Perhaps you should try some spelling variations:
thuoc cao » thuoc co, thuc cao, thuoc bao
doc sach » hoc sach, toc sach, nuoc sach
hieu van » hieu va, thien van, lieu va
tang xa » trang xa, tang ma, lang xa
thuc ca » thuc cua, thuc can, thuc cao
sach ky » sac ky, sach y, sach ty
ky tang » ky nang, ky dang, kho tang
va cau » van cau, va dau, va cao

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky tang xa hoi. hieu van nam ((thuc ca) or (thuoc cao)) dan ((va cau) OR (va cac)) treo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky tang xa hoi. hieu van nam ((thuc ca) OR (thuoc cao)) dan ((va cau) OR (va cac)) treo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky tang xa hoi. hieu van nam ((thuc ca) or (thuoc cao)) dan ((va cau) OR (va cac)) treo".
• Adding a wildcard symbol may retrieve word variants: doc sach ky tang xa hoi. hieu van nam ((thuc ca) or (thuoc cao)) dan ((va cau) OR (va cac)) treo*.