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21.
J. J. Travadi M. S. Vadodaria K. D. Ladva A. V. Doshi 《Molecular Crystals and Liquid Crystals》2016,626(1):21-30
A novel homologous series of liquid crystal (LC) derivatives of general structure: RO·C6H4·COO·C6H3·OCH3(ortho)CH = CH·COO·(n)C5H11 was synthesized and studied with a view to understanding the effect of molecular structure on liquid crystal behavior with reference to lateral –OCH3 and terminal end group. Homologous series consists of 12 derivatives (C1–C16), the first five (C1–C5), and the last (C16) members are not liquid crystals and the rest of the homologs (C6–C14) are enantiotropically smectogenic without exhibition of the nematic phase. The textures of the smectic phases are focal conic fan shaped or batonets of smectic-A or smectic-C. Average thermal stability for smectic is 81.8°C and mesophase length ranges from 9°C to 31°C. Transition curves of a phase diagram (Sm-I and Cr-Sm/I) behave in a normal manner. The Sm-I transition curve exhibits an odd-even effect. Analytical and spectral data support the molecular structures. The series is smectogenic of a middle ordered melting type. LC properties of the present series are compared with structurally similar known homologous series. Transition temperatures were determined by an optical polarizing microscope equipped with a heating stage. 相似文献
22.
Aerobic oxidation of methanol to formic acid on Au20-: a theoretical study on the reaction mechanism
Bobuatong K Karanjit S Fukuda R Ehara M Sakurai H 《Physical chemistry chemical physics : PCCP》2012,14(9):3103-3111
The aerobic oxidation of methanol to formic acid catalyzed by Au(20)(-) has been investigated quantum chemically using density functional theory with the M06 functional. Possible reaction pathways are examined taking account of full structure relaxation of the Au(20)(-) cluster. The proposed reaction mechanism consists of three elementary steps: (1) formation of formaldehyde from methoxy species activated by a superoxo-like anion on the gold cluster; (2) nucleophilic addition by the hydroxyl group of a hydroperoxyl-like complex to formaldehyde resulting in a hemiacetal intermediate; and (3) formation of formic acid by hydrogen transfer from the hemiacetal intermediate to atomic oxygen attached to the gold cluster. A comparison of the computed energetics of various elementary steps indicates that C-H bond dissociation of the methoxy species leading to formation of formaldehyde is the rate-determining step. A possible reaction pathway involving single-step hydrogen abstraction, a concerted mechanism, is also discussed. The stabilities of reactants, intermediates and transition state structures are governed by the coordination number of the gold atoms, charge distribution, cooperative effect and structural distortion, which are the key parameters for understanding the relationship between the structure of the gold cluster and catalytic activity in the aerobic oxidation of alcohols. 相似文献
23.
Experimental observations of optical bistability in Coumarin-450 dye molecule entrapped in polymeric (PMMA) host inside Fabry–Perot cavity have been reported. Efforts have been made to demonstrate the nonlinear behavior of optical materials in solid form using 532 nm of Nd: YAG laser. The nonlinearity in terms of optical bistability and excited state absorption (ESA) has been discussed. The nonlinearity in Coumarin-450 dye molecule originated from unique intensity dependence of the complex index of refraction. It has been observed that nonlinear refraction dominates over nonlinear absorption in giving rise to the optical bistability. Nonlinear refractive index in both polymeric and liquid samples has been calculated. 相似文献
24.
Matthew Scott Reginald Paul Karan V. I. S. Kaler 《Journal of colloid and interface science》2000,230(2):388
The expressions obtained in the previous paper for electrode polarization are applied to a homogeneous planar electrode and a planar array of electrodes used in the generation of nonuniform fields. The effective far field experienced outside the double layer is computed for both electrodes, and sample spectra are provided. The effective far field expression contains the electrode impedance and the effects of concentration polarization due to the static double layer on the electrode generated by the ζ potential. The effective far field results are compact and contain simple integrals that can be evaluated numerically. 相似文献
25.
26.
Interfacial interactions of Nafion ionomer with superhydrophilic (Pt, Au), hydrophilic (SiO2), and hydrophobic (graphene, octyltrichlorosilane [OTS]‐modified SiO2) is investigated, using in situ thermal ellipsometry, by quantification of substrate‐ and thickness‐dependent thermal properties of the ultrathin Nafion films of nominal thickness ranging 25–135 nm. For sub‐50 nm thin Nafion films, the thermal expansion coefficient of films decreased in the order of most hydrophobic to most hydrophilic substrate: OTS > graphene > SiO2 > Au > Pt, implying weaker interpolymer and polymer–substrate interactions for films on hydrophobic substrates. Expansion coefficient of films on SiO2, graphene, and OTS‐modified SiO2 decreased with thickness whereas that of films on Au and Pt substrates increased with thickness. Above ~100 nm of thickness, films on all substrates converged toward a common value representative of bulk Nafion. Thermal transition temperature was found to be higher for films on hydrophilic SiO2 than that for films on hydrophobic graphene and OTS‐modified SiO2 but was not discernible for films on Au and Pt substrates. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 343–352 相似文献
27.
Madhu Sudan Saha Devproshad K. Paul Brant A. Peppley Kunal Karan 《Electrochemistry communications》2010,12(3):410-413
A decal transfer method based on colloidal ink was developed for the fabrication of membrane electrode assemblies (MEAs). The new method requires fewer steps and utilizes H+ form of membrane compared to conventional decal method based on solution ink utilizing Na+ form of membrane. The structural features of the electrodes made by the modified decal method were investigated by scanning electron microscopy (SEM). The performance of fabricated electrode was evaluated for oxygen reduction reaction in a proton exchange membrane fuel cell. The results indicate that the modified decal method has the potential to be a facile method of fabricating electrodes with high performance. 相似文献
28.
A critically important strategy for synthetic chemistry is the development of "domino" processes: those capable of concatenating multiple transformations into a single step. Such transformations not only provide an increase in synthetic efficiency, but also imply the development of a significant degree of mechanistic understanding. We report herein a new domino reaction, in which a chromium-manganese redox couple is employed both to catalytically reduce an o-hydroxy nitroarene and to oxidatively cyclize a subsequently formed imine. We find that the reaction is most effective for starting o-hydroxy nitroarenes with a strongly electron-withdrawing group at the para position. 相似文献
29.
Srivastava and Jhajj (1981) proposed a class of estimators for population mean of a character using auxiliary information and optimum values involving unknown parameters. From the practical point of view, their results have very little utility. In view of practical utility, we propose a class of estimators with estimated optimum values. Further, it is shown that the proposed class with estimated optimum values attains the same minimum mean square error of the class of estimators based on optimum values. 相似文献
30.
A p-version least squares finite element formulation for non-linear problems is applied to the problem of steady, two-dimensional, incompressible fluid flow. The Navier-Stokes equations are cast as a set of first-order equations involving viscous stresses as auxiliary variables. Both the primary and auxiliary variables are interpolated using equal-order C0 continuity, p-version hierarchical approximation functions. The least squares functional (or error functional) is constructed using the system of coupled first-order non-linear partial differential equations without linearization, approximations or assumptions. The minimization of this least squares error functional results in finding a solution vector {δ} for which the partial derivative of the error functional (integrated sum of squares of the errors resulting from individual equations for the entire discretization) with respect to the nodal degrees of freedom {δ} becomes zero. This is accomplished by using Newton's method with a line search. Numerical examples are presented to demonstrate the convergence characteristics and accuracy of the method. 相似文献