Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
hieu van » hieu va, thien van, hieu ve
dao cua » dai cua, day cua, dan cua
va danh » va dinh, va dan, va hanh
va lanh » va lang, va hanh, va anh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
o hai » co hai, so hai, o lai

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

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang o hai. ((hieu van) OR (lieu va)) nam thuc ((va lanh) OR (va danh)) dao cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang o hai. ((hieu van) or (lieu va)) nam thuc ((va lanh) OR (va danh)) dao cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang o hai. ((hieu van) or (lieu va)) nam thuc ((va lanh) OR (va danh)) dao cua tre*.