全文获取类型
收费全文 | 4893篇 |
免费 | 211篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 122篇 |
大气科学 | 404篇 |
地球物理 | 1122篇 |
地质学 | 1809篇 |
海洋学 | 353篇 |
天文学 | 881篇 |
综合类 | 17篇 |
自然地理 | 448篇 |
出版年
2022年 | 28篇 |
2021年 | 63篇 |
2020年 | 67篇 |
2019年 | 90篇 |
2018年 | 143篇 |
2017年 | 150篇 |
2016年 | 152篇 |
2015年 | 133篇 |
2014年 | 185篇 |
2013年 | 261篇 |
2012年 | 204篇 |
2011年 | 266篇 |
2010年 | 207篇 |
2009年 | 263篇 |
2008年 | 213篇 |
2007年 | 190篇 |
2006年 | 177篇 |
2005年 | 174篇 |
2004年 | 184篇 |
2003年 | 161篇 |
2002年 | 163篇 |
2001年 | 81篇 |
2000年 | 89篇 |
1999年 | 75篇 |
1998年 | 90篇 |
1997年 | 68篇 |
1996年 | 65篇 |
1995年 | 61篇 |
1994年 | 57篇 |
1993年 | 65篇 |
1992年 | 48篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 41篇 |
1988年 | 47篇 |
1987年 | 53篇 |
1986年 | 49篇 |
1985年 | 57篇 |
1984年 | 67篇 |
1983年 | 51篇 |
1982年 | 57篇 |
1981年 | 47篇 |
1980年 | 47篇 |
1979年 | 46篇 |
1978年 | 43篇 |
1977年 | 37篇 |
1976年 | 31篇 |
1975年 | 32篇 |
1974年 | 33篇 |
1973年 | 31篇 |
排序方式: 共有5156条查询结果,搜索用时 312 毫秒
931.
Using reflectance values from the seven MODIS “land” bands with 250 or 500 m resolution, along with a corresponding cloud product, we estimate the fraction of each 500 m pixel that snow covers, along with the albedo of that snow. The daily products have data gaps and errors because of cloud cover and sensor viewing geometry. Rather than make users interpolate and filter these patchy daily maps without completely understanding the retrieval algorithm and instrument properties, we use the daily time series to improve the estimate of the measured snow properties for a particular day. We use a combination of noise filtering, snow/cloud discrimination, and interpolation and smoothing to produce our best estimate of the daily snow cover and albedo. We consider two modes: one is the “predictive” mode, whereby we estimate the snow-covered area and albedo on that day using only the data up to that day; the other is the “retrospective” mode, whereby we reconstruct the history of the snow properties for a previous period. 相似文献
932.
Joanna Staneva Emil V. Stanev Jörg-Olaf Wolff Thomas H. Badewien Rainer Reuter Burghard Flemming Alexander Bartholomä Karsten Bolding 《Continental Shelf Research》2009
This work deals with analysis of hydrographic observations and results of numerical simulations. The data base includes acoustic Doppler current profilers (ADCP) observations, continuous measurements on data stations and satellite data originating from the medium resolution imaging spectrometer (MERIS) onboard the European Space Agency (ESA) satellite ENVISAT with a spatial resolution of 300 m. Numerical simulations use nested models with horizontal resolutions ranging from 1 km in the German Bight to 200 m in the East Frisian Wadden Sea coupled with a suspended matter transport model. Modern satellite observations have now a comparable horizontal resolution with high-resolution numerical model of the entire area of the East Frisian Wadden Sea allowing to describe and validate new and so far unknown patterns of sediment distribution. The two data sets are consistent and reveal an oscillatory behaviour of sediment pools to the north of the back-barrier basins and clear propagation patterns of tidally driven suspended particulate matter outflow into the North Sea. The good agreement between observations and simulations is convincing evidence that the model simulates the basic dynamics and sediment transport processes, which motivates its further use in hindcasting, as well as in the initial steps towards forecasting circulation and sediment dynamics in the coastal zone. 相似文献
933.
Nathalie Vigouroux A. E. Williams-Jones Paul Wallace Thomas Staudacher 《Bulletin of Volcanology》2009,71(9):1077-1089
The November 2002 eruption of Piton de la Fournaise in the Indian Ocean was typical of the activity of the volcano from 1999
to 2006 in terms of duration and volume of magma ejected. The first magma erupted was a basaltic liquid with a small proportion
of olivine phenocrysts (Fo81) that contain small numbers of melt inclusions. In subsequent flows, olivine crystals were more abundant and richer in Mg
(Fo83–84). These crystals contain numerous melt and fluid inclusions, healed fractures, and dislocation features such as kink bands.
The major element composition of melt inclusions in this later olivine (Fo83–84) is out of equilibrium with that of its host as a result of extensive post-entrapment crystallization and Fe2+ loss by diffusion during cooling. Melt inclusions in Fo81 olivine are also chemically out of equilibrium with their hosts but to a lesser degree. Using olivine–melt geothermometry,
we determined that melt inclusions in Fo81 olivine were trapped at lower temperature (1,182 ± 1°C) than inclusions in Fo83–84 olivine (1,199–1,227°C). This methodology was also used to estimate eruption temperatures. The November 2002 melt inclusion
compositions suggest that they were at temperatures between 1,070°C and 1,133°C immediately before eruption and quenching.
This relatively wide temperature range may reflect the fact that most of the melt inclusions were from olivine in lava samples
and therefore likely underwent minor but variable amounts of post-eruptive crystallization and Fe2+ loss by diffusion due to their relatively slow cooling on the surface. In contrast, melt inclusions in tephra samples from
past major eruptions yielded a narrower range of higher eruption temperatures (1,163–1,181°C). The melt inclusion data presented
here and in earlier publications are consistent with a model of magma recharge from depth during major eruptions, followed
by storage, cooling, and crystallization at shallow levels prior to expulsion during events similar in magnitude to the relatively
small November 2002 eruption. 相似文献
934.
