全文获取类型
收费全文 | 937篇 |
免费 | 54篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 73篇 |
地球物理 | 198篇 |
地质学 | 379篇 |
海洋学 | 88篇 |
天文学 | 172篇 |
综合类 | 4篇 |
自然地理 | 65篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 14篇 |
2018年 | 33篇 |
2017年 | 30篇 |
2016年 | 41篇 |
2015年 | 31篇 |
2014年 | 42篇 |
2013年 | 56篇 |
2012年 | 52篇 |
2011年 | 60篇 |
2010年 | 41篇 |
2009年 | 65篇 |
2008年 | 55篇 |
2007年 | 53篇 |
2006年 | 52篇 |
2005年 | 43篇 |
2004年 | 24篇 |
2003年 | 35篇 |
2002年 | 36篇 |
2001年 | 27篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1967年 | 1篇 |
排序方式: 共有999条查询结果,搜索用时 15 毫秒
121.
Fedor Baart Gerben de Boer Wim de Haas Gennadii Donchyts Marc Philippart Mark van Koningsveld Maarten Plieger 《Transactions in GIS》2012,16(2):249-265
Numerical models produce output with a large number of variables, grid cells and time steps. The same applies to algorithms that produce gridded datasets from sparse or abundant raw data. Further use of the resulting data products has been challenging, especially for dissemination outside the institute of origin. Due to the gradually increasing size of data products, simply downloading copies of them is becoming impossible. A gradual transition from traditional download methods to web services is therefore observed. Web services allow for on‐the‐fly access to subsets of data that were hitherto considered as indivisible granules. Here we compare the most mature candidates to serve gridded data through the web: the Open‐source Project for a Network Data Access Protocol (OPeNDAP) and Web Coverage Service (WCS) protocols. In the framework of the new Dutch National Model and Data Centre (NMDC.eu) a distributed data storage has been created by coupling OPeNDAP servers. A WCS service layer is provided for the same data. This allows us to compare OPeNDAP and WCS. Using several use cases, we compare the usability, performance and features of the two protocols. 相似文献
122.
Brendon Blue Claire Gregory Kiely McFarlane Marc Tadaki Petra van Limburg‐Meijer Nick Lewis 《New Zealand geographer》2012,68(1):62-66
The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently. 相似文献
123.
Nikki Vercauteren Elie Bou-Zeid Marc B. Parlange Ulrich Lemmin Hendrik Huwald John Selker Charles Meneveau 《Boundary-Layer Meteorology》2008,128(2):205-228
We examine the dynamics of turbulence subgrid (or sub-filter) scales over a lake surface and the implications for large-eddy
simulations (LES) of the atmospheric boundary layer. The analysis is based on measurements obtained during the Lake-Atmosphere
Turbulent EXchange (LATEX) field campaign (August–October, 2006) over Lake Geneva, Switzerland. Wind velocity, temperature
and humidity profiles were measured at 20 Hz using a vertical array of four sonic anemometers and open-path gas analyzers.
The results indicate that the observed subgrid-scale statistics are very similar to those observed over land surfaces, suggesting
that the effect of the lake waves on surface-layer turbulence during LATEX is small. The measurements allowed, for the first
time, the study of subgrid-scale turbulent transport of water vapour, which is found to be well correlated with the transport
of heat, suggesting that the subgrid-scale modelling of the two scalars may be coupled to save computational resources during
LES. 相似文献
124.
A Hybrid Spectral/Finite-Volume Algorithm for Large-Eddy Simulation of Scalars in the Atmospheric Boundary Layer 总被引:2,自引:2,他引:0
Pseudospectral methods are frequently used in the horizontal directions in large-eddy simulation of atmospheric flows. However,
the same approach often creates unphysical oscillations for scalar fields if there are horizontal heterogeneities in the sources
and/or sinks, as is usual in air pollution problems. A hybrid approach is developed to combine the use of pseudospectral representation
of the velocity field and bounded finite-volumes for the scalar concentration. An interpolation scheme that yields a divergence-free
interpolated velocity field is derived and implemented, and its importance is illustrated by two sample applications. 相似文献
125.
Marc Poumadère Claire Mays Gabriela Pfeifle Athanasios T. Vafeidis 《Climatic change》2008,91(1-2):123-143
Risk policy and public attitudes appear disconnected from research predicting warmer climate partially due to human activity. To step out of this stalled situation, a worst case scenario of a 5- to 6-m sea level rise (SLR) induced by the collapse of the WAIS and occurring during the period 2030–2130 is constructed and applied to the Rhone delta. Physical and socio-economic scenarios developed with data from the Rhone delta context are developed and submitted to stakeholders for a day-long workshop. Group process analysis shows a high level of trust and cooperation mobilized to face the 5–6 m SLR issue, despite potentially diverging interests. Two sets of recommendations stem from the scenario workshop. A conservative “wait and see” option is decided when the risk of the WAIS collapse is announced in 2030. After WAIS collapse generates an effective 1 m SLR rise by 2050, decisions are taken for total retreat and rendering of the Rhone delta to its hydrological function. The transposition of these results into present-day policy decisions could be considered. The methodology developed here could be applied to other risk objects and situations, and serve for policy exercises and crisis prevention. 相似文献
126.
127.
