全文获取类型
收费全文 | 1780篇 |
免费 | 208篇 |
国内免费 | 280篇 |
专业分类
测绘学 | 99篇 |
大气科学 | 173篇 |
地球物理 | 572篇 |
地质学 | 564篇 |
海洋学 | 310篇 |
天文学 | 149篇 |
综合类 | 64篇 |
自然地理 | 337篇 |
出版年
2024年 | 8篇 |
2023年 | 14篇 |
2022年 | 51篇 |
2021年 | 51篇 |
2020年 | 58篇 |
2019年 | 68篇 |
2018年 | 48篇 |
2017年 | 74篇 |
2016年 | 74篇 |
2015年 | 76篇 |
2014年 | 88篇 |
2013年 | 111篇 |
2012年 | 72篇 |
2011年 | 85篇 |
2010年 | 96篇 |
2009年 | 108篇 |
2008年 | 116篇 |
2007年 | 117篇 |
2006年 | 123篇 |
2005年 | 100篇 |
2004年 | 93篇 |
2003年 | 75篇 |
2002年 | 60篇 |
2001年 | 61篇 |
2000年 | 83篇 |
1999年 | 47篇 |
1998年 | 55篇 |
1997年 | 41篇 |
1996年 | 28篇 |
1995年 | 22篇 |
1994年 | 36篇 |
1993年 | 20篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 1篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2268条查询结果,搜索用时 15 毫秒
171.
L. E. Sjöberg 《Journal of Geodesy》2007,81(5):345-350
This study emphasizes that the harmonic downward continuation of an external representation of the Earth’s gravity potential
to sea level through the topographic masses implies a topographic bias. It is shown that the bias is only dependent on the
topographic density along the geocentric radius at the computation point. The bias corresponds to the combined topographic
geoid effect, i.e., the sum of the direct and indirect topographic effects. For a laterally variable topographic density function,
the combined geoid effect is proportional to terms of powers two and three of the topographic height, while all higher order
terms vanish. The result is useful in geoid determination by analytical continuation, e.g., from an Earth gravity model, Stokes’s
formula or a combination thereof. 相似文献
172.
利用德国降水预报输出的24和48h降水预报产品,对2005年1—12月巴音郭楞蒙古自治州(简称巴州,下同)9个气象站分别进行了降水预报效果的检验分析,统计分析其在各月、各季、年的降水预报能力,得出其空报率较大,准确率和漏报率较低,但对巴州南部地区的大降水天气有一定的指导意义。 相似文献
173.
On the use of microtremor recordings in seismic microzonation 总被引:4,自引:0,他引:4
M. Bour D. Fouissac P. Dominique C. Martin 《Soil Dynamics and Earthquake Engineering》1998,17(7-8):465-474
Experimental methods involving microtremor recordings are useful for determining site effects in regions of moderate seismic activity where ground motion records are few, and in urban or industrial contexts where the noise level is high. The aim of this study is to establish a microzonation by using the Nogoshi–Nakamura method,[1, 2] a simple experimental technique based on microtremor recordings. Since the physical phenomena underlying the method are only partially understood, the spectral responses obtained cannot be used alone. We, therefore, complete our experimental results by comparing them with the solutions of a one-dimensional numerical simulation (SHAKE91).[3, 4] The experimental programme was carried out on a plain near the Rhone Delta (South of France). H/V spectral ratios were calculated at 137 noise measurement points. In addition, we were able to compute the numerical transfer functions from soil columns defined by geotechnical characteristics inside the studied region. A comparison of the results obtained by the experimental and numerical methods showed that the fundamental frequencies are in good agreement, but that the amplitudes obtained by the two techniques are sometimes different. The analysis of H/V spectral ratios enabled us to establish maps to characterize the region: a resonance frequency map and maps of amplification levels as a function of frequency range, leading to a seismic microzonation for the whole of the region. 相似文献
174.
