Perhaps you should try some spelling variations:
thiet hach » thien hach, thuyet hach, chiet tach
thiet hai » thiet bi, thi hai, thien tai
ban huong » bang phuong, ban hang, anh huong
tang cua » hang cua, tang luan, thong cua
mang cua » manh cua, dung cua, ban cua
dan toan » van toan, dan than, manh toan
toan cau » toan cao, toan ban, toan tap

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

• Performing a fuzzy search may retrieve terms with similar spellings: hoc ((thiet hach) or (thiet hai)) - hanh ((tang cua) or (mang cua)) ban huong dan toan cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((thiet hach) OR (thiet hai)) - hanh ((tang cua) OR (mang cua)) ban huong dan toan cau.
• Adding a wildcard symbol may retrieve word variants: hoc ((thiet hach) or (thiet hai)) - hanh ((tang cua) or (mang cua)) ban huong dan toan cau*.