Não informado. (1978). Abstracts of bulgarian scientific literature. Central Institute for Scientific, Technical and Economic Information.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Abstracts of Bulgarian Scientific Literature. Sofia: Central Institute for Scientific, Technical and Economic Information, 1978.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Abstracts of Bulgarian Scientific Literature. Central Institute for Scientific, Technical and Economic Information, 1978.
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