全文获取类型
收费全文 | 590篇 |
免费 | 124篇 |
国内免费 | 54篇 |
专业分类
测绘学 | 94篇 |
大气科学 | 48篇 |
地球物理 | 299篇 |
地质学 | 121篇 |
海洋学 | 74篇 |
天文学 | 34篇 |
综合类 | 38篇 |
自然地理 | 60篇 |
出版年
2024年 | 6篇 |
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 28篇 |
2020年 | 32篇 |
2019年 | 22篇 |
2018年 | 16篇 |
2017年 | 22篇 |
2016年 | 25篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 23篇 |
2012年 | 37篇 |
2011年 | 28篇 |
2010年 | 26篇 |
2009年 | 32篇 |
2008年 | 42篇 |
2007年 | 56篇 |
2006年 | 50篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 31篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有768条查询结果,搜索用时 15 毫秒
671.
672.
介绍了TOPAS PS18系统设备的基本组成、参量阵技术原理以及在深远海应用中的参数设置。另外选取西太平洋地区一水深超过1 000 m的穿越海山测线,通过对该测线海山山顶及边缘浅地层剖面的层位解释和分析,发现该火山顶部主要经历了T0、T1和T2共3期构造及沉积作用,在T2时期曾爆发过小规模的火山侵入活动。通过对该段资料的分析,展示了TOPAS PS18浅地层剖面仪在深远海的探测效果及浅地层层序结构,分析了研究区的沉积演化规律,为后期进行更深入的地质构造分析及矿产分布调查奠定了基础。 相似文献
673.
Sebastián Oriolo Bernhard Schulz Silvana Geuna Pablo DGonzález Juan E.Otamendi JiíSláma Elena Druguet Siegfried Siegesmund 《地学前缘(英文版)》2021,12(1):109-130
Early Paleozoic accretionary orogens dominated the Western Gondwana margin and were characterized by nearly continuous subduction associated with crustal extension and back-arc basin development.The southwestern margin is represented by Famatinian and Pampean basement realms exposed in South America,both related to the protracted Paleozoic evolution of the Terra Australis Orogen,whereas the northwestern margin is mainly recorded in Cadomian domains of Europe and adjacent regions.However,no clear relationships between these regions were so far established.Based on a compilation and reevaluation of geological,paleomagnetic,petrological,geochronological and isotopic evidence,this contribution focuses on crustal-scale tectonic and geodynamic processes occurring in Western Gondwana accretionary orogens,aiming at disentangling their common Early Paleozoic evolution.Data show that accretionary orogens were dominated by high-temperature/lowpressure metamorphism and relatively high geothermal gradients,resulting from the development of extended/hyperextended margins and bulk transtensional deformation.In this sense,retreating-mode accretionary orogens characterized the Early Paleozoic Gondwana margin,though short-lived pulses of compression/transpression also occurred.The existence of retreating subduction zones favoured mantle-derived magmatism and mixing with relatively young(meta)sedimentary sources in a thin continental crust.Crustal reworking of previous forearc sequences due to trenchward arc migration thus took place through assimilation and anatexis in the arc/back-arc regions.Therefore,retreating-mode accretionary orogens were the locus of Early Paleozoic crustal growth in Western Gondwana,intimately associated with major flare-up events,such as those related to the Cadomian and Famatian arcs.Slab roll back,probably resulting from decreasing convergence rates and plate velocities after Gondwana assembly,was a key factor for orogen-scale geodynamic processes.Coupled with synchronous oblique subduction and crustal-scale dextral deformation,slab roll back might trigger toroidal mantle flow,thus accounting for bulk dextral transtension,back-arc extension/transtension and a large-scale anticlockwise rotation of Gondwana mainland. 相似文献
674.
A new approach on numerical modeling of wave propagation is introduced and is used to analyze the effect of earthquake magnitudes (ground motion amplitudes) on wave propagation. In this method, the sum of the maximum amplitudes of the first output model at time 0 s and rest of the output models at different times are normalized to unity. Considering this as a constraint, the sum of the weighted‐squared Fourier amplitudes is minimized by using the Lagrange multiplier method. The proposed method can reveal the relationship of actual time histories by showing simple clear peaks. This method is used to analyze the time histories of various earthquake events at different vertical array sites of the Kashiwazaki–Kariwa nuclear power plant of Tokyo electric power company (TEPCO). The wave arrival times obtained from this method and down‐hole measurements are compared. The results show increase in the arrival times at surface layer when the magnitude of earthquake is large. The results reveal that the amplitudes of small magnitude earthquakes at depths are small and are largely amplified at surface, whereas in case of large magnitude earthquakes, the amplitudes are large at depths and are deamplified at surface reflecting the effects of the strain‐dependent soil properties that result in non‐linear site response to strong shaking. The results also show that the reflected peak amplitudes are higher for small magnitude earthquakes than for large magnitude earthquakes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
675.
