Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
specialize [ˈspɛʃəlaɪz] vi
to specialize (in) специализи́роваться (impf/perf) (в or на +prp)
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: