全文获取类型
收费全文 | 620篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 44篇 |
大气科学 | 45篇 |
地球物理 | 144篇 |
地质学 | 201篇 |
海洋学 | 21篇 |
天文学 | 112篇 |
综合类 | 5篇 |
自然地理 | 74篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 14篇 |
2020年 | 12篇 |
2019年 | 21篇 |
2018年 | 20篇 |
2017年 | 17篇 |
2016年 | 28篇 |
2015年 | 23篇 |
2014年 | 24篇 |
2013年 | 50篇 |
2012年 | 37篇 |
2011年 | 22篇 |
2010年 | 24篇 |
2009年 | 40篇 |
2008年 | 25篇 |
2007年 | 30篇 |
2006年 | 23篇 |
2005年 | 32篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有646条查询结果,搜索用时 15 毫秒
11.
Oliver K. Manuel 《Icarus》1980,41(2):312-315
Isotopically anomalous xenon in chondrites is closely associated with low-Z noble gases, but there is no helium (or neon) in the noble gas component with normal xenon. The correlation of elemental and isotopic heterogeneities in meteoritic noble gases places stringent limits on the origin of isotopically anomalous elements in meteorites and on the formation of the solar system. 相似文献
12.
Nicole Vatin-Prignon Pierre Goemans Richard A. Oliver Eduardo Parra Palacio 《Journal of Volcanology and Geothermal Research》1990,41(1-4)
Trace-element concentrations of the eruptive products from the Nevado del Ruiz volcano indicate that at least for the last 1 Ma, the major controlling factor in the evolution of the magma has been a simple fractional crystallization.The Zr/Hf ratios suggest that the source material is mantle-like in origin and whilst subduction-related contamination of the source material has taken place, there is no evidence that assimilation of continental crust has affected the series.No convincing geochemical evidence for magma mixing was found, and data on banded pumices of Pleistocene, Historic and the 1985 eruptions strongly support a crystal fractionation model to explain the compositional variation of their glasses. Therefore, if mixing has taken place it can only be a mixing of layers within a stratified or partially stratified magma chamber.Modeling of fractional crystallization using a stepwise program has been undertaken and least-squares approximations with small residuals are commensurate with analyzed samples. Crystal fractionation models with plagioclase dominating two-pyroxenes and iron oxides give good fits for all calculations. We conclude that simple crystal fractionation is the process most consistent with major- and trace-element variations in the Ruiz series. This closed-system model requires at least 77% crystal fractionation of a basaltic parent to generate the observed compositions of dacites. 相似文献
13.
This paper is concerned with numerical tests of several rock physical relationships. The focus is on effective velocities and scattering attenuation in 3D fractured media. We apply the so‐called rotated staggered finite‐difference grid (RSG) technique for numerical experiments. Using this modified grid, it is possible to simulate the propagation of elastic waves in a 3D medium containing cracks, pores or free surfaces without applying explicit boundary conditions and without averaging the elastic moduli. We simulate the propagation of plane waves through a set of randomly cracked 3D media. In these numerical experiments we vary the number and the distribution of cracks. The synthetic results are compared with several (most popular) theories predicting the effective elastic properties of fractured materials. We find that, for randomly distributed and randomly orientated non‐intersecting thin penny‐shaped dry cracks, the numerical simulations of P‐ and S‐wave velocities are in good agreement with the predictions of the self‐consistent approximation. We observe similar results for fluid‐filled cracks. The standard Gassmann equation cannot be applied to our 3D fractured media, although we have very low porosity in our models. This is explained by the absence of a connected porosity. There is only a slight difference in effective velocities between the cases of intersecting and non‐intersecting cracks. This can be clearly demonstrated up to a crack density that is close to the connectivity percolation threshold. For crack densities beyond this threshold, we observe that the differential effective‐medium (DEM) theory gives the best fit with numerical results for intersecting cracks. Additionally, it is shown that the scattering attenuation coefficient (of the mean field) predicted by the classical Hudson approach is in excellent agreement with our numerical results. 相似文献
14.