基于雷声到达时间差的单站闪电通道三维定位系统 总被引:2,自引:0,他引:2
利用麦克风阵列采集雷声信号,设计了一套由麦克风阵列和便携式数据采集存储设备组成的单站闪电通道三维定位系统,采用CCF相关函数法计算了雷声脉冲信号到达不同麦克风的时间差,通过最小二乘法获得声源的方向角和仰角信息,并结合声源与麦克风阵列的距离定位声源的三维位置。对一次包括8次回击的人工触发闪电过程进行了观测,得到多个声源点的三维定位信息。系统的定位结果与高速摄像的观测结果具有较好的一致性,定位方法合理、可行,为进一步研发便携式闪电通道三维定位系统奠定了基础。 相似文献
676.
677.
AbstractFor high frequency ocean acoustic modeling applications, seabed reflection loss is a useful alternative input compared to conventional geoacoustic model parameters. Reflection loss can be estimated by comparing the noise intensity of the up and down components of the ambient noise vertical directionality pattern. The potential of this method is demonstrated with experimental data spanning one week, collected off shallow east coast of India using a 21 element vertical hydrophone array. The compact and easily operable vertical array has been designed for high frequency directionality estimation in the band 2–10?kHz. The ambient noise data are beam formed to arrive at the vertical directionality pattern. Further reflection loss values as a function of frequency and grazing angle have been estimated for 1/3 octave bands for a sandy sea bed in warm tropical waters. This has been compared with modeled reflection loss estimates using OASR reflection loss module of OASES. This will serve as inputs to propagation models for applications such as inverse techniques, ambient noise modelling, and sonar system performance prediction. 相似文献
678.
The study of contourite drifts is an increasingly used tool for understanding the climate history of the oceans. In this paper we analyse two contourite drifts along the continental margin west of Spitsbergen, just south of the Fram Strait where significant water mass exchanges impact the Arctic climate. We detail the internal geometry and the morphologic characteristics of the two drifts on the base of multichannel seismic reflection data, sub-bottom profiles and bathymetry. These mounded features, that we propose to name Isfjorden and Bellsund drifts, are located on the continental slope between 1200 and 1800 m depth, whereas the upper slope is characterized by reduced- or non-deposition. The more distinct Isfjorden Drift is about 25 km wide and 45 km long, and over 200 ms TWT thick. We revise the 13 years-long time series of velocity, temperature, and salinity obtained from a mooring array across the Fram Strait. Two distinct current cores are visible in the long-term average. The shallower current core has an average northward velocity of about 20 cm/s, while the deeper bottom current core at about 1450 m depth has an average northward velocity of about 9 cm/s. We consider Norwegian Sea Deep Water episodically ventilated by relatively dense and turbid shelf water from the Barents Sea responsible for the accumulation of the contourites. The onset of the drift growth west of Spitsbergen is inferred to be about 1.3 Ma and related to the Early Pleistocene glacial expansion recorded in the area. The lack of mounded contouritic deposits on the continental slope of the Storfjorden is related to consecutive erosion by glacigenic debris flows. The Isfjorden and Bellsund drifts are inferred to contain the record of the regional palaeoceanography and glacial history and may constitute an excellent target of future scientific drilling. 相似文献
679.
Improving microseismic monitoring efficiency and accuracy at a mine requires an integrated effort. This article discusses
a case study which demonstrates that the monitoring efficiency and accuracy can be drastically improved through optimally
using the existing array, efficient techniques for signal processing and noise separation, and the advanced location algorithm
which not only offers a robust search scheme, but also features the techniques for efficient data utilization and further
error detection and minimization. The study is a collaborated research between Penn State and NIOSH researchers for the better
use of microseismic technique for mine safety, ground control and roof fall prediction. 相似文献
680.