全文获取类型
收费全文 | 697篇 |
免费 | 13篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 123篇 |
地球物理 | 119篇 |
地质学 | 278篇 |
海洋学 | 25篇 |
天文学 | 125篇 |
综合类 | 3篇 |
自然地理 | 21篇 |
出版年
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 18篇 |
2014年 | 12篇 |
2013年 | 18篇 |
2012年 | 19篇 |
2011年 | 18篇 |
2010年 | 24篇 |
2009年 | 40篇 |
2008年 | 32篇 |
2007年 | 37篇 |
2006年 | 23篇 |
2005年 | 28篇 |
2004年 | 26篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 14篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1957年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有716条查询结果,搜索用时 15 毫秒
131.
132.
Anna Schneider Horst H. Gerke Thomas Maurer Stefan Seifert Rossen Nenov Reinhard F. Hüttl 《地球表面变化过程与地形》2012,37(7):708-725
To quantify landscape change resulting from processes of erosion and deposition and to establish spatially distributed sediment budgets, ‘models of change’ can be established from a time series of digital elevation models (DEMs). However, resolution effects and measurement errors in DEMs may propagate to these models. This study aimed to evaluate and to modify remotely‐sensed DEMs for an improved quantification of initial sediment mass changes in an artificially‐created catchment. DEMs were constructed from photogrammetry‐based, airborne (ALS) and ground‐based laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three‐dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region‐by‐region for rill, interrill and alluvial areas, based on logical and hydro‐geomorphological principles. Additional DEMs were constructed by combining multi‐source, modified data. Models were evaluated by comparison with d‐GPS reference data and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics. Photogrammetry‐based DEMs were suited to quantification of change in interrill areas but strongly underestimated surface lowering in erosion rills. TLS DEMs were best suited to rill areas, while ALS DEMs performed best in vegetation‐covered alluvial areas. Agreement with reference data and budget plausibility were improved by modifications to photogrammetry‐ and TLS‐based DEMs. Results suggest that artefacts in DEMs can be reduced and hydro‐geomorphic surface structures can be better represented by applying region‐specific modifications. Photogrammetry‐based DEMs can be improved by combining higher and lower resolution data in defined structural units and applying modifications based on principles given by characteristic hydro‐geomorphic evolution. Results of the critical comparative evaluation of remotely‐sensed elevation data can help to better interpret DEM‐based quantifications of earth‐surface processes. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
133.
Exploring the impact of diagenesis on (isotope) geochemical and microstructural alteration features in biogenic aragonite 下载免费PDF全文
Ann‐Christine Ritter Vasileios Mavromatis Martin Dietzel Ola Kwiecien Felix Wiethoff Erika Griesshaber Laura A. Casella Wolfgang W. Schmahl Jennifer Koelen Rolf D. Neuser Albrecht Leis Dieter Buhl Andrea Niedermayr Sebastian F. M. Breitenbach Stefano M. Bernasconi Adrian Immenhauser 《Sedimentology》2017,64(5):1354-1380
For the Quaternary and Neogene, aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment. Conversely, pre‐Neogene aragonite is often diagenetically altered and calcite archives are studied instead. Nevertheless, the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material. Here, experiments were performed to understand biogenic aragonite alteration processes and products. Shell subsamples of the bivalve Arctica islandica were exposed to hydrothermal alteration. Thermal boundary conditions were set at 100°C, 175°C and 200°C. These comparably high temperatures were chosen to shorten experimental durations. Subsamples were exposed to different 18O‐depleted fluids for durations between two and twenty weeks. Alteration was documented using X‐ray diffraction, cathodoluminescence, fluorescence and scanning electron microscopy, as well as conventional and clumped isotope analyses. Experiments performed at 100°C show redistribution and darkening of organic matter, but lack evidence for diagenetic alteration, except in Δ47 which show the effects of annealing processes. At 175°C, valves undergo significant aragonite to calcite transformation and neomorphism. The δ18O signature supports transformation via dissolution and reprecipitation, but isotopic exchange is limited by fluid migration through the subsamples. Individual growth increments in these subsamples exhibit bright orange luminescence. At 200°C, valves are fully transformed to calcite and exhibit purple‐blue luminescence with orange bands. The δ18O and Δ47 signatures reveal exchange with the aqueous fluid, whereas δ13C remains unaltered in all experiments, indicating a carbonate‐buffered system. Clumped isotope temperatures in high‐temperature experiments show compositions in broad agreement with the measured temperature. Experimentally induced alteration patterns are comparable with individual features present in Pleistocene shells. This study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits. The limitations of a study restricted to a single test organism are acknowledged and call for refined follow‐up experiments. 相似文献
134.
