The stock market weakened in early afternoon trading as the S&P 500 gave up gains and traded with a loss. The Dow Jones industrial average guarded a 0.3% gain. The S&P 500 peeked above the 1500 mark for the first time since December 2007, then reversed and was down a fraction. The Apple-hampered Nasdaq continued to lag with a 0.7% loss. Volume was higher compared with the same time Wednesday. 3D Systems (DDD) pared its early advance to 2%