全文获取类型
收费全文 | 77篇 |
免费 | 13篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 49篇 |
地球物理 | 14篇 |
地质学 | 52篇 |
海洋学 | 13篇 |
天文学 | 2篇 |
综合类 | 1篇 |
自然地理 | 6篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 5篇 |
2007年 | 10篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1985年 | 1篇 |
排序方式: 共有142条查询结果,搜索用时 15 毫秒
61.
K-均值聚类法用于西北太平洋热带气旋路径分类 总被引:7,自引:0,他引:7
热带气旋(Tropical Cyclone,简称TC)路径分类是获得TC特征和影响评估的重要途径。采用联合台风警报中心(Joint Typhoon Warning Center,简称JTWC)近45年最佳台风路径资料,基于TC位置、强度、路径长度和方向等主要信息的特征参数,利用K-均值聚类法建立了西北太平洋TC路径的客观分类方法,并对分类得到的7个路径类型TC在生命史、能量、活动季节和登陆概率等方面进行了对比分析。结果表明各类TC的这些特征量具有明显的差异。从近20年的变化趋势看,西转向类(占总样本的21.3%)的频数为增加趋势,其生命史呈小幅增长趋势,和其余各类(或全部TC)的减小趋势或变化很小不一致。各类TC的年PDI(能量耗散指数)变化趋势主要取决于强度和频数的变化,多数类别的年PDI和强度的变化趋势一致,但西北行转向类和远海西-西北行类的年PDI变化趋势主要取决于频数的变化。 相似文献
62.
Three-dimensional simulation of track on poroelastic half-space vibrations due to a moving point load 总被引:1,自引:0,他引:1
An analytical approach is used to investigate dynamic responses of a track system and the poroelastic half-space soil medium subjected to a moving point load under three-dimensional condition. The whole system is divided into two separately formulated substructures, the track sub-system and the ground. The ballast supporting rails and sleepers is placed on the surface of the ground. The rail is modeled by introducing the Green function for an infinitely long Euler beam subjected to the action of the moving point load and the reaction of sleepers represented by a continuous mass. Using the double Fourier transform, the governing equations of motion are then solved analytically in the frequency–wave-number domain. The time domain responses are evaluated by the inverse Fourier transform computation for a certain load velocities. Computed results show that dynamic responses of the soil medium are considerably affected by the fluid phase as well as the load velocity. 相似文献
63.
本文从涡度和高度的垂直分布及卫星云图的分析揭示了副热带高层冷涡的结构和生消。高层冷涡存在时与之相距10个纬距的台风将受其牵引,并做穿越低层副热带高压的运动;这类登陆台风,中低层为副高控制,其影响范围仅限于台风中心附近较小的范围内。 相似文献
64.
记叙了中国陕西省商洛市邵涧村下白垩统东河群2个大型兽脚类恐龙足迹,并将其归于Megalosauripus isp.。
东河群的时代与热河生物群同期,邵涧Megalosauripus isp. 可能可与热河生物群的大型兽脚类恐龙之足部形态做简
单对比。此外,邵涧Megalosauripus isp.造迹者的体长约为7.4m,这意味着早白垩世的陕西中南部亦存在着大型的
兽脚类恐龙。邵涧Megalosauripus isp.的发现,不仅为中国早白垩世恐龙足迹增加了新的成员,而且为将来在该地
区下白垩统中发现大型兽脚类恐龙的骨骼化石提供了确凿的依据。 相似文献
65.
In this study, a newly developed method, termed moving empirical orthogonal function analysis (MEOF), is applied to the study of midlatitude baroclinic waves over the wintertime North Pacific from 1979 to 2009. It is shown that when the daily, high-pass filtered (2-10 days) meridional wind at 250 hPa is chosen as the variable of the MEOF analysis, typical features of baroclinic waves/storm tracks over the wintertime North Pacific can be well described by this method. It is found that the first two leading modes of the MEOF analysis, MEOF1 and MEOF2, assume quite different patterns. MEOF1 takes the form of a single wave train running in the east-west direction along 40°N, while MEOF2 is a double wave train pattern running in the east-west direction along 50°N and 30°N, respectively. The shift composites of various anomalous fields based on MEOF1 and MEOF2 assume typical baroclinic wave features. MEOF1 represents a primary storm track pulsing with an intrinsic time scale of two days. It shows significant "midwinter suppression" and apparent interannual variability. It is stronger after the mid-1990s than before the mid-1990s. MEOF2 represents a double-branch storm track, also with an intrinsic time scale of approximately two days, running along 50°N and 30°N, respectively. It shows no apparent seasonal variation, but its interannual and decadal variation is quite clear. It oscillates with larger amplitude and longer periods after the mid-1990s than before the mid-1990s, and is heavily modulated by El Niño-Southern Oscillation (ENSO). 相似文献
66.
67.
