Perhaps you should try some spelling variations:
thuat sach » thuat lanh, thuat san
duoc may » duoc ma, duoc ly, hoc may
nam duoc » nam thuoc, da duoc, dat duoc
hieu van » hieu va, thien van, lieu va
sang ma » tang ma, sang tao, mang may
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, nang cao, mang may
va cao » va cac, va co, va dao
va ca » va cac, va cai, va cau

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuat sach ky ((nang ma) or (sang ma)) hoi. hieu van nam duoc may tinh ((va ca) OR (va cao)) tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat sach ky ((nang ma) OR (sang ma)) hoi. hieu van nam duoc may tinh ((va ca) OR (va cao)) tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuat sach ky ((nang ma) or (sang ma)) hoi. hieu van nam duoc may tinh ((va ca) OR (va cao)) tren".
• Adding a wildcard symbol may retrieve word variants: thuat sach ky ((nang ma) or (sang ma)) hoi. hieu van nam duoc may tinh ((va ca) OR (va cao)) tren*.