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291.
Frank M. RICHTER Ruslan A. MENDYBAEV John N. CHRISTENSEN Denton EBEL Amy GAFFNEY 《Meteoritics & planetary science》2011,46(8):1152-1178
Abstract– Evaporation rates of K2O, Na2O, and FeO from chondrule‐like liquids and the associated potassium isotopic fractionation of the evaporation residues were measured to help understand the processes and conditions that affected the chemical and isotopic compositions of olivine‐rich type IA and type IIA chondrules from Semarkona. Both types of chondrules show evidence of having been significantly or totally molten. However, these chondrules do not have large or systematic potassium isotopic fractionation of the sort found in the laboratory evaporation experiments. The experimental results reported here provide new data regarding the evaporation kinetics of sodium and potassium from a chondrule‐like melt and the potassium isotopic fractionation of evaporation residues run under various conditions ranging from high vacuum to pressures of one bar of H2+CO2, or H2, or helium. The lack of systematic isotopic fractionation of potassium in the type IIA and type IA chondrules compared with what is found in the vacuum and one‐bar evaporation residues is interpreted as indicating that they evolved in a partially closed system where the residence time of the surrounding gas was sufficiently long for it to have become saturated in the evaporating species and for isotopic equilibration between the gas and the melt. A diffusion couple experiment juxtaposing chondrule‐like melts with different potassium concentrations showed that the diffusivity of potassium is sufficiently fast at liquidus temperatures (DK > 2 × 10?4cm2 s?1 at 1650 °C) that diffusion‐limited evaporation cannot explain why, despite their having been molten, the type IIA and type IA chondrules show no systematic potassium isotopic fractionation. 相似文献
292.
Lisa A. Needles Sarah E. Lester Richard Ambrose Anders Andren Marc Beyeler Michael S. Connor James E. Eckman Barry A. Costa-Pierce Steven D. Gaines Kevin D. Lafferty Hunter S. Lenihan Julia Parrish Mark S. Peterson Amy E. Scaroni Judith S. Weis Dean E. Wendt 《Estuaries and Coasts》2015,38(1):35-48
Managers are moving from a model of managing individual sectors, human activities, or ecosystem services to an ecosystem-based management (EBM) approach which attempts to balance the range of services provided by ecosystems. Applying EBM is often difficult due to inherent tradeoffs in managing for different services. This challenge particularly holds for estuarine systems, which have been heavily altered in most regions and are often subject to intense management interventions. Estuarine managers can often choose among a range of management tactics to enhance a particular service; although some management actions will result in strong tradeoffs, others may enhance multiple services simultaneously. Management of estuarine ecosystems could be improved by distinguishing between optimal management actions for enhancing multiple services and those that have severe tradeoffs. This requires a framework that evaluates tradeoff scenarios and identifies management actions likely to benefit multiple services. We created a management action-services matrix as a first step towards assessing tradeoffs and providing managers with a decision support tool. We found that management actions that restored or enhanced natural vegetation (e.g., salt marsh and mangroves) and some shellfish (particularly oysters and oyster reef habitat) benefited multiple services. In contrast, management actions such as desalination, salt pond creation, sand mining, and large container shipping had large net negative effects on several of the other services considered in the matrix. Our framework provides resource managers a simple way to inform EBM decisions and can also be used as a first step in more sophisticated approaches that model service delivery. 相似文献
293.
294.
Environmental learning and the social construction of an exurban landscape in Fremont County, Colorado 总被引:1,自引:0,他引:1
Across the rural American West, the restructuring of rural capitalism has transformed production landscapes into those increasingly structured by the development and consumption of natural and cultural amenities. This project used principles from symbolic interactionism, ethnographic methods, and the analytical framework of regional political ecology to understand the role of environmental learning in negotiating the new management regime associated with amenity-based capitalism in rural Fremont County, Colorado. The study found that most amenity residents participate regularly in social learning about the environment through a variety of interpersonal and organizational behaviors. In addition, they are responding collectively to environmental risks and opportunities associated with wildfire, noxious weeds and invasive grass species, prospective uranium mining, and restoration of cultural-landscape features. Ultimately, the practices of environmental learning concern how private properties and assets will be managed relative to the social construction of the environment as an amenity for personal consumption. Conservation and management prospects in this and other rural areas in the postindustrial world can be enhanced by understanding the microsociology of exurban geographies and by engaging the social forms and processes related to this distinctive landscape construction. 相似文献
295.
296.
Charles E. Tilburg Shaun M. Gill Stephan I. Zeeman Amy E. Carlson Timothy W. Arienti Jessica A. Eickhorst Philip O. Yund 《Estuaries and Coasts》2011,34(4):785-799
Interest in the coastal dynamics of river plumes has mainly focused on large rivers, but plumes from the more numerous smaller
rivers have important local consequences and may, in aggregate, be significant contributors to coastal circulation. We studied
the dynamics of the plume from the Saco River in Saco Bay, Gulf of Maine, over a 3-year period. The transport and salinity
in the region are governed by river discharge, tides, winds, and interaction with the Western Maine Coastal Current. The dynamics
of the flow field vary with location within the plume and discharge. The far-field dynamics of the Saco River plume are dominated
by inertial processes (hence qualifying it as a small-scale river plume), during times of low discharge, with low salinity
water present both up and downstream of the river mouth, but are dominated by rotational processes during times of high discharge
(thus qualifying it as a large-scale river plume), with buoyant water primarily advected downshelf. Near-field dynamics are
governed by weak, subcritical flow during low discharge but strongly inertial, supercritical flow during high discharge. Offshore
movement of the plume is not governed by Ekman dynamics but is instead a result of discharge, wind-induced vertical mixing,
and the geography of the coastline and adjacent islands. 相似文献
297.
