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

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 treo) OR (cau tren))~.
• 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 treo) OR (cau tren)).
• 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 treo) OR (cau tren))".
• 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 treo) OR (cau tren))*.