Perhaps you should try some spelling variations:
van cham » van chat, van tham, va cham
hieu van » hieu va, thien van, lieu va
dua tren » dung tren
van hanh » van thanh, ban hanh, van anh
cham hoc » cham soc, chat hoc, cham hoi
hoc van » hoc dan, hoc va, hoc vat
bo sach » co sach, hoc sach
sach ky » sac ky, sach y, sach ty
lang xa » lang ha, dang xay, lang van
nang xa » nang x, nang ma, mang xa
cuu tre » cua tre, cau tren, cau treo

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

• Performing a fuzzy search may retrieve terms with similar spellings: bo sach ky ((nang xa) or (lang xa)) hoi. hieu van cham hoc van hanh vi ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: bo sach ky ((nang xa) OR (lang xa)) hoi. hieu van cham hoc van hanh vi ((dua tren) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: bo sach ky ((nang xa) or (lang xa)) hoi. hieu van cham hoc van hanh vi ((dua tren) or (cuu tre))*.