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排序方式: 共有337条查询结果,搜索用时 46 毫秒
331.
Nick Middleton 《Natural Hazards》2018,92(1):57-70
This paper examines the theory and supporting evidence for links between desertification, drought and dust storms with a particular focus on studies undertaken in and around the Gobi Desert. Overgrazing of rangeland by pastoralists has been the most commonly cited cause of desertification in global drylands for more than 30 years, but the evidence supporting this link is not always convincing. Nonetheless, overgrazing, desertification and dust storms are frequently connected, regardless. Drought is another well-known and important driver of vegetation cover change. Distinguishing between vegetation cover adversely affected by drought and that reduced by grazing is imperative for policy makers because identifying the incorrect driver of vegetation change risks the development of inappropriate policy. 相似文献
332.
Rachel M.L. Wignall John E. Gordon Vanessa Brazier Colin C.J. MacFadyen Nick S. Everett 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):120-134
Climate change is a significant concern for nature conservation in the 21?st century. One of the goals of the 2014 Scottish Climate Change Adaptation Programme is to identify the consequences of climate change for protected areas and to put in place adaptation or mitigation measures. As a contribution to the process, this paper develops a methodology to identify the relative level of risk to nationally and internationally important geological and geomorphological sites in Scotland from the impacts of climate change. The methodology is based on existing understanding of the likely responses of different types of geosite to specific aspects of climate change, such as changes in rainfall, rising sea levels or increased storminess, and is applied to assess the likelihood of damaging impacts on groups of similar geoheritage features in sites with similar characteristics. The results indicate that 80 (8.8%) of the ~900 nationally and internationally important geoheritage sites in Scotland are at ‘high’ risk from climate change. These include active soft-sediment coastal and fluvial features, finite Quaternary sediment exposures and landforms in coastal and river locations, active periglacial features, sites with palaeoenvironmental records, finite or restricted rock exposures and fossils. Using this risk-based assessment, development of indicative geoheritage climate-change actions have been prioritised for these sites. Depending on the characteristics of the sites, management options may range from ‘do nothing’ to rescue excavations and posterity recording. Monitoring is an essential part of the management process to trigger evidence-based interventions. 相似文献
333.
正The idea that plate tectonics may not have operated deep in Earth's Precambrian past has a long legacy.What predated plate tectonics is unknown,and advances in data-from geochemical,geological and tectonic,to paleomagnetic,as well as modelling ap- 相似文献
334.
335.
Nick Novakowski 《GeoJournal》2010,75(6):553-565
This research provides a comparative examination of Ottawa as an archetype of a knowledge city. Among Canada’s four largest
cities, Ottawa is unique in terms of the characteristics of its labor force, the nature of its employment mix, and its infrastructure.
Since the high-tech downturn of 2001, some of Ottawa’s options as a knowledge city seem to be contracting, despite some simultaneously
encouraging signs (like recovering employment levels in the high-tech sector). This raises a question about Ottawa’s potential
longevity as a knowledge center. The challenge is to understand the inventory of obstacles faced by the city, and address
the sort of alchemy required to maintain and improve its competitiveness as a knowledge city. 相似文献
336.
John C. BRIDGES Mark J. BURCHELL Hitesh C. CHANGELA Nick J. FOSTER J. Alan CREIGHTON James D. CARPENTER Steve J. GURMAN Ian A. FRANCHI Henner BUSEMANN 《Meteoritics & planetary science》2010,45(1):55-72
Abstract– We have used synchrotron Fe‐XANES, XRS, microRaman, and SEM‐TEM analyses of Stardust track 41 slice and track 121 terminal area slices to identify Fe oxide (magnetite‐hematite and amorphous oxide), Fe‐Ti oxide, and V‐rich chromite (Fe‐Cr‐V‐Ti‐Mn oxide) grains ranging in size from 200 nm to ~10 μm. They co‐exist with relict FeNi metal. Both Fe‐XANES and microRaman analyses suggest that the FeNi metal and magnetite (Fe2O3FeO) also contain some hematite (Fe2O3). The FeNi has been partially oxidized (probably during capture), but on the basis of our experimental work with a light‐gas gun and microRaman analyses, we believe that some of the magnetite‐hematite mixtures may have originated on Wild 2. The terminal samples from track 121 also contain traces of sulfide and Mg‐rich silicate minerals. Our results show an unequilibrated mixture of reduced and oxidized Fe‐bearing minerals in the Wild 2 samples in an analogous way to mineral assemblages seen in carbonaceous chondrites and interplanetary dust particles. The samples contain some evidence for terrestrial contamination, for example, occasional Zn‐bearing grains and amorphous Fe oxide in track 121 for which evidence of a cometary origin is lacking. 相似文献
337.
新疆伊犁吐拉苏地区的线性构造及控矿特征 总被引:4,自引:0,他引:4
采用多种数值图像进行线性构造解译,其中DEM和NOAA主要用于区域尺度,TM用于勘探区尺度,地面磁法数据用于靶区范围的解译分析。研究认为该区线性构造与金矿床的空间分布关系密切,表现为:(1)区域尺度的一级控矿构造为NEE、NE和NW向构造的交汇部位;吐拉苏地区的一级控矿构造为WNW和NNW及NE方向构造的交汇部位;(2)吐拉苏地区的次级控矿构造为NNE和环形构造的交汇部位;(3)靶区的一级控矿构造为NE、SN和环形构造。线性构造异常分析结果显示,当线性构造的优益度大于40时,有较大的成矿可能性。 相似文献