Perhaps you should try some spelling variations:
van thanh » ban thanh, van tuan
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cam thuc » am thuc, cam thu, can thuc
hieu van » hieu va, thien van, lieu va
dang xay » dang van, van xay
xay hoi » xa hoi, tay hoi, cay phoi
bai cua » ban cua, bai ca, hai cua
sach o » sach lo, sac o, sach y
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 o dang xay hoi. hieu van ((cam thuc) OR (nam thuc)) van thanh ((bai cua) or (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach o dang xay hoi. hieu van ((cam thuc) OR (nam thuc)) van thanh ((bai cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach o dang xay hoi. hieu van ((cam thuc) OR (nam thuc)) van thanh ((bai cua) or (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: toc sach o dang xay hoi. hieu van ((cam thuc) OR (nam thuc)) van thanh ((bai cua) or (dai cua)) tre*.