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161.
Varela M Bode A Lorenzo J Alvarez-Ossorio MT Miranda A Patrocinio T Anadón R Viesca L Rodríguez N Valdés L Cabal J Urrutia A García-Soto C Rodríguez M Alvarez-Salgado XA Groom S 《Marine pollution bulletin》2006,53(5-7):272-286
Chlorophyll, primary production, zooplankton biomass and the species composition of phytoplankton and zooplankton were studied in 2003, after the Prestige shipwreck. The information obtained was compared to previous data series available for the area affected by the spill. A large data series on plankton variables for the N-NW Spanish coast existed, and therefore a realistic evaluation of the effects by comparison with the range of natural variability could be carried out. We emphasized the evaluation of impact during the spring bloom, the first important biological event after the spill. Some minor changes were observed occasionally, but they did not show any clear pattern and were more related to the natural variability of the ecosystem than to effect of the spill. Plankton community structure did not undergo any changes. Only a few species were more abundant during spring 2003 than in previous years. No significant changes were detected in the planktonic community during productive periods, such as the spring bloom and the summer blooms related to intrusions of East North Atlantic Central Waters. The lack of evidence of the effects of the spill on planktonic communities is discussed in terms of the characteristics of the fuel, the high dynamics of the water masses, the biological mechanisms through which the fuel from the surface waters is transferred to the sea floor and, particularly, the influence of the natural variability by means of large and meso-scale hydrographic processes in the area under study. At the present time it is not possible to determine any minor effects the spill may have had on the plankton owing to the great variability of the planktonic cycles and the short-term impact of the oil from the Prestige on the pelagic system. 相似文献
162.
Gabriel Chvez Cabello Roberto Molina Garza Luis Delgado Argote Rubn Contreras Flores Elisa Ramírez Amabel Ortega Rivera Harald Bhnel James Lee 《Tectonophysics》2006,424(1-2):1-17
The 102 Ma El Potrero pluton, in the western foothills of Sierra San Pedro Mártir, in north-central Baja California, was emplaced during a long period of contractional deformation bracketed between 132 and 85 Ma that affected this segment of the Peninsular Ranges Batholith. The pluton records regional and emplacement related deformation manifested by: (1) a solid-state fabric developed on its eastern contact, which is produced by eastward lateral pluton expansion; (2) cleavage triple point zones in the host-rock NW and SE of the pluton; (3) subhorizontal ductile shear zones indicative of top-to-the-east transport; (4) magmatic and tectonic foliations parallel to regional structural trends and regional shear zones; (5) variable axial ratios of microgranitoid enclaves close to pluton–wall rock contacts; (6) evidence of brittle-emplacement mechanisms in the western border of the pluton, which contrast with features indicating mainly ductile mechanisms toward the east; and, (7) markedly discordant paleomagnetic directions that suggest emplacement in an active tectonic setting. The overall mean for 9 accepted paleomagnetic sites is Dec = 34.6°, I = 25.7° (k = 88.3, α95 = 5.5°), and is deviated 35° with respect to the reference cratonic direction. This magnetization is interpreted to indicate a combination of tilt due to initial drag during vertical diapiric ascent (or westward lateral-oblique expansion) of the adjacent San Pedro Mártir pluton and later rotation ( 15°) by Rosarito Fault activity in the southwest; this rotation may have occurred as eastward contraction acted to fill the space emptied by the ascending San Pedro Mártir pluton. The Rosarito fault may have tilted several plutons in the area (Sierra San Pedro Mártir, El Potrero, San José, and Encinosa). Magnetic susceptibility fabrics for 13 sites reflect mostly emplacement-related stress and regional stress. Paleomagnetic data and structural observations lead us to interpret the El Potrero pluton as a syntectonic pluton, emplaced within a regional shear zone delimited by the Main Mártir Thrust and the younger Rosarito Fault. 相似文献
163.
Alberto G. Fairén Dirk Schulze-Makuch Wolfgang Fink Esther R. Uceda Ricardo Amils 《Planetary and Space Science》2009,57(3):276-318
The Mars Exploration Rover (MER) missions have confirmed aqueous activity on Mars. Here we review the analyses of the field-based MER data, and conclude that some weathering processes in Meridiani Planum and Gusev crater are better explained by late diagenetic water-rock interactions than by early diagenesis only. At Meridiani, the discovery of jarosite by MER-1 Opportunity indicates acidic aqueous activity, evaporation, and desiccation of rock materials. MER-based information, placed into the context of published data, point to local and limited aqueous activity during geologically recent times in Meridiani. Pre-Amazonian environmental changes (including important variations in the near-surface groundwater reservoirs, impact cratering, and global dust storms and other pervasive wind-related erosion) are too extreme for pulverulent jarosite to survive over extended time periods, and therefore we argue instead that jarosite deposits must have formed in a climatically more stable period. Any deposits of pre-existent concretionary jarosite surviving up to the Amazonian would not have reached completion in the highly saline and acidic brines occurring at Meridiani. MER-2 Spirit has also revealed evidence for local and limited Amazonian aqueous environmental conditions in Gusev crater, including chemical weathering leading to goethite and hematite precipitation, rock layering, and chemical enhancement of Cl, S, Br, and oxidized iron in rocks and soils. The estimated relative age of the impact crater materials in Gusev indicates that these processes have taken place during the last 2 billion years. We conclude that minor amounts of shallow acidic liquid water have been present on the surface of Mars at local scales during the Amazonian Period. 相似文献
164.
