Perhaps you should try some spelling variations:
hieu van » thien van, lieu va, hieu ve
so sach » so sanh, bo sach, co sach
sach ly » sach y, sach lo, sach ty
ly nang » ky nang, ly hang, ly vang
nang ma » tang ma, sang ma, nang cao
hieu va » lieu va, hieu qua
ca tren » cau tren, cu tren, la tren
ma hoi » mai hoi, xa hoi, ma hoa
xac va » tac va, ac va, bac va
vi ca » vit ca, li ca, va ca

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ly nang ma hoi. ((hieu van) or (hieu va)) cam ((xac va) or (duc va)) hanh vi ca tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ly nang ma hoi. ((hieu van) OR (hieu va)) cam ((xac va) OR (duc va)) hanh vi ca tren.
• Adding a wildcard symbol may retrieve word variants: so sach ly nang ma hoi. ((hieu van) or (hieu va)) cam ((xac va) or (duc va)) hanh vi ca tren*.