Shallow circulations are central to many tropical cloud systems. We investigate the potential of existing and upcoming data to document these circulations. Different methods to observe or constrain atmospheric circulations rely on satellite-borne instruments. Direct observations of the wind are currently possible at the ocean surface or using tracer patterns. Satellite-borne wind lidar will soon be available, with a much better coverage and accuracy. Meanwhile, circulations can be constrained using satellite observations of atmospheric diabatic heating. We evaluate the commonalities and discrepancies of these estimates together with reanalysis in systems that include shallow circulations. It appears that existing datasets are in qualitative agreement, but that they still differ too much to provide robust evaluation criteria for general circulation models. This state of affairs highlights the potential of satellite-borne wind lidar and of further work on current satellite retrievals. 相似文献
15.
Hartmut H. Hellmer Monika Rhein Günther Heinemann Janna Abalichin Wafa Abouchami Oliver Baars Ulrich Cubasch Klaus Dethloff Lars Ebner Eberhard Fahrbach Martin Frank Gereon Gollan Richard J. Greatbatch Jens Grieger Vladimir M. Gryanik Micha Gryschka Judith Hauck Mario Hoppema Oliver Huhn Torsten Kanzow Boris P. Koch Gert König-Langlo Ulrike Langematz Gregor C. Leckebusch Christof Lüpkes Stephan Paul Annette Rinke Bjoern Rost Michiel Rutgers van der Loeff Michael Schröder Gunther Seckmeyer Torben Stichel Volker Strass Ralph Timmermann Scarlett Trimborn Uwe Ulbrich Celia Venchiarutti Ulrike Wacker Sascha Willmes Dieter Wolf-Gladrow 《Ocean Dynamics》2016,66(11):1379-1413
16.
17.
18.
19.
G. Christakos C. T. Miller D. Oliver 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(3):213-239
As is well known, a complete stochastic solution of the stochastic differential equation governing saturated groundwater flow leads to an infinite hierarchy of equations in terms of higher-order moments. Perturbation techniques are commonly used to close this hierarchy, using power-series expansions. These methods are applied by truncating the series after a finite number of terms, and products of random gradients of conductivity and head potential are neglected. Uncertainty regarding the number or terms required to yield a sufficiently accurate result is a significant drawback with the application of power series-based perturbation methods for such problems. Low-order series truncation may be incapable of representing fundamental characteristics of flow and can lead to physically unreasonable and inaccurate solutions of the stochastic flow equation. To support this argument, one-dimensional, steady-state, saturated groundwater flow is examined, for the case of a spatially distributed hydraulic conductivity field. An ordinary power-series perturbation method is used to approximate the mean head, using second-order statistics to characterize the conductivity field. Then an interactive perturbation approach is introduced, which yields improved results compared to low-order, power-series perturbation methods for situations where strong interactions exist between terms in such approximations. The interactive perturbation concept is further developed using Feynman-type diagrams and graph theory, which reduce the original stochastic flow problem to a closed set of equations for the mean and the covariance functions. Both theoretical and practical advantages of diagrammatic solutions are discussed; these include the study of bounded domains and large fluctuations. 相似文献
20.
Volker Haak 《Surveys in Geophysics》1980,4(1-2):57-69
Laboratory data of the electrical conductivity of rocks and minerals pertinent to the deeper crust and upper mantle and summarized. They are discussed in the context of a theory to calculate effective conductivities of materials in the state of partial melt. Most published data have been obtained by too rapid measurements, i.e. without reaching an equilibrium state of the sample. Conductivity measurements on a material similar to the composition of pyrolite are not het known, their importance is outlined. A global conductivity distribution obtained by electromagnetic induction studies is represented by a few results covering oceanic and continental areas. Till today it seems to be a doubtful venture to deduce the temperature of the upper mantle or even the existence of a partial molten asthenosphere from a global conductivity distribution. On a more local scale the correlation of electrical conductivity with temperature and state of the material seems to be more realistic. This is tentatively shown by two petrological models of the Afar depression in Ethiopia and of the midoceanic rift. 相似文献