  The electron transport in a 1D conductor with an isolated local defect such
as an impurity or a non-adiabatic contact is studied theoretically. New regime
of conduction in correlated 1D systems is predicted beyond the well-known
regime of tunneling resulting in the power-law I-V-curves. In this regime a
quantum wire becomes "opened" at voltage biases above the threshold value
$V_T$, giving rise to a rapid increase of the dc current, $\bar I$, accompanied
by ac oscillations of frequency $f = \bar I/e$. The effect of ac generation is
related to sliding of the Friedel oscillations of electronic density produced
by the defect. Manifestations of the effect resemble the Coulomb blockade and
the Josephson effect. The spin bias applied to the system is shown to affect
the I-V curves due to violation of the spin-charge separation at the defect
site. In short quantum wires of length $L < L_0 \sim \hbar v_F/eV_T$ and at
high temperatures $T > T_0 \sim eV_T/k_B$ the effect is destroyed by
fluctuations. The threshold voltage $V_T$ is determined by $2k_F$-component of
impurity potential renormalized by fluctuations. The 1D conductor is described
in terms of the Tomonaga-Luttinger Hamiltonian with short range or long-range
Coulomb interaction by means of the bosonization technique. We derive boundary
conditions that take into account relaxation in the leads and permit to solve
non-equilibrium problems. Charge fluctuations are studied by means of Gaussian
model which can be justified strictly in the limit of large voltages or strong
enough inter-electronic repulsion. Spin fluctuations are taken into account
strictly by means of the refermionization technique applicable in case of
spin-rotation invariant interaction.
