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排序方式: 共有278条查询结果,搜索用时 46 毫秒
181.
Journal of Radioanalytical and Nuclear Chemistry - Polycarbonate (PC) loaded with different filler levels equal to 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 2.5, 3.5 and 5.0 wt% (weight percent) of... 相似文献
182.
In this review we collect certain results obtained in the last decades on vibrating systems with concentrated masses. In particular, we show the connection of the eigenvalues and eigenfunctions of the local problem with the low and high frequency vibrations of the original problem. To cite this article: M. Lobo, E. Pérez, C. R. Mecanique 331 (2003). 相似文献
183.
Christian Constanda Miguel Lobo Eugenia Prez 《Mathematical Methods in the Applied Sciences》1995,18(5):337-344
The method of matched asymptotic expansions is used to find a homogenized problem whose solution is an approximation to the solution of a mixed periodic boundary value problem in the theory of bending of thin elastic plates. A critical size for the fixed parts of the boundary is found such that the boundary condition of the homogenized problem is an intermediate case between that for the clamped edge plate and that for the free boundary plate. 相似文献
184.
Danielle Goveia Fabiana A. Lobo Iramaia C. Bellin Leonardo F. Fraceto Amauri A. Menegário Peter Burba 《International journal of environmental analytical chemistry》2013,93(13):1296-1309
The present study deals with a new analytical procedure based on a cellulose diffusion membrane and immobilised tetraethylene-pentamine-hexaacetate chelator (DM-TEPHA) for an in situ differentiation of labile and inert metal species in aquatic systems. The DM-TEPHA system was prepared by placing TEPHA chelator in pre-purified cellulose bags and in situ applied immersing the system in two Brazilian rivers to study the relative lability of metal species (Cu, Pb, Fe, Mn and Ni) as a function of the time and the quantity of exchanger, respectively. The procedure is simple and enables a new perspective for understanding the complexation, transport, stability and lability of metal species in aquatic systems rich in organic matter. 相似文献
185.
M. Eugenia Cornejo David Lobo Jesús Medina 《Mathematical Methods in the Applied Sciences》2019,42(17):5779-5793
Bipolar fuzzy relation equations arise as a generalization of fuzzy relation equations considering unknown variables together with their logical connective negations. The occurrence of a variable and the occurrence of its negation simultaneously can give very useful information for certain frameworks where the human reasoning plays a key role. Hence, the resolution of bipolar fuzzy relation equations systems is a research topic of great interest. This paper focuses on the study of bipolar fuzzy relation equations systems based on the max‐product t‐norm composition. Specifically, the solvability and the algebraic structure of the set of solutions of these bipolar equations systems will be studied, including the case in which such systems are composed of equations whose independent term be equal to 0. As a consequence, this paper complements the contribution carried out by the authors on the solvability of bipolar max‐product fuzzy relation equations. 相似文献
186.
Ana C. F. Ribeiro Marisa C. F. Barros Luis M. P. Verissimo Victor M. M. Lobo Artur J. M. Valente 《Journal of solution chemistry》2014,43(1):83-92
Although aspartic acid is a non-essential amino acid, its importance is crucial for a major metabolic pathway and it is present in different types of foods. This highlights the need of a better knowledge of its transport properties. A Taylor dispersion technique has been used for measuring mutual diffusion coefficients of binary aqueous solutions of l-aspartic acid, an associated electrolyte, and the corresponding salt sodium l-aspartate, which behaves as a non-associated electrolyte, at 298.15 K and concentrations ranging from (0.001 to 0.100) mol·dm?3. Thermodynamic factors for the diffusion of aspartic acid and sodium aspartate have been estimated on the basis of the Onsager–Fuoss equation. Furthermore, experimental diffusion coefficients of aspartic acid are compared with those computed by the modified Onsager–Fuoss equation, applied for partially dissociated electrolytes. 相似文献
187.
