Subjects Category

The complex networks related research was distributed in the subjects of physics, computer science, biochemistry & molecular biology, mathematics and engineering. Most complex networks outputs were produced under the subject of physics due to

Fig. 2 Subjects co-occurrence networks of SCI&SSCI papers

it is a branch of theoretical physics originally. As time went by, this approach was used in bioscience or engineering to solve many problems as a migrating concept, which proved its superiority for many disciplines from the metadata of SCI & SSCI papers. Through the subject co-occurrence networks it can be known that the complex network is based on the mathematics and computer science, and be successfully used in engineering and related sciences, which is shown in Fig. 2. Bio-related sciences such as biochemistry, biophysics, biotechnology, and cell biology are the best domains in which complex networks being well developed. In future, there will be more and more bio-scientists put their attention into complex networks research.

Journals Analysis

The complex networks research was published mainly in physics related journals such as Physical Review E and Physica A, which published most complex networks papers in all journals from the SCI&SSCI database. PLoS One produced 217 papers and ranked third, European physical journal B with 205 papers in forth and Chaos with 205 papers in fifth for publications in the complex networks research. The American journals PNAS and Physical Review Letters were two journals with the highest impact factor in 2011. The annual publications distribution about complex networks papers are shown in Fig. 3. The research in this field attracted the most attentions from scientists far in the year 2001. Physical Review E was the main publisher of complex networks in the last decade, while Physica A reached the publication level of Physical Review E in 2007 once. Other journals kept a stable publication state in the past decade with about 30 papers per year in SCI&SSCI database; PLoS One (Full name of Public Library of Science One) was the only exception with a dramatically increasing rate in recent three years.

Fig. 3 Annual SCI&SSCI journals outputs distribution during 2001–2012

Fig. 4 Annual country record distribution in the complex networks study

Countries Analysis

In all complex networks publications, the United States of America and the People's Republic of China contributed the most parts as shown in Fig. 4. Hence the research centre was located in these two countries at present. However, the USA started

Fig. 5 Citation distribution of global SCI&SSCI papers

complex networks research as early in 1997 but dropped behind P.R. China in productions after 2007. Other countries such as Germany, Italy, England and Spain produced less outputs with a stable increasing rate in complex networks related publications. While in total these European countries published more papers than former other countries.

Active degree is defined as the outputs number in recent three years to all years' publication number in general bibliometric research. P.R. China had the highest active degree of 52.3 % in all countries in the world, indicating that the research of complex networks was treasured much and in fact such activity as the Conference for Chinese Complex Networks (short for CCCN) was held for eight times already in recent years in P.R. China (Fig. 5).

The SCI&SSCI papers' citations results were shown in Fig. 4. From this figure it can be found that the USA obtained the most citations, which attested its high level in the field of complex network research. The highest citation per paper was from European countries such as England and Germany. P.R. China's average citation was relatively lower than most European countries and Brazil or Japan, but not far behind the USA with less total citations.

In the international collaboration of papers of complex networks, the USA, Germany and P.R. China are located in the central positions which can be seen in Fig. 6. It is also clear that USA is in the centre of collaborating activities. Other countries such as England, France, Italy, Spain and Switzerland had less cooperation in complex networks research in SCI&SSCI publications. The cooperation network between top productive countries reflected the knowledge transmission in the field of complex networks research in the world.

Fig. 6 The international collaboration network of complex networks

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