RUSINOVA, Evgeniya. Approaches to Measuring the Efficiency of the Bulgarian Libraries. Qualitative and Quantitative Methods in Libraries, [S.l.], v. 5, n. 2, p. 379-383, july 2017. ISSN 2241-1925. Available at: <http://qqml-journal.net/index.php/qqml/article/view/348>. Date accessed: 17 feb. 2020.