Bogolyubov, N.N & Mitropolskii, Yu.A <br/><br/>
Asymptotic methods to theory of non-linear oscillations 
N.N. Bogolyubov & Yu.A. Mitropolskii 
 - Moscow  Physico Math. Literature  1963 
 - 410 
<br/><br/> Russian 
<br/><br/><label>Dewey Class. No.: </label>6.06+4.04  / BOGO