Perhaps you should try some spelling variations:
thuat mach » thuat sach, thuat tach, thuyet mach
thu mach » thu sach, thu hoach, thuc cach
hoa khoa » khoa khoa, chua khoa, chia khoa
khoa hoc » hoa hoc
thi khoa » thai khoa, thit khoa, tai khoa
cao ban » cao bang, can ban, cao van
dien » bien, vien, tien

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( ((thu mach) OR (thuat mach)) dien hoa khoa hoc ) or ( su ((cao ban) or (co ban)) thi khoa hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( ((thu mach) OR (thuat mach)) dien hoa khoa hoc ) OR ( su ((cao ban) OR (co ban)) thi khoa hoc )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( ((thu mach) OR (thuat mach)) dien hoa khoa hoc ) or ( su ((cao ban) or (co ban)) thi khoa hoc ))".
• Adding a wildcard symbol may retrieve word variants: (( ((thu mach) OR (thuat mach)) dien hoa khoa hoc ) or ( su ((cao ban) or (co ban)) thi khoa hoc ))*.