E. G. . Vartanyan, “Bulgaria and Russia of the early 20th century: from the correspondence of N. S. Derzhavin with Bulgarian scientists”, Журнал БГУ. История, no. 2, pp. 33–40, May 2024, Accessed: Jul. 18, 2026. [Online]. Available: https://journals.bsu.by/index.php/history/article/view/6007