全文获取类型
收费全文 | 1151篇 |
免费 | 56篇 |
国内免费 | 281篇 |
专业分类
测绘学 | 51篇 |
大气科学 | 118篇 |
地球物理 | 555篇 |
地质学 | 426篇 |
海洋学 | 160篇 |
天文学 | 80篇 |
综合类 | 26篇 |
自然地理 | 72篇 |
出版年
2023年 | 16篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 13篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 26篇 |
2012年 | 40篇 |
2011年 | 88篇 |
2010年 | 23篇 |
2009年 | 28篇 |
2008年 | 73篇 |
2007年 | 61篇 |
2006年 | 56篇 |
2005年 | 71篇 |
2004年 | 71篇 |
2003年 | 55篇 |
2002年 | 45篇 |
2001年 | 35篇 |
2000年 | 65篇 |
1999年 | 34篇 |
1998年 | 34篇 |
1997年 | 41篇 |
1996年 | 29篇 |
1995年 | 34篇 |
1994年 | 27篇 |
1993年 | 48篇 |
1992年 | 30篇 |
1991年 | 41篇 |
1990年 | 34篇 |
1989年 | 28篇 |
1988年 | 23篇 |
1987年 | 35篇 |
1986年 | 16篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1979年 | 4篇 |
1959年 | 4篇 |
1937年 | 5篇 |
1935年 | 5篇 |
1934年 | 4篇 |
1923年 | 4篇 |
排序方式: 共有1488条查询结果,搜索用时 0 毫秒
771.
772.
特大地震的同震及震后滑动能引起地壳介质的时间变化,这是因为强地面震动破坏了近地表的沉积层,或者应力扰动改变了裂隙密度和/或深部流体的移动。这种随时间变化的地壳属性可引起地震波速度出现部分变化,并可根据互相关波形和测量重复地震序列内它们的时间滞后探测到。本文根据2004年苏门答腊—安达曼特大地震和2005年尼亚斯—锡默卢特大地震的重复余震序列,分析了高频(0.5~2.0Hz)P尾波和S尾波以及长周期(0.03~0.1Hz)面波的滞后时间。观测到的滞后时间揭示出几个主要特征:(1)2004年地震序列的S尾波滞后时间系列!(t)基本上在0值附近波动,有时随消逝时间而变为负值,而2005年地震序列的S尾波的!(t)则表现为随消逝时间而单调增长;(2)S尾波的平均速度降低(-δV S)是P尾波平均速度降低(-δV P)的2倍,瑞利波的平均速度降低(-δV LR)比勒夫波的平均速度降低(-δV LQ)大3~4倍;(3)δV S和δV LR显示了速度随时间的恢复,特别是2005年地震的序列。2005年地震序列δV S速度随时间恢复的形状与附近大地测量台站得到的位移时间系列类似。尽管我们讨论了可能的人为结果,如震源间距、噪声场的时间变化和仪器响应,但观测结果均表明地壳内的非均匀波速时间降低是由2004年和2005年的特大地震的同震和/或震后滑动引起的。 相似文献
773.
Böttcher H Freibauer A Scholz Y Gitz V Ciais P Mund M Wutzler T Schulze ED 《Carbon balance and management》2012,7(1):5-18
Background
No consensus has been reached how to measure the effectiveness of climate change mitigation in the land-use sector and how to prioritize land use accordingly. We used the long-term cumulative and average sectorial C stocks in biomass, soil and products, C stock changes, the substitution of fossil energy and of energy-intensive products, and net present value (NPV) as evaluation criteria for the effectiveness of a hectare of productive land to mitigate climate change and produce economic returns. We evaluated land management options using real-life data of Thuringia, a region representative for central-western European conditions, and input from life cycle assessment, with a carbon-tracking model. We focused on solid biomass use for energy production.Results
In forestry, the traditional timber production was most economically viable and most climate-friendly due to an assumed recycling rate of 80% of wood products for bioenergy. Intensification towards "pure bioenergy production" would reduce the average sectorial C stocks and the C substitution and would turn NPV negative. In the forest conservation (non-use) option, the sectorial C stocks increased by 52% against timber production, which was not compensated by foregone wood products and C substitution. Among the cropland options wheat for food with straw use for energy, whole cereals for energy, and short rotation coppice for bioenergy the latter was most climate-friendly. However, specific subsidies or incentives for perennials would be needed to favour this option.Conclusions
When using the harvested products as materials prior to energy use there is no climate argument to support intensification by switching from sawn-wood timber production towards energy-wood in forestry systems. A legal framework would be needed to ensure that harvested products are first used for raw materials prior to energy use. Only an effective recycling of biomaterials frees land for long-term sustained C sequestration by conservation. Reuse cascades avoid additional emissions from shifting production or intensification. 相似文献774.
