Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh tai » thanh tai, hang tai, han tai
hieu van » thien van, lieu va, hieu ve
sach ky » sac ky, sach y, sach ty
tai cua » thai cua, tai cuc, tri cua
truc va » thuc va, thuc vat, trung va
tang xa » trang xa, tang ma, lang xa
hieu va » lieu va, hieu qua
ky tang » ky nang, ky dang, kho tang
tuc va » thuc va, tuc xa, duc va
cua te » cua tu

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 ky tang xa hoi. ((hieu van) or (hieu va)) cau ((tuc va) OR (truc va)) hanh tai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky tang xa hoi. ((hieu van) OR (hieu va)) cau ((tuc va) OR (truc va)) hanh tai cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky tang xa hoi. ((hieu van) or (hieu va)) cau ((tuc va) OR (truc va)) hanh tai cua te".
• Adding a wildcard symbol may retrieve word variants: toc sach ky tang xa hoi. ((hieu van) or (hieu va)) cau ((tuc va) OR (truc va)) hanh tai cua te*.