We estimated the net annual air–sea exchange of carbon dioxide (CO2) using monitoring data from the East Gotland Sea, Bornholm Sea, and Kattegat for the 1993–2009 period. Wind speed and the sea surface partial pressure of CO2 (pCO2w), calculated from pH, total alkalinity, temperature, and salinity, were used for the flux calculations. We demonstrate that regions in the central Baltic Sea and the Kattegat alternate between being sinks (−) and sources (+) of CO2 within the −4.2 to +5.2 mol m−2 yr−1 range. On average, for the 1994–2008 period, the East Gotland Sea was a source of CO2 (1.64 mol m−2 yr−1), the Bornholm Sea was a source (2.34 mol m−2 yr−1), and the Kattegat was a sink (−1.16 mol m−2 yr−1). Large inter-annual and regional variations in the air–sea balance were observed. We used two parameterizations for the gas transfer velocity (k) and the choice varied the air–sea exchange by a factor of two. Inter-annual variations in pCO2w between summers were controlled by the maximum concentration of phosphate in winter. Inter-annual variations in the CO2 flux and gas transfer velocity were larger between winters than between summers. This indicates that the inter-annual variability in the total flux was controlled by winter conditions. The large differences between the central Baltic Sea and Kattegat were considered to depend partly on the differences in the mixed layer depth. 相似文献
135.
Development of a modelling methodology for simulation of long-term morphological evolution of the southern Baltic coast 总被引:1,自引:1,他引:0
The Darss–Zingst peninsula at the southern Baltic Sea is a typical wave-dominated barrier island system which includes an
outer barrier island and an inner lagoon. The formation of the Darss–Zingst peninsula dates back to the Littorina Transgression
onset about 8,000 cal BP. It originated from several discrete islands, has been reshaped by littoral currents, wind-induced
waves during the last 8,000 years and evolved into a complex barrier island system as today; thus, it may serve as an example
to study the coastal evolution under long-term climate change. A methodology for developing a long-term (decadal-to-centennial)
process-based morphodynamic model for the southern Baltic coastal environment is presented here. The methodology consists
of two main components: (1) a preliminary analysis of the key processes driving the morphological evolution of the study area
based on statistical analysis of meteorological data and sensitivity studies; (2) a multi-scale high-resolution process-based
model. The process-based model is structured into eight main modules. The two-dimensional vertically integrated circulation
module, the wave module, the bottom boundary layer module, the sediment transport module, the cliff erosion module and the
nearshore storm module are real-time calculation modules which aim at solving the short-term processes. A bathymetry update
module and a long-term control function set, in which the ‘reduction’ concepts and technique for morphological update acceleration
are implemented, are integrated to up-scale the effects of short-term processes to a decadal-to-centennial scale. A series
of multi-scale modelling strategies are implemented in the application of the model to the research area. Successful hindcast
of the coastline change of the Darss–Zingst peninsula for the last 300 years validates the modelling methodology. Model results
indicate that the coastline change of the Darss–Zingst peninsula is dominated by mechanisms acting on different time scales.
The coastlines of Darss and the island of Hiddensee are mainly reshaped by long-term effects of waves and longshore currents,
while the coastline change of the Zingst peninsula is due to a combination of long-term effects of waves and short-term effects
caused by wind storms. 相似文献
136.
Oleg V. Melnichenko Nikolai A. Maximenko Niklas Schneider Hideharu Sasaki 《Ocean Dynamics》2010,60(3):653-666
Recently, prominent jet-like features of the ocean circulation, called striations, with a meridional scale of O(300–500 ;km)
and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. In this paper, we study quasi-stationary striations, which are best
seen in the multi-year time-averaged velocity fields. Using 1993–2002 mean dynamic ocean topography, satellite altimeter observations,
and output of the Ocean General Circulation Model for the Earth Simulator, the dynamics of the quasi-stationary striations
in the eastern parts of the subtropical North and South Pacific are examined by assessing individual terms in the time-averaged
equations of relative and potential vorticity. While non-linear effects are found to be essential in the dynamics of the striations,
rejecting some linear hypotheses forwarded in the earlier studies, the relevance of the Rhines mechanism is not confirmed.
Eddy flux does not act as a relative vorticity source for the striations. Using the potential vorticity (PV) diagnostics,
we show that the time-mean PV is not conserved along the time-mean streamlines, and on the scale of the striations these changes
in PV are largely induced by the eddy flux of layer thickness. The fact that eddy fluxes contribute to the striations’ time-mean
PV budget suggests that the striations are not a kinematical artifact of time-averaging of westward-propagating eddies. 相似文献
137.
