全文获取类型
收费全文 | 218篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 11篇 |
地球物理 | 45篇 |
地质学 | 85篇 |
海洋学 | 22篇 |
天文学 | 41篇 |
自然地理 | 17篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 10篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 7篇 |
2011年 | 23篇 |
2010年 | 17篇 |
2009年 | 11篇 |
2008年 | 20篇 |
2007年 | 10篇 |
2006年 | 16篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有231条查询结果,搜索用时 11 毫秒
141.
Humberto C. Godinez Esteban Rougier Dave Osthus Zhou Lei Earl Knight Gowri Srinivasan 《国际地质力学数值与分析法杂志》2019,43(1):30-44
Fracture propagation plays a key role for a number of applications of interest to the scientific community, from dynamic fracture processes like spallation and fragmentation in metals to failure of ceramics, airplane wings, etc. Simulations of material deformation and fracture propagation rely on accurate knowledge of material characteristics such as material strength and the amount of energy being dissipated during the fracture process. Within the combined finite-discrete element method (FDEM) framework material fracture behavior is typically described through a parametrized softening curve, which defines a stress-strain relationship unique to each material. We apply the Fourier amplitude sensitivity test to explore how each of these parameters influences the simulated damage processes and to determine the key input parameters that have the most impact on the model response. We present several sensitivity numerical experiments for the simulation of a split Hopkinson pressure bar (SHPB) test for weathered granite samples using different combinations of model parameters. We validate the obtained results against SHPB experimental data. The experiments show that the model is mostly sensitive to parameters related to tensile and shear strengths, even in the presence of other parameter perturbations. The results suggest that the specification of tensile and shear strengths at the interfaces dominate the stress-time history of the FDEM simulation of SHPB test. 相似文献
142.
Simulation of frictional contact between soils and rigid or deformable structure in the framework of smoothed particle hydrodynamics (SPH) is presented in this study. Two algorithms are implemented into the SPH code to describe contact behavior, where the contact forces are calculated using the law of conservation of momentum based on ideal plastic collision or using the criteria of partial penetrating. In both algorithms, the problem of boundary deficiency inherited from SPH is properly handled so that the particles located at contact boundary can have precise acceleration, which is critical for contact detection. And the movement and rotation of the rigid structure are taken into account so that it is easy to simulate the process of pile driving or movement of a retaining wall in geotechnical engineering analysis. Furthermore, the capability of modeling deformability of a structure during frictional contact simulations broadens the fields of SPH application. In contrast to previous work dealing with contact in SPH, which usually use particle‐to‐particle contact or ignoring sliding between particles and solid structure, the method proposed here is more efficient and accurate, and it is suitable to simulate interaction between soft materials and rigid or deformable structures, which are very common in geotechnical engineering. A number of numerical tests are carried out to verify the accuracy and stability of the proposed algorithms, and their results are compared with analytical solutions or results from finite element method analysis. Good agreement obtained from these comparisons suggests that the proposed algorithms are robust and can be applied to extend the capability of SPH in solving geotechnical problems. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
143.
Guan-Wei Lin Hongey Chen Dave N. Petley Ming-Jame Horng Shuei-Ji Wu Bin Chuang 《Engineering Geology》2011,117(1-2):97-103
Typhoon-triggered landslides deliver huge amounts of sediment to the upstream channel of the Shihmen Reservoir in northern Taiwan. Observation data regarding landsliding, sediment discharge and water turbidity following five major typhoon events from 1985 to 2006 demonstrated that each time water turbidity in the reservoir area rapidly increased up to ten-fold from the river catchment drainage, and the weight of landslide debris exceeded total sediment discharge five-fold. The fact that huge amounts of landslide debris still remained on upstream slopes and water turbidity suddenly increased in the reservoir area but not in upstream channel implied that the increasing water turbidity in the Shihmen Reservoir was indirectly related to the large landslides occurring in the upstream catchment. The main cause of high turbidity in the reservoir area was that, during a typhoon event, high water discharge flowing into the reservoir scoured the fine fraction sediment at the bottom of the reservoir and formed hyperpycanl flow with high turbidity, which then ascended to contaminate the reservoir surface water. 相似文献
144.
This paper describes two projects requiring production of national floodplain maps for England and Wales – some 80,000 km of river. The novel solutions developed have brought together a national Digital Elevation Model (DEM), automatically-generated peak flow estimates at intervals along the watercourses and two alternative methods of calculating the outlines: normal depth calculation; and a purpose-built 2-dimensional raster-based floodplain model, JFLOW. The DEM was derived using Interferometric Synthetic Aperture Radar (IFSAR) techniques and has a vertical precision of ±0.5 m–1.0 m (RMSE) and a 5 m horizontal resolution. The flow estimates were derived by automating Flood Estimation Handbook (FEH) techniques. The normal depth calculations are applied at a number of discrete cross-sections with linear interpolation between to form a 3-dimensional water surface. This is overlain on the DEM to produce the flood outline. Careful manual checking is required at a number of stages. The JFLOW model is based on a discretised form of the 2-dimensional diffusive wave equation and directly simulates the flood outline in a series of overlapping short (1 km) reaches. Flood outlines from the overlapping reaches are merged to produce the overall flood envelope. The model has been written to work as a screen-saver, allowing distributed processing across all computers in an office and manual intervention is minimal. In simple valley situations both methods give similar results, but show differences in more complex areas. Each has advantages and disadvantages, but both have been shown to be a practicable solution to allow production of 160,000 km of flood outline in 12 months. 相似文献
145.
