Citation counts are based on a 3-year window with a 2-year lag. For example, citations for 1999 are references made in articles published in 1999 to articles published in 1995–97. Country/economy is determined by the cited article’s institutional address. German data for 1992 includes former East Germany. SOURCES: Institute for Scientific Information, Science Citation Index and Social Sciences Citation Index; CHI Research, Inc.; and National Science Foundation, Division of Science Resources Statistics, special tabulations.
Scource: Science & Engineering Indicators – 2004