全文获取类型
收费全文 | 906篇 |
免费 | 27篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 60篇 |
地球物理 | 274篇 |
地质学 | 316篇 |
海洋学 | 44篇 |
天文学 | 146篇 |
综合类 | 2篇 |
自然地理 | 83篇 |
出版年
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 7篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 33篇 |
2011年 | 41篇 |
2010年 | 22篇 |
2009年 | 26篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 37篇 |
2005年 | 37篇 |
2004年 | 32篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1997年 | 21篇 |
1996年 | 8篇 |
1995年 | 22篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1975年 | 15篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1971年 | 6篇 |
1970年 | 9篇 |
1954年 | 8篇 |
1951年 | 6篇 |
排序方式: 共有944条查询结果,搜索用时 31 毫秒
891.
Comparison of Hydraulic Tomography with Traditional Methods at a Highly Heterogeneous Site
下载免费PDF全文
![点击此处可从《Ground water》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Over the past several decades, different groundwater modeling approaches of various complexities and data use have been developed. A recently developed approach for mapping hydraulic conductivity (K) and specific storage (Ss) heterogeneity is hydraulic tomography, the performance of which has not been compared to other more “traditional” methods that have been utilized over the past several decades. In this study, we compare seven methods of modeling heterogeneity which are (1) kriging, (2) effective parameter models, (3) transition probability/Markov Chain geostatistics models, (4) geological models, (5) stochastic inverse models conditioned to local K data, (6) hydraulic tomography, and (7) hydraulic tomography conditioned to local K data using data collected in five boreholes at a field site on the University of Waterloo (UW) campus, in Waterloo, Ontario, Canada. The performance of each heterogeneity model is first assessed during model calibration. In particular, the correspondence between simulated and observed drawdowns is assessed using the mean absolute error norm, (L1), mean square error norm (L2), and correlation coefficient (R) as well as through scatterplots. We also assess the various models on their ability to predict drawdown data not used in the calibration effort from nine pumping tests. Results reveal that hydraulic tomography is best able to reproduce these tests in terms of the smallest discrepancy and highest correlation between simulated and observed drawdowns. However, conditioning of hydraulic tomography results with permeameter K data caused a slight deterioration in accuracy of drawdown predictions which suggests that data integration may need to be conducted carefully. 相似文献
892.
We present a new visualization method for human inspection of seismic data called supersonograms, which maximizes the amount of time and stations visible on screen while retaining the possibility to detect short and low-signal to noise ratio (SNR) signals. This visualization approach is integrated into a seismological software suite used in the seismic aftershock monitoring system (SAMS) of Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) on-site inspections (OSI) to detect suspicious events eventually representing aftershocks from an underground nuclear explosion (UNE). During an OSI, huge amounts of continuous waveform data accumulate from up to 50 six-channel mini-arrays covering an inspection area of 1,000 square kilometers. Sought-after events can have magnitude as low as $\hbox{M}_{\rm L}\,{-2.0}$ and duration of just a few seconds, which makes it particularly hard to discover them in large, noisy datasets. Therefore, the data visualization is based on nonlinearly scaled, noise-adapted spectrograms, i.e., sonograms, which help to distinguish weak signal energy from stationary background noise. Four single-trace sonograms per mini-array can be combined into supersonograms, since the array aperture is small and sonograms suppress differences of local site noise, allowing an analyst to check array-wide signal coherence quickly. In this paper, we present the supersonograms and the software on the basis of a dataset from a creeping, inhabited landslide in Austria where the same station layout is used as in an OSI. Detected signals are fracture processes in the sedimentary landslide, i.e., slidequakes, with $\hbox{M}_{\rm L}\,{-0.5} \,\hbox{\,to}\,{-2.5}$ between July 2009 and July 2011. These signals are comparable in magnitude and duration to expected weak UNE aftershocks. 相似文献
893.
