  We present the results of our radio interferometric observations of pulsars
at 325 MHz and 610 MHz using the Giant Metrewave Radio Telescope (GMRT). We
used the imaging method to estimate the flux densities of several pulsars at
these radio frequencies. The analysis of the shapes of the pulsar spectra
allowed us to identify five new gigahertz-peaked spectra (GPS) pulsars. Using
the hypothesis that the spectral turnovers are caused by thermal free-free
absorption in the interstellar medium, we modeled the spectra of all known
objects of this kind. Using the model, we were able to put some observational
constrains on the physical parameters of the absorbing matter, which allows us
to distinguish between the possible sources of absorption. We also discuss the
possible effects of the existence of GPS pulsars on future search surveys,
showing that the optimal frequency range for finding such objects would be from
a few GHz (for regular GPS sources) to possibly 10 GHz for pulsars and
radio-magnetars exhibiting very strong absorption.
