Perhaps you should try some spelling variations:
viet khoang » viet hoang, viet thong, viet hang
thiet luan » thien luan, thi luan, thiet lap
thien quan » trien quang, lien quan, thien van
khoang hoc » khoang thoi, khoa hoc, hoang hoa
vien than » vien thanh, dien than, vien nhan
dien han » dien phan, dien than, dien dan
van cua » vang cua, ban cua, dan cua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: giao trinh ((thiet luan) OR (thien quan)) van cua nguoi viet khoang hoc ((dien han) or (vien than))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: giao trinh ((thiet luan) OR (thien quan)) van cua nguoi viet khoang hoc ((dien han) OR (vien than)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "giao trinh ((thiet luan) OR (thien quan)) van cua nguoi viet khoang hoc ((dien han) or (vien than))".
• Adding a wildcard symbol may retrieve word variants: giao trinh ((thiet luan) OR (thien quan)) van cua nguoi viet khoang hoc ((dien han) or (vien than))*.