Perhaps you should try some spelling variations:
van thanh » ban thanh, van tuan
van hanh » ban hanh, van anh, van ban
tu sach » thu sach, su sach, te sach
cac duc » cac du, cao duc, cac dac
vai cua » dai cua, hai cua, lai cua
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
lang xa » lang ha, dang xay, lang van
sang ma » tang ma, nang ma, sang tao
cua tre » cua te, cuu tre, cua triet

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