·[新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Black and White黑与白Sometimes you hear it said that white is a combination of all the colors of the rainbow -- and that black is the absence of color. Find out more about whether black and white are colors -- today on 英语四级听力. JB: This is 英语四级听力. A listener wants to know, "Are black and white really colors?"DB: Color isnt a physical quality. Its a phenomenon of light and perception. Matter and energy are colorless. Its really our eyes and br……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Sierra Treeline 山脊树林Could global warming allow forests to expand into higher elevations than they have reached in more than a thousand years? Learn more about studying alpine treelines -- today on 英语四级听力.JB: This is 英语四级听力. The highest point that trees grow on a mountain -- called the treeline -- is based in part on temperature.DB: Andy Bunn is a PhD candidate at Montana State University. He suspects that treelines around the world will expand up mountain slo……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Fire Regime 火Fire was a creation of life -- born from oxygen and organic matter -- ignited by lightning. Thus fire has been a fundamental feature of the Earth for at least 400 million years. A scientist talks about fire -- today on 英语四级听力.JB: This is 英语四级听力, speaking with fire expert Steve Pyne, in the Biology and Society program at Arizona State University in Tempe.Steve Pyne: Fire looks the way it does on Earth today because of what people have done and not……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Fire Cycle 火灾规律The El Nino phenomenon of 1997-98 unleashed torrential rain in some parts of the world, while creating abnormally dry conditions in others. And it sparked record numbers of wildfires. Learn more about climate and wildfire -- today on 英语四级听力.JB: This is 英语四级听力. We spoke with fire expert Steve Pyne of Arizona State University in Tempe -- about fire and climate, the long term pattern of weather.Steve Pyne: Climate is of course one of the fundament……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Global Warming and Ozone 全球变暖和臭氧Could the coming century bring a new threat to the ozone layer? Discover one scientists model of the effect of global warming and greenhouse gases on ozone -- on todays 英语四级听力. DB: This is 英语四级听力.JB: After 30 years of steady decline, Earths ozone layer is thinner but seems to be stable. A ban on ozone-depleting CFCs is largely responsible. Computer modeling gives reason to hope for an almost ful……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Sunscreened Plants 遮光植物A NASA researcher is finding that alfalfa plants grow more poorly when exposed to UVB -- ultraviolet B radiation from the sun. Learn more about sunscreened plants -- today on 英语四级听力.JB: This is 英语四级听力. Earths ozone layer protects us from the suns ultraviolet -- or UV, radiation. Ozone depletion has been blamed for an increase in skin cancers in human beings. DB: And this radiation seems to have a negative effect on plants as well. Jay S……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Moon and Jupiter 月球和木星After traveling behind the sun for several months, the planet Jupiter is now visible again, just before sunup. Learn how to see Jupiter near the waning moon on Wednesday morning -- on todays 英语四级听力. JB: This is 英语四级听力. The highest point that trees grow on a mountain -- called the treeline -- is based in part on temperature.DB: Andy Bunn is a PhD candidate at Montana State University. He suspects that treelines around the world will expan……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Climate Puzzles 气候之迷Scientists who predict Earths future climate wish they knew how climate has changed in the past few thousand years. Learn more about modeling global climate -- today on 英语四级听力.JB: This is 英语四级听力. Most scientists agree that humans are having an impact on Earths climate. But theyre also still discovering natural ways that global climate changes. DB: For example, the sun doesnt give us exactly the same amount of heat each year -- and the suns……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Titicaca Reedbeds 的的喀喀湖的芦苇地An ancient lake high in the mountains of South America holds lessons about indigenous peoples and sustainability. Discover Lake Titicaca -- today on 英语四级听力. DB: This is 英语四级听力. Lake Titicaca is high in the Andes Mountains of South America. At three million years of age, its among the worlds most ancient lakes. JB: The lake has an abundance of reedbeds that cover an area 2 1/2 times the s……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Galactic Rotation 银河系自转Astronomers calculate there is ten times more matter in our Milky Way galaxy than we can actually see. Discover how the orbital motions of stars in the galaxy reveal dark matter -- on todays 英语四级听力.JB: Im Joel Block.DB: And Im Deborah Byrd for 英语四级听力. A listener writes, I was wondering if the sun (and its solar system) revolve around the center of the Milky Way? In other words, does the Milky Way rotate? JB: Our sun and solar system orb……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Plant Signals 植物的语言Can plants smell and taste in the same way that animals do? Can they talk to each other and to insects? Learn how scientists hope to unravel some of the mysteries of plant senses -- on todays 英语四级听力.JB: This is 英语四级听力. If an insect is damaging a plant, the plant may send out an airborne signal -- like an odor -- attracting just the right predators -- perhaps flies or wasps to attack the offending insect. DB: Penn State entomologist Jack Sch……
·[ 新窗口浏览 MediaPlayer 文件 或是右键“目标另存为”下载]Moon and Venus月球和金星The planet Venus is now low in the west after sunset. Its not up for long after the sun goes down, but its very, very bright. Learn how to see Venus tonight near Earths companion moon -- today on 英语四级听力.JB: This is 英语四级听力. Earths ozone layer protects us from the suns ultraviolet -- or UV, radiation. Ozone depletion has been blamed for an increase in skin cancers in human beings. DB: And this radiation seems to have a negative effect on plan……
返回首页 
您现在的位置： 
