As noted in section 5.84 of the MLA Handbook, for works consulted online, “the location, in order of preference, is the DOI, permalink, or URL.” If you are citing an article found in a library database (or other type of database), and the article does not include a DOI, you can give a permalink or, in the absence of a permalink, a URL, even if the permalink or URL leads to gated content.
Remember that DOIs should always be preceded by https://doi.org/ (MLA Handbook 5.93), as in the following example:
Bockelman, Brian. “Buenos Aires Bohème: Argentina and the Transatlantic Bohemian Renaissance, 1890–1910.” Modernism/Modernity, vol. 23, no. 1, Jan. 2016, pp. 37–63. Project Muse, https://doi.org/10.1353/mod.2016.0011.
However, http:// and https:// can usually be omitted in permalinks and URLs (5.96).
Work Cited
MLA Handbook. 9th ed., Modern Language Association of America, 2021. MLA Handbook Plus, 2021, mlahandbookplus.org/.