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81.
The addition of monovalent, divalent, and trivalent metal ions to three anionic ethyl meso-thiacarbocyanine dyes, an ethyl meso-oxacarbocyanine, and an imidacarbocyanine in aqueous solution at room temperature results in the production of J-aggregates within the range of tens to hundreds of seconds. The rate of formation of J-aggregates correlates with the rate of decay of dimers or monomers and is dependent on the type of metal ion, dye structure, and temperature. The rate of formation of J-aggregates increases as the temperature decreases and the dye and salt concentrations increase, and the rate is highest for trivalent ions and smallest for monovalent ions, independent of the type of anion. The time course of formation of J-aggregates is described in most cases by a sigmoidal curve, and the kinetics and mechanism are discussed within the framework of autocatalysis. Computer simulations reveal that the sigmoidal time dependence is transferred to an exponential-like curve by substantially increasing the rate constant for the noncatalytic step. The reaction pathway into J-aggregates can be switched from dimeric ion pairs as the reactant to monomeric ion pairs, when the rate constant for the catalytic step via the monomer becomes larger with respect to that via the dimer. 相似文献
82.
Vladimir E. Vigdergauz Tatyana V. Nedosekina 《Journal of Solid State Electrochemistry》1998,2(1):50-57
Experimental methods for the evaluation of the wettability of electrodes made from natural mineral sulfides are discussed
for the case of potentiostatic polarization. The wettability, induced by xanthates with different lengths of the alkyl chain,
was studied for the case of pyrite, chalcopyrite, galena, arsenopyrite and chalcocite. Therefore measurements of the detachment
force of an air bubble (ABDF) and of the induction time (ABIT) were performed. The first of these allows us to estimate the
conditions for the destruction of the bubble-mineral complex, and the second allows us to estimate the conditions of aggregate
formation under collision. The study was carried out at various polarization potentials in a borate buffer solution. The results
of the measurements are compared with thermodynamic data and with experimental results obtained for representative cases such
as xanthate sorption and flotation recovery. A correlation of the flotation experiments with the ABDF results can be demonstrated.
Received: 28 February 1997 / Accepted: 12 August 1997 相似文献
83.
Afiyatullov SSh Kalinovsky AI Pivkin MV Dmitrenok PS Kuznetsova TA 《Natural product research》2006,20(10):902-908
Three new diterpene glycosides, virescenosides V (1), W (2), and X (3) have been isolated from a marine strain of Acremonium striatisporum KMM 4401 associated with the holothurian Eupentacta fraudatrix. Their structures have been elucidated on the basis of high resolution mass spectrometry, 1D and 2D NMR (1H, 13C, DEPT, COSY 45, COSY RCT, HSQC, HMBC, and NOESY spectra) as 19-O-beta-D-altropyranosyl-7-oxo-isopimara-8(14),15-diene-2alpha,3beta-diol (1), 19-O-beta-D-altropyranosyl-isopimara-7,15-diene-2 alpha,3 beta,6 alpha-triol (2), and 19-O-beta-D-altropyranosyl-isopimara-8,15-diene-2 alpha,3 beta,7 alpha-triol (3). 相似文献
84.
The kinetics of formation of J-aggregates for 3,3'-bis[sulfopropyl]-R-4',5'-dibenzo-9-ethylthiacarbocyanines (R=5-methoxy; R=4,5-dibenzo) and 3,3'-bis[sulfopropyl]-5,5'-diphenyl-9-ethyloxacarbocyanine were studied in aqueous solution in the presence of gelatin at different pH values and at room and elevated temperatures. Addition of gelatin at concentrations of 0.0005-0.05 wt % to solutions of dyes results in the production of J-aggregates in the tens of seconds to tens of minutes range. The rate of J-aggregate formation increases with increasing concentrations of dye and gelatin, correlates with the rate of decay of dimers, and is also dependent on the dye structure, temperature, and pH. The rate of J-aggregation is increased for and decreased for with an increase in temperature. For and, the rate increases with increasing [H+] and reaches the maximum value at pH 3.3-4.3 for 3. The interaction of with gelatin is considered to be a cooperative binding process, and J-aggregation is characterized by the time-dependent rate constant. Sigmoidal- and nonsigmoidal-type kinetic curves of both formation of J-aggregates and decay of the dimers are best fitted with a stretched exponential function. 相似文献
85.