Panarea, characterized by gas unrest in 2002–2003, is the volcanic island with the least constrained structure in the eastern-central Aeolian Arc (Italy). Based on structural measurements, we define here its deformation pattern relative to the Arc. The main deformations are subvertical extension fractures (63% of data), normal faults (25%) and dikes (12%). The mean orientation of the extension fractures and faults is N38°E, with a mean opening direction of N135° ± 8°, implying extension with a moderate component of dextral shear. These data, matched with those available for Stromboli volcano (pure opening) and Vulcano, Lipari and Salina volcanoes (predominant dextral motions) along the eastern-central Arc, suggest a progressive westward rotation of the extension direction and an increase in the dextral shear. The dextral shear turns into compression in the western arc. The recent unrest at Panarea, coeval to that of nearby Stromboli, may also be explained by the structural context, as both volcanoes lie along the portion of the Arc subject to extension. 相似文献
935.
Existing analytical solutions to 2D and 3D contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. An approximate method is developed herein for coordinate mapping of 2D (vertically-averaged) transport solutions to non-uniform steady-state irrotational and divergence-free flow fields in single-layer aquifers. The method enables existing analytical transport solutions to be applied to aquifer systems with wells, non-uniform saturated thickness, surface water features, and (to a limited degree) heterogeneous hydraulic conductivity and recharge. This mass-conservative coordinate mapping approach is inexact in its approximation of the dispersion process but is still sufficiently accurate for many simple flow systems. The degree of model error is directly proportional to the variation of velocity magnitude within the domain. These mapped analytical solutions are compared to numerical simulation results and the coordinate mapping errors are investigated. The methods described herein may be used in the traditional capacity of analytical transport models, i.e., screening and preliminary site assessment, without sacrificing accuracy by assuming locally uniform flow conditions or applying an ad-hoc coordinate transformation. The solutions benefit from the traditional advantages of analytical methods, particularly the removal of artifacts due to spatial and temporal discretization: no time-stepping or numerical discretization is required. 相似文献
936.
937.
Susanne Benze Cora E. Randall Matthew T. DeLand Gary E. Thomas David W. Rusch Scott M. Bailey James M. Russell William McClintock Aimee W. Merkel Chris Jeppesen 《Journal of Atmospheric and Solar》2009,71(3-4):365-372
We compare measurements from the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) experiment to the NOAA-17 solar backscatter ultraviolet (SBUV/2) instrument during the 2007 Northern Hemisphere polar mesospheric cloud (PMC) season. Daily average Rayleigh scattering albedos determined from identical footprints from the CIPS nadir camera and SBUV/2 agree to better than ~5% throughout the season. Average PMC brightness values derived from the two instruments agree to within ±10%. PMC occurrence frequencies are on average ~5% to nearly a factor of two higher in CIPS, depending on latitude. Agreement is best at high latitudes where clouds are brighter and more frequent. The comparisons indicate that AIM CIPS data are valid for scientific analyses. They also show that CIPS measurements can be linked to the long time series of SBUV/2 data to investigate long-term variability in PMCs. 相似文献
938.
In a recent intercomparison of the response of general circulation models (GCMs) to high-latitude freshwater forcing (Stouffer
et al., J Climate 19(8):1365–1387, 2006), a number of the GCMs investigated showed a localised warming response in the high-latitude North Atlantic, as opposed to
the cooling that the other models showed. We investigated the causes for this warming by testing the sensitivity of the meridional
overturning circulation (MOC) to variations in freshwater forcing location, and then analysing in detail the causes of the
warming. By analysing results from experiments with HadCM3, we are able to show that the high-latitude warming is independent
of the exact location of the additional freshwater in the North Atlantic or Arctic Ocean basin. Instead, the addition of freshwater
changes the circulation in the sub-polar gyre, which leads to enhanced advection of warm, saline, sub-surface water into the
Greenland–Iceland–Norwegian Sea despite the overall slowdown of the MOC. This sub-surface water is brought to the surface
by convection, where it leads to a strong warming of the surface waters and the overlying atmosphere. 相似文献
939.
Towards continuous long-term measurements of suspended particulate matter (SPM) in turbid coastal waters 总被引:1,自引:1,他引:0
Thomas H. Badewien Elke Zimmer Alexander Bartholomä Rainer Reuter 《Ocean Dynamics》2009,59(2):227-238
The dynamics of sediment transport in the East Frisian Wadden Sea are important for the coastal zone and for ecosystem functioning.
The tidal inlets between the East Frisian islands connect the back-barrier intertidal flats to the North Sea. Here, concentrations
of suspended particulate matter (SPM) in the water column are highly variable, depending on weather conditions and tides.
In order to estimate the nature and quantity of sediment transport, in situ measurements were carried out at a Time Series
Station in the tidal inlet between the islands of Spiekeroog and Langeoog. This study shows the suitability of multispectral
transmissometry (MST) for obtaining long-term SPM measurements with high resolution. The comparability of this technique to
the standard filter method and the laser diffraction method [laser in situ scattering and transmissometry (LISST)] is demonstrated.
In addition, the Junge coefficients derived from both MST and LISST measurements are compared. A time series of SPM data covering
nearly 4 months is presented. As a major result, the data reveal that a single storm surge can have less impact on SPM dynamics
than longer-lasting gales. This high-resolution long-term data set is very valuable for modelling suspended matter flux. It
also provides background information for studying the influence of SPM dynamics on coastal sediments. 相似文献
940.