DOI = Digital Object Identifier
This is a unique alphanumeric identifier assigned to some journal articles. It's becoming more common for journal articles in the social sciences and sciences. If you find a source that has as DOI, include that in an APA style citation.
Example with DOI:
Goff, W., & Veresov, N. (2015). Examining teacher-researcher collaboration through the cultural interface. Cultural Studies Of Science Education, 10(3), 621-627. https://doi.org/10.1007/s11422-015-9665-9
No DOI? Then just cite it as you normally would.
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