Perhaps you should try some spelling variations:
"phat trien khoa hoc" » "phat trien nha hoc", "phat trien khai hoc", "phat trien hoat hoc", "phat trien hoa hoc", "phan trien khoa hoc", "pham trien khoa hoc", "nhat trien khoa hoc"
"phap tieng khoa hoc" » "phap tien hoa hoc", "phap tuong khoa hoc", "phap hien khoa hoc", "phap tieng hoa hoc"
"phap vien khoa hoc" » "phap viet khoa hoc", "phap bien khoa hoc", "phap dien khoa hoc", "phap von khoa hoc", "phap lieu khoa hoc", "phap van khoa hoc", "phap vien hoa hoc"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("phat trien khoa hoc") or ((("phap tieng khoa hoc") OR ("phap vien khoa hoc"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("phat trien khoa hoc") OR ((("phap tieng khoa hoc") OR ("phap vien khoa hoc")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"phat trien khoa hoc\") or (((\"phap tieng khoa hoc\") OR (\"phap vien khoa hoc\"))))".
• Removing quotes may allow a broader search: (( phat trien khoa hoc ) or ((( phap tieng khoa hoc ) OR ( phap vien khoa hoc )))).
• Adding a wildcard symbol may retrieve word variants: (("phat trien khoa hoc") or ((("phap tieng khoa hoc") OR ("phap vien khoa hoc"))))*.