The beginning of April is a busy period in Amsterdam, please book your hotel room as soon as possible.
Hotel Casa 400
Amsterdam Tropen Hotel
Hotel Mercure Sloterdijk
Any hotel in the Amsterdam Central Station area, from there you can take the direct train to Science Park.
The hotels can be booked through Booking.com, you can also do a search through Booking.com in the Schiphol Airport area. From Schiphol there is a direct train to Science Park.
Or you could condsider staying in Utrecht or Haarlem in the area of the Central Station, from both cities you can be in 30 minutes at Science Park. For planning your trip: http://9292.nl/en