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排序方式: 共有190条查询结果,搜索用时 531 毫秒
141.
Prodromos B. Issopoulos Pantelis T. Economou 《Fresenius' Journal of Analytical Chemistry》1992,343(6):518-522
Summary A new analytical method for the spectrophotometric determination of Carbidopa (CBDA), either in pure form or in tablets is described. The method is based on a ternary complex formation between CBDA, iron(III) and phenylfluorone (Phfl) in the presence of Tween 20 as a surfactant. At the optimum pH 9.55, the ternary complex shows an absorption maximum at =636 nm, with an apparent molar absorptivity of 1.098×105 l mol–1 cm–1 and a Sandell's sensitivity of 2.22 ng cm–2. The solution of the ternary complex obeys Beer's law in the concentration range of 0.1–3.0 ppm of CBDA. The correlation coefficient was found to be r=0.9999. Results obtained by application of the proposed method and the B.P. 1988 official one were in good agreement and a statistical comparison by means of the Student's t-test as well as by the variance ratio F-test shows no significant difference between the two analytical methods. 相似文献
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Ni(II) and Co(II) have been determined simultaneously by means of adsorptive cathodic stripping voltammetry (AdCSV) in a computerised flow injection system. The working electrode was a glassy carbon disk that was fitted in a wall-jet flow cell. The electrode was initially electrochemically coated with a mercury film at -1.0 V by injecting a Hg(II) solution in the flow stream. Then, the sample, containing Ni(II) and Co(II), was mixed on-line with a solution containing dimethylgyoxime (DMG) at pH 9 in order to selectively complex the metal ions and was injected in the flow system. After a number of successive injections during which accumulation took place under controlled potentiostatic conditions, the surface-bound complexes were reduced in ammonia buffer at pH 9 by a cathodic scan of the potential of the working electrode in the square wave mode and the current-potential response was recorded. Finally, the electrode surface was regenerated by a potentiostatic polarisation at -1.4 V in the same buffer. The apparatus could be easily converted for continuous flow accumulation in order to increase the sensitivity; in this mode of operation, instead of performing discrete injections, the sample was continuously pumped through the cell. Various parameters associated with the preconcentration, stripping and regeneration steps were optimised for the determination of Ni(II) and Co(II). The selectivity of the method was demonstrated for the analysis of high purity iron; the accuracy for the determination of Ni(II) and Co(II) was 11 and 3%, respectively while the coefficient of variation was 10 and 8%, respectively. 相似文献
145.
M. Makowska-Janusik H. Reis M. G. Papadopoulos I.G. Economou 《Theoretical chemistry accounts》2005,114(1-3):153-158
The electric field poling process of free-standing films of poly(methyl methacrylate) (PMMA) matrix doped with the nonlinear
optical compound 4-(dimethylamino)-4'-nitrostilbene (DMANS) was investigated by molecular simulation methods. The influence
of the vacuum/bulk interfacial regions on static and dynamic properties, including the glass transition temperature Tg and the field-induced chromophore reorientation, was studied by employing films of three different thicknesses and by comparison
with previous work on the bulk system. The interfacial region, defined as the region, where the local density increases from
zero to the bulk density, is about 2 nm wide, independent of the film thickness. Tg decreases with decreasing film thickness, in accord with previous experimental work and theoretical predictions. The resistance
against field-induced chromophore reorientation in the liquid state is found to increase strongly with the film thickness. 相似文献
146.
Nikolaos I. Papadimitriou Ioannis G. Economou Athanassios K. Stubos 《Molecular physics》2016,114(18):2664-2671
ABSTRACTWe use grand canonical Monte Carlo simulations to examine the effect of the size of hydrate cavities (as reflected through the lattice constant of the hydrate unit cell) on the efficiency of clathrate hydrates in storing hydrogen gas. With this approach, the hydrate lattice is treated as a solid substrate where gas absorption takes place. Of practical interests are cases, where the lattice-size parameters are changed in such a way that they can promote/enhance multiple cavity occupancy, namely the presence of more than one guest-gas molecule in the same hydrate cavity. This phenomenon is commonly observed in the case of hydrogen hydrates and could increase their storage capacity. A parametric analysis is also carried out to quantify the correlation between the change in the lattice constant and the storage capacity since small changes in the size of the crystal unit cell may induce significant changes in the storage capacity especially in cases where multiple cavity occupancy occurs. 相似文献
147.
Georgios Bountas Vlastimil Vyskocil Bohumil Kratochvil Alena Michalcova Anastasios Economou Jiri Barek 《Electroanalysis》2023,35(7):e202200437
Nitrophenols are important environmental pollutants and their monitoring is important because of their genotoxic and ecotoxic properties. Easy electrochemical reduction of nitro groups can be used for their voltammetric determination using mercury based electrodes. However, requirements of green analytical chemistry prompted us to investigate a novel type of silver porous electrode (AgPE) prepared by powder metallurgy compatible with both “green” and “white” analytical chemistry requirements. In this paper, AgPE was for the first time successfully used for differential pulse voltammetric determination of micromolar concentrations of 2-nitrophenol (NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) in aqueous media. The main advantage of the novel method is the possibility to use small sample volume (down to 25 μL) and to work in the presence of oxygen when using supporting electrolyte of pH 3. This advantage partially compensates the fact that the obtained sensitivity and limit of detection are not better than with the previously investigated electrodes. 相似文献
148.
149.
Ioannis N. Tsimpanogiannis Vasileios K. Michalis Ioannis G. Economou 《Molecular physics》2020,118(9-10)
Methane hydrates are encountered in a plethora of industrial and geological or environmental applications. In the current study, we present a novel methodology which is based on molecular dynamics simulations for the calculation of the enthalpy of enclathration of sI methane hydrates. Simulations are performed along the three-phase (Hydrate – Liquid water – Vapour; H–Lw–V) equilibrium line in the temperature range 274–310?K. The methodology takes into account the two different types of cages that are present in the sI methane hydrate and provides results for the enthalpy of enclathration for both types of cages, while it avoids performing calculations with the metastable, completely empty hydrate lattice. The formulation proposed is general and can be also applied to sII hydrates, while it can be modified/extended appropriately for use in the case of sH hydrates. Comparison is provided with available data from the literature and good agreement is observed. 相似文献
150.