全文获取类型
收费全文 | 321篇 |
免费 | 52篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 22篇 |
地球物理 | 66篇 |
地质学 | 152篇 |
海洋学 | 54篇 |
天文学 | 2篇 |
综合类 | 13篇 |
自然地理 | 71篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 20篇 |
2015年 | 17篇 |
2014年 | 23篇 |
2013年 | 30篇 |
2012年 | 22篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 20篇 |
2008年 | 16篇 |
2007年 | 15篇 |
2006年 | 22篇 |
2005年 | 9篇 |
2004年 | 16篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有396条查询结果,搜索用时 15 毫秒
51.
Schmidt‐hammer exposure‐age dating (SHD) of snow‐avalanche impact ramparts in southern Norway: approaches,results and implications for landform age,dynamics and development 下载免费PDF全文
Schmidt‐hammer exposure‐age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river‐bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high‐precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHDmean) and the maximum age (SHDmax) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R‐value distributions. SHDmean ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHDmax ages (expected to be exceeded by <5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHDmean ages indicate differences in recent levels of snow‐avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHDmax ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
52.
利用原地生宇生核素测定暴露年代时,通常会假设地貌体侵蚀速率为0。研究表明,该假设会低估地貌体的真实暴露年代。搜集2009~2012年全球不同区域56个岩石样品的宇生核素10Be测年数据,探讨侵蚀速率为0对于侵蚀速率为0.5、1以及2 mm/ka的样品,在不同暴露尺度上对暴露年代计算的影响幅度。结果表明,对于1×104a尺度的样品暴露年代可能低估约0.5%,1%,2%;对于10×104a尺度的样品可能低估约5%,7%,20%;对于50×104a尺度的样品可能低估约40%,70%甚至100%以上。 相似文献
53.
极端事件对人类系统的影响 总被引:1,自引:0,他引:1
在IPCC特别报告《管理极端事件和灾害风险,推进气候变化适应》中,极端天气气候事件对人类系统的影响是最重要的影响评估内容之一,其评估结果为:极端影响可能缘于极端天气气候事件,但也可能并非极端事件的后果。暴露度和脆弱性是灾害风险的重要决定因素;极端和非极端天气气候事件的严重程度和影响在很大程度上取决于对这些事件的脆弱性和暴露度水平;人居模式、城市化和社会经济状况的变化已经影响观测到的脆弱性和暴露度的变化趋势;无论在发达国家还是发展中国家,沿海人居环境均暴露于极端事件,并受其影响,如小岛屿国家和亚洲大三角洲地区;脆弱人口还包括难民、国内流离失所的人和那些生活在边远地区的人;极端事件将极大地影响与气候联系密切的部门,如水、农业、食物安全、健康和旅游业。 相似文献
54.
Effects of soil compaction,rain exposure and their interaction on soil carbon dioxide emission 总被引:2,自引:0,他引:2
Agata Novara Alona Armstrong Luciano Gristina Kirk T. Semple John N. Quinton 《地球表面变化过程与地形》2012,37(9):994-999
Soils release more carbon, primarily as carbon dioxide (CO2), per annum than current global anthropogenic emissions. Soils emit CO2 through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO2 emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO2 emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO2 release. We conducted a factorial laboratory experiment with three soil types after sieving (clay, silt and sand soil), three different bulk densities (1·1 g cm–3, 1·3 g cm–3, 1·5 g cm–3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO2 release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO2 is positive: CO2 emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO2 emission: soil compacted to a bulk density of 1·1 g cm–3 emitted 32% more CO2 than soil compacted to 1·5 g cm–3. Furthermore we found that the magnitude of CO2 effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO2 emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
55.
?о???????????????????????RFID????POS??????????????????????????????RFID?????????????????????????д洢??Ψ???????е??????????????????????????λ????????????????????????????????????????????,?????????????????????????Щ?????????????????????????????????????????????? 相似文献
56.
??????????????????????????????????????????????????????????????????????????????????????С????????????????????????????????????????????????????????????????,??????????????????????????????????????????????壬??????????????????????????????????Ч???б???????ж?????????????????????????????????????δ?????????????????ó??????????????????????GRACE?????????????????????????????????????Ч?????????????????? 相似文献
57.
The endolithic lichen Lecidea auriculata is known to enhance rock surface weathering on the Little Ice Age moraines of the glacier Storbreen in Jotunheimen, central southern Norway. This study demonstrates the reduction in Schmidt hammer Rvalues that followed the rapid colonization by this lichen of pyroxene‐granulite boulders on terrain deglaciated over the last 88 years. In the absence of this lichen, the characteristic mean R‐value of boulder surfaces is 61.0 ± 0.3; where this lichen is present, R‐values are lower by at least 20 units on surfaces exposed for 30–40 years. A similar reduction in rock hardness on rock surfaces without a lichen cover requires about 10 ka. The rapid initial weakening of the rock surfaces is indicative of rates of biological weathering by endolithic lichens that may be two orders of magnitude (200–300 times) faster than rates of physico‐chemical weathering alone. If not avoided, the effects of this type of lichen are likely to negate the effectiveness of the Schmidt hammer and other methods for exposure‐age dating, including cosmogenic‐nuclide dating, in severe alpine and polar periglacial environments. The results also suggest a new method for dating rock surfaces exposed for <50 years. 相似文献
58.
59.
横断山区垂直带谱的分布模式与坡向效应 总被引:5,自引:1,他引:4
根据收集到的横断山区山地垂直带谱数据,对山地垂直带的坡向效应和空间分布规律进行了分析和研究.结果表明:1)主要的垂直带和垂直带界线如林线、暗针叶林带、雪线等的纬度和经度地带性分布规律明显并且分布模式都相似,纬向上呈开口向下的二次曲线分布模式,经向上呈开口向上的二次曲线分布模式,两者共同形成"双曲抛物面"分布模式,充分反映了横断山区的环境与生态的复杂性和独特性,也进一步丰富和发展了山地垂直带谱的二次曲线假说; 2)横断山区山地垂直带谱表现出明显的基于水分驱动的坡向效应,主要表现为同一山体的东、西坡往往具有不同的基带和带谱结构,相同类型的带谱出现的海拔和分布范围不同,迎风坡表现出较为湿润的类型和带谱结构,而背风坡则表现出更为干旱的类型和组成结构;横断山区的坡向效应主要是由于山体对当地盛行季风的影响,造成迎风坡和背风坡水热条件相差很大,从而发育不同的山地垂直带谱类型.从横断山区山地垂直带谱的空间分布规律来看, 28°~29°N、98°~101°E范围内,即大致在澜沧江以东-雅砻江以西,山地垂直带谱普遍表现出干热的特点,为横断山区干热气候的核心地带.但如何定量分析山地的坡向效应尚有待于进一步的研究和讨论.此外、数据质量和数据误差也对分析的结果,尤其是空间分布模式的数学模拟结果产生一定的影响,在以后的研究中尚需进一步完善. 相似文献
60.
针对单层异形柱框架,通过高温数值分析,考察了支撑设置和受火位置对结构高温变形及内力的影响。研究结果表明:对于单层多跨异形柱框架,当只有一端有支撑跨时,会在一定程度上增大另一端的边节点水平位移和边柱侧向变形,对结构整体抗火不利;当左、右两端均有支撑跨时,非支撑跨在火灾作用下的梁轴力比很大,升温后期可能因梁跨中竖向位移急剧增大而发生破坏。基于上述研究结果,给出了4类单层带支撑异形柱框架火灾行为的初步判定方法。 相似文献