全文获取类型
| 收费全文 | 104篇 |
| 免费 | 8篇 |
专业分类
| 测绘学 | 3篇 |
| 大气科学 | 3篇 |
| 地球物理 | 37篇 |
| 地质学 | 29篇 |
| 海洋学 | 11篇 |
| 天文学 | 17篇 |
| 综合类 | 1篇 |
| 自然地理 | 11篇 |
出版年
| 2022年 | 1篇 |
| 2021年 | 1篇 |
| 2020年 | 4篇 |
| 2019年 | 1篇 |
| 2018年 | 2篇 |
| 2017年 | 5篇 |
| 2016年 | 2篇 |
| 2015年 | 4篇 |
| 2014年 | 5篇 |
| 2013年 | 3篇 |
| 2012年 | 3篇 |
| 2011年 | 8篇 |
| 2010年 | 9篇 |
| 2009年 | 7篇 |
| 2008年 | 9篇 |
| 2007年 | 7篇 |
| 2006年 | 2篇 |
| 2005年 | 4篇 |
| 2004年 | 4篇 |
| 2003年 | 3篇 |
| 2002年 | 4篇 |
| 2000年 | 3篇 |
| 1999年 | 2篇 |
| 1997年 | 1篇 |
| 1996年 | 3篇 |
| 1995年 | 1篇 |
| 1993年 | 1篇 |
| 1988年 | 1篇 |
| 1987年 | 1篇 |
| 1986年 | 1篇 |
| 1984年 | 4篇 |
| 1979年 | 1篇 |
| 1975年 | 1篇 |
| 1973年 | 1篇 |
| 1970年 | 2篇 |
| 1944年 | 1篇 |
排序方式： 共有112条查询结果，搜索用时 234 毫秒
101.
Numerical modeling of zero-offset laboratory data in a strong topographic environment: results for a spectral-element method and a discretized Kirchhoff integral method 
下载免费PDF全文
下载免费PDF全文 Nathalie Favretto-Cristini Anastasiya Tantsereva Paul Cristini Bjørn Ursin Dimitri Komatitsch Arkady M. Aizenberg 《地震科学（英文版）》2014,27(4):391-399
Accurate simulation of seismic wave propagation in complex geological structures is of particular interest nowadays. However conventional methods may fail to simulate realistic wavefields in environments with great and rapid structural changes, due for instance to the presence of shadow zones, diffractions and/or edge effects. Different methods, developed to improve seismic modeling, are typically tested on synthetic configurations against analytical solutions for simple canonical problems or reference methods, or via direct comparison with real data acquired in situ. Such approaches have limitations, especially if the propagation occurs in a complex environment with strong-contrast reflectors and surface irregularities, as it can be difficult to determine the method which gives the best approximation of the “real” solution, or to interpret the results obtained without an a priori knowledge of the geologic environment. An alternative approach for seismics consists in comparing the synthetic data with high-quality data collected in laboratory experiments under controlled conditions for a known configuration. In contrast with numerical experiments, laboratory data possess many of the characteristics of field data, as real waves propagate through models with no numerical approximations. We thus present a comparison of laboratory-scaled measurements of 3D zero-offset wave reflection of broadband pulses from a strong topographic environment immersed in a water tank with numerical data simulated by means of a spectral-element method and a discretized Kirchhoff integral method. The results indicate a good quantitative fit in terms of time arrivals and acceptable fit in amplitudes for all datasets. 相似文献
102.