Extensive Reduction in Back Electron Transfer in Twisted Intramolecular Charge‐Transfer (TICT) Coumarin‐Dye‐Sensitized TiO2 Nanoparticles/Film: A Femtosecond Transient Absorption Study 下载免费PDF全文
Tushar Debnath Partha Maity Hyacintha Lobo Balvant Singh Dr. Ganapati S. Shankarling Dr. Hirendra N. Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(12):3510-3519
We report the synthesis, characterization, and optical and electrochemical properties of two structurally similar coumarin dyes ( C1 and C2 ). These dyes have been deployed as sensitizers in TiO2 nanoparticles and thin films, and the effect of molecular structure on interfacial electron‐transfer dynamics has been studied. Steady‐state optical absorption, emission, and time‐resolved emission studies on both C1 and C2 , varying the polarity of the solvent and the solution pH, suggest that both photoexcited dyes exist in a locally excited (LE) state in solvents of low polarity. In highly polar solvents, however, C1 exists in an intramolecular charge‐transfer (ICT) state, whereas C2 exists in both ICT and twisted intramolecular charge‐transfer (TICT) states, their populations depending on the degree of polarity of the solvent and the pH of the solution. We have employed femtosecond transient absorption spectroscopy to monitor the charge‐transfer dynamics in C1 ‐ and C2 ‐sensitized TiO2 nanoparticles and thin films. Electron injection has been confirmed by direct detection of electrons in the conduction band of TiO2 nanoparticles and of radical cations of the dyes in the visible and near‐IR regions of the transient absorption spectra. Electron injection in both the C1 /TiO2 and C2 /TiO2 systems has been found to be pulse‐width limited (<100 fs); however, back‐electron‐transfer (BET) dynamics has been found to be slower in the C2 /TiO2 system than in the C1 /TiO2 system. The involvement of TICT states in C2 is solely responsible for the higher electron injection yield as well as the slower BET process compared to those in the C1 /TiO2 system. Further pH‐dependent experiments on C1 ‐ and C2 ‐sensitized TiO2 thin films have corroborated the participation of the TICT state in the slower BET process in the C2 /TiO2 system. 相似文献
188.
189.
R. F.M. Lobo N. T. Silva B. M.N. Vicente I. M.V. Gouveia F. M.V. Berardo J. H.F. Ribeiro 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):35-45
The crossed molecular beam technique is used for producing C60- species through potassium-buckyball collision processes, and studying the collision dynamics in an energy ranging from 10 eV
up to 500 eV. At low collision energies only the negative parent ion is formed. As long as the collision energy is increased
the fragmentation pattern of the fullerene negative ion could be identified and relative total cross-sections could be measured.
Surprisingly, some satellite contributions have been observed in the band structure of C60- parent ion time-of-flight spectrum, which points to the existence of distinct conformational C60- isomers, which are likely to be formed during the collision, favoured by the strong polarization of the C60- in the presence of the K+ projectile ion. Such presumed detection of different spheroidal metastable C60- conformers was made possible due to an electric effect operating at the nanoscale. 相似文献
190.
Portfolio optimization with linear and fixed transaction costs 总被引:1,自引:0,他引:1
We consider the problem of portfolio selection, with transaction costs and constraints on exposure to risk. Linear transaction
costs, bounds on the variance of the return, and bounds on different shortfall probabilities are efficiently handled by convex
optimization methods. For such problems, the globally optimal portfolio can be computed very rapidly. Portfolio optimization
problems with transaction costs that include a fixed fee, or discount breakpoints, cannot be directly solved by convex optimization.
We describe a relaxation method which yields an easily computable upper bound via convex optimization. We also describe a
heuristic method for finding a suboptimal portfolio, which is based on solving a small number of convex optimization problems
(and hence can be done efficiently). Thus, we produce a suboptimal solution, and also an upper bound on the optimal solution.
Numerical experiments suggest that for practical problems the gap between the two is small, even for large problems involving
hundreds of assets. The same approach can be used for related problems, such as that of tracking an index with a portfolio
consisting of a small number of assets. 相似文献