9Ang B W. Monitoring Changes in Economy -wide Energy Efficien- cy : From Energy - GDP Ratio to COmposite Efficiency Index [ J ]. Energy Policy, 2006, 34(5) :574 -582.
10Mukherjee K. Energy Use Efficiency in US Manufacturing: A Non- parametric Analysis [J]. Energy Economics, 2008, 30( 1 ) :76 - 96.