  The Parkes telescope has been monitoring 286 radio pulsars approximately
monthly since 2007 at an observing frequency of 1.4 GHz. The wide dispersion
measure (DM) range of the pulsar sample and the uniformity of the observing
procedure make the data-set extremely valuable for studies of flux density
variability and the interstellar medium. Here, we present flux density
measurements and modulation indices of these pulsars over this period. We
derive the structure function from the light curves and discuss the
contributions to it from measurement noise, intrinsic variability and
interstellar scintillation. Despite a large scatter, we show that the
modulation index is inversely correlated with DM, and can be generally
described by a power-law with an index of $\sim-0.7$ covering DMs from $\sim10$
to 1000 cm$^{-3}$ pc. We present refractive timescales and/or lower limits for
a group of 42 pulsars. These often have values significantly different from
theoretical expectations, indicating the complex nature of the interstellar
medium along individual lines of sight. In particular, local structures and
non-Kolmogorov density fluctuations are likely playing important roles in the
observed flux density variation of many of these pulsars.
