6Hirsche & Weygandt (1985)Hirschey,M.and J.Weygandt. Amortization Policy for Advertising and Research and Development Expenditures:Journal of Accounting and Research,1985,23:326-335.
7Cohen. W and D.Levinthal,1989,Innovation and Learning:The Two faces of R&D.Economic Journal, vol 99,569-596.
8John Doukas, Lome Switzer. The Stock Market's Valuation of R&D Spending and Market Concentration.Journal of Economics & Business, May 1992,Vol.44 Issue 2,p95,20p,6charts.