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排序方式: 共有95条查询结果,搜索用时 15 毫秒
81.
Naïma Belhaneche-Bensemra Belkacem Belaabed Abdelmalik Bedda 《Macromolecular Symposia》2002,180(1):203-216
The aim of this paper is to study the miscibility and the thermal degradation of PVC/PMMA blends. For that purpose, blends of variable compositions from 0 to 100 wt% were prepared with and without plasticizer. Their physico-chemical characterization was carried out by differential scanning calorimetric analysis (DSC) and Fourier transform infrared spectroscopy (FTIR). Their thermal degradation under nitrogen at 185°C was studied and the HCl evolved from PVC was measured by the pH method. Degraded samples were characterized, after purification, by FTIR and UV-visible spectroscopy. The DSC analysis showed polymer miscibility up to 60 wt% of PMMA. This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (C=O) of PMMA and hydrogen from (CHCl) groups of PVC as evidenced by FTIR analysis. On the other hand, it was found that PMMA exerted a stabilizing effect on the thermal degradation of PVC by reducing the zip dehydrochlorination and by leading to the formation of short polyenes. 相似文献
82.
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84.
This paper revisits a few aspects of laser-dynamics with a strong-harmonic expansion analysis from which new analytical information, within the intrinsic pulsing regime that characterizes the non-linearly coupled differential Lorenz–Haken equations, is extracted. The analysis is expected to provide clearer insights to the physics involved in the laser-dynamics issue. Carried out to third-order in electric field amplitude, the procedure allows for the derivation of a closed form expression which describes the permanent-oscillation frequency of the unstable periodic state. Comparison between the frequency values evaluated from the literal formula and those obtained through direct numerical simulations shows a realistic fit inside the control parameters space that displays symmetric period-one pulsing solutions. 相似文献
85.
Belkacem Benmerad Acoura Guehria‐Laïdoudi Slimane Dahaoui Claude Lecomte 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(3):m119-m122
The title compound, triaquatris(glutarato)dilanthanum(III) dihydrate, {[La2(C5H6O4)3(H2O)3]·2H2O}n, is the first reported glutarate coordination polymer of lanthanum(III) without a protonated ligand. The noteworthy features in the structure are, firstly, the unusual binuclear lanthanum cage formed by three bridging bonds through O atoms involved in different coordination modes and, secondly, the very rare `malonate' mode exhibited by a dicarboxylate ligand with an alkyl chain of five C atoms. To our knowledge, this η7 chelation for the glutarate ligand has not been reported and was thought to be forbidden for steric reasons. The gauche–gauche conformation of the corresponding ligand favours cage formation, but trans geometries created along the ligating O atoms prevent cluster packing. The two independent La atoms are nine‐ and tenfold coordinated, leading to distorted one‐face‐sharing LaO7(H2O)2 and LaO9(H2O) polyhedra, respectively. In the three‐dimensional framework, these asymmetric subunits are linked in a zigzag manner via one‐edge‐sharing LaO9(H2O) polyhedra and are connected by the carbon backbone chains of the ligands. The structure is very compact and, unlike many other reported dicarboxylate lanthanides, connectivity between the two metal atoms and the three ligands yields a crystal packing with cavities accommodating two guest water molecules but without an open framework. 相似文献
86.
Ahmed Kadari Khaled Mahi Luiz Oliveira Faria Belkacem Saoula Bouziane Adila 《Chinese Journal of Physics (Taipei)》2017,55(1):127-132
Alumina (Al2O3) powders doped with different amounts of zirconium (Zr) ions were synthesized by the sol-gel process. The Zr concentration was changed from 0 to 3%. Here we attempted to fabricate Zr doped Al2O3 samples and characterized them for their optical and structural properties. Ultraviolet-Visible analysis (UV-Vis), infrared spectroscopy (FT-IR) and powder X-ray diffraction (XRD) have been used to characterize the optical properties, phase evolution and crystallinity of the obtained samples. X-ray diffraction patterns revealed that all the Al2O3 powders obtained were completely amorphous. An optical study was employed to determine the band gap of the samples. The transmittance had decreased from 90 to 86% and the band gap of pure Al2O3 was found to be 4.116 eV, and it was shifted to 4.038 eV for 3% Zr doped Al2O3. The results obtained in this study are discussed comparatively with those cited in the literature. 相似文献
87.
