Perhaps you should try some spelling variations:
dua tren » dung tren
dinh tri » chinh tri
hieu va » lieu va, hieu qua
nam duc » nam duoc, pham duc, nam thuc
nang xa » nang x, lang xa, mang xa
nang ma » tang ma, sang ma, nang cao
va dinh » van dinh, va kinh, va tinh
te sac » te sach, te cac, te san
va nam » van nam, ha nam, va nay
sac ky » cac ky, sai ky
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: te sac ky ((nang xa) OR (nang ma)) hoi. hieu va nam duc va dinh tri ((dua tren) or (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sac ky ((nang xa) OR (nang ma)) hoi. hieu va nam duc va dinh tri ((dua tren) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sac ky ((nang xa) OR (nang ma)) hoi. hieu va nam duc va dinh tri ((dua tren) or (cua te))".
• Adding a wildcard symbol may retrieve word variants: te sac ky ((nang xa) OR (nang ma)) hoi. hieu va nam duc va dinh tri ((dua tren) or (cua te))*.