Silvia Toonen Clovis Hopman Marc Freitag 《Monthly notices of the Royal Astronomical Society》2009,398(3):1228-1234
Stars on eccentric orbits around a massive black hole (MBH) emit bursts of gravitational waves (GWs) at periapse. Such events may be directly resolvable in the Galactic Centre. However, if the star does not spiral in, the emitted GWs are not resolvable for extragalactic MBHs, but constitute a source of background noise. We estimate the power spectrum of this extreme mass ratio burst background (EMBB) and compare it to the anticipated instrumental noise of the Laser Interferometer Space Antenna (LISA). To this end, we model the regions close to an MBH, accounting for mass segregation, and for processes that limit the presence of stars close to the MBH, such as GW inspiral and hydrodynamical collisions between stars. We find that the EMBB is dominated by GW bursts from stellar mass black holes, and the magnitude of the noise spectrum ( fS GW )1/2 is at least a factor of ∼10 smaller than the instrumental noise. As an additional result of our analysis, we show that LISA is unlikely to detect relativistic bursts in the Galactic Centre. 相似文献
128.
Erika?Kaufmann Günter?Kargl Norbert?I.?K?mleEmail author Manfred?Steller Johann?Hasiba Florian?Tatschl Stefan?Ulamec Jens?Biele Marc?Engelhardt Jens?Romstedt 《Earth, Moon, and Planets》2009,105(1):11-29
One possibility to explore the subsurface layers of icy bodies is to use a probe with a “hot tip", which is able to penetrate
ice layers by melting. Such probes have been built and used in the past for the exploration of terrestrial polar ice sheets
and may also become useful tools to explore other icy layers in the Solar System. Examples for such layers are the polar areas
of Mars or the icy crust of Jupiter’s moon Europa. However, while on Earth a heated probe launched into an ice sheet always
causes melting with subsequent refreezing, the behaviour of such a probe in a low pressure environment is quite different.
We report on the results of some experiments with a simple “melting probe" prototype with two different kinds of hot tips
in a vacuum environment. For one of the tips the probe moved into two types of ice samples: (i) compact water ice and (ii)
porous water ice with a snow (firn) like texture. It was also found that the penetration behaviour was basically different
for the two sample types even when the same kind of tip was used. While in the porous sample the ice was only subliming, the
phase changes occurring during the interaction of the tip with the compact ice are much more complex. Here alternating phases
of melting and sublimation occur. The absence of the liquid phase has severe consequences on the performance of a “melting
probe" under vacuum conditions: In this environment we find a high thermal resistance between the probe surface and the underlying
ice. Therefore, only a low percentage of the heat that is generated in the tip is used to melt or sublime the ice, the bulk
of the power is transferred towards the rear end of the probe. This is particularly a problem in the initial phases of an
ice penetration experiment, when the probe has not yet penetrated the ice over its whole length. In the compact ice sample,
phases could be observed, where a high enough gas pressure had built up locally underneath the probe, so that melting becomes
possible. Only during these melting periods the thermal contact between the probe and the ice is good and in consequence the
melting probe works effectively. 相似文献
129.
Marc Fries Mark Burchell Anton Kearsley Andrew Steele 《Meteoritics & planetary science》2009,44(10):1465-1474
Abstract— It is reasonable to expect that cometary samples returned to Earth by the Stardust space probe have been altered to some degree during capture in aerogel at 6.1 km/s. In order to help interpret the measured structure of these particles with respect to their original cometary nature, a series of coal samples of known structure and chemical composition was fired into aerogel at Stardust capture velocity. This portion of the study analyzed the surfaces of aerogel‐embedded particles using Raman spectroscopy. Results show that particle surfaces are largely homogenized during capture regardless of metamorphic grade or chemical composition, apparently to include a devolatilization step during capture processing. This provides a possible mechanism for alteration of some aliphatic compound‐rich phases through devolatilization of cometary carbonaceous material followed by re‐condensation within the particle. Results also show that the possibility of alteration must be considered for any particular Stardust grain, as examples of both graphitization and amorphization are found in the coal samples. It is evident that Raman G band (~1580 cm?1) parameters provide a means of characterizing Stardust carbonaceous material to include identifying those grains which have been subjected to significant capture alteration. 相似文献
130.
Oxygen isotopic analyses were performed in the surface layers of lunar metallic grains from lunar regolith samples 71501 and 79035, presumably exposed at the Moon surface at different times. We were able to reproduce the two extreme O components previously found [Hashizume K. and Chaussidon M. (2005) A non-terrestrial 16O-rich isotopic composition for the protosolar nebula. Nature434, 619-622; Ireland T. R., Holden P., Norman M. D. and Clarke J. (2006) Isotopic enhancements of 17O and 18O from solar wind particles in the lunar regolith. Nature440, 776-778], with a range observed of −12 ± 5 < Δ17O < +33 ± 3‰ (1σ). The relatively minor 16O-rich component corresponding to an end-member Δ17O value lower than −20‰ is likely the solar component. This comes from the fact that its concentration roughly agrees with the maximum solar wind abundance expected among the grains from the two samples. At variance the 16O-poor component is 5-10 times more abundant and thus likely non-solar. The δ18O range found for the 16O-poor component may reflect various processes such as isotope exchange reaction during oxidation of metallic iron and/or isotope fractionation by evaporation/condensation at the surface of the Moon or during implantation at depth in the lunar metallic grains. The present study suggests that planetary solid materials in bulk are systematically depleted in 16O relative to the solar isotopic composition, suggesting the existence of non-mass-dependent isotopic fractionations associated to the formation of solids in the accretion disk. 相似文献