Source:
Research Papers of the Wroclaw University of Economics / Prace Naukowe Uniwersytetu Ekonomicznego we Wroclawiu. 2013, Issue 291, p552-563. 12p.
Source:
Research Papers of the Wroclaw University of Economics / Prace Naukowe Uniwersytetu Ekonomicznego we Wroclawiu; 2012 Part 2, Issue 267, p9-18, 10p