The purpose of the present study is to investigate experimentally the development of bedforms in a configuration where the sediment supply is limited. The experimental setup is a rectangular closed duct combining an innovative system to control the rate of sediment supply Qin , and a digitizing system to measure in real time the 3D bedform topography. We carried out different sets of experiments with two sediment sizes (100 µm and 500 µm) varying both the sediment supply and the water flow rate to obtain a total of 46 different configurations. After a transient phase, steady sub‐centimeter bedforms of various shapes have been observed: barchans dunes, straight transverse dune, linguoid transverse dunes and bedload sheets. Height, spacing, migration speed, and mean bed elevation of the equilibrium bedforms were measured. For a given flow rate, two regimes were identified with fine sediment: (i) a monotonic increasing regime where the equilibrium bedform height and velocity increase with the sediment supply rate Qin and (ii) an invariant regime for which both parameters are almost independent of Qin. For coarse sediment, only the first regime is observed. We interpret the saturation of height and velocity for fine sediment bedforms as the transition from a supply‐limited regime to a transport‐limited regime in which the bedload flux has reached its maximum value under the prevailing flow conditions. We also demonstrate that all experiments can be rescaled if the migration speed and height of the bedforms are, respectively, divided and multiplied by the cube of the shear velocity. This normalization is independent of grain size and of bedform morphology. These experimental results provide a new quantification of the factors controlling equilibrium height and migration speed of bedforms in supply‐limited conditions against which theoretical and numerical models can be tested. 相似文献
103.
Dimitri Alexei Gadotti Ronaldo Eustáquio de Souza 《Astrophysics and Space Science》2003,284(2):527-530
To further enhance our understanding on the formation and evolution of bars in lenticular (S0) galaxies, we are undertaking
a detailed photometric and spectroscopic study on a sample of 22 objects. Here we report the results of a 2D structural analysis
on two barred face-on S0's, which indicate that presently these galaxies do not possess disks. We discuss two possibilities
to explain these surprising results, namely strong secular evolution and bar formation without disks.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
104.
The earthquake of April 30, 1954, in Sophades (Central Greece) 总被引：1，自引：0，他引：1
105.
Aristidis V. Asimakopoulos Dimitris L. Karabalis Dimitri E. Beskos 《地震工程与结构动力学》2007,36(14):2171-2188
A procedure for treating the P– Δ effect in the direct displacement‐based seismic design of regular steel moment resisting frames with ideal elastoplastic material behaviour is proposed. A simple formula for the yield displacement amplification factor as a function of ductility and the stability coefficient is derived on the basis of the seismic response of an inelastic single degree‐of‐freedom system taking into account the P– Δ effect. Extensive parametric seismic inelastic analyses of plane moment resisting steel frames result in a simple formula for the dynamic stability coefficient as a function of the number of stories of a frame and the column to beam stiffness ratio. Thus, the P– Δ effect can be easily taken into account in a direct displacement‐based seismic design through the stability coefficient and the yield displacement amplification factor. A simple design example serves to illustrate the application of the proposed method and demonstrate its merits. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
106.
Europium redox equilibria in aqueous solution 总被引：6，自引：0，他引：6
Dimitri A. Sverjensky 《Earth and Planetary Science Letters》1984,67(1):70-78
Thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous Eu2+ and Eu3+ over a wide range of temperatures and pressures. At low temperatures, near earth surface conditions, the aqueous geochemistry of europium should be dominated by the trivalent state, except possibly in the most reducing, alkaline pore waters of anoxic marine sediments. However, at temperatures greater than about 250°C and elevated pressures, divalent europium should predominate. Even with significant amounts of complexing, trivalent europium is not stable at elevated temperatures and pressures. Consequently, under most hydrothermal and metamorphic conditions, europium in aqueous solution should be divalent. At intermediate temperatures, around 100°C, significant activities of both Eu2+ and Eu3+, and related complexes, can occur in aqueous solutions, depending on the oxidation state and the pH of the solutions, and the activities of potential ligands such as sulfate, carbonate and chloride. The predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high-temperature barites of hydrothermal and metamorphic origin reported by Guichard et al. [5] and with the observed depletion of europium as a result of high-temperature sericitization of feldspar-bearing assemblages discovered by Alderton et al. [1]. It is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high-temperature hydrothermal alteration processes, such as in the mid-oceanic ridge systems, because of the expected stability of divalent europium during these processes. 相似文献
107.
