全文获取类型
收费全文 | 945篇 |
免费 | 32篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 63篇 |
地球物理 | 288篇 |
地质学 | 331篇 |
海洋学 | 53篇 |
天文学 | 147篇 |
综合类 | 2篇 |
自然地理 | 85篇 |
出版年
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 18篇 |
2016年 | 20篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 44篇 |
2012年 | 35篇 |
2011年 | 44篇 |
2010年 | 25篇 |
2009年 | 31篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 37篇 |
2005年 | 39篇 |
2004年 | 33篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 20篇 |
1998年 | 18篇 |
1997年 | 22篇 |
1996年 | 8篇 |
1995年 | 25篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 10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 |
1973年 | 8篇 |
1971年 | 6篇 |
1970年 | 9篇 |
1968年 | 6篇 |
1954年 | 8篇 |
1951年 | 6篇 |
排序方式: 共有988条查询结果,搜索用时 22 毫秒
931.
Steven J. Skotnicki Andrew C. Hill Malcolm Walter Richard Jenkins 《Precambrian Research》2008,165(3-4):243-259
Detailed mapping and C and O stable isotopic data from sedimentary carbonate in units both above and below the paleo-erosion surface on the Bitter Springs Formation (BSF) in the northeastern Amadeus Basin, Australia, have clarified the stratigraphy of the area. Isotopic data indicate that the top of the Loves Creek Member of the Bitter Springs Formation is preserved near Corroboree Rock, and is overlain by fenestrate-carbonate-clast breccia, and dolomitic quartz sandstone and chert-pebble conglomerate of the Pioneer Sandstone. The isotopic data, as well as lithologic data, indicate the presence of a 1–2 m-thick cap carbonate preserved between Corroboree Rock and areas 10 km to the northeast. In many places the cap carbonate layer is mostly a syn-sedimentary dolomite-clast breccia, consistent with deposition and disturbance in shallow water. C and O isotopic data also indicate that thin-bedded sandstone and dolomite above the Bitter Springs Formation at Ellery Creek, and a newly discovered massive chert-bearing dolomite at Ross River could both belong to the glaciogenic Olympic Formation. Detailed mapping also provides a more detailed context for the famous black chert microfossil locality in the Bitter Springs Formation at Ross River. 相似文献
932.
Sources and transport of carbon and nitrogen in the River Sava watershed, a major tributary of the River Danube 总被引:1,自引:0,他引:1
Nives Ogrinc Roland Markovics Tjaa Kandu
Lynn M. Walter Stephen K. Hamilton 《Applied Geochemistry》2008,23(12):3685-3698
Carbon and nitrogen dynamics were examined throughout the River Sava watershed, a major tributary of the River Danube, in 2005 and 2006. The River Sava exported 2.1 × 1011 mol C/yr as dissolved inorganic carbon (DIC), and emitted 2.5 × 1010 mol C/yr as CO2 to the atmosphere. Stable carbon isotope ratios indicate that up to 42% of DIC originated from carbonate weathering and 23% from degradation of organic matter. Loads of dissolved and particulate organic carbon increased with discharge and export rates were calculated to be 2.1 × 1010 mol C/yr and up to 4.1 × 109 mol C/yr, respectively. Isotopic compositions (δ13C and δ15N) and C/N ratios indicated that soil organic matter was the dominant source of particulate organic matter for 59% of the samples. Eighteen percent of the samples were dominated by plankton, 12% by periodic inputs of fresh terrestrial plant detritus with C/N > 15, and about 11% of the samples were dominated by the contribution of aquatic vascular plants. Nitrate inputs were controlled by land use in the River Sava watershed. δ15NNO3 values <6‰ were found in predominantly forested watersheds, while values >6‰ typically represented watersheds with a higher percentage of agricultural and/or urban land use. Elevated δ15NNO3 values (up to +25.5‰) at some sites were probably due to the combined effects of low-flow and inputs from sewage and/or animal waste. 相似文献
933.
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
934.
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
935.
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
936.
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
937.
Bruno Collischonn Walter Collischonn Carlos Eduardo Morelli Tucci 《Journal of Hydrology》2008,360(1-4):207-216
Rainfall measurements by conventional raingauges provide relatively accurate estimates at a few points of a region. The actual rainfield can be approximated by interpolating the available raingauge data to the remaining of the area of interest. In places with relatively low gauge density such interpolated rainfields will be very rough estimates of the actual events. This is especially true for tropical regions where most rainfall has a convective origin with high spatial variability at the daily level. Estimates of rainfall by remote sensing can be very useful in regions such as the Amazon basin, where raingauge density is very low and rainfall highly variable. This paper evaluates the rainfall estimates of the Tropical Rainfall Measuring Mission (TRMM) satellite over the Tapajós river basin, a major tributary of the Amazon. Three-hour TRMM rainfall estimates were aggregated to daily values and were compared with catch of ground-level precipitation gauges on a daily basis after interpolating both data to a regular grid. Both daily TRMM and raingauge-interpolated rainfields were then used as input to a large-scale hydrological model for the whole basin; the calculated hydrographs were then compared to observations at several streamgauges along the river Tapajos and its main tributaries. Results of the rainfield comparisons showed that satellite estimates can be a practical tool for identifying damaged or aberrant raingauges at a basin-wide scale. Results of the hydrological modeling showed that TRMM-based calculated hydrographs are comparable with those obtained using raingauge data. 相似文献
938.
J. Ruch J. Anderssohn T.R. Walter M. Motagh 《Journal of Volcanology and Geothermal Research》2008,174(4):337-344
Collapsed calderas are the structural surface expression of the largest volcanic eruptions on Earth and may reach diameters of tens of kilometres while erupting volumes larger than 1000 km3. Remnants of collapse calderas can be found along the South American volcanic arc and are thought to be inactive. However, this study shows that systems of such dimension may become active in a relatively short period of time without attracting much attention. Using satellite-based InSAR data, a 45 km wide elongated area of ground deformation was observed in the Lazufre volcanic region (Chile), where no deformation was detected 10 years ago. The deformation signal shows an uplift of up to ~ 3 cm yr− 1 during 2003–2006, affecting an area of about 1100 km2, comparable in size to super-volcanoes such as Yellowstone or Long Valley. This deformation signal can be explained by an inflating magma body at about 10 km depth, expanding and propagating laterally at a velocity of up to 4 km per year. Although it is not clear whether this intrusion will lead to an eruption, its dimensions and the rapid deformation rate insinuate that a potentially large volcanic system is forming. 相似文献
939.
Maps of shallow depth (down to −250 m) temperature distribution across Canada show large variability, related mainly to surface
climatic forcing. Very small changes of temperature with depth in the upper 250 m are related to heat gained by the subsurface
due to recent global warming. Temperature data compiled from precise temperature logs in equilibrium wells, and temperature
time series from a network of meteorological stations, allow calculation of the available heat energy for heating in the cold
period and for cooling in peak warm months. Utilization of this energy resource has the potential for significant CO2 reduction in Canada. The geothermal energy stored in the ground can be used, with the help of heat pumps, for heating, given
very low winter temperatures. The amount of potential heat available is vast. In Canada, south of permafrost border, the integrated
value of potentially available heat during the heating season down to −50 m is 1.1 E21 J (1100 quads). 相似文献
940.
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