全文获取类型
收费全文 | 627篇 |
免费 | 40篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 28篇 |
地球物理 | 186篇 |
地质学 | 248篇 |
海洋学 | 78篇 |
天文学 | 68篇 |
综合类 | 8篇 |
自然地理 | 37篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 23篇 |
2017年 | 33篇 |
2016年 | 31篇 |
2015年 | 37篇 |
2014年 | 30篇 |
2013年 | 34篇 |
2012年 | 34篇 |
2011年 | 55篇 |
2010年 | 33篇 |
2009年 | 53篇 |
2008年 | 52篇 |
2007年 | 23篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 19篇 |
2002年 | 14篇 |
2001年 | 9篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1961年 | 1篇 |
1952年 | 4篇 |
1950年 | 1篇 |
排序方式: 共有675条查询结果,搜索用时 859 毫秒
181.
182.
Pablo Diego GonzAlez Ana Maria Sato Eduardo Jorge Llambias Miguel A.S. Basei Silvio R.F. Vlach 《Gondwana Research》2004,7(4):1157-1170
Structural, metamorphic and isotopic data obtained from the Nogoli Metamorphic Complex of western Sierra de San Luis indicate that the Early Paleozoic Famatinian Orogeny overprinted an already structured and metamorphosed older basement. The older geological features are relict NW trending fabric associated with high-grade (amphibolite facies) regional metamorphism preserved within thin strips of schists and paragneisses and in the core of mafic to ultramafic lenses. Arc magmatism, medium P (Barrovian type)/high T (amphibolite to granulite facies) regional metamorphism and penetrative NNE to NE trending foliation are related to the building of the Famatinian orogenic belt. The P-T conditions of the Famatinian prograde metamorphism reached a pressure peak of ca. 8 kb, with a thermal peak from -750°C up to -820°C. U-Pb conventional and chemical dating and Ar-Ar plateau ages constrain the peak of the main orogenic phase related to the Famatinian belt to 470–457 Ma (Early to Mid-Ordovician). Greenschist facies retrograde metamorphism closely associated with shear zones and secondary Ar-Ar plateau and Sm-Nd ages suggest that a late to post-orogenic phase of the Famatinian belt was active at least since -445 Ma. This phase continued during the Silurian to Late Devonian times through multiple reactivation of early shear zones. The Famatinian Orogeny reset a previous thermal history and therefore, the timing of the relict fabric could not be constrained conclusively with radiometric dates. Despite this difficulty, a range of 520 to 490 Ma suggests some inheritance from Pampean events registered by the older NW-SE fabric. The Early to Mid-Ordovician regional metamorphism and ductile deformation of the western Sierra de San Luis is interpreted as the orogenic effects of the collision of the allochthonous Cuyania terrane with the autochthonous proto-Pacific margin of Gondwana during the Famatinian Orogeny. 相似文献
183.
Juan C. Carvajal Víctor M. Taboada-Urtuzustegui Miguel P. Romo 《Soil Dynamics and Earthquake Engineering》2002,22(4)
The installation of vertical downhole arrays in the field that record the soil behavior during earthquakes, has opened the opportunity of exploring another alternate method for assessing the soil dynamic properties by solving the inverse problem. This article proposes a methodology for solving this problem using spectral analysis of downhole arrays records. The one-dimensional shear wave propagation model was used, considering a homogeneous-viscoelastic medium. This methodology was applied at the site known as Central de Abasto Oficinas (CAO), which is located in the lake zone of the Mexico City. The results indicate that even relatively low frequencies have a noticeable effect on dynamic soil properties. Shear modulus increases and damping ratio lessens when the frequency rises. 相似文献
184.
Guillermo Booth-Rea José Miguel Azañón Vı́ctor Garcı́a-Dueñas Romain Augier Mario Sánchez-Gómez 《Comptes Rendus Geoscience》2003,335(2):265-274
The Santi Petri dome (western Betics, southern Spain) shows a core-complex-like structure, where migmatitic gneisses and schists outcrop below low-grade slates and phyllites, all of which form the basement of the Neogene Málaga basin. The migmatites and schists suffered a coaxial-flattening event during isothermal decompression and were later exhumed by ductile ESE non-coaxial stretching. Further exhumation was achieved by W- to SW-transport brittle low-angle normal faulting. Subsequently these extensional structures were gently folded in the core of a NE/SW-oriented antiform during the Tortonian. Finally the Santi Petri domal geometry was accentuated by the interference of orthogonal high-angle faults with ENE–WSW and NNW–SSE orientation. This core-complex-like structure, formed by superposition of extensional and compressive tectonic events, does not represent a classical, purely extensional core complex, which shows that metamorphic structure and geometry are not decisive criteria to define a core-complex. 相似文献
185.
