BEIJING, July 24 (Xinhua) -- More than 500 investment applications by Taiwan businesses worth more than 3.5 billion U.S.dollars were approved by mainland authorities in the first half of this year, statistics from Taiwan economic statistics show.     Investment in the first six months of the year was up 35.21 percent year-on-year.     It is expected that Taiwan investment for the full year in the mainland will surpass the record high 6.94 billion dollars in 2004.     Last month alone, 93 applications were ratified involving 680 million dollars. Enditem