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101.
Late Holocene upper bounds of flood magnitudes and twentieth century large floods in the ungauged, hyperarid alluvial Nahal Arava, Israel 总被引:1,自引:0,他引:1
Yael Jacoby Tamir Grodek Yehouda Enzel Naomi Porat Eric V. McDonald Ofer Dahan 《Geomorphology》2008,95(3-4):274-294
The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine long-term upper bounds to flood stages and magnitudes. Along most of its course Nahal Paran, a major tributary that impacts the morphology, floods and sediments of Nahal Arava at the study reach, is a coarse-gravel, braided ephemeral stream. Downstream of the Arava–Paran confluence, aeolian and fluvial sand delivered from eastern Arava valley alters the channel morphology. The sand has accreted up to 2.5 m above the distinct current channels, facilitating the recording of large floods. This sand enhances the establishment of denser riparian vegetation (mainly Tamarix nilotica and Haloxylon persicum) that interacts with floods and affects stream morphology. A temporal association was found between specific floods recorded upstream and tree-ring ages of re-growth of flood-damaged tamarix trees (‘Sigafoos trees’) in the past 30 years. This association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region. The minimum magnitude of the largest flood that covered the entire channel width, estimated from flood deposits, is approximately 1700–1800 m3s− 1. This is a larger magnitude than the largest gauged flood of 1150 m3s− 1 that occurred in 1970 about 30 km upstream in Nahal Paran. Our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods. Based on Holocene alluvial stratigraphy and OSL dating in the study reach we also conclude that flood stages did not reach the late Holocene ( 2.2 ka) surface and therefore we estimate a non-exceedance upper bound of 2000 m3s− 1 flood magnitudes for Nahal Arava during that interval. This study indicates that in unfavorable areas the combination of hydrology, fluvial morphology and botanic evidence can increase our understanding of ungauged basins and give information crucial for hydrology planning. 相似文献
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105.
王志强 《地质灾害与环境保护》2017,28(1)
随着社会经济的快速发展,地质勘查工作逐渐完善,其中水工环地质勘查是较为基础的工作,其重要性日益显著,但水工环地质勘查在发展过程中受诸多因素的制约,其技术不能满足地质勘查的需求,也不能满足经济发展的需要。在此基础上,本文将分析水工环地质勘查技术的概况,并阐述水工环地质勘查技术的实际应用,旨在提高水工环地质勘查技术应用的能力,促进水工环地质勘查工作的有序开展。 相似文献
106.
汶川大地震触发了多处高速远程滑坡,导致了大量的人员伤亡及财产损失。其中,东河口滑坡是这次地震触发的最为典型的高速远程滑坡之一,同时也是目前备受关注、争论颇多的滑坡之一。野外调研结果表明,该滑坡的成因和动力特征主要包括震裂溃屈、水平抛射、碎屑流化和振动液化等4个方面。为了对该滑坡滑动过程中的振动液化这一动力特征进行模拟再现,在东河口滑坡体上采集了具有代表性的滑带土作为试验样品,并以该地震时的实测地震波作为动力输入,利用目前国际上最先进的DPRI环剪试验机,对滑坡滑动过程中的振动液化现象进行了一系列环剪试验研究。结果表明,地震作用过程中,发生在滑坡潜在滑面上的振动液化现象是导致高速远程滑坡产生的一个重要因素;伴随着振动液化过程,滑体的剪切强度迅速降低并产生逐渐增大的剪切位移,为高速远程滑坡的形成提供了条件 相似文献
107.
Tree ring dating plays an important role in obtaining past climate information.The fundamental study of obtaining tree ring samples in typical climate regions is particularly essential.The optimum distribution of tree ring sampling sites based on climate information from the Climate Observation Network(ORPOM model) is presented in this article.In this setup,the tree rings in a typical region are used for surface representation,by applying excellent correlation with the climate information as the main principle.Taking the Horqin Sandy Land in the cold and arid region of China as an example,the optimum distribution range of the tree ring sampling sites was obtained through the application of the ORPOM model,which is considered a reasonably practical scheme. 相似文献
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Adam R. Hoffman David E. Armstrong Richard C. Lathrop Michael R. Penn 《Aquatic Geochemistry》2009,15(3):371-389
We investigated the accumulation and influence of bioavailable P (BAP) in sediments of a stream located in an agricultural
area of the Lake Mendota watershed in Wisconsin, USA. During hydrologic events, the stream carried high concentrations of
suspended sediment (up to 250 mg/l) and BAP (up to 2.5 mg/l). Bed sediments were highly enriched in BAP, as inventories of
BAP in the top 10 cm of sediment ranged from 143 to 14,500 μg P/cm2. Space variations in BAP inventories were related to site-specific hydrodynamics and geochemical factors, including iron
(Fe; r
2 = 0.71) and aluminum (Al; r
2 = 0.54) concentrations. Most sites behaved as potential sinks for dissolved reactive phosphate during hydrologic events and
potential sources during base-flow periods. Through the combination of site-specific factors and geochemical controls, Dorn
Creek modifies the amount, timing, and composition of P delivered from the watershed to downstream sites and water bodies. 相似文献
110.
大兴安岭岩石圈地幔特征——哈拉哈河-绰尔河橄榄岩捕虏体的证据 总被引:6,自引:4,他引:2
大兴安岭哈拉哈河-绰尔河第四纪火山岩中含有尖晶石相和石榴石相橄榄岩捕虏体.本文报道的尖晶石相橄榄岩包括方辉橄榄岩和二辉橄榄岩两类,前者分布数量略高于后者.方辉橄榄岩多数具有较高的平衡温度(1072~1193℃),矿物化学成分变化大,含有高Mg橄榄石和高Cr#尖晶石,这些特征一致表明是古老岩石圈地幔残余的样品.而二辉橄榄岩显示相对均一的矿物化学成分和很宽的平衡温度变化范围(636~1178℃),代表了明显受到改造的岩石圈地幔,可能反映岩石圈地幔的不同深度和局部经历了软流圈与岩石圈相互作用.通过与华北克拉通的对比,发现地处兴蒙造山带的大兴安岭岩石圈地幔中仍保留有相当量的古老岩石圈地幔残余,区别于遭受强烈改造和破坏的华北克拉通东部地区的岩石圈地幔. 相似文献