Attenuation Tomography of the Yellow Sea/Korean Peninsula from Coda-source normalized and direct Lg Amplitudes 总被引:1,自引:0,他引:1
Sean R. Ford William S. Phillips William R. Walter Michael E. Pasyanos Kevin Mayeda Douglas S. Dreger 《Pure and Applied Geophysics》2010,167(10):1163-1170
We invert for regional attenuation of the crustal phase Lg in the Yellow Sea/Korean Peninsula (YSKP) using three different amplitude attenuation tomography methods. The first method solves for source, site, and path attenuation. The second method uses a scaling relationship to set the initial source amplitude and interpret the source term after inversion. The third method implements a coda-derived source spectral correction. By comparing methods with slightly different assumptions we are able to make a more realistic assessment of the uncertainties in the resulting attenuation maps than is obtainable through formal error analysis alone. We compare the site, source and path-terms produced by each method and comment on attenuation, which correlates well with tectonic and topographic features in the region. Source terms correlate well with each other and with magnitude. Site terms are similar except for two stations that are located in a region that has the greatest difference in path term, which demonstrates the site/path trade-off. Another region of path term difference has the fewest crossing paths, where the tomography method employing the coda-derived spectral correction may perform more accurately since it is not as susceptible to the source/path trade-off. The Bohai Bay basin, an area of extension, is a region of high attenuation, and regions of low attenuation occur along topographic highs located in the Da-xin-an-ling and Changbai Mountains and Mount Taishan. 相似文献
894.
Xiangzheng Deng Jikun Huang Fangbin Qiao Rosamond L. Naylor Walter P. Falcon Marshall Burke Scott Rozelle David Battisti 《地理学报(英文版)》2010,20(1):3-16
This paper aims to demonstrate the relationships between ENSO and rice production of Jiangxi province in order to identify
the reason that ENSO might have little effect on Chinese rice production. Using a data set with measures of Jiangxi’s climate
and rice production, we find the reason that during 1985 and 2004 ENSO’s well correlated with rainfall did not promote Chinese
rice production. First, the largest effects of ENSO mostly occur in the months when there is no rice in the field. Second,
there is almost no temperature effect. Finally, the monthly distribution of rainfall is almost the same in ENSO and neutral
years because the largest effects are during months when there is the least rain. In addition, due to the high irrigation
share and reliable and effective irrigation facilities of cultivated land, China’s rice production is less climate-sensitive. 相似文献
895.
Elisa Zuccolo Tony Gibbs Carlo G. Lai Joan L. Latchman Walter Salazar Luigi Di Sarno Anthony Farrell Lloyd Lynch Addison Workman 《Bulletin of Earthquake Engineering》2016,14(9):2579-2605
A feasibility study of an earthquake early warning (EEW) system was conducted for the Eastern Caribbean region using scenario earthquakes, corresponding to the maximum credible earthquakes and to the earthquakes associated with a return period of 475 years. Broadband synthetic seismograms were produced at selected critical facilities, where there is potential interest in the installation of an EEW system. The expected damage was derived from the synthetic seismograms and compared with the lead-time determined for both a regional and on-site EEW configuration. Next, the Virtual Seismologist EEW algorithm, as included in SeisComP3, was tested. Additional broadband synthetic seismograms were produced for the stations in the Eastern Caribbean seismic networks in order to simulate the real time behaviour of the seismic networks during the occurrence of the synthetic earthquakes and to assess the predictive capacity of the selected ground motion prediction equation. Expected peak ground parameters and lead-times at the critical facilities constitute the major outcome of the study. 相似文献
896.
