Perhaps you should try some spelling variations:
sach thi » sach tai, sach thieu, sach tham
hanh vai » hanh vi, hanh va, hanh tai
sach thu » sach thue, sach thieu, sach tham
xa hanh » xa thanh, xa khanh, va hanh
cac toc » cac toi, cac nuoc, cac thoi
hieu va » lieu va, hieu qua
cac tuc » cac tu, cac tac, cac nuoc
hanh ca » hanh cac, hanh cat, hanh cua
ca hoi » cau hoi, cua hoi, xa hoi
vai va » mai va, dai va, hai 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: doc ((sach thi) or (sach thu)) hanh ca hoi. hieu va ((cac tuc) or (cac toc)) xa hanh vai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc ((sach thi) OR (sach thu)) hanh ca hoi. hieu va ((cac tuc) OR (cac toc)) xa hanh vai va thiet.
• Adding a wildcard symbol may retrieve word variants: doc ((sach thi) or (sach thu)) hanh ca hoi. hieu va ((cac tuc) or (cac toc)) xa hanh vai va thiet*.