J. Paul F. Blume S. Jade V. Kumar P. S. Swathi M. B. Ananda V. K. Gaur Roland Burgmann Roger Bilham B. Namboodri Dave Mencin 《Journal of Earth System Science》1995,104(1):131-146
We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related
to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of
India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using
GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey
to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional
dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In
addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994)
in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate
motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern
Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya
of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian
plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin,
which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent
deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region
of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence
intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation
of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates
that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable
scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of
the 19th century GTS survey. 相似文献
146.
To understand the evolution of a disaster, we propose a Framework for Assessing Crisis in a System Environment (FACSE). FACSE is set in a multi-system environment, containing the human system as well as the various natural and technological systems that interact with people. We take a lifecycle perspective, via which we quantify rhythms of life exhibited in multiple systems, across different scales, at different times. The lifecycle perspective also implies a relative approach in that rhythms of life during time t can be compared against those during t-1. We illustrate how rhythms of life in the human system can be measured at different scales. We propose a new concept??the degree of disaster, which is a composite score that encompasses the various measurements of rhythms of life from multiple systems, across different scales. We conclude the paper by discussing the potential offered by FACSE in disaster research as well as the limitations. 相似文献
147.
Electrical resistivity ground imaging (ERGI): a new tool for mapping the lithology and geometry of channel-belts and valley-fills 总被引:1,自引:0,他引:1
Dave Baines Derald G. Smith Duane G. Froese Paul Bauman† Grant Nimeck† 《Sedimentology》2002,49(3):441-449
Efforts to map the lithology and geometry of sand and gravel channel‐belts and valley‐fills are limited by an inability to easily obtain information about the shallow subsurface. Until recently, boreholes were the only method available to obtain this information; however, borehole programmes are costly, time consuming and always leave in doubt the stratigraphic connection between and beyond the boreholes. Although standard shallow geophysical techniques such as ground‐penetrating radar (GPR) and shallow seismic can rapidly obtain subsurface data with high horizontal resolution, they only function well under select conditions. Electrical resistivity ground imaging (ERGI) is a recently developed shallow geophysical technique that rapidly produces high‐resolution profiles of the shallow subsurface under most field conditions. ERGI uses measurements of the ground's resistance to an electrical current to develop a two‐dimensional model of the shallow subsurface (<200 m) called an ERGI profile. ERGI measurements work equally well in resistive sediments (‘clean’ sand and gravel) and in conductive sediments (silt and clay). This paper tests the effectiveness of ERGI in mapping the lithology and geometry of buried fluvial deposits. ERGI surveys are presented from two channel‐fills and two valley‐fills. ERGI profiles are compared with lithostratigraphic profiles from borehole logs, sediment cores, wireline logs or GPR. Depth, width and lithology of sand and gravel channel‐fills and adjacent sediments can be accurately detected and delineated from the ERGI profiles, even when buried beneath 1–20 m of silt/clay. 相似文献
148.
Reactive transport modelling of reflux dolomitization in the Arab‐D reservoir,Ghawar field,Saudi Arabia 下载免费PDF全文
It has long been recognized that the Arab‐D reservoir in Ghawar field has been significantly dolomitized and that the distribution of dolomites is highly heterogeneous across this reservoir. Previous studies indicated that dolomite occurs with either a stratigraphic or non‐stratigraphic distribution; when mapped, dolomite tends to form several parallel linear trends across the field. Although stratigraphic dolomite was suggested to be formed early from highly evaporated pore fluids sourced from overlying evaporite deposits, non‐stratigraphic dolomite was thought to be generated primarily from hydrothermal fluids sourced from below. This study focuses primarily on these non‐stratigraphic dolomites, and proposes that: (i) these dolomites initially formed via seepage reflux, but were reinforced by late stage hydrothermal dolomitization; and (ii) reflux is also responsible for the formation of parallel, linear trends of dolomite. The reflux model hypothesizes that an evaporative lagoon (which is the source of dolomitizing fluids) formed during the falling stage systems tract of a depositional sequence, and that with continuing sea‐level fall this lagoon migrated progressively towards deeper parts of an intrashelf basin adjacent to the Ghawar field, leaving behind lines of dolomite bodies along a series of temporary coastlines. Two‐dimensional reactive transport models have been built to test this hypothesis, and have resulted in a predicted pattern of dolomite bodies that agrees with both the observed vertical distribution of non‐stratigraphic dolomite, as well as the mapped lateral distribution of the dolomite trends. In addition, the major ion compositions of Late Jurassic seawater are calculated based on fluid inclusion data in the literature. Using Jurassic seawater in current models leads to the absence of anhydrite cements and less potential of over‐dolomitization than using modern seawater. 相似文献
149.
R. B. Gajjar A. M. Shekh A. J. Dave C. T. Patel R. S. Parmar N. K. Patel J. G. Talati 《Journal of the Indian Society of Remote Sensing》2005,33(1):147-153
A field experiment was conducted on wheat crop during rabi seasons of 1995–96, 1996–97 and 1997–98 to study the spectral response
of wheat crop (between 490 to 1080 nm) under water and nutrient stress condition. An indigenously developed ground truth radiometer
having narrow band in visible and near infrared region (490 – 1080 nm) was used. Vegetation indices derived using different
band combinations and related to crop growth parameters. The near infrared spectral region of 710 – 1025 nm was found most
important for monitoring stress condition. Relationship has been developed between crop growth parameters and vegetation indices.
Leaf Area Index (LAI) and chlorophyll could be predicted by knowing different reflectance ratios at milking stage of crop
with R2 value of 0.78 and 0.89, respectively. Dry biomass (DBM), Plant Water Content (PWC) and grain yield are also significantly
related with reflectance ratios at flowering stage of crop with R2 value of 0.90, 0.98 and 0.74, respectively. 相似文献
150.