《Geodinamica Acta》2013,26(6):455-473
Apatite/zircon fission track (FT) records of the Argentera external crystalline massif (Western Alps) show three tectonic pulses, respectively at 22 Ma (zircons), 6 and 3.5 Ma (apatites). The first pulse is consistent with the basement exhumation and initiation of the major deformation recorded in the foreland of the belt from Middle to early Upper Miocene. The two others might be respectively local expressions of the syncollisional extension mainly controlled by a westward sedimentary cover detachment and a Plio-Quaternary uplift acceleration. Zircon ages of 50-80 Ma in a limited NW area and evidence of an uplift elsewhere show that in a large fraction of the massif, temperatures in post-Variscan times never reached 320°C. Finally, FT data show that the Argentera massif did not behave as a single block during its denudation. First, in the NW of the massif, a small fault-limited block was already separated since the Cretaceous and later on recorded the 6 Ma denudation event, the 22 Ma pulse being recorded only in the remaining part of the massif. Second, less than 3.5 Ma ago, the northeastern part of the massif overthrust the southwestern block along the Bersézio-Veillos fault zone. 相似文献
68.
喀斯特石漠化演变轨迹的典型案例研究——以贵州盘县为例 总被引:3,自引:0,他引:3
本文以1974年MSS、1999年TM、2007年TM影像为基本数据源,辅以实地踏勘,考虑一个完整的峰丛洼地等,扣除其平坝部分后作为评价单元,获得了贵州省盘县3个时期的石漠化数据并计算了石漠化和无石漠化土地的演变轨迹。相应于1974年、1999年、2007年3个时段,研究区土地退化演变轨迹可分为8种,并可进一步归纳为不变型、逆转减弱型、反复型和加重型4种演变过程类型,从1974年、1999年到2007年未发生过变化的不变型轨迹面积占较高的比例。研究区的喀斯特土地可分为石漠化土地、无石漠化土地、石漠化已恢复土地和潜在可恢复石漠化土地。 相似文献
69.
JUAN PEDRO RODRÍGUEZ‐LÓPEZ CARLOS L. LIESA JAN VAN DAM PALOMA LAFUENTE LUIS ARLEGUI LOPE EZQUERRO POPPE L. DE BOER 《Sedimentology》2012,59(5):1536-1567
An aeolian dune field migrating to the east encroached on the toes of alluvial fans in the Teruel Basin (eastern Spain) during a short interval in the Late Pliocene (ca 2·9 to 2·6 Ma), when Northern Hemisphere glaciation and strong glacial–interglacial cycles began. Preservation of the dune field was controlled by syn‐sedimentary activity of a normal fault. Ephemeral water discharge eroded aeolian sands and formed V‐shaped channels in which aeolian sandstone blocks accumulated. The incorporation of loose aeolian sand in wadi waters modified the sediment/water ratio, changing the physical properties of the flows as they penetrated the aeolian dune field. The erosion and cover of aeolian dune foresets by sheetflood deposits suggest that dune‐damming caused the intermittent ponding of water behind the dunes and its flashy release. The arid climate in the Late Pliocene western Mediterranean realm favoured the transport of windblown sediments from northern Africa and western Mediterranean land masses into the Mediterranean. The formation of the studied aeolian dune field (2·9 to 2·6 Ma) and possibly others (for example, the Atacama, Namib and Sahara deserts) correlates with a strong increase of the influence of obliquity, which can be attributed to the combination of a regional expression related to the reduced effect of precession due to a minimum in the long‐period (2·3 Ma) eccentricity cycle and a remote expression of the onset of the Northern Hemisphere glaciation. 相似文献
70.
Annealing behavior of alpha recoil tracks in phlogopite 总被引:1,自引:0,他引:1
Wanming Yuan Richard A. Ketcham Shaokai Gao Jinquan Dong Zenkuan Bao Jun Deng 《Chemical Geology》2009,266(3-4):343-349
In this study we present and interpret a new experimental data set documenting thermal annealing of alpha recoil tracks (ARTs) in phlogopite. Through improvements in experimental technique, difficulties in obtaining useable data from material with an uneven distribution of U and Th were overcome. The resulting annealing pattern was well organized on an Arrhenius plot, allowing construction of a simple, 3-parameter annealing model of parallel contours of constant annealing with a linear progression. Our data and model indicate that phlogopite ARTs anneal at very low temperatures on geological time scales. At the million-year time scale, full annealing requires a temperature of only 33 °C, and we infer closure temperatures from 26–37 °C for cooling rates of 10–100 °C/m.y. Phlogopite ART analysis is thus likely to be primarily useful in relatively young (<1 Ma) terrains featuring either recent volcanism or recent, fast exhumation. In such situations, however, it may provide unique information on the timing of the final stages of unroofing. Comparison of our results with previous studies on ART and fission-track annealing in phlogopite and biotite indicates that these two types of radiation damage anneal at disparate time and temperature conditions in biotite-series micas. 相似文献