Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cau tren » cu tren, dau tren, ca tren
dang xay » dang van, van xay
xay hoi » xa hoi, tay hoi, cay phoi
hieu ha » hieu hoa, hieu ca, hieu xa
hieu va » lieu va, hieu qua
sach ty » sach y, sach tu, sach thu
ty dang » ty xang, ky dang, ty hang
thuc va » thuc vat, thuc dan, thuc day
dan vai » dan tai, dan vat, den vai
dan va » doan va, dan ca, ban va

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ty dang xay hoi. ((hieu ha) OR (hieu va)) nam thuc va ((dan vai) or (dan va)) cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty dang xay hoi. ((hieu ha) OR (hieu va)) nam thuc va ((dan vai) OR (dan va)) cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty dang xay hoi. ((hieu ha) OR (hieu va)) nam thuc va ((dan vai) or (dan va)) cau tren".
• Adding a wildcard symbol may retrieve word variants: toc sach ty dang xay hoi. ((hieu ha) OR (hieu va)) nam thuc va ((dan vai) or (dan va)) cau tren*.