate this convergence through a FreeFem++ implementation which provides a movie available online. In the Dirichlet-to-Neumann semigroup represented by P. Lax the conductivity \(\gamma \) is the identity matrix \(I_n\) , but for a different conductivity \(\gamma \) , the authors of Cornean et al. (J Inverse Ill-posed Prob 12:111–134, 2006) supplied an estimation of the operator norm of the difference between the Dirichlet-to-Neumann operator \(\Lambda _\gamma \) and \(\Lambda _1\) , when \(\gamma =\beta I_n\) and \(\beta =1\) near the boundary \(\partial \Omega \) (see Lemma 2.1). We will use this result to estimate the accuracy between the correspondent Dirichlet-to-Neumann semigroup and the Lax semigroup, for \(f\in H^{1/2}(\partial \Omega )\) . 相似文献
67.
Nasri N Tlili N Elfalleh W Cherif E Ferchichi A Khaldi A Triki S 《Natural product research》2011,25(18):1733-1742
Natural chemical compounds are a widely researched topic worldwide because of their potential activity against cerebrovascular diseases. Chemicals from Juniperus phoenicea berries are reported in this study. Lipids (11%) from seeds are mainly unsaturated (86%). Minerals are also quantified like Na (63.8?mg per 100?g?DW) or K (373.9?mg per 100?g?DW). Total reduced sugars are ca 192.6?mg?g(-1)?DW. Polyphenols and flavonoids from berries are highly present with an average of 1764?±?174.3?mg gallic acid per 100?g?DW and 890?±?47.6?mg rutin per 100?g?DW, respectively. Mean free radical scavenging activities, determined by DPPH and ABTS, are 1337?±?126.2?mM TEAC per 100?g?DW and 1105.7?±?95.9?mM TEAC per 100?g?DW, respectively. All findings improve the possible presence of biologically active fractions in phytocomplex that could be used as such and/or extracted for the formulation of supplements and/or ingredients for the pharmaceutical industry. 相似文献
68.
A. Keita F. Lazrak E. M. Essassi I. Cherif Alaoui Y. Kandri Rodi J. Bellan 《Phosphorus, sulfur, and silicon and the related elements》2013,188(7):1541-1548
We describe herein the synthesis of new macrocycles 5 et 6 derived from 1,5-benzodiazepine-2,4-dione in a heterogenous media using phase transfer catalysis conditions. A crystallographic study by x-ray of 5 was carried out to confirm the structure suggested; moreover the macrocycle 6 presents chelating properties with respect to the ion Ag + easily observed by IR and UV spectroscopies. 相似文献
69.
Sabri Messaoudi Bechir Bejaoui Fourat Akrout Malika Bel Hassen Cherif Sammari 《International journal of quantum chemistry》2013,113(11):1633-1640
The heterogeneous uptake of N2O5 on mineral dust particles may play an important role in the removal of nitrogen oxides from the atmosphere. However, the reaction of N2O5 with the mineral particles is not well understood. The reaction of N2O5 with two Si(OH)4 monomers is explored using theoretical methods. This study represents a first step towards understanding the interaction of N2O5 with the hydroxyl groups of silica particles. Energies are calculated using MP2 single point calculations on the B3LYP optimized geometries and including B3LYP thermodynamic corrections. Four mechanisms are considered for the formation of two HNO3 and one H6Si2O7. The rate limiting activation barrier of the most favorable path is found to be 12.5 kcal mol?1. This reaction appears to be more favorable than the hydrolysis of N2O5 with one water molecule. These results are in agreement with experimental observations, which show that N2O5 reacts with OH groups of Saharan dust to form nitrate. © 2012 Wiley Periodicals, Inc. 相似文献