全文获取类型
收费全文 | 278篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 27篇 |
地球物理 | 83篇 |
地质学 | 109篇 |
海洋学 | 9篇 |
天文学 | 23篇 |
自然地理 | 32篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 12篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2010年 | 18篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 5篇 |
2004年 | 11篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有291条查询结果,搜索用时 31 毫秒
61.
Stability analysis of the 2007 Chehalis lake landslide based on long-range terrestrial photogrammetry and airborne LiDAR data 总被引:1,自引:1,他引:0
Marc-André Brideau Matthieu Sturzenegger Doug Stead Michel Jaboyedoff Martin Lawrence Nicholas J. Roberts Brent C. Ward Thomas H. Millard John J. Clague 《Landslides》2012,9(1):75-91
On December 4th 2007, a 3-Mm3 landslide occurred along the northwestern shore of Chehalis Lake. The initiation zone is located at the intersection of the
main valley slope and the northern sidewall of a prominent gully. The slope failure caused a displacement wave that ran up
to 38 m on the opposite shore of the lake. The landslide is temporally associated with a rain-on-snow meteorological event
which is thought to have triggered it. This paper describes the Chehalis Lake landslide and presents a comparison of discontinuity
orientation datasets obtained using three techniques: field measurements, terrestrial photogrammetric 3D models and an airborne
LiDAR digital elevation model to describe the orientation and characteristics of the five discontinuity sets present. The
discontinuity orientation data are used to perform kinematic, surface wedge limit equilibrium and three-dimensional distinct
element analyses. The kinematic and surface wedge analyses suggest that the location of the slope failure (intersection of
the valley slope and a gully wall) has facilitated the development of the unstable rock mass which initiated as a planar sliding
failure. Results from the three-dimensional distinct element analyses suggest that the presence, orientation and high persistence
of a discontinuity set dipping obliquely to the slope were critical to the development of the landslide and led to a failure
mechanism dominated by planar sliding. The three-dimensional distinct element modelling also suggests that the presence of
a steeply dipping discontinuity set striking perpendicular to the slope and associated with a fault exerted a significant
control on the volume and extent of the failed rock mass but not on the overall stability of the slope. 相似文献
62.
Stephen Walsh Kevin Anderson John Hathaway Brent Pulsipher 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(6):805-814
We present a statistical methodology which aims to monitor and assess the progress of unexploded ordnance remediation. We
explicitly quantify the probability that each buried sensor-identified anomaly is not a target of interest conditional on
the information gleaned from anomalies which have been dug and identified. We provide a measure of confidence that the anomalies
which remain onsite after remediation are not unexploded ordnance—this measure of confidence is gleaned through Monte Carlo
methods. The methodology is iterative in that, at any point in the remediation process, we can assess remediation progress
and compute the probability that no targets of interest remain given the available dig information. 相似文献
63.
Francesca A. McInerney Brent R. Helliker Katherine H. Freeman 《Geochimica et cosmochimica acta》2011,75(2):541-554
We analyzed hydrogen isotope ratios of high-molecular weight n-alkanes (δDl) and oxygen isotope ratios of α-cellulose (δ18OC) for C3 and C4 grasses grown in the field and in controlled-environment growth chambers. The relatively firm understanding of 18O-enrichment in leaf water and α-cellulose was used to elucidate fractionation patterns of δDl signatures. In the different relative humidity environments of the growth chambers, we observed clear and predictable effects of leaf-water enrichment on δ18OC values. Using a Craig-Gordon model, we demonstrate that leaf water in the growth chamber grasses should have experienced significant D-enriched due to transpiration. Nonetheless, we found no effect of transpirational D-enrichment on the δDl values. In field samples, we saw clear evidence of enrichment (correlating with relative humidity of the field sites) in both δ18OC and δDl. These seemingly contrasting results could be explained if leaf waxes are synthesized in an environment that is isotopically similar to water entering plant roots due to either temporal or spatial isolation from evaporatively enriched leaf waters. For grasses in the controlled environment, there was no enrichment of source water, whereas enrichment of grass source water via evaporation from soils and/or stems was likely for grass samples grown in the field.Based on these results, evaporation from soils and/or stems appears to affect δDl, but transpiration from leaves does not. Further evidence for this conclusion is found in modeling expected net evapotranspirational enrichment. A Craig-Gordon model applied to each of the field sites yields leaf water oxygen isotope ratios that can be used to accurately predict the observed δ18OC values. In contrast, the calculated leaf water hydrogen isotope ratios are more enriched than what is required to predict observed δDl values. These calculations lend support to the conclusion that while δ18OC reflects both soil evaporation and transpiration, δDl appears to only record evaporation from soils and/or stems. Therefore, the δD of n-alkanes can likely be used to reconstruct the δD of water entering a leaf, supporting the soil-enrichment model of Smith and Freeman (2006). In both the field and controlled studies, we found significant photosynthetic pathway effects on n-alkane δD suggesting that biochemical pathways or plant phylogeny have a greater effect on leaf wax δD than leaf-water enrichment in grasses. 相似文献
64.