Model‐based evaluation of impact of soil redistribution on soil organic carbon stocks in a temperate hedgerow landscape
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Agroforestry systems are promoted for providing a number of ecosystem services and environmental benefits, including soil protection and carbon sequestration. This study proposes a modelling approach to quantify the impact of soil redistribution on soil organic carbon (SOC) storage in a temperate hedgerow landscape. Evolution of SOC stocks at the landscape scale was examined by simulating vertical and horizontal SOC transfers in the 0–105 cm soil layer due to soil redistribution by tillage and water processes. A spatially explicit SOC dynamics model (adapted from RothC‐26.3) was used, coupled with a soil‐redistribution model (LandSoil). SOC dynamics were simulated over 90 years in an agricultural hedgerow landscape dedicated to dairy farming, with a mix of cropping and grasslands. Climate and land use were simulated considering business‐as‐usual scenarios derived from existing information on the study area. A net decrease in SOC stocks was predicted at the end of the simulation period. Soil redistribution induced a net SOC loss equivalent to 2 kg C ha?1 yr?1 because of soil exportation out of the study site and an increase in SOC mineralization. Hedgerows and woods were the only land use in which soil redistribution induced net SOC storage. Soil tillage was the main process that induced soil redistribution within cultivated fields. Soil exportation out of the study area was due to erosion by water, but remained low because of the protective role of the hedgerow network. These soil transfers redistributed SOC stocks in the landscape, mostly within cultivated fields. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
897.
The formation of ring faults yields important implications for understanding the structural and dynamic evolution of collapse
calderas and potentially associated ash-flow eruptions. Caldera collapse occurred in 2000 at Miyakejima Island (Japan) in
response to a lateral intrusion. Based on geophysical data it is inferred that a set of caldera ring faults was propagating
upward. To understand the kinematics of ring-fault propagation, linkage, and interaction, we describe new laboratory sand-box
experiments that were analyzed through Digital Image Correlation (DIC) and post-processed using 2D strain analysis. The results
help us gain a better understanding of the processes occurring during caldera subsidence at Miyakejima. We show that magma
chamber evacuation induces strain localization at the lateral chamber margin in the form of a set of reverse faults that sequentially
develops and propagates upwards. Then a set of normal faults initiates from tension fractures at the surface, propagating
downwards to link with the reverse faults at depth. With increasing amounts of subsidence, interaction between the reverse-
and normal-fault segments results in a deactivation of the reverse faults, while displacement becomes focused on the outer
normal faults. Modeling results show that the area of faulting and collapse migrates successively outward, as peak displacement
transfers from the inner ring faults to later developed outer ring faults. The final structural architecture of the faults
bounding the subsiding piston-like block is hence a consequence of the amount of subsidence, in agreement with other caldera
structures observed in nature. The experimental simulations provide an analogy to the observations and seismic records of
caldera collapse at Miyakejima volcano, but are also applicable to caldera collapse in general. 相似文献
898.
Programs for evaluating proposed discharges of dredged material into waters of the United States specify a tiered testing and evaluation protocol that includes performance of acute and chronic bioassays to assess toxicity of the dredged sediments. Although these evaluations reflect the toxicological risks associated with disposal activities to some degree, analysis activities are limited to the sediments of each dredging project separately. Cumulative risks to water column and benthic organisms at and near the designated disposal site are therefore difficult to assess. An alternate approach is to focus attention on the disposal site, with the goal of understanding more directly the risks of multiple disposal events to receiving ecosystems. Here we review current US toxicity testing and evaluation protocols, and describe an application of ecological risk assessment that allows consideration of the temporal and spatial components of risk to receiving aquatic ecosystems. When expanded to include other disposal options, this approach can provide the basis for holistic management of dredged material disposal. 相似文献
899.
900.
Walter Flury 《Earth, Moon, and Planets》1995,70(1-3):79-91
37 years of space activities have led to a large number of anthropogenic objects orbiting the Earth. Ground-based observations with radar and optical facilities reveal the existence of about 7500 objects in space, which do not represent an immediate excessive danger. However, adequate actions are required to keep the long-term debris hazard for manned and unmanned missions within acceptable tolerances. In this paper the space debris environment of the Earth and its future evolution are described. New developments which could have a major impact on the space environment, are the the planned multi-satellite constellations for communications purposes or solar power stations in Earth orbit. Finally, methods for debris reduction are outlined. Space debris is a global problem which can only be effectively solved by international cooperation. 相似文献