Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
tri thuc » tri tue
thuc anh » thuc hanh, thuy anh, thu anh
khong he » khong khi, hong ha, khong _
tu sach » thu sach, su sach, te sach
khoa he » hoa he, khoa hoc, khoa thu
thong » trong

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) or (((toc sach) or (doc sach)))) tri thuc anh ((khoa he) OR (khong he)) thong~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (((toc sach) OR (doc sach)))) tri thuc anh ((khoa he) OR (khong he)) thong.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (((toc sach) or (doc sach)))) tri thuc anh ((khoa he) OR (khong he)) thong".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (((toc sach) or (doc sach)))) tri thuc anh ((khoa he) OR (khong he)) thong*.