全文获取类型
收费全文 | 187篇 |
免费 | 28篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 16篇 |
地球物理 | 52篇 |
地质学 | 73篇 |
海洋学 | 12篇 |
天文学 | 36篇 |
自然地理 | 21篇 |
出版年
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 20篇 |
2015年 | 9篇 |
2014年 | 13篇 |
2013年 | 21篇 |
2012年 | 10篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 6篇 |
2005年 | 17篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1998年 | 3篇 |
1995年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有218条查询结果,搜索用时 25 毫秒
11.
In this paper, we present a semi-implicit method for the incompressible three-phase flow equations in two dimensions. In particular, a high-order discontinuous Galerkin spatial discretization is coupled with a backward Euler discretization in time. We consider a pressure-saturation formulation, decouple the pressure and saturation equations, and solve them sequentially while still keeping each equation implicit in its respective unknown. We present several numerical examples on both homogeneous and heterogeneous media, with varying permeability and porosity. Our results demonstrate the robustness of the scheme. In particular, no slope limiters are required and a relatively large time step may be taken. 相似文献
12.
Arif Mohaimin Sadri Satish V. Ukkusuri Seungyoon Lee Rosalee Clawson Daniel Aldrich Megan Sapp Nelson Justin Seipel Daniel Kelly 《Natural Hazards》2018,90(3):1377-1406
The factors that explain the speed of recovery after disaster remain contested. While many have argued that physical infrastructure, social capital, and disaster damage influence the arc of recovery, empirical studies that test these various factors within a unified modeling framework are few. We conducted a mail survey to collect data on household recovery in four small towns in southern Indiana that were hit by deadly tornadoes in March 2012. The recovery effort is ongoing; while many of the homes, businesses, and community facilities were rebuilt in 2013, some are still under construction. We investigate how households in these communities are recovering from damage that they experienced and the role of social capital, personal networks, and assistance from emergency responders on the overall recovery experience. We used an ordered probit modeling framework to test the combined as well as relative effects of (a) damage to physical infrastructures (houses, vehicles, etc.); (b) recovery assistance from emergency responders (FEMA) as well as friends and neighbors; (c) personal network characteristics (size, network density, proximity, length of relationship); (d) social capital (civic engagement, contact with neighbors, trust); and (e) household characteristics. Results show that while households with higher levels of damage experienced slower recovery, those with recovery assistance from neighbors, stronger personal networks, and higher levels of social capital experienced faster recovery. The insights gained in this study will enable emergency managers and disaster response personnel to implement targeted strategies in facilitating post-disaster recovery and community resilience. 相似文献
13.
Goodman Zachary T. Stamatis Caitlin A. Stoler Justin Emrich Christopher T. Llabre Maria M. 《Natural Hazards》2021,106(3):2731-2749
Natural Hazards - Socially vulnerable communities experience disproportionately negative outcomes following natural disasters and underscoring a need for well-validated measures to identify those... 相似文献
14.
Alan D. Ziegler Edwin P. Maurer Justin Sheffield Bart Nijssen Eric F. Wood Dennis P. Lettenmaier 《Climatic change》2005,72(1-2):17-36
We use diagnostic studies of off-line variable infiltration capacity (VIC) model simulations of terrestrial water budgets
and 21st-century climate change simulations using the parallel climate model (PCM) to estimate the time required to detect
predicted changes in annual precipitation (P), evapotranspiration (E), and discharge (Q) in three sub-basins of the Mississippi River Basin. Time series lengths on the order of 50–350 years are required to detect
plausible P, E, and Q trends in the Missouri, Ohio, and Upper Mississippi River basins. Approximately 80–160, 50, and 140–350 years, respectively,
are needed to detect the predicted P, E, and Q trends with a high degree of statistical confidence. These detection time estimates are based on conservative statistical
criteria (α = 0.05 and β = 0.10) associated with low probability of both detecting a trend when it is not occurring (Type
I error) and not detecting a trend when it is occurring (Type II error). The long detection times suggest that global-warming-induced
changes in annual basin-wide hydro-climatic variables that may already be occurring in the three basins probably cannot yet
be detected at this level of confidence. Furthermore, changes for some variables that may occur within the 21st century might
not be detectable for many decades or until the following century – this may or may not be the case for individual recording
station data. The long detection times for streamflow result from comparatively low signal-to-noise ratios in the annual time
series. Finally, initial estimates suggest that faster detection of acceleration in the hydrological cycle may be possible
using seasonal time series of appropriate hydro-climatic variables, rather than annual time series. 相似文献
15.
