Perhaps you should try some spelling variations:
hanh hai » thanh hai, nhanh hai, hang hai
dang xay » dang van, van xay
su sach » so sach, vu sach
va hanh » van hanh, va thanh, va danh
sach de » cach de, sach dao, sach dat
mang xa » lang xa, mang may, mang cua
ve cao » va cao, ve bao, ve co
ve cac » va cac, vien cac
hai va » hai van, thai va, hoi va
thiet » thieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach de ((mang xa) or (dang xay)) hoi. hieu ((ve cao) OR (ve cac)) duc va hanh hai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach de ((mang xa) OR (dang xay)) hoi. hieu ((ve cao) OR (ve cac)) duc va hanh hai va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach de ((mang xa) or (dang xay)) hoi. hieu ((ve cao) OR (ve cac)) duc va hanh hai va thiet".
• Adding a wildcard symbol may retrieve word variants: su sach de ((mang xa) or (dang xay)) hoi. hieu ((ve cao) OR (ve cac)) duc va hanh hai va thiet*.