2N2904 is basically a general purpose amplifier. It is used for the basic functions of general purpose amplifier and switch. As a switch, the practical dynamic range is 100mA and for an amplifier, frequency is of the order of 100 MA. When you look at the 2N3904 Datasheet, you will find the Absolute Maximum Ratings which are noted at 25 degree Celsius. These readings, as you will read the manual, are steady state limits. Thermal characteristics, again, are measured under the same conditions. Apart from the electrical characteristics of this amplifier, which are mentioned at length, the ordering information is also clarified. Hence, you would want to download the 2N3904 DATASHEET.