Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
cau tren » cu tren, dau tren, ca tren
sach ky » sac ky, sach y, sach ty
ky sang » ky nang, ky dang, ky tang
dai moi » doi moi, dai hoi
van cac » van hac, van cau, van bac
va danh » va dinh, va dan, va hanh
danh vi » hanh vi, dinh vi, danh di
ma hoi » mai hoi, xa hoi, ma hoa
vi cau » va cau, ve cau, di cau

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 sang ((ma hoi) or (dai moi)). hieu van cac nuoc va danh vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky sang ((ma hoi) OR (dai moi)). hieu van cac nuoc va danh vi cau tren.
• Adding a wildcard symbol may retrieve word variants: toc sach ky sang ((ma hoi) or (dai moi)). hieu van cac nuoc va danh vi cau tren*.