Não informado. (1978). Abstracts of bulgarian scientific literature. Central Institute for Scientific, Technical and Economic Information.
শিকাগো স্টাইল (17 তম সংস্করণ) উদ্ধৃতিNão informado. Abstracts of Bulgarian Scientific Literature. Sofia: Central Institute for Scientific, Technical and Economic Information, 1978.
M.L.A (8 ম সংস্করণ) উদ্ধৃতিNão informado. Abstracts of Bulgarian Scientific Literature. Central Institute for Scientific, Technical and Economic Information, 1978.
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