Perhaps you should try some spelling variations:
trinh cai » trinh tai, trinh cau, trinh cac
trinh ca » trinh cau, trinh cua, trinh cac
cau cong » cac cong, cuu cong, cao cong
hai viet » thai viet, mai viet, tai viet
cong hoa » dong hoa, dong hoc, hang hoa
hoi viet » oi viet, thai viet, cuoi viet
cac tay » cac tac, cac tai, cac tap
cai tao » cau tao, tai tao, ai tao
cau dan » cau danh, cac dan, cu dan
cac cau » cac mau, bac cau, ca cau
cac cay » ca cay, cac cam, cac cap
dao va » dao van, do va, cao va
co hai » co dai, o hai, cong hai
co hoi » co hoc, co loi
so hai » son hai, su hai, so ha
cay co » cac co, tay co, cay cong
ca dan » cac dan
tay so » tay son, tai so, tay co

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

• Performing a fuzzy search may retrieve terms with similar spellings: (((( cong trinh cai tao va cac cay co hoi viet nam ) or ((( cong trinh ca dao va cac cay co hai viet nam ) or ( cong trinh ca dao va cac tay so hai viet nam ))))) or ( cong trinh ((cau dan) OR (ca dan)) va cac cau cong hoa viet nam ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((( cong trinh cai tao va cac cay co hoi viet nam ) OR ((( cong trinh ca dao va cac cay co hai viet nam ) OR ( cong trinh ca dao va cac tay so hai viet nam ))))) OR ( cong trinh ((cau dan) OR (ca dan)) va cac cau cong hoa viet nam )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(((( cong trinh cai tao va cac cay co hoi viet nam ) or ((( cong trinh ca dao va cac cay co hai viet nam ) or ( cong trinh ca dao va cac tay so hai viet nam ))))) or ( cong trinh ((cau dan) OR (ca dan)) va cac cau cong hoa viet nam ))".
• Adding a wildcard symbol may retrieve word variants: (((( cong trinh cai tao va cac cay co hoi viet nam ) or ((( cong trinh ca dao va cac cay co hai viet nam ) or ( cong trinh ca dao va cac tay so hai viet nam ))))) or ( cong trinh ((cau dan) OR (ca dan)) va cac cau cong hoa viet nam ))*.