Gwen C. Woods Brent G. Pautler Melissa J. Lafrenière 《Geochimica et cosmochimica acta》2011,75(22):7226-7241
Arctic landscapes are believed to be highly sensitive to climate change and accelerated disturbance of permafrost is expected to significantly impact the rate of carbon cycling. While half the global soil organic matter (SOM) is estimated to reside in Arctic soils, projected warmer temperatures and permafrost disturbance will release much of this SOM into waterways in the form of dissolved organic matter (DOM). The spring thaw and subsequent flushing of soils releases the highest contributions of DOM annually but has historically been undersampled due to the difficulties of sampling during this period. In this study, passive samplers were placed throughout paired High Arctic watersheds during the duration of the 2008 spring flush in Nunavut, Canada. The watersheds are very similar with the exception of widespread active layer detachments (ALDs) that occurred within one of the catchments during a period of elevated temperatures in the summer of 2007. DOM samples were analyzed for structural and spectral characteristics via nuclear magnetic resonance (NMR) and fluorescence spectroscopy as well as vulnerability to degradation with simulated solar exposure. Lignin-derived phenols were further assessed utilizing copper(II) oxide (CuO) oxidation and gas chromatography/mass spectrometry (GC/MS). The samples were found to have very low dissolved lignin phenol content (∼0.07% of DOC) and appear to originate from primarily non-woody angiosperm vegetation. The acid/aldehyde ratios for dissolved vanillyl phenols were found to be high (up to 3.6), indicating the presence of highly oxidized lignin. Differences between DOM released from the ALD vs. the undisturbed watershed suggest that these shallow detachment slides have significantly impacted the quality of Arctic DOM. Although material released from the disturbed catchment was found to be highly oxidized, DOM in the lake into which this catchment drained had chemical characteristics indicating high contributions from microbial and/or primary productivity. The resulting pool of dissolved carbon within the lake appears to be more biologically- and photochemically-labile than material from the undisturbed system. These disturbances may have implications for projected climate warming; sustained elevated temperatures would likely perpetuate widespread ALDs and further affect carbon cycling in this environment. 相似文献
65.
Troy P. Sampere Thomas S. Bianchi Mead A. Allison Brent A. McKee 《Estuarine, Coastal and Shelf Science》2011
The primary focus of this paper is to better understand carbon burial on the Louisiana continental margin using spatial scales that covered various shelf depositional areas far-field and near-field (sediment and organic carbon inputs relative to river mouth proximity) and covering a variety of sedimentation rates. Box-cores samples were collected in July 2003; cores were collected along two depositional transects extending westward and southward from the Southwest Pass (SW Pass). A key difference between the two transects sampled in this study was the greater occurrence of mobile muds derived from spillover from shallower regions along the westward 50 m isobaths. The dominant mechanism for mixing in the surface active zone (SAZ) on the inner Louisiana shelf was due to physical, not biological, forces. Burial efficiencies for organic carbon (57.2–91.5%) and total nitrogen (44.2–86.9%) ranged widely across all shelf stations. Lower burial efficiencies for bulk organic carbon, total nitrogen, and pigment biomarkers were associated with mobile muds west of Southwest Pass. Chlorophyll a concentrations were significantly higher than pheopigments at depth at the Mississippi River and Southwest Pass stations, making up 40.4 and 77.4% of total pigment concentrations in the (SAZ) and 46.2 and 63.2% in the accumulation zone (AZ), respectively. These results are in agreement with earlier plant pigment studies which showed that a large fraction of the phytodetritus delivered to the inner shelf was derived from coastal and river diatoms. The amount of lignin preserved with depth decreased with increasing residence time in the SAZ and diagenetic zone (DZ) along the canyon transect but not along the western transect. Trends for lignin concentration followed previously identified surface sediment trends indicating overall lower burial of refractory terrestrial material at depth with greater distance offshore. 相似文献
66.
