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Patents and R&D : an econometric investigation using applications for German, European and US patents by German companies
Licht, Georg, (1998)
Licht, Georg, (2000)
Patents, R&D and lag effects : evidence from flexible methods for count panel data on manufacturing firms
Gurmu, Shiferaw, (2008)
The value of patents as indicators of inventive activity
Griliches, Zvi, (1986)
R&D, patents and market value revisited : is there a second (technological opportunity) factor?
Griliches, Zvi, (1991)