Bulgarian Academy of Sciences. (1978). Abstracts of Bulgarian Scientific Literature. Scientific Information Centre.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रBulgarian Academy of Sciences. Abstracts of Bulgarian Scientific Literature. Sofia: Scientific Information Centre, 1978.
एमएलए (8वां संस्करण) प्रशस्ति पत्रBulgarian Academy of Sciences. Abstracts of Bulgarian Scientific Literature. Scientific Information Centre, 1978.
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