中国科学院数学与系统科学研究院期刊网
AMS
Two-Dimensional Invariant Tori in the Neighborhood of an Elliptic Equilibrium of Hamiltonian Systems
Hui LU, Jian Gong YOU
Acta Mathematica Sinica . 2009, (8): 1363 -1378 .  DOI: 10.1007/s10114-009-7053-7