Não informado. (1957). Abstracts of Bulgarian Scientific Literature. Centre of Scientific Information and Documentation.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Abstracts of Bulgarian Scientific Literature. Sofia: Centre of Scientific Information and Documentation, 1957.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Abstracts of Bulgarian Scientific Literature. Centre of Scientific Information and Documentation, 1957.
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