中国科学院数学与系统科学研究院期刊网
AMS
On the Self-adjointness of the Product Operators of Two mth-Order Differential Operators on [0, +∞)
Jian Ye AN, Jiong SUN
Acta Mathematica Sinica . 2004, (5): 793 -802 .  DOI: 10.1007/s10114-004-0386-3