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生命周期理论视角下的中小企业集群发展机制思考 被引量:1
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作者 李曼 《云南社会主义学院学报》 2014年第1期366-367,共2页
借鉴生命周期理论,产业集群发展阶段也可分为萌芽期、成长期、成熟期和衰退期。中小企业产业集群的四个阶段并非顺序发展,这个发展过程不仅会停滞不前,更会倒退或提前衰退。在中小企业产业集群中,存在着促进聚集的向心力和导致分散的离... 借鉴生命周期理论,产业集群发展阶段也可分为萌芽期、成长期、成熟期和衰退期。中小企业产业集群的四个阶段并非顺序发展,这个发展过程不仅会停滞不前,更会倒退或提前衰退。在中小企业产业集群中,存在着促进聚集的向心力和导致分散的离心力。本文指出,企业逐利与产业共同发展的矛盾、企业规模化与产业灵活性的矛盾、企业增长性与产业资源有限性的矛盾构成了中小企业产业集群发展重要的离心力。集群一旦开始萌芽后,除了离心力不断增大外,还将遇到资源枯竭陷阱、经济周期陷阱、联盟封闭陷阱、机会主义陷阱和路径依赖陷阱等,导致产业集群成长逆转。中小企业产业集群是一个资源不断更替和流动的过程,政府应成为市场的有效补充,善待每一个中小企业并不断促进资源流动。 展开更多
关键词 生命周期理论 产业集群 中小企业 成长逆转
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A novel strategy to derive iPS cells from porcine fibroblasts 被引量:2
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作者 RUAN WeiMin HAN JianYong +4 位作者 LI Pin CAO SuYing AN Yang LIM Bing LI Ning 《Science China(Life Sciences)》 SCIE CAS 2011年第6期553-559,共7页
Induced pluripotent stem (iPS) cell technology demonstrates that somatic cells can be reprogrammed to a pluripotent state by over-expressing four reprogramming factors.This technology has created an interest in derivi... Induced pluripotent stem (iPS) cell technology demonstrates that somatic cells can be reprogrammed to a pluripotent state by over-expressing four reprogramming factors.This technology has created an interest in deriving iPS cells from domesticated animals such as pigs,sheep and cattle.Moloney murine leukemia retrovirus vectors have been widely used to generate and study mouse iPS cells.However,this retrovirus system infects only mouse and rat cells,which limits its use in establishing iPS cells from other mammals.In our study,we demonstrate a novel retrovirus strategy to efficiently generate porcine iPS cells from embryonic fibroblasts.We transfected four human reprogramming factors (Oct4,Sox2,Klf4 and Myc) into fibroblasts in one step by using a VSV-G envelope-coated pantropic retrovirus that was easily packaged by GP2-293 cells.We established six embryonic stem (ES)-like cell lines in human ES cell medium supplemented with bFGF.Colonies showed a similar morphology to human ES cells with a high nuclei-cytoplasm ratio and phase-bright flat colonies.Porcine iPS cells could form embryoid bodies in vitro and differentiate into the three germ layers in vivo by forming teratomas in immunodeficient mice. 展开更多
关键词 induced pluripotent stem cells Moloney murine leukemia retrovirus vectors embryoid body TERATOMA
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