Não informado. (1972). Abstracts of Bulgarian Scientific Literature. Center for Scientific, Technical and Economic Information.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Abstracts of Bulgarian Scientific Literature. Sofia: Center for Scientific, Technical and Economic Information, 1972.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Abstracts of Bulgarian Scientific Literature. Center for Scientific, Technical and Economic Information, 1972.
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