Perhaps you should try some spelling variations:
nam thuoc » nam thu, nha thuoc, cay thuoc
dang xay » dang van, van xay
hieu van » hieu va, thien van, lieu va
nam thuc » am thuc, nam thu, nam tu
vanh dai » van dai, vanh tai, lanh dao
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
ky dang » ky nang, ky danh
xay hoi » xa hoi, tay hoi, cay phoi
va vanh » va van, va danh, va hanh
cua tre » cuu tre, cua triet, dua tren
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: tu sach ky dang xay hoi. hieu van ((nam thuc) OR (nam thuoc)) va vanh dai ((cua tre) or (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky dang xay hoi. hieu van ((nam thuc) OR (nam thuoc)) va vanh dai ((cua tre) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky dang xay hoi. hieu van ((nam thuc) OR (nam thuoc)) va vanh dai ((cua tre) or (cua te))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky dang xay hoi. hieu van ((nam thuc) OR (nam thuoc)) va vanh dai ((cua tre) or (cua te))*.