This paper investigates the extent to which entrenched interests of stakeholder groups both maintain water use practice, and may be confronted. The focus is on the agricultural sectors of Yemen and Jordan, where water resource policymakers face resistance in their attempts to reduce water use to environmentally sustainable levels through implementation of water demand management (WDM) activities. Some farmers in both countries that have invested in irrigated production of high-value crops (such as qat and bananas) benefit from a political economy that encourages increased rather than reduced water consumption. The resultant over-exploitation of water resources affects groups in unequal measures. Stakeholder analysis demonstrates that the more ‘powerful’ groups (chiefly the large landowners and the political elites, as well as the ministries of irrigation over which they exert influence) are generally opposed to reform in water use, while the proponents of WDM (e.g. water resource managers, environmental ministries and NGOs, and the international donor community) are found to have minimal influence over water use policy and decisionmaking. Efforts and ideas attempted by this latter group to challenge the status quo are classified here as either (a) influencing or (b) challenging the power asymmetry, and the merits and limits of both approaches are discussed. The interpretation of evidence suggests current practice is likely to endure, but may be more effectively challenged if a long-term approach is taken with an awareness of opportunities generated by windows of opportunity and the participation of ‘overlap groups’. 相似文献
775.
YOUNG R. Jeremy BOWN R. Paul WADE S. Bridget PEDDER E. Brian HUBER T. Brian LAZARUS B. David 《《地质学报》英文版》2019,93(Z1):70-72
正Planktonic microfossils have played an enormously important role in modem earth science,notably including industrial hydrocarbon exploration and academic Deep Sea Drilling,providing essential data for age models and rich suites of palaeoceanographic data.Conversely this broad application has resulted in the development of detailed knowledge of planktonic microfossils and in stimulating study of them.Over 50 years of 相似文献
776.
A dynamic response analysis of tension leg platform (TLP) to deterministic first order wave forces is presented, considering coupling between various degrees of freedom surge, sway, heave, pitch, roll and yaw. The analysis duly considers nonlinearities produced due to changes in cable-tension and due to nonlinear hydro-dynamic drag forces. The wave forces on the elements of the pontoon structure are calculated using Airy's wave theory and Morison's equation. The nonlinear equation of motion is solved in the time domain by Newmark's β-method. With the help of proposed analysis, some example problems are solved in order to investigate the effects of different important factors that influence the response of TLP. 相似文献
777.
779.
景观是由一组相互作用的植物群丛或生态系统组成、并以相似的形式重复出现的,具有数平方公里范围的区域;所以,景观生态学就是研究景观的结构、功能和动态。景观结构组分或称景观要素,是指几个原生的镶块体(Patch)、四种类型的廊道(Corridor)和一个模地(Matrix)。本文引用实例说明大镶块体在景观中的重要意义。 相似文献
780.
至少在中世纪,阿拉伯航海家们就已观察到了南亚与东非之间热带海面上风向季节转换的情况。这些季节性风,就是南亚季风。季风这一名词人们相信是源自阿拉伯名词“maurim”或马来文“maurin”一词(两者都意为“季节性”)。许多世纪以后,英国人哈莱于1907年对这些季节性风(南亚季风)提出了一个直到现在仍在沿用的解释。 相似文献