Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
hieu van » hieu va, thien van, lieu va
mang xa » lang xa, mang may, dang xay
sach ky » sac ky, sach y, sach ty
van dau » van dao, phan dau
dau tuc » dau tu, dao tuc, cau truc
xa hanh » xa thanh, xa khanh, va hanh
cuu tre » cua tre, cau treo
tu sach » thu sach, su sach, te sach

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 ((mang xa) or (nang x)) hoi. hieu van dau tuc xa hanh vi ((cuu tre) OR (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((mang xa) OR (nang x)) hoi. hieu van dau tuc xa hanh vi ((cuu tre) OR (cau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((mang xa) or (nang x)) hoi. hieu van dau tuc xa hanh vi ((cuu tre) OR (cau tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((mang xa) or (nang x)) hoi. hieu van dau tuc xa hanh vi ((cuu tre) OR (cau tren))*.