Resistivity of high- T sub c superconductors in a vortex-liquid state

The theory of pinning of a vortex liquid by weak disorder is developed. Two different vortex-liquid dissipative regimes are shown to exist: the flux flow above some crossover temperature {ital T}{sub {ital k}}, where the vortex liquid is unpinned, and the thermally assisted flux flow below {ital T}{sub {ital k}}. The activation barriers in the latter regime are those associated with the plastic motion of the vortices in the liquid.