全文获取类型
收费全文 | 185篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 20篇 |
地球物理 | 64篇 |
地质学 | 54篇 |
海洋学 | 11篇 |
天文学 | 43篇 |
综合类 | 2篇 |
自然地理 | 7篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 12篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1984年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 5篇 |
1965年 | 1篇 |
排序方式: 共有203条查询结果,搜索用时 15 毫秒
21.
22.
Stream-water temperature is a key variable controlling chemical, biological, and ecological processes in freshwater environments. Most models focus on a single river cross-section; however, temperature gradients along stretches and tributaries of a river network are crucial to assess ecohydrological features such as aquatic species suitability, growth and feeding rates, or disease transmission. We propose SESTET, a deterministic, spatially explicit stream temperature model for a whole river network, based on water and energy budgets at a reach scale and requiring only commonly available spatially distributed datasets, such as morphology and air temperature, as input. Heat exchange processes at the air–water interface are modelled via the widely used equilibrium temperature concept, whereas the effects of network structure are accounted for through advective heat fluxes. A case study was conducted on the prealpine Wigger river (Switzerland), where water temperatures have been measured in the period 2014–2018 at 11 spatially distributed locations. The results show the advantages of accounting for water and energy budgets at the reach scale for the entire river network, compared with simpler, lumped formulations. Because our approach fundamentally relies on spatially distributed air temperature fields, adequate spatial interpolation techniques that account for the effects of both elevation and thermal inversion in air temperature are key to a successful application of the model. SESTET allows the assessment of the magnitude of the various components of the heat budget at the reach scale and the derivation of reliable estimates of spatial gradients of mean daily stream temperatures for the whole catchment based on a limited number of conveniently located (viz., spanning the largest possible elevation range) measuring stations. Moreover, accounting for mixing processes and advective fluxes through the river network allows one to trust regionalized values of the parameters controlling the relationship between equilibrium and air temperature, a key feature to generalize the model to data-scarce catchments. 相似文献
23.
Andreas J. Scheib Manfred Birke Enrico Dinelli GEMAS Project Team 《Boreas: An International Journal of Quaternary Research》2014,43(1):175-192
Hafnium (Hf) and zirconium (Zr) concentrations measured in over 4100 agricultural soil samples from Europe were assessed with the focus on their relationship to the distribution of aeolian deposits, such as loess and coversands. Comparison of extractable (aqua regia; ICP‐MS) and total (XRFS) concentrations shows that only 1.0 to 1.7% of the total Hf and Zr is chemically extractable because of the resistant nature of their host minerals. Resistate minerals, such as zircon, are commonly found in the predominantly silty fraction of loess deposits. In this study a statistical analysis of total Hf and Zr soil data from areas with and without loess was carried out to derive threshold values of 10 mg kg?1 (Hf) and 318 mg kg?1 (Zr). These values were subsequently applied across the project area in an attempt to indicate the presence of aeolian deposits. The spatial distribution of above‐threshold concentrations suggests a more extensive and coherent loess belt across central and eastern Europe, providing additional evidence of loess across Brittany, Aquitaine and near the Vosges mountains in France as well as in the basins of central and northern Spain. Above‐threshold concentrations were also detected in loess regardless of its thickness, emphasising the importance of the abundance of zircon in the upper part of the soil profile rather than the actual thickness of the deposit. Soil data however, failed to indicate various loess facies within most of the Pannonian Basin, suggesting that this approach only works where deposits contain a sufficient amount of zircon. This may also explain why the extensive coversands across northern Germany and Poland were largely undetected. This study demonstrates that continental‐scale soil geochemical data can help identify and map the distribution of zircon‐rich loess and coversand, and subsequently enhance and improve current knowledge of the extent of these deposits. 相似文献
24.
25.
For seismic analysis of unreinforced masonry (URM) buildings characterized by a box-like behavior, a widely accepted model is based on the equivalent frame idealization of walls. The equivalent frame model uses 1D elements to represent the vertical piers and horizontal spandrels which are connected by rigid nodes. The mechanical characterization of the elements is one of the crucial aspects to predict reasonably the building seismic behavior. Through the comparison with pseudo-static and dynamic experimental tests performed on two-story full-scale buildings, this paper validates the frame modeling in the OpenSees framework, which includes a fiber-section force-based beam element for the axial-flexural behavior, coupled with a cyclic shear-deformation phenomenological law. 相似文献
26.