Characterization of the Structure of River-Bed Gravels Using Two-Dimensional Fractal Analysis 总被引:7,自引:0,他引:7
This paper is concerned with the application of fractal analysis to understand the structure of water-worked gravel-bed river surfaces. High resolution digital elevation models, acquired using digital photogrammetric methods, allowed the application of two-dimensional fractal methods. Previous gravel-bed river studies have been based upon sampled profiles and hence one-dimensional fractal characterisation. After basic testing that bed elevation increments are Gaussian, the paper uses two-dimensional variogram surfaces to derive directionally dependent estimates of fractal dimension. The results identify mixed fractal behavior with two characteristic fractal bands, one associated with the subgrain scale and one associated with the grain scale. The subgrain scale characteristics were isotropic and sensitive to decisions made during the data collection process. Thus, it was difficult to differentiate whether these characteristics were real facets of the surfaces studied. The second band was anisotropic and not sensitive to data collection issues. Fractal dimensions were greater in the downstream direction than in other directions suggesting that the effects of water working are to alter the level of surface organisation, by increasing surface irregularity and hence roughness. This is an important observation as it means that water-worked surfaces may have a distinct anisotropic signal, revealed when using a fractal type analysis. 相似文献
16.
17.
We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2–13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment. 相似文献
18.
Due to their complex nature, river models require extensive calibration in order to achieve reliable model predictions. Manually
fitting the numerous parameters included in this procedure can be a laborious and repetitive process. This paper presents
a new instrument, developed specifically for the automatic calibration of river models based on the software MHYSER. The instrument
is completely autonomous and returns the model with the parameter values giving rise to the smallest difference between the
model-generated observations and the measured observations. It utilises the software PEST to fit continuous calibration parameters
and exceeds the program’s capabilities in order to also fit discontinuous calibration parameters. Testing of the instrument
is accomplished using three models, one of which was developed during a study on the dynamics of sediments on the Romaine
River, situated in the Eastern region of the Province of Quebec. 相似文献
19.
Synoptic atmospheric eddies are affected by lower tropospheric air-temperature gradients and by turbulent heat fluxes from the surface. In this study we examine how ocean fronts affect these quantities and hence the storm tracks. We focus on two midlatitude regions where ocean fronts lie close to the storm tracks: the north-west Atlantic and the Southern Ocean. An atmospheric climate model of reasonably high resolution (~50 km) is applied in a climate-length (60 year) simulation in order to obtain stable statistics. Simulations with frontal structure in the sea surface temperature (SST) in one of the regions are compared against simulations with globally smoothed SST. We show that in both regions the ocean fronts have a strong influence on the transient eddy heat and moisture fluxes, not just in the boundary layer, but also in the free troposphere. Local differences in these quantities between the simulations reach 20–40 % of the maximum values in the simulation with smoothed SST. Averaged over the entire region of the storm track over the ocean the corresponding differences are 10–20 %. The effect on the transient eddy meridional wind variance is strong in the boundary layer but relatively weak above that. The potential mechanisms by which the ocean fronts influence the storm tracks are discussed, and our results are compared against previous studies with regional models, Aquaplanet models, and coarse resolution coupled models. 相似文献
20.
Will climate change exacerbate water stress in Central Asia? 总被引:3,自引:0,他引:3
Tobias Siegfried Thomas Bernauer Renaud Guiennet Scott Sellars Andrew W. Robertson Justin Mankin Peter Bauer-Gottwein Andrey Yakovlev 《Climatic change》2012,112(3-4):881-899
Millions of people in the geopolitically important region of Central Asia depend on water from snow- and glacier-melt driven international rivers, most of all the Syr Darya and Amu Darya. The riparian countries of these rivers have experienced recurring water allocation conflicts ever since the Soviet Union collapsed. Will climate change exacerbate water stress and thus conflicts? We have developed a coupled climate, land-ice and rainfall-runoff model for the Syr Darya to quantify impacts and show that climatic changes are likely to have consequences on runoff seasonality due to earlier snow-melt. This will increase water stress in unregulated catchments because less water will be available for irrigation in the summer months. Threats from geohazards, above all glacier lake outbursts, are likely to increase as well. The area at highest risk is the densely populated, agriculturally productive, and politically unstable Fergana Valley. Targeted infrastructural developments will be required in the region. If the current mismanagement of water and energy resources can be replaced with more effective resource allocation mechanisms through the strengthening of transboundary institutions, Central Asia will be able to successfully address these future climate-related challenges. 相似文献