The Permo‐Carboniferous to Eocene Sverdrup Basin in Canada's Arctic Archipelago is strongly influenced by evaporite diapirism. However, salt structures within the basin have not been extensively investigated recently due to their remote location. This study includes the interpretation of legacy seismic reflection and borehole data to characterize the geometry of selected evaporite domes, and 1D backstripping of wells to investigate tectonic and sedimentary influences on diapirism. Extensional rift‐structures appear to have played a significant role in the formation of evaporite domes by triggering and directing salt movement. Diapirism was initiated by at least the Middle Triassic and continued to develop during the Mesozoic. Differential loading of salt on opposing east–west dome margins led to their present day asymmetric geometries. Diapir growth rates in the Mesozoic were closely linked to the rate of sedimentation and influenced by regional tectonism. 相似文献
67.
Noreen J. Evans Brent I. A. McInnes Brad McDonald Martin Danišík Fred Jourdan Celia Mayers Eric Thern Dudley Corbett 《Mineralium Deposita》2013,48(3):413-421
The diamondiferous Ellendale 9 (E9) pipe is a funnel-shaped maar-diatreme volcano consisting of inward-dipping tuff sequences intruded by lamproite plugs and dykes. The host rocks for the E9 pipe are Permian sandstones. The multiple lithological contacts exposed within the mined maar volcano provide a natural laboratory in which to study the effect of volcanic processes on U–Th–Pb–He systematics. Zircon from the regional sandstone and E9 lamproite display a bimodal distribution of ages on (U–Th)/He–U/Pb plots. The zircon U/Pb ages for the E9 pipe (n?=?52) range from 440 to 2,725 Ma, while the cluster of (U–Th)/He ages for the lamproite dyke zircon indicate that dyke emplacement occurred at 20.6?±?2.8 Ma, concordant with a maximum emplacement age of about ≤22 Ma from phlogopite 40Ar/39Ar. These ages indicate a xenocrystic origin for the zircon entrained in the E9 dyke. The U/Pb ages of detrital zircon from the regional sandstone host (373–3,248 Ma; n?=?41) are indistinguishable from those of the lamproite zircon xenocrysts, whereas the detrital zircon in the host sandstone yield (U–Th)/He ages from 260 to 1,500 Ma. A thermochronology traverse across the E9 lamproite dyke reveals that the zircon (U–Th)/He ages in the host sandstone have not been significantly thermally reset during dyke emplacement, even at the contact. The capability of the zircon (U–Th)/He method to distinguish deep, mantle source lithologies from upper crustal source lithologies could be used in geochemical exploration for diamonds. Pre-screening of detrital samples using etching and helium assay methods will improve the efficiency and decrease the cost of greenfields exploration. 相似文献
68.