Pablo Pulido-Leboeuf Antonio Pulido-Bosch Maria Luisa Calvache Ángela Vallejos José Miguel Andreu 《Comptes Rendus Geoscience》2003,335(14):1039-1048
The strontium content and the SO42?/Cl? and Mg2+/Ca2+ ratios were used as natural tracers of the residence time of seawater intrusion into the Castell de Ferro aquifer. Analysis of these parameters indicated the existence of two principal flowpaths in the aquifer. The first flows through the eastern part of the aquifer, through the karstified Castell de Ferro massif; it accommodates a larger and more rapid flow, so that the residence time is shorter, leading to lower SO42+/Cl? ratios, lower Sr2+ content and higher Mg2+/Ca2+ ratios. The second flowpath is in the western sector, and flows exclusively through alluvial deposits; the flow here is slower, particularly that flowing towards the sea. Thus the residence time of the water here will be longer and there is scant flushing of the intruded seawater; this is manifested in the high Sr2+ content, high SO42+/Cl? and low Mg2+/Ca2+ ratios. To cite this article: P. Pulido-Leboeuf et al., C. R. Geoscience 335 (2003). 相似文献
186.
Miguel A. LOSADA 《中国海洋工程》1999,(1)
—According to the energy equation,the relation between reflection and energy losses for shortwaves from mild beaches is established and analysed.A reflection coefficient varying with position and en-ergy losses is proposed.Different reflection tests are conducted to check the theoretical analysis.A modi-fied method to estimate the reflection coefficient at varied water depths is suggested based on the linearwave theory.The study indicates that the reflection coefficient from mild beaches has a changing trend forshort waves approaching shoreline. 相似文献
187.
Corpas-Burgos Francisca Martinez-Beneito Miguel A. 《Stochastic Environmental Research and Risk Assessment (SERRA)》2020,34(3):531-544
Stochastic Environmental Research and Risk Assessment - Conditional autoregressive distributions are commonly used to model spatial dependence between nearby geographic units in disease mapping... 相似文献
188.
The buildings’ capacity to maintain minimum structural safety levels during natural disasters, such as earthquakes, is recognisably one of the aspects that most influence urban resilience. Moreover, the public investment in risk mitigation strategies is fundamental, not only to promote social and urban and resilience, but also to limit consequent material, human and environmental losses. Despite the growing awareness of this issue, there is still a vast number of traditional masonry buildings spread throughout many European old city centres that lacks of adequate seismic resistance, requiring therefore urgent retrofitting interventions in order to both reduce their seismic vulnerability and to cope with the increased seismic requirements of recent code standards. Thus, this paper aims at contributing to mitigate the social and economic impacts of earthquake damage scenarios through the development of vulnerability-based comparative analysis of some of the most popular retrofitting techniques applied after the 1998 Azores earthquake. The influence of each technique individually and globally studied resorting to a seismic vulnerability index methodology integrated into a GIS tool and damage and loss scenarios are constructed and critically discussed. Finally, the economic balance resulting from the implementation of that techniques are also examined. 相似文献
189.
How does anisotropy in bedrock river granitic outcrops influence pothole genesis and development?
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Pothole formation and development may be influenced by joint sets and other heterogeneities within bedrock, as well as by hydraulics. Previous research indicates that most potholes found in rivers of the mountainous Spanish Central System exhibit preferred orientations associated with dominant joints and correlate more strongly with variations in substrate resistance than with hydraulics. Weathering and erosion weaken rock surfaces, which leads to decreased mechanical resistance. We start from the hypothesis that different mechanisms of pothole formation may create around the pothole a distinctive signature in terms of ultrasound pulse velocity and surface hardness. We develop a conceptual model and test it using potholes for which we know the mechanism of formation, demonstrating that the spatial and statistical distributions of dynamical mechanical properties and surface hardness of a pothole may provide insight into its genesis. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
190.
Jos Pablo Gmez‐Barrn Miguel ngel Manso‐Callejo Ramn Alcarria 《Transactions in GIS》2019,23(5):976-1007
Volunteered geographic information (VGI) has been studied extensively within various contexts, however, generally focusing on isolated aspects of data. Therefore, we still need to advance the structured knowledge of the mechanisms that affect and support its creation. This article aims to contribute to the integrated study of VGI systems (VGIS) in order to enhance design processes that lead to a more systematic and efficient VGI management. We define VGIS, their main components, and general architectures. Then, we use the service blueprinting technique to conduct the case study of several systems, identifying system actions to find the processes and technologies forming the different functional components of VGIS: elements of the technological infrastructure that implement diverse processes to facilitate participation and data management. Integrated in the data collection component, we also propose a typology of crowdsourcing tasks that—coupled with the functional components—establishes a foundation for VGIS research and design. We characterize these components, arguing that they are necessary in the development of VGIS, however, there is still a need for a more detailed study of the flow of processes and subprocesses and how they work under the criteria of different types of projects to continue facilitating their design. 相似文献