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71.
Dominique Bourn Nelson Martins-Ferreira Andrea Montoli Manuela Sobral 《Semigroup Forum》2014,88(3):739-752
We explore some properties of Schreier split epimorphisms between monoids, which correspond to monoid actions. In particular, we prove that the split short five lemma holds for monoids, when it is restricted to Schreier split epimorphisms, and that any Schreier reflexive relation is transitive, partially recovering in monoids a classical property of Mal’tsev varieties. 相似文献
72.
Cláudia T. Arranja Mariana Marcos Manuela R. Silva M. Ermelinda S. Eusébio Ricardo A. E. Castro Abílio J. F. N. Sobral 《Journal of Thermal Analysis and Calorimetry》2014,117(3):1375-1383
In this work, 3,5-bis(decyloxy)benzaldehyde, a precursor of long chain amphiphilic BODIPYs, was synthesized and its polymorphic behavior was characterized by differential scanning calorimetry, polarized light thermo microscopy, infrared spectroscopy, and XRPD. From the combined use of these techniques, an interesting polymorphic behavior was observed, and four polymorphs were identified. The initial compound melts around room temperature, ca. 30 °C, and several polymorphic forms of lower melting point are obtained by cooling the melt. A thermal program could be developed that allows obtaining each form independently. 相似文献
73.
In this work, we present an algorithm for solving constrained optimization problems that does not make explicit use of the objective function derivatives. The algorithm mixes an inexact restoration framework with filter techniques, where the forbidden regions can be given by the flat or slanting filter rule. Each iteration is decomposed into two independent phases: a feasibility phase which reduces an infeasibility measure without evaluations of the objective function, and an optimality phase which reduces the objective function value. As the derivatives of the objective function are not available, the optimality step is computed by derivative-free trust-region internal iterations. Any technique to construct the trust-region models can be used since the gradient of the model is a reasonable approximation of the gradient of the objective function at the current point. Assuming this and classical assumptions, we prove that the full steps are efficient in the sense that near a feasible nonstationary point, the decrease in the objective function is relatively large, ensuring the global convergence results of the algorithm. Numerical experiments show the effectiveness of the proposed method. 相似文献
74.
In this work we investigated a novel configuration of the orthogonal geometry for double pulse laser ablation. In this arrangement, a laser is focused onto a target generating a highly directed plume; after that, an additional laser produces a second plasma onto another perpendicular target. In this way, the second plume is expanded through the first plume region. Ablation of carbon was carried out in vacuum (10− 4 Pa) by two delayed lasers. The first pulse corresponds to a Nd:yttrium–aluminum–garnet (YAG) (1064 nm) and the second one to an excimer (248 nm) laser. Results show that plasma interactions produce different species emission enhancement depending on the delay between lasers, laser fluences and the spatial overlapping between plumes. Approximately an 100-fold increase in emission signal was measured as the observation distance grows. 相似文献
75.
Ana C.F. Ribeiro Luís M.P. Veríssimo Abílio J.F.N. Sobral Victor M.M. Lobo Miguel A. Esteso 《Comptes Rendus Chimie》2013,16(5):469-475
Diffusion coefficients of silver salts in aqueous solutions are estimated from Onsager-Fuoss and Pikal models, using different values of the mean distance of closest approach of ions, a, determined from different theoretical procedures. The influence of this parameter on the diffusion of these systems is discussed. 相似文献
76.
António Santos António M. Rodrigues Abílio J. F. N. Sobral Paula V. Monsanto Winchil L. C. Vaz Maria João Moreno 《Photochemistry and photobiology》2009,85(6):1409-1417
We studied the interaction of hematoporphyrin IX (HpIX) with bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) containing cholesterol at a molar fraction between 0 and 0.5. The membrane-associated fraction of HpIX decreases significantly over a period of hours, for porphyrin concentrations in the aqueous phase above 50 n m . This was attributed to self-aggregation of HpIX and was well described by a dimerization process. A model was developed to correct for aggregation and obtain the true partition coefficient which is dependent on the molar fraction of cholesterol with a maximum at 20 mol%. The chemical and physical effects on the lipid bilayer upon irradiation of HpIX were studied for lipid bilayers with POPC:Chol 1:1. Exposure of these bilayers to visible light in the presence of HpIX leads to several cholesterol oxidation products that were identified using GC-MS. A dramatic increase in the membrane leakiness was also observed, even for short irradiation times and small light intensities, as evaluated from the rate of pH equilibration and dithionite permeability. The relevance of these results for the mechanism of photodynamic therapy is discussed. 相似文献
77.
Many derivative-free methods for constrained problems are not efficient for minimizing functions on “thin” domains. Other algorithms, like those based on Augmented Lagrangians, deal with thin constraints using penalty-like strategies. When the constraints are computationally inexpensive but highly nonlinear, these methods spend many potentially expensive objective function evaluations motivated by the difficulties in improving feasibility. An algorithm that handles this case efficiently is proposed in this paper. The main iteration is split into two steps: restoration and minimization. In the restoration step, the aim is to decrease infeasibility without evaluating the objective function. In the minimization step, the objective function f is minimized on a relaxed feasible set. A global minimization result will be proved and computational experiments showing the advantages of this approach will be presented. 相似文献
78.
Bredice F.O. Orzi D.J.O. Schinca D. Sobral H. Villagran-Muniz M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2002,30(6):2139-2143
The perturbation produced by pulsed laser generated discharge in an electric field is studied as a tool for breakdown characterization. A focused high-power pulsed laser induces a discharge in air or in a solid target, that is placed between the plates of a planar charged capacitor. The induced discharge generates a temporal redistribution of the electrical charges on the plates that can be easily measured by a resistor connected to the ground plate. This signal depends on the energy used to generate the breakdown, the capacitor applied voltage, and the distance between the plates. In this work, we show that this signal can be readily used to optimize the relevant parameters involved in laser-induced breakdown spectroscopy in gases and in solid targets. 相似文献
79.
80.
Keli A. Sobral Regina O. Rodrigues Rogério D. Oliveira José E. Olivo Flávio F. de Moraes Gisella M. Zanin 《Applied biochemistry and biotechnology》2003,108(1-3):809-819
An experimental design with factorial planning was used for the immobilization of the enzyme cyclodextringlycosyltransferase
(CGTase) from Bacillus firmus (strain no.37) to select the best combination of support, method of immobilization, and conditions that gives primarily higher
average values for the specific immobilized enzyme activity, and secondarily, higher average values for the percentage of
protein fixation. The experimental design factors were as follows: supports—controlled-pore silica, chitosan, and alumina;
immobilization methods—adsorption, and two covalent bonding methods, either with γ-aminopropyltriethoxysilane or hexamethylenediamine
(HEMDA); conditions—7°C without agitation and 26°C with stirring. The best combination of factors that lead to higher average
values of the response variables was obtained with immobilization of CGTase in silica with HEMDA at 7°C. However, immobilization
in chitosan at 7°C gave the highest immobilized CGTase specific activity, 0.25 μmole of β-CD/(min·mg protein). Physical adsorption
gave low specific enzyme activities, and, in general, a high load of enzyme leads to lower specific enzyme activity. 相似文献