Since 1990, a large and dynamic global science system has evolved, based on grass roots collaboration, and resting on the resources, infrastructure and personnel housed by national science systems. Euro-American science systems have become intensively networked in a global duopoly; and many other countries have built national science systems, including a group of large- and middle-sized countries that follow semi-autonomous trajectories based on state investment, intensive national network building, and international engagement, without integrating tightly into the global duopoly. The dual global/national approach pursued by these systems, including China, South Korea, Iran and India, is not always fully understood in papers on science. Nevertheless, China is now the number two science country in the world, the largest producer of papers and number one in parts of STEM physical sciences. The paper investigates the remarkable evolution of China's science funding, output, discipline balance, internationalisation strategy and national and global networking. China has combined global activity and the local/national building of science in positive sum manner, on the ground of the nationally nested science system. The paper also discusses limits of the achievement, noting that while China-US relations have been instrumental in building science, a partial decoupling is occurring and the future is unclear.