  The influence of oscillatory perturbations on autonomous strongly nonlinear
systems in the plane is investigated. It is assumed that the intensity of
perturbations decays with time, and their frequency increases according to a
power law. The long-term behaviour of perturbed trajectories is discussed. It
is shown that, depending on the structure and the parameters of perturbations,
there are at least two different asymptotic regimes: a phase locking and a
phase drifting. In the case of phase locking, resonant solutions with an
unlimitedly growing energy occur. The stability and asymptotics at infinity of
such solutions are investigated. The proposed analysis is based on a
combination of the averaging technique and the method of Lyapunov functions.
