  We report on the experimental study of electron transport in sub-micron-wide
''wires'' fabricated from Si $\delta $-doped GaAs. These quasi-one-dimensional
(Q1D) conductors demonstrate the crossover from weak to strong localization
with decreasing the temperature. On the insulating side of the crossover, the
resistance has been measured as a function of temperature, magnetic field, and
applied voltage for different values of the electron concentration, which was
varied by applying the gate voltage. The activation temperature dependence of
the resistance has been observed with the activation energy close to the mean
energy spacing of electron states within the localization domain. The study of
non-linearity of the current-voltage characteristics provides information on
the distance between the critical hops which govern the resistance of Q1D
conductors in the strong localization (SL) regime. We observe the exponentially
strong negative magnetoresistance; this orbital magnetoresistance is due to the
universal magnetic-field dependence of the localization length in Q1D
conductors. The method of measuring of the single-particle density of states
(DoS) in the SL regime has been suggested. Our data indicate that there is a
minimum of DoS at the Fermi level due to the long-range Coulomb interaction.
