APA

[National Academy of Sciences], . (1973). Permafrost. North American Contribution. International conference. 2. Yakutsk, USSR 1973. Washington DC: [National Academy of Sciences].

Chicago

[National Academy of Sciences], . 1973. Permafrost. North American Contribution. International conference. 2. Yakutsk, USSR 1973. Washington DC: [National Academy of Sciences].

Harvard

[National Academy of Sciences], . (1973). Permafrost. North American Contribution. International conference. 2. Yakutsk, USSR 1973. Washington DC: [National Academy of Sciences].

MLA

[National Academy of Sciences], . Permafrost. North American Contribution. International conference. 2. Yakutsk, USSR 1973. Washington DC: [National Academy of Sciences]. 1973.