The electronic transmission and conductance produced by Dirac electrons in an armchair graphene nanoribbon under an external voltage are investigated with the transfer matrix method. We investigate the velocity and voltage of nanoribbons in the presence of single and multiple barriers and show that the transmission coefficients can be controlled by varying the order of the mode, the number of carbon atoms, and the barrier velocities. In particular, we find that the nanoribbon appears to be

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... transparent when the barrier and Fermi velocities are equal. Our numerical results show that the electronic conductance is sensitive to the applied external voltage and number of carbon atoms, which can be used to tailor the electronic properties of graphenebased devices.