ÜNSAL, Belkıs, et al. “Gastric Metaplasia and Helicobacter Pylori Prevalance in Patients With Duodenal Ulcer”. Turkish Journal of Gastroenterology, vol. 6, no. 1, Jan. 1995, pp. 119-20, https://www.turkjgastroenterol.org/index.php/tjg/article/view/586.