首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   152篇
  免费   3篇
测绘学   1篇
大气科学   7篇
地球物理   17篇
地质学   38篇
海洋学   21篇
天文学   59篇
综合类   1篇
自然地理   11篇
  2023年   2篇
  2021年   2篇
  2020年   1篇
  2018年   3篇
  2017年   1篇
  2016年   5篇
  2015年   6篇
  2014年   3篇
  2013年   13篇
  2012年   6篇
  2011年   4篇
  2010年   4篇
  2009年   15篇
  2008年   8篇
  2007年   10篇
  2006年   8篇
  2005年   6篇
  2004年   8篇
  2003年   4篇
  2002年   8篇
  2001年   3篇
  2000年   5篇
  1999年   3篇
  1998年   2篇
  1997年   2篇
  1996年   2篇
  1995年   1篇
  1994年   3篇
  1993年   1篇
  1992年   3篇
  1991年   1篇
  1989年   5篇
  1988年   1篇
  1987年   1篇
  1984年   2篇
  1981年   1篇
  1974年   1篇
  1966年   1篇
排序方式: 共有155条查询结果,搜索用时 15 毫秒
51.
52.
Gallagher  Peter T.  Moon  Y.-J.  Wang  Haimin 《Solar physics》2002,209(1):171-183
This paper discusses a near real-time approach to solar active-region monitoring and flare prediction using the Big Bear Solar Observatory Active Region Monitor (ARM). Every hour, ARM reads, calibrates, and analyses a variety of data including: full-disk Hα images from the Global Hα Network; EUV, continuum, and magnetogram data from the Solar and Heliospheric Observatory (SOHO); and full-disk magnetograms from the Global Oscillation Network Group (GONG). For the first time, magnetic gradient maps derived from GONG longitudinal magnetograms are now available on-line and are found to be a useful diagnostic of flare activity. ARM also includes a variety of active-region properties from the National Oceanic and Atmospheric Administration's Space Environment Center, such as up-to-date active-region positions, GOES 5-min X-ray data, and flare-to-region identifications. Furthermore, we have developed a Flare Prediction System which estimates the probability for each region to produce C-, M-, or X-class flares based on nearly eight years of NOAA data from cycle 22. This, in addition to BBSO's daily solar activity reports, has proven a useful resource for activity forecasting. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1020950221179  相似文献   
53.
In continental areas it is often difficult to determine the cause of intraplate magmatism. Large volumes of magma, high eruption rates, and the presence of a hotspot trace on the adjacent ocean floor, are all evidence for the presence of an anomalously hot mantle. However, in many continental magmas there are chemical variations with time which are inferred to reflect changes from asthenospheric to predominantly lithospheric source regions, or vice versa. It is argued that these chemical characteristics constrain whether magmatism was triggered by the emplacement of a mantle plume, or by lithospheric extension.  相似文献   
54.
55.
56.
57.
2020 is the year of wildfire records. California experienced its three largest fires early in its fire season. The Pantanal, the largest wetland on the planet, burned over 20% of its surface. More than 18 million hectares of forest and bushland burned during the 2019–2020 fire season in Australia, killing 33 people, destroying nearly 2500 homes, and endangering many endemic species. The direct cost of damages is being counted in dozens of billion dollars, but the indirect costs on water-related ecosystem services and benefits could be equally expensive, with impacts lasting for decades. In Australia, the extreme precipitation (“200 mm day −1 in several location”) that interrupted the catastrophic wildfire season triggered a series of watershed effects from headwaters to areas downstream. The increased runoff and erosion from burned areas disrupted water supplies in several locations. These post-fire watershed hazards via source water contamination, flash floods, and mudslides can represent substantial, systemic long-term risks to drinking water production, aquatic life, and socio-economic activity. Scenarios similar to the recent event in Australia are now predicted to unfold in the Western USA. This is a new reality that societies will have to live with as uncharted fire activity, water crises, and widespread human footprint collide all-around of the world. Therefore, we advocate for a more proactive approach to wildfire-watershed risk governance in an effort to advance and protect water security. We also argue that there is no easy solution to reducing this risk and that investments in both green (i.e., natural) and grey (i.e., built) infrastructure will be necessary. Further, we propose strategies to combine modern data analytics with existing tools for use by water and land managers worldwide to leverage several decades worth of data and knowledge on post-fire hydrology.  相似文献   
58.
