Complex sentence: Inter-Research (IR) is a very small company, compared to the great publishing houses that own thousands of scientific journals, but maintains its independence, as opposed to numerous other small publishers who have been taken over by the major players.
Split into simpler sentences: Inter-Research (IR) is a small company, compared to the big publishing houses that own thousands of scientific journals. It maintains its independence, as opposed to numerous other small publishers who have been taken over by the major players.