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排序方式: 共有125条查询结果,搜索用时 15 毫秒
61.
Karla Calfumán Paulina Dreyse Camilo García Maria J. Aguirre Tomás Beltrán Eva Guillamón Iván Sorribes Cristian Vicent Rosa Llusar Mauricio Isaacs 《Macromolecular Symposia》2011,304(1):93-100
Summary: This paper describes the electrochemical reduction of nitrite ion in 0.1 M NaClO4, on glassy carbon or ITO electrodes modified with mixtures PVC- tetraruthenated metalloporphyrins. This electrode is able to keep the extraordinary electrocatalytic properties of the macrocycle allowing multielectronic transfers and a great stability as a consequence of the inclusion of the macrocycles into a polymeric support such as PVC. On the other hand, the electrochemical reduction of nitrite ion on these modified electrodes studied by cyclic voltammetry shows an enhancement in the current values and lower overpotential compared with the activity of the bare glassy carbon electrode. Controlled potential electrolysis experiments verify the production of ammonia, hydrazine and hydroxylamine, showing the electrocatalytic character and the stability of this modified electrode. 相似文献
62.
Fernanda Peres FerreiraEduardo Henck Marturano Carlos Alexandre CarolloDionéia Camilo Rodrigues de Oliveira 《Tetrahedron letters》2011,52(2):297-299
A novel labdane diterpene was isolated from the plant Acritopappus longifolius. The structure of this compound was established by 1D- and 2D-nuclear magnetic resonance spectroscopic techniques and mass spectrometry data. N-Methyl-4-hydroxy-trans-proline, stigmasterol-3-O-β-d-glycoside, and the flavonoids quercetin, luteolin, kaempferol, and rutin were also isolated. 相似文献
63.
Camilo García Cristian Domínguez Alvaro Aliaga Betty Matsuhiro Leonora Mendoza María J. Aguirre Mauricio Isaacs 《Electroanalysis》2011,23(6):1401-1409
A new conducting film derived from the complex [Fe (diaphen)3]2+, (diaphen=5,6‐diamino‐1,10‐phenanthroline) was electropolymerized by cyclic voltammetry onto a glassy carbon electrode. Poly‐[FeII (diaphen)3] was studied by cyclic voltammetry, SEM, UV‐vis and micro‐Raman spectroscopy. Poly‐[FeII (diaphen)3] shows electrocatalytic activity in HSO3? reduction in an ethanol/water solution. Electrocatalysis is centered at the π ring of phenanthroline. Rotating disk electrode studies showed a 0.117 V/dec Tafel slope, suggesting an EC process where the electrochemical process is the determining step. The chemical step was studied by UV‐vis spectroelectrochemistry. Amperometric behavior showed a linear range between 47.5 µM to 417 µM and the LOD was 19.5 µM. 相似文献
64.
Renato D. C. Monteiro Camilo Ortiz Benar F. Svaiter 《Computational Optimization and Applications》2014,57(1):45-69
In this paper, we consider block-decomposition first-order methods for solving large-scale conic semidefinite programming problems given in standard form. Several ingredients are introduced to speed-up the method in its pure form such as: an aggressive choice of stepsize for performing the extragradient step; use of scaled inner products; dynamic update of the scaled inner product for properly balancing the primal and dual relative residuals; and proper choices of the initial primal and dual iterates, as well as the initial parameter for the scaled inner product. Finally, we present computational results showing that our method outperforms the two most competitive codes for large-scale conic semidefinite programs, namely: the boundary-point method introduced by Povh et al. and the Newton-CG augmented Lagrangian method by Zhao et al. 相似文献
65.
Veras G Gomes Ade A da Silva AC de Brito AL de Almeida PB de Medeiros EP 《Talanta》2010,83(2):565-568
This article describes the classification of biodiesel samples using NIR spectroscopy and chemometric techniques. A total of 108 spectra of biodiesel samples were taken (being three samples each of four types of oil, cottonseed, sunflower, soybean and canola), from nine manufacturers. The measurements for each of the three samples were in the spectral region between 12,500 and 4000 cm−1. The data were preprocessed by selecting a spectral range of 5000-4500 cm−1, and then a Savitzky-Golay second-order polynomial was used with 21 data points to obtain second derivative spectra. Characterization of the biodiesel was done using chemometric models based on hierarchical cluster analysis (HCA), principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) elaborated for each group of biodiesel samples (cotton, sunflower, soybean and canola). For the HCA and PCA, the formation of clusters for each group of biodiesel was observed, and SIMCA models were built using 18 spectral measurements for each type of biodiesel (training set), and nine spectral measurements to construct a classification set (except for the canola oil which used eight spectra). The SIMCA classifications obtained 100% accurate identifications. Using this strategy, it was feasible to classify biodiesel quickly and nondestructively without the need for various analytical determinations. 相似文献
66.
