Perhaps you should try some spelling variations:
thanh doi » thanh loi, thanh moi, thanh do
hoc sach » hoc sinh, hoc cac, hoc anh
thuc dan » thuc hanh, hoc dan
hieu van » hieu va, thien van, lieu va
tay lang » tai lang, tay tang, tay quang
lang xa » lang ha, dang xay, lang van
van cam » van nam, van lam, van cau
so sanh » do sanh
doi qua » doi cua, hoi qua, doi quy

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((hoc sach) or (so sanh)) tay lang xa hoi. hieu van cam ((thuc dan) OR (thuc vat)) thanh doi qua su~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((hoc sach) OR (so sanh)) tay lang xa hoi. hieu van cam ((thuc dan) OR (thuc vat)) thanh doi qua su.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((hoc sach) or (so sanh)) tay lang xa hoi. hieu van cam ((thuc dan) OR (thuc vat)) thanh doi qua su".
• Adding a wildcard symbol may retrieve word variants: ((hoc sach) or (so sanh)) tay lang xa hoi. hieu van cam ((thuc dan) OR (thuc vat)) thanh doi qua su*.