APA

Djulgerov N., . (1989). Nature protection is a social necessity. : Sofia Press.

Chicago

Djulgerov Nikolaj, . 1989. Nature protection is a social necessity. : Sofia Press.

Harvard

Djulgerov N., . (1989). Nature protection is a social necessity. : Sofia Press.

MLA

Djulgerov Nikolaj, . Nature protection is a social necessity. : Sofia Press. 1989.