Perhaps you should try some spelling variations:
pham thuc » phap thuc, pham chuc, nham thuc
toc sach » hoc sach, doc sach, thuoc sach
dinh vi » dinh ve, dinh viet, dinh tri
thuc va » thuc vat, thuc dan, thuc day
ve pham » vi pham, v pham, ve phan
hieu ve » hieu va, hieu van
sach ty » sach y, sach tu, sach thu
sang ma » tang ma, sang tao, mang may
nang ma » tang ma, nang cao, mang may
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: toc sach ty ((nang ma) OR (sang ma)) hoi. hieu ve pham thuc va ((dinh vi) or (chinh tri)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ty ((nang ma) OR (sang ma)) hoi. hieu ve pham thuc va ((dinh vi) OR (chinh tri)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ty ((nang ma) OR (sang ma)) hoi. hieu ve pham thuc va ((dinh vi) or (chinh tri)) cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ty ((nang ma) OR (sang ma)) hoi. hieu ve pham thuc va ((dinh vi) or (chinh tri)) cua tre*.