Self-organised patterns of stone stripes, polygons, circles and clastic solifluction lobes form by the sorting of clasts from fine-grained sediments in freeze-thaw cycles. We present new High Resolution Imaging Science Experiment (HiRISE) images of Mars which demonstrate that the slopes of high-latitude craters, including Heimdal crater - just 25 km east of the Phoenix Landing Site - are patterned by all of these landforms. The order of magnitude improvement in imaging data resolution afforded by HiRISE over previous datasets allows not only the reliable identification of these periglacial landforms but also shows that high-latitude fluviatile gullies both pre- and post-date periglacial patterned ground in several high-latitude settings on Mars. Because thaw is inherent to the sorting processes that create these periglacial landforms, and from the association of this landform assemblage with fluviatile gullies, we infer the action of liquid water in a fluvio-periglacial context. We conclude that these observations are evidence of the protracted, widespread action of thaw liquids on and within the martian regolith. Moreover, the size frequency statistics of superposed impact craters demonstrate that this freeze-thaw environment is, at least in Heimdal crater, less than a few million years old. Although the current martian climate does not favour prolonged thaw of water ice, observations of possible liquid droplets on the strut of the Phoenix Lander may imply significant freezing point depression of liquids sourced in the regolith, probably driven by the presence of perchlorates in the soil. Because perchlorates have eutectic temperatures below 240 K and can remain liquid at temperatures far below the freezing point of water we speculate that freeze-thaw involving perchlorate brines provides an alternative “low-temperature” hypothesis to the freeze-thaw of more pure water ice and might drive significant geomorphological work in some areas of Mars. Considering the proximity of Heimdal crater to the Phoenix Landing Site, the presence of such hydrated minerals might therefore explain the landforms described here. If this is the case then the geographical distribution of martian freeze-thaw landforms might reflect relatively high temperatures (but still below 273 K) and the locally elevated concentration of salts in the regolith.  相似文献   
59.
60.
New mapping at Anglesea coal mine, and coal resource and deep groundwater drilling have provided new perspectives on the economically important Eastern View Group coal bearing sedimentary succession in the onshore Torquay Basin. In the Anglesea Syncline, the upper 35 m thick brown coal seam of the Eastern View Group is overlain by a low angle unconformity. Units overlying the coal seams include high energy, cross cutting sand channels of the Boonah Formation and lower energy channel and interchannel systems of the overlying Salt Creek and Anglesea Formations. The mine section can be correlated from borehole data with the Eastern View Group and Demons Bluff Group exposed in coastal cliff sections along the adjacent Anglesea to Torquay coast. Recently drilled coal and groundwater exploration bores provide new data on the extent of the coal measures in the Anglesea area, and details of the underlying Tertiary succession that include typical Otway Basin units such as the Pember Mudstone and Pebble Point Formations. The stratigraphy below the coal measures suggests that the Otway Ranges were not present during Palaeogene times. The rank of the brown coals on and around the Otway Ranges is higher than any other Tertiary coals in onshore Victoria, and they preserve similar patterns of rank distribution to the high rank black coals in the underlying Lower Cretaceous Otway Group. Evidence for large overburden thicknesses is lacking, and the high ranks may have been augmented by higher than normal geothermal gradients in the Early Tertiary. Comparisons between the observed depositional cycles, sequence stratigraphic cycles, and worldwide coastal onlap curves suggest that the observed disconformity boundaries are sequence boundaries that provide a chronostratigraphic framework. Sequences present may include TB4.1–4.5 in the overburden units, and TB 2.4–3.6 in the coal bearing interval.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号