Perhaps you should try some spelling variations:
dan thanh » dang thanh, danh thanh, ban thanh
toc sach » doc sach, thuoc sach, nuoc sach
cam thuc » am thuc, nam thuc, cam thu
hoc sach » hoc sinh, hoc cac, hoc anh
dang xay » dang van, van xay
thuc dan » thuc hanh, hoc dan, thuc vat
vai cua » hai cua, lai cua, bai cua
hieu ve » hieu va, hieu van
xay hoi » xa hoi, tay hoi, cay phoi
ve cam » ve cham, ve cac, va cam
o dang » xo dang, do dang, so dang

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) OR (hoc sach)) o dang xay hoi. hieu ve cam thuc dan thanh ((vai cua) or (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) o dang xay hoi. hieu ve cam thuc dan thanh ((vai cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (hoc sach)) o dang xay hoi. hieu ve cam thuc dan thanh ((vai cua) or (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (hoc sach)) o dang xay hoi. hieu ve cam thuc dan thanh ((vai cua) or (dai cua)) tre*.