Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
dat duoc » dat nuoc, da duoc, luat duoc
dang vat » dang van, dong vat, dang nhat
hanh va » hang va, hanh vi
va hanh » van hanh, va thanh, va danh
duoc va » nuoc va, duc va, duoc ma
hieu ve » hieu va, hieu van
dang ma » dang mau, dang mam, dang mat
ve dat » de dat, va dat, ve dao
o viet » so viet, hoc viet
va o » va co, va do, va mo

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) or (doc sach)) thu ((dang ma) or (dang vat)) hoi. hieu ve dat duoc va hanh va o viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) thu ((dang ma) OR (dang vat)) hoi. hieu ve dat duoc va hanh va o viet.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (doc sach)) thu ((dang ma) or (dang vat)) hoi. hieu ve dat duoc va hanh va o viet*.