الوصول الحر: https://doaj.org/article/2950671e43df461fba99d304a2fcf743Test
الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::0a54ef841128a86fcdf40ffd6b30ba12Testhttp://www.sciencedirect.com/science/article/pii/S2211124720311736Test