全文获取类型
收费全文 | 103篇 |
免费 | 0篇 |
专业分类
系统科学 | 3篇 |
理论与方法论 | 7篇 |
现状及发展 | 34篇 |
研究方法 | 17篇 |
综合类 | 41篇 |
自然研究 | 1篇 |
出版年
2017年 | 1篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 4篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 1篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1989年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有103条查询结果,搜索用时 109 毫秒
101.
How organisms (including people) recognize distant objects is a fundamental question. The correspondence between object characteristics (distal stimuli), like visual shape, and sensory characteristics (proximal stimuli), like retinal projection, is ambiguous. The view that sensory systems are 'designed' to 'pick up' ecologically useful information is vague about how such mechanisms might work. In echolocating dolphins, which are studied as models for object recognition sonar systems, the correspondence between echo characteristics and object characteristics is less clear. Many cognitive scientists assume that object characteristics are extracted from proximal stimuli, but evidence for this remains ambiguous. For example, a dolphin may store 'sound templates' in its brain and identify whole objects by listening for a particular sound. Alternatively, a dolphin's brain may contain algorithms, derived through natural endowments or experience or both, which allow it to identify object characteristics based on sounds. The standard method used to address this question in many species is indirect and has led to equivocal results with dolphins. Here we outline an appropriate method and test it to show that dolphins extract object characteristics directly from echoes. 相似文献
102.
Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration 总被引:35,自引:0,他引:35
Oosthuyse B Moons L Storkebaum E Beck H Nuyens D Brusselmans K Van Dorpe J Hellings P Gorselink M Heymans S Theilmeier G Dewerchin M Laudenbach V Vermylen P Raat H Acker T Vleminckx V Van Den Bosch L Cashman N Fujisawa H Drost MR Sciot R Bruyninckx F Hicklin DJ Ince C Gressens P Lupu F Plate KH Robberecht W Herbert JM Collen D Carmeliet P 《Nature genetics》2001,28(2):131-138
Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons. 相似文献