Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
hieu van » hieu va, thien van, lieu va
cau tren » cu tren, dau tren, ca tren
dai moi » doi moi, dai hoi
sach ky » sac ky, sach y, sach ty
van cac » van hac, van cau, van bac
ky sang » ky nang, ky dang, ky tang
va danh » va dinh, va hanh, dia danh
ma hoi » mai hoi, xa hoi, ma hoa
va dan » ca dan, va dao, va dau
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) OR (va dan)) 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) OR (va dan)) vi cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky sang ((ma hoi) or (dai moi)). hieu van cac nuoc ((va danh) OR (va dan)) 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) OR (va dan)) vi cau tren*.