Kreidi K Akoury D Jahnke T Weber T Staudte A Schöffler M Neumann N Titze J Schmidt LP Czasch A Jagutzki O Costa Fraga RA Grisenti RE Smolarski M Ranitovic P Cocke CL Osipov T Adaniya H Thompson JC Prior MH Belkacem A Landers AL Schmidt-Böcking H Dörner R 《Physical review letters》2008,100(13):133005
We investigate single-photon double ionization of H(2) by 130 to 240 eV circularly polarized photons. We find a double slitlike interference pattern in the sum momentum of both electrons in the molecular frame which survives integration over all other degrees of freedom. The difference momentum and the individual electron momentum distributions do not show such a robust interference pattern. We show that this interference results from a non-Heitler-London fraction of the H(2) ground state where both electrons are at the same atomic center. 相似文献
88.
Dauvergne D Belkacem A Barrué F Bocquet JP Chevallier M Feinberg B Kirsch R Poizat JC Ray C Rebreyend D 《Physical review letters》2003,90(15):153002
We report a measurement of photon impact ionization of K and L shell of Au and K shell of Ag targets in the 1-GeV energy range. We show that the cross section is dominated by a contribution from a new channel called vacuum-assisted photoionization. In this process the energy-momentum balance associated with the removal of the innershell electron is obtained by conversion of a high-energy photon into an electron-positron pair. This measurement is consistent with the theoretical prediction that vacuum-assisted photoionization is the most probable ionization mechanism at very high energies. 相似文献
89.
Belkacem Said-Houari 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2011,110(1):115-133
This work is concerned with a system of nonlinear viscoelastic wave equations with nonlinear damping and source terms acting
in both equations. We will prove that the energy associated to the system is unbounded. In fact, it will be proved that the
energy will grow up as an exponential function as time goes to infinity, provided that the initial data are large enough.
The key ingredient in the proof is a method used in Vitillaro (Arch Ration Mech Anal 149:155–182, 1999) and developed in Said-Houari
(Diff Integr Equ 23(1–2):79–92, 2010) for a system of wave equations, with necessary modification imposed by the nature of
our problem. 相似文献
90.
Tao H Allison TK Wright TW Stooke AM Khurmi C van Tilborg J Liu Y Falcone RW Belkacem A Martinez TJ 《The Journal of chemical physics》2011,134(24):244306
Using a combined theoretical and experimental approach, we investigate the non-adiabatic dynamics of the prototypical ethylene (C(2)H(4)) molecule upon π → π? excitation. In this first part of a two part series, we focus on the lifetime of the excited electronic state. The femtosecond time-resolved photoelectron spectrum (TRPES) of ethylene is simulated based on our recent molecular dynamics simulation using the ab initio multiple spawning method with multi-state second order perturbation theory [H. Tao, B. G. Levine, and T. J. Martinez, J. Phys. Chem. A 113, 13656 (2009)]. We find excellent agreement between the TRPES calculation and the photoion signal observed in a pump-probe experiment using femtosecond vacuum ultraviolet (hν = 7.7 eV) pulses for both pump and probe. These results explain the apparent discrepancy over the excited state lifetime between theory and experiment that has existed for ten years, with experiments [e.g., P. Farmanara, V. Stert, and W. Radloff, Chem. Phys. Lett. 288, 518 (1998) and K. Kosma, S. A. Trushin, W. Fuss, and W. E. Schmid, J. Phys. Chem. A 112, 7514 (2008)] reporting much shorter lifetimes than predicted by theory. Investigation of the TRPES indicates that the fast decay of the photoion yield originates from both energetic and electronic factors, with the energetic factor playing a larger role in shaping the signal. 相似文献