You can take buses 113, 123, or 409 to Houjiutiao Station. From there, it's about 200 meters to the Beijing Science Center, a 2-3 minute walk. Alternatively, you can take buses 27 or 88 to Dezhenmenxi Station. From there, walk east along Dezhenmenxi Avenue, then turn left into Xinchakou Outer Avenue, and continue north along this avenue. Turn right at Ren dinghu North Alley to reach the entrance of the Science Center.