Perhaps you should try some spelling variations:
tu tieng » luc tieng, tu tuong, tu trong
dua tren » dung tren
van hanh » van thanh, ban hanh, van anh
truc van » truc va, thuc van, truc ban
dau truc » cau truc, dai truc, doan truc
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
va dau » va dao

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