Freedman, P., & Waddington, C. H. (1960). The principles of scientific research (2nd ed.). Oxfoed: Pergamon Press.
Παραπομπή Chicago StyleFreedman, Paul, and C. H. Waddington. The Principles of Scientific Research. 2nd ed. Oxfoed: Pergamon Press, 1960.
Παραπομπή MLAFreedman, Paul, and C. H. Waddington. The Principles of Scientific Research. 2nd ed. Oxfoed: Pergamon Press, 1960.
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