Stocks extended their gains heading into the final hour of the regular trading session Monday. The Nasdaq was up 0.4%, while the S&P 500 rose 0.3% and the Dow Jones industrial average 0.2%. Volume was tracking higher on the Nasdaq but remained lower on the NYSE compared with the same time Friday. A number of big tech names boosted the Nasdaq as Internet retail, toymakers and solar stocks led on the stock market today.