Comparison of Galerkin-type discretization techniques for two-phase flow in heterogeneous porous media 总被引:1,自引:0,他引:1
A comparison of Standard Galerkin, Petrov-Galerkin, and Fully-Upwind Galerkin methods for the simulation of two-phase flow in heterogeneous porous media is presented. On the basis of the coupled pressure-saturation equations, a generalized formulation for all three finite element methods is derived and analysed. For flow in homogeneous media, the Petrov-Galerkin method gives excellent results. But this method fails miserably for problems with heterogeneous media. This is because it is not able to capture correctly processes that take place at interfaces when, for instance, the capillary pressure-saturation relationship after Brooks and Corey is assumed. The Fully-Upwind Galerkin method is superior to the Petrov-Galerkin approach because it is able to give correct results for flow in homogeneous and heterogeneous media for the two models of van Genuchten and Brooks-Corey. The widely used formulation which is correct for the homogeneous case cannot be used for heterogeneous media. Instead the straightforward approach of gradpc in combination with a chord-slope technique must be utilized. 相似文献
175.
S. Esposito A. Riccardi & R. Ragazzoni 《Monthly notices of the Royal Astronomical Society》1998,294(3):489-493
The usefulness of tracking the Rayleigh portion of a mesospheric sodium laser guide star as reference for absolute tip–tilt recovery in the frame of the auxiliary telescopes technique is shown. This approach leads to the reduction of the ground occupation needed to attain a given sky coverage by more than one order of magnitude. Speed, tracking precision, and the number of auxiliary telescopes are also reduced, making this new approach a more attractive one. The use of a low-altitude Rayleigh spot reinforces the fundamental limitations affecting this and other techniques, thus degrading significantly the quality of the recovered tip–tilt. However, it is shown that, provided adequate care is taken in the collection and treatment of data, an interesting tilt signal can still be retrieved. 相似文献
176.
177.
The paper presents a mechanical model for non‐isothermal behaviour of unsaturated soils. The model is based on an incrementally non‐linear hypoplastic model for saturated clays and can therefore tackle the non‐linear behaviour of overconsolidated soils. A hypoplastic model for non‐isothermal behaviour of saturated soils was developed and combined with the existing hypoplastic model for unsaturated soils based on the effective stress principle. Features of the soil behaviour that are included into the model, and those that are not, are clearly distinguished. The number of model parameters is kept to a minimum, and they all have a clear physical interpretation, to facilitate the model usefulness for practical applications. The step‐by‐step procedure used for the parameter calibration is described. The model is finally evaluated using a comprehensive set of experimental data for the thermo‐mechanical behaviour of an unsaturated compacted silt. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
178.
This study investigates the effect of a heat‐treatment upon the thermo‐mechanical behaviour of a model cement‐based material, i.e. a normalized mortar, with a (w/c) ratio of 0.5. First, a whole set of varied experimental results is provided, in order to either identify or validate a thermo‐mechanical constitutive model, presented in the second paper part. Experimental responses of both hydraulic and mechanical behaviour are given after different heating/cooling cycling levels (105, 200, 300, 400°C). The reference state, used for comparison purposes, is taken after mass stabilization at 60°C. Typical uniaxial compression tests are provided, and original triaxial deviatoric compressive test responses are also given. Hydraulic behaviour is identified simultaneously to triaxial deviatoric compressive loading through gas permeability Kgas assessment. Kgas is well correlated with volumetric strain evolution: gas permeability increases hugely when εv testifies of a dilatant material behaviour, instead of contractile from the test start. Finally, the thermo‐mechanical model, based on a thermodynamics approach, is identified using the experimental results on uniaxial and triaxial deviatoric compression. It is also positively validated at residual state for triaxial deviatoric compression, but also by using a different stress path in lateral extension, which is at the origin of noticeable plasticity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
179.
This paper is devoted to micromechanical modeling of induced anisotropic damage in brittle geomaterials. The formulation of the model is based on a proper homogenization procedure by taking into account unilateral effects and interactions between microcracks. The homogenization procedure is developed in the framework of Eshelby's inclusion solution and Ponte‐Castaneda and Willis (J. Mech. Phys. Solids 1995; 43 :1919–1951) estimate. The homogenization technique is combined with the thermodynamics framework at microscopic level for the determination of damage evolution law. A rigorous crack opening–closure transition condition is established and an energy‐release‐rate‐based damage criterion is proposed. Computational aspects on the implementation of micromechanical model are also discussed. The proposed model is evaluated by comparing numerical predictions with experimental data for various laboratory tests on concrete. Parametric studies on unilateral effects and influences of microcracks interactions are finally performed and analyzed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
180.