Geological and thermochronological studies of the Dashui gold deposit, West Qinling Orogen, Central China 总被引:3,自引:0,他引:3
Qingtao Zeng Noreen J. Evans Brent I. A. McInnes Geoffrey E. Batt Campbell T. McCuaig Leon Bagas Eric Tohver 《Mineralium Deposita》2013,48(3):397-412
The Dashui gold deposit is a structurally controlled, Carlin-type gold deposit hosted by recrystallised limestone in the West Qinling Orogen of Central China. The major, structurally late east-trending Dashui Fault forms the hanging wall to the gold mineralisation at the Dashui mine and defines the contact between Middle Triassic limestone and a steeply dipping overlying succession of Middle Triassic argillaceous limestone, dolomite, and sandstone. Multiple carbonate veins and large-scale supergene enrichment, represented by hematite, goethite, limonite and jarosite, characterise the deposit. Detailed geochronological investigation using zircon SHRIMP U-Pb dating reveals that volcanic rocks closely associated with the Dashui gold deposit were synchronous with the Ge’erkuohe Granite and pre-date mineralisation. The igneous dyke sample from the hanging wall has the same U-Pb zircon age as the footwall, ca. 213 Ma. (U-Th)/He thermochronology on dykes in the hanging wall and footwall of the Dashui Fault yields identical (U-Th)/He zircon ages of ca. 210 Ma but distinct (U-Th)/He apatite ages of ca. 136 and 211 Ma, respectively. Therefore, the hanging wall and footwall are interpreted as having distinct post-mineralisation exhumation histories. Reverse fault movement exhumed the hanging wall ~2 to 4 km since the Late Triassic with the main component of faulting taking place between the Late Triassic and Early Cretaceous. These relationships suggest a Late Triassic to Early Cretaceous age for the primary gold mineralisation at the Dashui gold deposit, with the corollary that any ‘missing portion’ of the deposit, previously hypothesised to exist in the hanging wall of the Dashui Fault, has been eroded away. The mineralisation in the footwall may have been supergene enriched soon after the primary mineralisation was emplaced, because it has been located at shallow depth since the Late Triassic. Semi-quantitative results obtained in this study also constrain the maximum depth of formation of the Dashui gold at no more than 2 km. 相似文献
69.
Brent P. Stafford Natalie L. Cápiro Pedro J.J. Alvarez William G. Rixey 《Ground Water Monitoring & Remediation》2009,29(3):93-104
Neat ethanol (75.7 L) was released into the upper capillary zone in a continuous-flow, sand-packed aquifer tank (8.2 m3 ) with an average seepage velocity of 0.75 m/day. This model aquifer system contained a residual nonaqueous phase liquid (NAPL) that extended from the capillary zone to 10 cm below the water table. Maximum aqueous concentrations of ethanol were 20% v/v in the capillary zone and 0.08% in the saturated zone at 25 and 30 cm downgradient from the emplaced NAPL source, respectively. A bench-scale release experiment was also conducted for a similar size spill (scaled to the plan area). The concentrations of ethanol in ground water for both the bench- and pilot-scale experiments were consistent with advective–dispersive limited mass transfer from the capillary to the saturated zone. Concentrations of monoaromatic hydrocarbons and isooctane increased in the pore water of the capillary zone as a result of both redistribution of residual NAPL (confirmed by visualization) and enhanced hydrocarbon dissolution due to the cosolvent effect exerted by ethanol. In the tank experiment, higher hydrocarbon concentrations in ground water were also attributed to decreased hydrocarbon biodegradation activity caused by preferential microbial utilization of ethanol and the resulting depletion of oxygen. These results infer that spills of highly concentrated ethanol will be largely confined to the capillary zone due to its buoyancy, and ethanol concentrations in near-source zone ground water will be controlled by mass transfer limitations and hydrologic conditions. Furthermore, highly concentrated ethanol releases onto pre-existing NAPL will likely exacerbate impacts to ground water, due to NAPL mobilization and dissolution, and decreased bioattenuation of hydrocarbons. 相似文献
70.
John E. Hathaway Richard O. Gilbert John E. Wilson Brent A. Pulsipher 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):253-261
After site clean-up teams have removed all of what they believe to be UXO within a specific impact area, statistical compliance
sampling is a possible method for verifying with a specified probability that this area has been cleaned to specifications.
Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] developed a compliance sampling methodology based on the hypergeometric distribution. Bowen and Bennett (1987) also use compliance sampling where they provide an approximation for estimating the number of samples (n) required to state with desired probability that the entire population of sample units (N, where n < N) are in compliance with cleanup goals. This article describes two methods (anomaly and transect) for applying the Schilling
[J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] compliance sampling method to military training sites. After describing these methods, a simulation study is presented which
demonstrates the performance of transect compliance sampling calculations based on varied degrees of clustered UXO within
a specific impact area and different types of sampling routines. 相似文献