Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
thanh hai » thanh phan, thanh hoa, thanh san
hieu va » lieu va, hieu qua
so viet » hoc viet
y tang » ky tang, 6 tang, 7 tang
ma hoi » mai hoi, ma hoa, me hoi
va cam » va cham, va cac, va cao
xuc va » tuc va, luc va, xac va
hai so » dai so, tai so, thai son

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuat sach y tang ((ma hoi) or (xa hoi)). hieu va cam ((xuc va) OR (duc va)) thanh hai so viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat sach y tang ((ma hoi) OR (xa hoi)). hieu va cam ((xuc va) OR (duc va)) thanh hai so viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuat sach y tang ((ma hoi) or (xa hoi)). hieu va cam ((xuc va) OR (duc va)) thanh hai so viet".
• Adding a wildcard symbol may retrieve word variants: thuat sach y tang ((ma hoi) or (xa hoi)). hieu va cam ((xuc va) OR (duc va)) thanh hai so viet*.