Perhaps you should try some spelling variations:
pham thuc » phap thuc, pham chuc, nham thuc
van pham » san pham, van phan, van phat
hang tai » hang va, dung tai
hanh tai » thanh tai, han tai, hinh tai
thuc xay » thuc day, tuc xay, thuat xay
hieu van » hieu va, thien van, lieu va
sach thu » sach thue, sach thieu, sach tham
tu sach » thu sach, su sach, te sach
hoan xa » hoang xa, hoa xa, toan xa
hoan va » khoan va, hoang va, doan va
cua tre » cua te, cuu tre, cua triet

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 thu ((hoan xa) OR (hoan va)) hoi. hieu van pham thuc xay ((hanh tai) or (hang tai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thu ((hoan xa) OR (hoan va)) hoi. hieu van pham thuc xay ((hanh tai) OR (hang tai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thu ((hoan xa) OR (hoan va)) hoi. hieu van pham thuc xay ((hanh tai) or (hang tai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach thu ((hoan xa) OR (hoan va)) hoi. hieu van pham thuc xay ((hanh tai) or (hang tai)) cua tre*.