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71.
A stochastic model is presented to calculate the number of chain segments entangled about a unit plane when the segment length is a stochastic variable. This crossing density to which the brittle fracture energy and the critical strength of entangled polymers scale is a function of the number of moles of entanglement network strands per unit volume and the mesh size of the entanglement network. Experimental results of the molecular weight dependence of the fracture energy and strength validate the theoretical predictions. 相似文献
72.
Hatzopouos A. Archontas N. Hastas N.A. Dimitriadis C.A. Kamarinos G. Georgoulas N. Thanailakis A. 《Electron Device Letters, IEEE》2004,25(6):390-392
Results on the impact of hot-carrier effects on the transfer and low-frequency noise characteristics of n-channel poly-crystalline silicon thin-film transistors (polysilicon TFTs) are presented. After stressing at the condition of maximum substrate current, the experimental data show that TFTs suffer from substantial on-current reduction. Through numerical simulation, it is shown that the stress-induced degradation increases the density of the band tail traps in a region extending 200 nm from the drain and the series resistance on the drain side. It is found that the origin of the noise is reverted from carrier number fluctuation for the unstressed to the mobility fluctuation for the stressed device. 相似文献
73.
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75.
N Wu A Messinis AS Batsanov Z Yang A Whiting TB Marder 《Chemical communications (Cambridge, England)》2012,48(80):9986-9988
A novel palladium(ii) catalysed tandem cyclisation of substituted 2-alkenylphenyl alkynones gives substituted 2-vinyl indenones and 6,5,6-fused tricyclic lactone skeletons (pyrones), in one-pot. Wagner-Meerwein-like rearrangements were observed which occur preferentially to conventional chloride-mediated chloropalladations of enynes. 相似文献
76.
Antonios Kolocouris 《Tetrahedron》2009,65(45):9428-9435
Dynamic NMR spectroscopy and ab initio correlated calculations revealed that the attachment of a spiroadamantane entity at the C-2 position of N-methylpyrrolidine or N-methylpiperidine induces a severe steric crowding around nitrogen, which changes the conformational space of the heterocycle resulting in: (a) the complete destabilization of the N-Me(eq) conformer in spiranic structures; in contrast the N-Me(eq) conformer corresponds to the global minimum in N-methylpyrrolidine or N-methylpiperidine. The spiroadamantane structure raises the energy of the equatorial conformer because of the severe van der Waals repulsion between the N-Me(eq) group and adamantane C-H bonds. (b) The interconversion between the only populated enantiomeric N-Me(ax) conformers ax→[eq]→ax′; the interconversion eq→ax between N-Me(eq) and N-Me(ax) conformers, which are both populated, is observed in N-methylpyrrolidine or N-methylpiperidine. (c) The raising of ring and nitrogen inversion barriers ax→ts by ∼4-6 kcal mol−1. The dynamic NMR study provides evidence that the most important process required for the enantiomerization between the axial N-Me conformers in spiropiperidine 4 and spiropyrrolidine 5 are different, i.e., a nitrogen inversion in 5 (9.10 kcal mol−1) and a ring inversion in 4 (15.2 kcal mol−1). While an enantiomerization interconverts N-Me axial conformers in spiropiperidine 5 and spiropyrrolidine 4, substitution of the pyrrolidine ring of 5 with a C-Me group effects a diastereomerization between two N-Me axial conformers and reduces effectively the nitrogen inversion barrier according to the protonation experiments and the calculations. In general, all the calculations levels used, i.e., the MM3, B3LYP/6-31+G∗∗ and MP2/6-311++G∗∗//B3LYP/6-31+G∗∗, predict correctly the different stability of the local minima; however only MP2/6-311++G∗∗//B3LYP/6-31+G∗∗ was found to be reliable for the calculation of the nitrogen inversion barriers. 相似文献
77.
