APA

(19). A directory of information resources in the United States. Washington: National Referal Center for Science and Technology.

Chicago

19. A directory of information resources in the United States. Washington: National Referal Center for Science and Technology.

Harvard

(19). A directory of information resources in the United States. Washington: National Referal Center for Science and Technology.

MLA

A directory of information resources in the United States. Washington: National Referal Center for Science and Technology. 19.