Eric?R.?Pinnick Camilo?E.?Calderon Andrew?J.?Rusnak Feng?WangEmail author 《Theoretical chemistry accounts》2012,131(3):1146
This paper studies the possibility of improving the convergence of ab initio free energy perturbation (FEP) calculations by
developing customized force fields with the adaptive force-matching (AFM) method. The ab initio FEP method relies on a molecular
mechanics (MM) potential to sample configuration space. If the Boltzmann weight of the MM sampling is close to that of the
ab initio method, the efficiency of ab initio FEP will be optimal. The difference in the Boltzmann weights can be quantified
by the relative energy difference distribution (REDD). The force field developed through AFM significantly improves the REDD
when compared with standard MM models, thus improving the convergence of the ab initio FEP calculation. The static dielectric
constant εs of ice-Ih was studied with PW-91 through ab initio FEP. With a customized force field developed through AFM, we were able
to converge εs to 80 ± 4 with 3,600 configurations. A similar ab initio FEP calculation with the TIP4P model would require 220 times more
configurations to achieve the same accuracy. Our study indicates that the PW-91 functional underestimates ice-Ih εs by about 20%. 相似文献
67.
Camilo Zúñiga Maria Soledad LarrechiGerard Lligadas Juan Carlos RondaMarina Galià Virginia Cádiz 《Polymer Degradation and Stability》2013
Flame retardant polybenzoxazine foams were prepared in a two step process, by heating mixtures of the benzoxazine derived from renewable diphenolic acid (DPA-Bz) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or 9,10-dihydro-9-oxa-10-(1-hydroxy-1-methylethyl) phosphaphenanthrene-10-oxide (DOPO-2Me) as additives. In the first step partial curing was achieved at different times and temperatures. In the second step, these materials underwent self foaming when heated at 220 °C. By means of a factorial design 23 the effect of curing conditions and type of additive on the foam density were evaluated. DOPO-2Me additive was found to partially react with the DPA-Bz leading to a decrease in the glass transition temperature of the materials. The cellular structure of the foams was characterized by scanning electron microscope in terms of cell size, cell size distribution, closed-cell content and anisotropy ratio. The presence of DOPO-2Me into the solid precursors and foams greatly influenced the thermal degradation and the flame retardancy properties as evaluated by TGA, LOI and UL-94 respectively. 相似文献
68.
Joaquín Peralta Camilo Valencia-Balvín 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(9):177
In this work, we present a structural and dynamic characterisation of six different types of sulvanites Cu3 X Y 4 with X = Nb, V and Ta, and Y = S and Se. These materials have been the subject of intense study in recent times primarily as potential candidates for solar cell devices, as well as for their enhanced opto-electrical properties. Here, by means of first-principles calculations, we study the structural and dynamic behaviour of these materials at different temperatures, which is important for use of these materials in high-temperature conditions. In this work the dynamic and structural properties are studied using the Density Functional Theory technique. The simulations were performed at four different temperatures, ranging from room temperature to ~1500 K. By using first-principles molecular dynamics in the microcanonical ensemble, we are able to determine the vibrational spectra of these sulvanites. With this information we report for the first time the partial vibrational density of states of these structures at different temperatures. With these results we determine the vibrational properties of the basic building blocks of those sulvanites and their dynamic behaviour under temperature effects. We also show that the building blocks that which make up these structures, remain stable as the temperature increases. 相似文献
69.
Margarita E. Aliaga Catalina Carrasco-Pozo Camilo López-Alarcón Hernán Speisky 《Transition Metal Chemistry》2010,35(3):321-329
Cu2+ ions and reduced glutathione (GSH) swiftly interact to form the physiologically occurring Cu(I)–[GSH]2 complex. Prompted by the recently reported ability of this complex to generate superoxide radicals from molecular oxygen,
the present study addressed how the concentration of Cu2+ and GSH, the pH, and the temperature affect the formation of the Cu(I)–[GSH]2 complex and its capacity to generate superoxide radicals and hydrogen peroxide. Increasing concentrations of Cu2+ and GSH, added at a fixed molar ratio of 1:3, led to a proportionally greater production of superoxide anions, hydrogen peroxide,
and oxidized glutathione (GSSG). GSSG formation was found to closely reflect the formation of Cu(I)–[GSH]2. Biologically relevant changes in pH (e.g., from 6.8 to 7.7) and temperature (from 22 to 37 °C) did not affect the formation
of the Cu(I)–[GSH]2, as assessed by GSSG production. However, production of superoxide radicals increased as the pH values were incremented.
An opposite effect was observed regarding hydrogen peroxide production. The ability of a freshly prepared Cu(I)–[GSH]2 complex (assayed within a minute from its formation) to generate superoxide radicals was incremented by as the temperature
was increased. Such ability, however, correlated inversely with the temperature when, before assaying for superoxide, the
earlier referred preparation was incubated during 30 min in the presence of oxygen. Under the latter condition, hydrogen peroxide
linearly accumulated in time, suggesting that an increased autodismutation underlies the apparent time-dependent “aging” of
the capacity of the complex to generate superoxide. 相似文献
70.
In this work we propose an exact semidefinite relaxation for non-linear, non-convex dynamical programs under discrete constraints
in the state variables and the control variables. We outline some theoretical features of the method and workout the solutions
of a benchmark problem in cybernetics and the classical inventory problem under discrete constraints. 相似文献