P.A.M. Dirac (1927). "The Quantum Theory of the Emission and Absorption of Radiation". Proceedings of the Royal Society of London A. 114 (767): 243–65. Bibcode:1927RSPSA.114..243D. doi:10.1098/rspa.1927.0039.
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P.A.M. Dirac (1927). "The Quantum Theory of the Emission and Absorption of Radiation". Proceedings of the Royal Society of London A. 114 (767): 243–65. Bibcode:1927RSPSA.114..243D. doi:10.1098/rspa.1927.0039.