Perhaps you should try some spelling variations:
nam truc » nam truoc, nam thuc, nam trung
va thanh » gia thanh, ban thanh, va tinh
hieu van » hieu va, thien van, lieu va
va hanh » van hanh, va danh, ban hanh
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
ky sang » ky dang, ky tang, duy sang
cua tre » cua te, cuu tre, cua triet
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ((ky sang) or (ky nang)) mai hoi. hieu van nam truc ((va hanh) OR (va thanh)) vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ky sang) OR (ky nang)) mai hoi. hieu van nam truc ((va hanh) OR (va thanh)) vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ky sang) or (ky nang)) mai hoi. hieu van nam truc ((va hanh) OR (va thanh)) vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ky sang) or (ky nang)) mai hoi. hieu van nam truc ((va hanh) OR (va thanh)) vi cua tre*.