86.
The dirichlet problem in lipschitz domains for higher order elliptic systems with rough coefficients
Vladimir. Maz’ya Marius Mitrea Tatyana Shaposhnikova 《Journal d'Analyse Mathématique》2010,110(1):167-239
We study the Dirichlet problem, in Lipschitz domains and with boundary data in Besov spaces, for divergence form strongly
elliptic systems of arbitrary order with bounded, complex-valued coefficients. A sharp corollary of our main solvability result
is that the operator of this problem performs an isomorphism between weighted Sobolev spaces when its coefficients and the
unit normal of the boundary belong to the space VMO. 相似文献
87.
For nearly a half century the dominant orthodoxy has been that the only effect of the Cooper pairing is the state with zero resistivity at finite temperatures, superconductivity. In this work we demonstrate that by the symmetry of the Heisenberg uncertainty principle relating the amplitude and phase of the superconducting order parameter, Cooper pairing can generate the dual state with zero conductivity in the finite temperature range, superinsulation. We show that this duality realizes in the planar Josephson junction arrays (JJA) via the duality between the Berezinskii–Kosterlitz–Thouless (BKT) transition in the vortex–antivortex plasma, resulting in phase-coherent superconductivity below the transition temperature, and the charge-BKT transition occurring in the insulating state of JJA and marking formation of the low-temperature charge-BKT state, superinsulation. We find that in disordered superconducting films that are on the brink of superconductor–insulator transition the Coulomb forces between the charges acquire two-dimensional character, i.e. the corresponding interaction energy depends logarithmically upon charge separation, bringing the same vortex-charge-BKT transition duality, and realization of superinsulation in disordered films as the low-temperature charge-BKT state. Finally, we discuss possible applications and utilizations of superconductivity–superinsulation duality. 相似文献
88.
Oleg P. Korobeinichev Alexander A. Paletsky Tatyana A. Bolshova Vadim D. Knyazev 《Combustion Theory and Modelling》2013,17(5):927-939
The phenomenon of superadiabatic flame temperature (SAFT) was discovered and investigated in a low-pressure HN3/N2 flame using numerical modelling. A previously developed mechanism of chemical reactions in the HN3/N2 flame at the pressure 50 Torr and the initial temperature T0 = 296 K was revised. Rate constants of several important reactions involving HN3 (HN3 (+N2) = N2 + NH (+N2), R1; HN3 (+HN3) = N2 + NH (+HN3), R2; HN3 + H = N2 + NH2, R4; HN3 + N = N2 + NNH, R5; and HN3 + NH2 = NH3 + N3, R7) were calculated using quantum chemistry and reaction rate theories. Modified Arrhenius expressions for these reactions are provided for the 300–3500 K temperature range. Modelling of the flame structure and flame propagation velocity of the HN3/N2 flame at p = 50 Torr and T0 = 296 K was performed using the revised mechanism. The results demonstrate the presence of the SAFT phenomenon in the HN3/N2 flame. Analysis of the flame structure and the kinetic mechanism indicates that the cause of SAFT is in the kinetic mechanism: exothermic reactions of radicals with hydrogen atoms occur in the post flame zone, which results in the formation of super equilibrium H2 concentrations. The flame propagation velocity is largely determined by the second-order HN3 decomposition reaction and not by the reaction of HN3 with H, as was previously assumed. Calculation of the flame propagation velocity according to the Zeldovich-Frank-Kamenetsky theory with the decomposition reaction as a limiting stage yielded a value that agrees with that obtained in numerical modelling using the complete reaction mechanism. 相似文献
89.
ABSTRACTInstead of using the full polynomial space, a conforming and a nonconforming finite element methods are designed where only harmonic polynomials (a much smaller space) are employed in the computation. The conforming quadratic harmonic polynomial finite element is defined only on a special triangular grid. The nonconforming quadratic harmonic finite element is defined on general triangular grids. The optimal order of convergence is proved for both finite element methods, and confirmed by numerical computations. In addition, numerical comparisons with the standard conforming and nonconforming finite elements are presented. 相似文献
90.