Perhaps you should try some spelling variations:
cua triet » cua viet, su triet, va triet
hieu van » hieu va, thien van, lieu va
de thanh » le thanh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
ky sang » ky nang, ky dang, ky tang
sang ma » tang ma, nang ma, sang tao
xe hanh » ve hanh, den hanh, deu hanh
cua tre » cua te, cuu tre, dua tren
ma hoi » mai hoi, xa hoi, ma hoa

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 ma hoi. hieu van nam thu ((xe hanh) OR (de thanh)) tai ((cua tre) or (cua triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky sang ma hoi. hieu van nam thu ((xe hanh) OR (de thanh)) tai ((cua tre) OR (cua triet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky sang ma hoi. hieu van nam thu ((xe hanh) OR (de thanh)) tai ((cua tre) or (cua triet))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky sang ma hoi. hieu van nam thu ((xe hanh) OR (de thanh)) tai ((cua tre) or (cua triet))*.