  We study transport through a one-dimensional quantum wire of correlated
fermions connected to semi-infinite leads. The wire contains either a single
impurity or two barriers, the latter allowing for resonant tunneling. In the
leads the fermions are assumed to be non-interacting. The wire is described by
a microscopic lattice model. Using the functional renormalization group we
calculate the linear conductance for wires of mesoscopic length and for all
relevant temperature scales. For a single impurity, either strong or weak, we
find power-law behavior as a function of temperature. In addition, we can
describe the complete crossover from the weak- to the strong-impurity limit.
For two barriers, depending on the parameters of the enclosed quantum dot, we
find temperature regimes in which the conductance follows power-laws with
"universal" exponents as well as non-universal behavior. Our approach leads to
a comprehensive picture of resonant tunneling. We compare our results with
those of alternative approaches.