298.
Snow is an important component of the earth's environment, and can significantly impact the everyday life of those living in a large portion of the United States. However, accurate and complete information on snowfall and snow cover is presently being collected at only 57% of the official climate observing stations in states where regional snows occur on an annual basis. The quality of the data varies significantly from one state to another, although it tends to be weakest where snow is least common. As a result of this evaluation, the list of stations with daily snow data published in National Oceanic and Atmospheric Administration Climatohgical Data publications has been revised and expanded. [Key words: snow, snow observations, climate data, United States.] 相似文献
299.
Xinhao Wang Amy Burgess Jeff Yang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(3):629-641
In this study a water consumption model is built into a scenario-based planning support system (SB-WCPSS). The SB-WCPSS consists of four components—(1) a model input graphic user interface, (2) a community spatial database, (3) a set of drinking water consumption models, and (4) output display. The SB-WCPSS is implemented with a commercial planning support system software package—CommunityViz. The model is applied using data in Cincinnati, Ohio, USA to demonstrate the scenario development. In the application, water consumption consists of land use based indoor, turf, and pool water usages. Climate change is reflected in monthly temperature and precipitation. By specifying anticipated future land uses and associated water consumption rates, temperature, and precipitation, SB-WCPSS users can analyze and compare water consumptions under various scenarios, using maps, graphs, and tables. Parcel-based daily water consumptions were computed and summarized spatially by neighborhood, block group, or land use type. The results demonstrate that water conservation strategies, such as xeriscape, can reduce turf water usage. Indoor water consumption depends on the number of people who use water and how they use water. The study shows that the SB-WCPSS structure is sound and user friendly. Future improvement will be on enhancing various components, such as using parcel-based data and more robust water consumption models. The system may be used by water resource managers and decision makers to adapt water resources (e.g., watersheds and infrastructure) to climate change and demographic and economic development. 相似文献
300.
Zoning of phosphorus in igneous olivine 总被引:2,自引:2,他引:0
Margaret S. Milman-Barris John R. Beckett Michael B. Baker Amy E. Hofmann Zachary Morgan Meghan R. Crowley Daniel Vielzeuf Edward Stolper 《Contributions to Mineralogy and Petrology》2008,155(6):739-765
We describe P zoning in olivines from terrestrial basalts, andesites, dacites, and komatiites and from a martian meteorite.
P2O5 contents of olivines vary from below the detection limit (≤0.01 wt%) to 0.2–0.4 wt% over a few microns, with no correlated
variations in Fo content. Zoning patterns include P-rich crystal cores with skeletal, hopper, or euhedral shapes; oscillatory
zoning; structures suggesting replacement of P-rich zones by P-poor olivine; and sector zoning. Melt inclusions in olivines
are usually located near P-rich regions but in direct contact with low-P olivine. Crystallization experiments on basaltic
compositions at constant cooling rates (15–30°C/h) reproduce many of these features. We infer that P-rich zones in experimental
and natural olivines reflect incorporation of P in excess of equilibrium partitioning during rapid growth, and zoning patterns
primarily record crystal-growth-rate variations. Occurrences of high-P phenocryst cores may reflect pulses of rapid crystal
growth following delayed nucleation due to undercooling. Most cases of oscillatory zoning in P likely reflect internal factors
whereby oscillating growth rates occur without external forcings, but some P zoning in natural olivines may reflect external
forcings (e.g., magma mixing events, eruption) that result in variable crystal growth rates and/or P contents in the magma.
In experimental and some natural olivines, Al, Cr, and P concentrations are roughly linearly and positively correlated, suggesting
coupled substitutions, but in natural phenocrysts, Cr zoning is usually less intense than P zoning, and Al zoning weak to
absent. We propose that olivines grow from basic and ultrabasic magmas with correlated zoning in P, Cr, and Al superimposed
on normal zoning in Fe/Mg; rapidly diffusing divalent cations homogenize during residence in hot magma; Al and Cr only partially
homogenize; and delicate P zoning is preserved because P diffuses very slowly. This interpretation is consistent with the
fact that zoning is largely preserved not only in P but also in Al, Cr, and divalent cations in olivines with short residence
times at high temperature (e.g., experimentally grown olivines, komatiitic olivines, groundmass olivines, and the rims of
olivine phenocrysts grown during eruption). P zoning is widespread in magmatic olivine, revealing details of crystal growth
and intra-crystal stratigraphy in what otherwise appear to be relatively featureless crystals. Since it is preserved in early-formed
olivines with prolonged residence times in magmas at high temperatures, P zoning has promise as an archive of information
about an otherwise largely inaccessible stage of a magma’s history. Study of such features should be a valuable supplement
to routine petrographic investigations of basic and ultrabasic rocks, especially because these features can be observed with
standard electron microprobe techniques. 相似文献