Shereen Haj Othman Uwe Ritter Eoin K. McCarthy Diogo Fernandes Antonios Kelarakis Nikos G. Tsierkezos 《Ionics》2017,23(8):2025-2035
Nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes (N-MWCNTs and N–P-MWCNTs, respectively) were fabricated by chemical vapor deposition and characterized using scanning electron microscopy and transmission electron microscopy in combination with energy dispersive X-ray spectroscopy and Raman spectroscopy. The electrochemical response of N-MWCNTs and N–P-MWCNTs towards ferrocyanide/ferricyanide was initially studied. The findings exhibit weakening of electrochemical response and sensitivity of nanotubes with phosphorus doping, and thus, within the composite films tested, those consist exclusively of N-MWCNTs exhibit the greatest electrocatalytic activity. N–P-MWCNT film was further applied for individual electrochemical analysis of ascorbic acid (AA), uric acid (UA), and dopamine (DA), and lower limits of detections of 11.6, 7.8, and 1.9 μM were estimated, respectively. The findings demonstrate that AA does not interfere with UA, but considerable interference of AA in analysis of DA was observed. Thus, the simultaneous analysis of AA, UA, and DA on N–P-MWCNTs appears to be restricted. 相似文献
78.
Clio Saglietti Philipp Schlatter Antonios Monokrousos Dan S. Henningson 《Theoretical and Computational Fluid Dynamics》2017,31(5-6):537-553
Optimization of natural convection-driven flows may provide significant improvements to the performance of cooling devices, but a theoretical investigation of such flows has been rarely done. The present paper illustrates an efficient gradient-based optimization method for analyzing such systems. We consider numerically the natural convection-driven flow in a differentially heated cavity with three Prandtl numbers (\(Pr=0.15{-}7\)) at super-critical conditions. All results and implementations were done with the spectral element code Nek5000. The flow is analyzed using linear direct and adjoint computations about a nonlinear base flow, extracting in particular optimal initial conditions using power iteration and the solution of the full adjoint direct eigenproblem. The cost function for both temperature and velocity is based on the kinetic energy and the concept of entransy, which yields a quadratic functional. Results are presented as a function of Prandtl number, time horizons and weights between kinetic energy and entransy. In particular, it is shown that the maximum transient growth is achieved at time horizons on the order of 5 time units for all cases, whereas for larger time horizons the adjoint mode is recovered as optimal initial condition. For smaller time horizons, the influence of the weights leads either to a concentric temperature distribution or to an initial condition pattern that opposes the mean shear and grows according to the Orr mechanism. For specific cases, it could also been shown that the computation of optimal initial conditions leads to a degenerate problem, with a potential loss of symmetry. In these situations, it turns out that any initial condition lying in a specific span of the eigenfunctions will yield exactly the same transient amplification. As a consequence, the power iteration converges very slowly and fails to extract all possible optimal initial conditions. According to the authors’ knowledge, this behavior is illustrated here for the first time. 相似文献
79.
Prakash Anupam Sikora Jamie Varvitsiotis Antonios Wei Zhaohui 《Mathematical Programming》2018,171(1-2):397-431
Mathematical Programming - An $$ntimes n$$ matrix X is called completely positive semidefinite (cpsd) if there exist $$dtimes d$$ Hermitian positive semidefinite matrices $${P_i}_{i=1}^n$$ (for... 相似文献
80.
Antonios Charalambopoulos Vanessa Markaki Drosos Kourounis 《Mathematical Methods in the Applied Sciences》2020,43(8):5032-5072
In this work, a novel approach for the solution of the inverse conductivity problem from one and multiple boundary measurements has been developed on the basis of the implication of the framework of functions. The space of the functions of bounded variation is recommended here as the most appropriate functional space hosting the conductivity profile under reconstruction. For the numerical investigation of the inversion of the inclusion problem, we propose and implement a suitable minimization scheme of an enriched—constructed herein—functional, by exploiting the inner structure of space. Finally, we validate and illustrate our theoretical results with numerical experiments. 相似文献