@techreport{ w7552,
 title = "Protecting Their Intellectual Assets: Appropriability Conditions and Why U.S. Manufacturing Firms Patent (or Not)",
 author = "Wesley M. Cohen and Richard R. Nelson and John P. Walsh",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Working Paper Series",
 number = "7552",
 year = "2000",
 month = "February",
 URL = "http://www.nber.org/papers/w7552",
}