基于GOODALL相近指数的遥感图像和其它空间数据综合分类方法 总被引:2,自引:0,他引:2
介绍DavidW.Goodall基于概率的相近指数理论,研究它被应用在遥感图像和其它空间数据综合分类中的可能性,并首次在GRASS环境下实现了基于DavidW.Goodall的相近指数的遥感图像和其它空间数据综合分类算法,并对该算法进行了测试,将分类结果 与其它几种较流行的分类方法结果进行了比较。 相似文献
27.
Nonstationary stochastic response of structural systems equipped with nonlinear viscous dampers under seismic excitation 总被引:1,自引:0,他引:1 下载免费PDF全文
Nonlinear viscous dampers are supplemental devices widely used for enhancing the performance of structural systems exposed to seismic hazard. A rigorous evaluation of the effect of these damping devices on the seismic performance of a structural system should be based on a probabilistic approach and take into account the evolutionary characteristics of the earthquake input and of the corresponding system response. In this paper, an approximate analytical technique is proposed for studying the nonstationary stochastic response characteristics of hysteretic single degree of freedom systems equipped with viscous dampers subjected to a fully nonstationary random process representing the seismic input. In this regard, a stochastic averaging/linearization technique is utilized to cast the original nonlinear stochastic differential equation of motion into a simple first‐order nonlinear ordinary differential equation for the nonstationary system response variance. In comparison with standard linearization schemes, the herein proposed technique has the significant advantage that it allows to handle realistic seismic excitations with time‐varying frequency content. Further, it allows deriving a formula for determining the nonlinear system response evolutionary power spectrum. By this way, ‘moving resonance’ effects, related to both the evolutionary seismic excitation and the nonlinear system behavior, can be observed and quantified. Several applications involving various system and input properties are included. Furthermore, various response parameters of interest for the seismic performance assessment are considered as well. Comparisons with pertinent Monte Carlo simulations demonstrate the reliability of the proposed technique. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
28.
Hemchandra Chaulagain Hugo Rodrigues Enrico Spacone Ramesh Guragain Radhakrishna Mallik Humberto Varum 《地震工程与工程振动(英文版)》2014,13(3):455-470
Most current seismic design includes the nonlinear response of a structure through a response reduction factor(R). This allows the designer to use a linear elastic force-based approach while accounting for nonlinear behavior and deformation limits. In fact, the response reduction factor is used in modern seismic codes to scale down the elastic response of a structure. This study focuses on estimating the actual ‘R' value for engineered design/construction of reinforced concrete(RC) buildings in Kathmandu valley. The ductility and overstrength of representative RC buildings in Kathmandu are investigated. Nonlinear pushover analysis was performed on structural models in order to evaluate the seismic performance of buildings. Twelve representative engineered irregular buildings with a variety of characteristics located in the Kathmandu valley were selected and studied. Furthermore, the effects of overstrength on the ductility factor, beam column capacity ratio on the building ductility, and load path on the response reduction factor, are examined. Finally, the results are further analyzed and compared with different structural parameters of the buildings. 相似文献
29.
30.
In this paper we describe an example of travertine fissure-ridge development along the trace of a normal fault with metre
displacement, located in the eastern margin of the Neogene–Quaternary Siena Basin, in the Terme S. Giovanni area (Rapolano
Terme, Italy). This morphotectonic feature, 250 m long, 30 m wide and 10 m high, formed from supersaturated hot waters (39.9°C)
flowing from thermal springs aligned along the trace of the normal fault dissecting travertines not older than Late Pleistocene
(24 ± 3 ka). A straight, continuous fissure with a maximum width of 20 cm occurs at the top of the ridge, along its crest.
Hot fluids flow from cones mainly located at the extremities of the ridge, where travertine is depositing. The travertine
fissure-ridge shows an asymmetrical profile since it buries the fault scarp. The difference in height of slopes corresponds
to the vertical displacement of the normal fault. Fissuring of the recent travertine deposits along the strike of the crestal
fissure, as well as recent hydrothermal circulation, lead us to believe that the Terme S. Giovanni normal fault may be currently
active. On the whole, the Terme S. Giovanni fissure ridge can be defined as a travertine fault trace fissure-ridge, adding
a helpful example for studying the relationship between faulting and travertine deposition. 相似文献