This paper addresses the dynamics of real processes of inclusive environmental governance by looking at the decision-maker/expert/lay person interplay. Specifically, we present a comparative ethnographic study that leads to a critical examination of Marteen Hajer’s concept of technological citizenship and its role in normative models of so-called inclusive environmental governance. First, we present the Bionatur project of MST (Movimento Sem Terra/Landless People’s Movement), the largest rural movement in Latin America. The project explicitly attempts to include lay/traditional knowledge into the processes of defining and protecting a regulatory space for “Creole seeds”. Second, we describe the formally open and inclusive environmental management of polluted sediments during harbour dredging in Norway. In both cases the actors are confronted with difficult problems bound by contradictory constraints of the institutional and cultural contexts. In complex relationships, trust, dependency, responsibility and opposition, encompass the decision-maker/expert/lay interplay. Embedded in these contexts, it is not always clear that non-experts want full autonomy and responsibility. In complex relationships, trust, dependency, responsibility and opposition, encompass the decision-maker/expert/lay person interplay. The results suggest that ideals, if instantiated, are reshaped within concrete contexts of action. Participatory ideals such as “technological citizenship”, inclusiveness, transparency and accountability need not be relativised, but they would better be expressed as regulative norms for practice rather than ideals from which an acontextual model or structure may be deduced. 相似文献
165.
Paulo Cesar Fernandes-da-Silva Ricardo Vedovello Claudio Jose Ferreira John Canning Cripps Maria Jose Brollo Amelia Joao Fernandes 《Environmental Earth Sciences》2010,61(8):1657-1675
Geo-environmental terrain assessments and territorial zoning are useful tools for the formulation and implementation of environmental
management instruments (including policy-making, planning, and enforcement of statutory regulations). They usually involve
a set of procedures and techniques for delimitation, characterisation and classification of terrain units. However, terrain
assessments and zoning exercises are often costly and time-consuming, particularly when encompassing large areas, which in
many cases prevent local agencies in developing countries from properly benefiting from such assessments. In the present paper,
a low-cost technique based on the analysis of texture of satellite imagery was used for delimitation of terrain units. The
delimited units were further analysed in two test areas situated in Southeast Brazil to provide estimates of land instability
and the vulnerability of groundwater to pollution hazards. The implementation incorporated procedures for inferring the influences
and potential implications of tectonic fractures and other discontinuities on ground behaviour and local groundwater flow.
Terrain attributes such as degree of fracturing, bedrock lithology and weathered materials were explored as indicators of
ground properties. The paper also discusses constraints on- and limitations of- the approaches taken. 相似文献
166.
The structural safety assessment procedures proposed in Part 3 of Eurocode 8 (EC8‐3) for the case of reinforced concrete structures are addressed. The practical evaluation of the member chord rotation demand according to EC8‐3 is examined in detail along with several alternative formulations. The need for these formulations is demonstrated by presenting example situations where the EC8‐3 proposal is difficult to apply. The effectiveness of the proposed approaches is assessed through an example application and recommendations for their practical use are defined. Given the importance of the shear span in this context, a sensitivity analysis of the EC8‐3 capacity models with respect to this parameter is carried out and discussed in a later section. This analysis aims to assess the validity of the simplifications proposed by a previous research study for the quantification of the EC8‐3 capacity values. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
167.
Claudia V. Rubinstein Marco Vecoli Ricardo A. Astini 《Journal of South American Earth Sciences》2011,31(1):124-138
Middle Ordovician acritarchs, including enigmatic, spore-like microfossils, are recorded from the Labrado and Capillas formations, of the Sierras Subandinas (Capillas River Section, Sierra de Zapla), northwestern Argentina. The Sierras Subandinas represent the outermost exposures of the Central Andean Basin that display an alternation of shallow-marine deltaic systems and estuarine environments, where relative sea-level fluctuations are frequent. The scarcity of fossils in the section, due to the marginal marine settings and frequent subaerial exposures, hinders the biostratigraphic constraining of these sedimentary successions. Based on the palynological assemblages, a probably Dapingian age is interpreted for the upper Lagunilla Member of the Labrado Formation, whereas the lower part of the Capillas Formation is assigned to the Darriwilian. Acritarchs from the lower part of the Capillas Formation indicate clear affinities with the “peri-Gondwana province”. However the lack of Frankea, a marker taxa for the Middle Ordovician, could be related either to the intermediate paleolatitudinal position of the Central Andean Basin or to local paleoenvironmental conditions. The facies analysis and the distribution of palynomorph assemblages throughout the studied section, suggest that organic-walled microfossils are influenced by local paleoenvironmental conditions. A probable non-marine origin is proposed for the spore-like microfossils co-occurring within the acritarch assemblages. 相似文献
168.