Measurements consistency-based Receiver Autonomous Integrity Monitoring (RAIM) is the main technique for monitoring the integrity of global satellite navigation systems at the user-level. Existing RAIM algorithms utilize two tests, in the position domain a test for RAIM availability and in the measurement domain a test for failure detection. These tests involve the computation of three parameters: test statistic, decision threshold, and protection level. The test statistic is based on the actual measurements in the form of the sum of the squared errors (SSE). The decision threshold is chosen on the basis of the statistical characteristics of the SSE including the assumption that the errors are normally distributed. However, in practice residual, error distributions exhibit heavier tails than predicted by the Gaussian model. Therefore, this paper challenges the normality assumption of the residual navigation errors in three ways. First, real data are used to assess its impact on the traditional RAIM algorithm. Second, extreme value theory is applied to the tails, and the generalized extreme value (GEV) distribution is derived to capture residual navigation errors. Third, the performance of the traditional RAIM approach is compared with that employing the GEV distribution. The results demonstrate that the GEV model is a more accurate representation of the distribution of residual navigation errors than the conventional Gaussian model and should be used in the development of integrity monitoring algorithms. 相似文献
108.
Dimitri A. Sverjensky 《Geochimica et cosmochimica acta》2006,70(10):2427-2453
Despite the fact that the bulk compositions of most low temperature natural surface waters, groundwaters, and porewaters are heavily influenced by alkaline earths, an understanding of the development of proton surface charge in the presence of alkaline earth adsorption on the surfaces of minerals is lacking. In particular, models of speciation at the mineral-water interface in systems involving alkaline earths need to be established for a range of different minerals. In the present study, X-ray standing wave results for Sr2+ adsorption on rutile as a tetranuclear complex [Fenter, P., Cheng, L., Rihs, S., Machesky, M., Bedyzk, M.D., Sturchio, N.C., 2000. Electrical double-layer structure at the rutile-water interface as observed in situ with small-period X-ray standing waves. J. Colloid Interface Sci.225, 154-165] are used as constraints for all the alkaline earths in surface complexation simulations of proton surface charge, metal adsorption, and electrokinetic experiments referring to wide ranges of pH, ionic strength, surface coverage, and type of oxide. The tetranuclear reaction
4>SOH+M2++H2O=(>SOH)2(>SO-)2_M(OH)++3H+ 相似文献
109.
110.
A precipiton‐based approach to model hydro‐sedimentary hazards induced by large sediment supplies in alluvial fans 下载免费PDF全文
下载免费PDF全文 Thomas Croissant Dimitri Lague Philippe Davy Tim Davies Philippe Steer 《地球表面变化过程与地形》2017,42(13):2054-2067
Mountain ranges are frequently subjected to mass wasting events triggered by storms or earthquakes and supply large volumes of sediment into river networks. Besides altering river dynamics, large sediment deliveries to alluvial fans are known to cause hydro‐sedimentary hazards such as flooding and river avulsion. Here we explore how the sediment supply history affects hydro‐sedimentary river and fan hazards, and how well can it be predicted given the uncertainties on boundary conditions. We use the 2D morphodynamic model Eros with a new 2D hydrodynamic model driven by a sequence of flood, a sediment entrainment/transport/deposition model and a bank erosion law. We first evaluate the model against a natural case: the 1999 Mount Adams rock avalanche and subsequent avulsion on the Poerua river fan (West Coast, New Zealand). By adjusting for the unknown sediment supply history, Eros predicts the evolution of the alluvial riverbed during the first post‐landslide stages within 30 cm. The model is subsequently used to infer how the sediment supply volume and rate control the fan aggradation patterns and associated hazards. Our results show that the total injected volume controls the overall levels of aggradation, but supply rates have a major control on the location of preferential deposition, avulsion and increased flooding risk. Fan re‐incision following exhaustion of the landslide‐derived sediment supply leads to sediment transfer and deposition downstream and poses similar, but delayed, hydro‐sedimentary hazards. Our results demonstrate that 2D morphodynamics models are able to capture the full range of hazards occurring in alluvial fans including river avulsion aggradation and floods. However, only ensemble simulations accounting for uncertainties in boundary conditions (e.g., discharge history, initial topography, grain size) as well as model realization (e.g., non‐linearities in hydro‐sedimentary processes) can be used to produce probabilistic hazards maps relevant for decision making. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献