Nabil Sultan Antonio Cattaneo Jean-Claude Sibuet Jean-Luc Schneider the Sumatra Aftershocks team 《International Journal of Earth Sciences》2009,98(4):823-837
The swath bathymetric data acquired during the “Sumatra Aftershocks” cruise from the Sunda trench in the Indian Ocean to the
north of the Sumatra Island imaged several scars and deposits. In situ pore pressure measurements using the Ifremer piezometer
and coring demonstrate that high excess pore pressure and sediment deformation was generated by a recent event in the scar
of the slope failure zone identified by J.T. Henstock and co-authors. This excess pore pressure is localized in the upper
sedimentary layers and is not related to an interplate subduction process. Numerical simulations of the hydrological system
that take into account the hydro-mechanical properties of the upper sediment layer show that the excess pore pressure and
sediment deformations could be generated at the time of the December 26, 2004 Great Sumatra Earthquake.
The Sumatra Aftershocks team: J.-C. Sibuet, S. Singh, R. Apprioual, N.C. Aryanto, J. Begot, A. Cattaneo, A.P.S. Chauchan,
R. Creach, J. Crozon, A. Domzig, N. Falleau, D. Graindorge, F. Harmegnies, Y. Haryadi, F. Klingelhoffer, S.K. Kolluru, J.-Y.
Landuré, C. Le Lann, J. Malod, A. Normand, G. Oggian, C. Rangin, D. Restunin Galih, J.-L. Schneider, N. Sultan, M. Taufik,
M. Umber and H. Yamaguchi. 相似文献
138.
Simon Schneider Franz T. Fürsich Winfried Werner 《International Journal of Earth Sciences》2009,98(8):1949-1970
Strontium isotope stratigraphy was performed on oyster shells from the Late Jurassic of the Lusitanian Basin (central Portugal). This represents the first approach to obtain numerical ages for these strata. The new chronostratigraphic data provide a more precise age determination of several units. After a basin-wide hiatus sedimentation in the Late Jurassic is proven in the Cabo Mondego and Cabaços formations to resume as early as the Middle Oxfordian. The Alcobaça formation can be placed in the latest Late Oxfordian to Late Kimmeridgian, while data from the upper part of the Abadia Formation indicate an Early to Late Kimmeridgian age. The Farta Pao formation ranges from the latest Kimmeridgian to the latest Tithonian. The largely synchronous Sobral, Arranhó I, and Arranhó II members are overlain by the late Early to Late Tithonian Freixial Member. The brief, local carbonate incursion of the Arranhó I member marks the Kimmeridgian–Tithonian boundary. Oysters are shown once more to be suitable for strontium isotope studies. Their calcitic shells are often unaffected by diagenesis. In particular for marginal marine Jurassic and Cretaceous strata, where belemnites are usually absent, oysters may serve as a valuable tool for isotope stratigraphy. 相似文献
139.
F. Reitsma J. Albrecht 《International journal of geographical information science》2013,27(10):1073-1090
The paper describes the development of a new methodological approach for simulating geographic processes through the development of a data model that represents a process. This methodology complements existing approaches to dynamic modelling, which focus on the states of the system at each time step, by storing and representing the processes that are implicit in the model. The data model, called nen, focuses existing modelling approaches on representing and storing process information, which provides advantages for querying and analysing processes. The flux simulation framework was created utilizing the nen data model to represent processes. This simulator includes basic classes for developing a domain specific simulation and a set of query tools for inquiring after the results of a simulation. The methodology is prototyped with a watershed runoff simulation. 相似文献
140.
Suturing of the Proto- and Paleo-Tethys oceans in the western Kunlun (Xinjiang, China) 总被引:16,自引:0,他引:16
The Proto-Tethys Ocean between the North and South Kunlun began to form during the Sinian. Remnants of this ocean are preserved at the Oytag-Kudi suture. The presence of Paleozoic arc batholiths in the northern South Kunlun and their absence in the North Kunlun indicates southward subduction of the Proto-Tethys Ocean beneath the South Kunlun. Opposite subduction polarity can be demonstrated for the Late Paleozoic to mid-Mesozoic when the southerly located Paleo-Tethys Ocean was consumed beneath the South Kunlun and generated a Late Carboniferous to mid-Jurassic magmatic arc in the southern South Kunlun. Arc magmatism affected the southern South Kunlun and the large Kara-Kunlun accretionary prism (a suture sensu lato) which formed as a result of Paleo-Tethys’ consumption. The dextral shear sense of ductile faults which are located at the margins of the arc batholiths, and which parallel the South Kunlun/Kara-Kunlun boundary, suggests oblique plate convergence with a dextral component. Different lines of evidence encourage us to interpret the Proto-Tethys ophiolites of the Oytag-Kudi zone as at least partly derived from an oceanic back-arc basin. In contrast, we assume that Paleo-Tethys was a large ocean basin which was eliminated directly at the southern margin of the South Kunlun where no oceanic back-arc region existed. 相似文献