Two success stories were announced Monday during Nebraska's latest trade mission to China.  Governor Dave Heineman said two Nebraska companies have signed agreements with Chinese partners.  Behlen Manufacturing of Columbus inked a deal with Beijing's 3rd largest construction company to erect Behlen's steel buildings in that country.  President T.R. Raimondo said future agreements will be sought for erection of other structures such as grain bins.  Vireo Resources of Blair, a drug maker, announced it had arrived at an agreement with a Chinese biotech company to market its pain reliever "Amino Active."  Dr. Michael Dixon, representing the University of Nebraska's Technology Transfer Company Unimed, said the arrangement will cause Viero Resources to expand its plant and payroll.