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@article{DAN_1965_163_6_a16, author = {Ya. B. Zel'dovich}, title = {The number of quanta as an invariant of classical electromagnetic field}, journal = {Doklady Akademii Nauk}, pages = {1359--1360}, publisher = {mathdoc}, volume = {163}, number = {6}, year = {1965}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DAN_1965_163_6_a16/} }
Ya. B. Zel'dovich. The number of quanta as an invariant of classical electromagnetic field. Doklady Akademii Nauk, Tome 163 (1965) no. 6, pp. 1359-1360. http://geodesic.mathdoc.fr/item/DAN_1965_163_6_a16/