We present deterministic ground motion simulations that account for the cyclic multiaxial response of sediments in the shallow crust. We use the Garner Valley in Southern California as a test case. The multiaxial constitutive model is based on the bounding surface plasticity theory in terms of total stress and is implemented in a high‐performance computing finite‐element parallel code. A major advantage of this model is the small number of free parameters that need to be calibrated given a shear modulus reduction curve and the ultimate soil strength. This, in turn, makes the model suitable for regional‐scale simulations, where geotechnical data in the shallow crust are scarce. In this paper, we first describe a series of numerical experiments designed to verify the model implementation. This is followed by a series of idealized large‐scale simulations in a 35 26 4.5 km domain that encompasses the Garner Valley downhole array site, which is an instrumented and well‐characterized site in Southern California. Material properties were extracted from the Southern California Earthquake Center Community velocity model, CVM‐S4.26, considering its optional geotechnical layer, while the modulus reduction curves and soil strength were selected empirically to constrain the nonlinear soil model parameters. Our nonlinear simulations suggest that peak ground displacements within the valley increase relative to the linear case, while peak ground accelerations can increase or decrease, depending on the frequency content of the excitation. The comparisons of our simulations against hybrid three‐dimensional–one‐dimensional site response analyses suggest the inadequacy of the latter to capture the complexity of fully three‐dimensional simulations. 相似文献
169.
Wenyang Zhang Doriam Restrepo Jorge G.F. Crempien Bulent Erkmen Ricardo Taborda Asli Kurtulus Ertugrul Taciroglu 《地震工程与结构动力学》2021,50(1):177-196
Scenario‐based earthquake simulations at regional scales hold the promise in advancing the state‐of‐the‐art in seismic risk assessment studies. In this study, a computational workflow is presented that combines (i) a broadband Green's function‐based fault‐rupture and ground motion simulation—herein carried out using the “UCSB (University of California at Santa Barbara) method”, (ii) a three‐dimensional physics‐based regional‐scale wave propagation simulation that is resolved at Hz, and (iii) a local soil‐foundation‐structure finite element analysis model. These models are interfaced with each other using the domain reduction method. The innermost local model—implemented in ABAQUS—is additionally enveloped with perfectly matched layer boundaries that absorb outbound waves scattered by the structures contained within it. The intermediate wave propagation simulation is carried out using Hercules , which is an explicit time‐stepping finite element code that is developed and licensed by the CMU‐QUAKE group. The devised workflow is applied to a km region on the European side of Istanbul, which was modeled using detailed soil stratigraphy data and realistic fault rupture properties, which are available from prior microzonation surveys and earthquake scenario studies. The innermost local model comprises a chevron‐braced steel frame building supported by a shallow foundation slab, which, in turn, rests atop a three‐dimensional soil domain. To demonstrate the utility of the workflow, results obtained using various simplified soil‐structure interaction analysis techniques are compared with those from the detailed direct model. While the aforementioned demonstration has a limited scope, the devised workflow can be used in a multitude of ways, for example, to examine the effects of shallow‐layer soil nonlinearities and surface topography, to devise site‐ and structure‐specific seismic fragilities, and for calibrating regional loss models, to name a few. 相似文献
170.
The apparent horizontal propagation velocity, that is the propagation velocity of seismic waves with respect to the ground surface, is discussed in this paper. This parameter is needed to determine the effects of earthquakes on long structures such as bridges and buried pipelines as well as the torsional rotation of foundations of multi-storey buildings. A time window intensity tensor introduced by Penzien and Kubo is used herein to determine the predominant directions of ground motion during an earthquake. Considering the reflection of waves at a free surface, an approximate relationship between the predominant direction and the angle of incidence of body waves with respect to the ground surface is presented. Knowing the material properties of the top layer and the angle of incidence, the desired propagation velocity with respect to the ground surface is readily calculated. The median value of the apparent propagation velocity of shear waves for near field sites which recorded the 1971 San Fernando earthquake was determined to be about 2-1 km/s using the above method. A similar value for the 1979 Imperial Valley earthquake is 3·7 km/s. These values are consistent with the range of values for the apparent propagation velocity determined by other researchers. 相似文献