Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh hai » thanh hai, nhanh hai, hang hai
sach ky » sac ky, sach y, sach ty
hai cua » thai cua, dai cua, hoi cua
truc va » thuc va, thuc vat, trung va
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
ky dang » ky nang, ky danh
ma hoi » mai hoi, xa hoi, me hoi
ve cam » ve cham, ve cac, va cam

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 dang ((ma hoi) OR (ma hoa)). hieu ve cam ((duc va) or (truc va)) hanh hai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky dang ((ma hoi) OR (ma hoa)). hieu ve cam ((duc va) OR (truc va)) hanh hai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky dang ((ma hoi) OR (ma hoa)). hieu ve cam ((duc va) or (truc va)) hanh hai cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky dang ((ma hoi) OR (ma hoa)). hieu ve cam ((duc va) or (truc va)) hanh hai cua tre*.