Complex sentence: Since 1970 he has been a researcher at the Institute for Nuclear Research of the USSR Academy of Sciences (Russian Academy of Sciences since 1991), where he earned his Ph.D. in physics in 1983.
Split into simpler sentences: Since 1970 he has been a researcher at the Institute for Nuclear Research of the USSR Academy of Sciences (Russian Academy of Sciences since 1991). He earned his Ph.D. in physics from the Institute for Nuclear Research in 1983.