全文获取类型
收费全文 | 309篇 |
免费 | 23篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 9篇 |
地球物理 | 75篇 |
地质学 | 151篇 |
海洋学 | 15篇 |
天文学 | 58篇 |
自然地理 | 20篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 26篇 |
2005年 | 17篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有332条查询结果,搜索用时 15 毫秒
271.
R. J. Glinski P. D. Michaels C. M. Anderson T. W. Schmidt R. G. Sharp M. L. Sitko L. S. Bernstein H. Van Winckel 《Astrophysics and Space Science》2009,323(4):337-344
In this paper we discuss our insights into several key problems in the identification of the Red Rectangle Bands (RRBs). We
have combined three independent sets of observations in order to try to define the constraints guiding the bands. We provide
a summary of the general behavior of the bands and review the evidence for a molecular origin of the bands. The extent, composition,
and possible absorption effects of the bands are discussed. Comparison spectra of the strongest band obtained at three different
spectral resolutions suggests that an intrinsic line width of individual rotational lines can be deduced. Spectroscopic models
of several relatively simple molecules were examined in order to investigate where the current data are weak. Suggestions
are made for future studies to enhance our understanding of these enigmatic bands. 相似文献
272.
273.
Physical modeling and visualization of soil liquefaction under high confining stress 总被引:1,自引:0,他引:1
Lenart González 《地震工程与工程振动(英文版)》2005,4(1):47-57
The mechanisms of seismically-induced liquefaction of granular soils under high confining stresses are still not fully understood. Evaluation of these mechanisms is generally based on extrapolation of observed behavior at shallow depths. Three centrifuge model tests were conducted at RPI‘s experimental facility to investigate the effects of confining stresses on the dynamic response of a deep horizontal deposit of saturated sand. Liquefaction was observed at high confining stresses in each of the tests. A system identification procedure was used to estimate the associated shear strain and stress time histories. These histories revealed a response marked by shear strength degradation and dilative patterns. The recorded accelerations and pore pressures were employed to generate visual animations of the models. These visualizations revealed a liquefaction front traveling downward and leading to large shear strains and isolation of upper soil layers. 相似文献
274.
Evaluating weather observations and the Climate Forecast System Reanalysis as inputs for hydrologic modelling in the tropics
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Daniel A. Auerbach Zachary M. Easton M. Todd Walter Alexander S. Flecker Daniel R. Fuka 《水文研究》2016,30(19):3466-3477
Correctly representing weather is critical to hydrological modelling, but scarce or poor quality observations can often compromise model accuracy. Reanalysis datasets may help to address this basic challenge. The Climate Forecast System Reanalysis (CFSR) dataset provides continuous, globally available records, and CFSR data have produced satisfactory hydrological model performance in some temperate and monsoonal locations. However, the use of CFSR for hydrological modelling in tropical and semi‐tropical basins has not been adequately evaluated. Taking advantage of exceptionally high rainfall station density in the catchments of the Rio Grande de Loiza above San Juan, Puerto Rico, we compared model performance based on CFSR records with that based on publicly available weather stations in the Global Historical Climate Network (GHCN, n = 21) and on a dataset of rainfall records maintained by the United States Geological Survey Caribbean Water Science Center (USGS, n = 24). For an implementation of the Soil and Water Assessment Tool (SWAT) with subbasins defined at 11 streamflow gages, uncalibrated measures of Nash–Sutcliffe efficiency (NSE) were >0 at 8 of 11 gages using USGS precipitation data for daily simulations over the period 1998–2012, but were <0 using GHCN weather station records (8 of 11) and CFSR reanalysis data (9 of 11). Autocalibration of individual SWAT models for each of the 11 basins against each of the available weather datasets yielded NSE values > 0 using all precipitation inputs, including CFSR. However, the ground weather station closest to the geographic basin centre produced the highest NSE values in only 5 of 11 cases. The spatially interpolated CFSR data performed as well or better than single ground observations made further than 20–30 km, and sometimes better than individual weather stations <10 km from the basin centroid. In addition to demonstrating the need to evaluate available weather inputs, this research reinforces the value of CFSR data as a means to supplement ground records and consistently determine a baseline for hydrologic model performance. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
275.
276.
Martin Sharp Keith Richards Ian Willis Neil Arnold Peter Nienow Wendy Lawson Jean-Louis Tison 《地球表面变化过程与地形》1993,18(6):557-571
As part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier. This structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio-echo sounding techniques. The two reconstructions simulate the drainage system structures expected for (a) closed channels, in which water is pressurized by the overlying ice, and (b) gravity-driven, open-channel flow. The closed-channel model provides the best fit to the observed structure, even though theoretical calculations suggest that, under summer discharge conditions, open-channel flow may be widespread beneath the glacier. Possible reasons for this apparent discrepancy are discussed. 相似文献
277.
The Delaware Estuary is heavily urbanized with elevated concentrations of phosphorus from industrial and municipal inputs. For 24 research cruises during 1986–1988, total phosphorus (TP) concentration was highest near maximum inputs in the tidal river and at low salinity where turbidity was maximal. In these contiguous regions, average TP concentration over the study period was 5.3–6.1 μM. Downstream of the TP peak in the high turbidity zone of the estuary, TP decreased to minimum concentrations (1.3–1.5 μM) near the mouth of Delaware Bay. Distributions of dissolved reactive (DRP), dissolved organic (DOP), and particulate (PP) phosphorus along the estuary reflected spatial and temporal patterns in phosphorus inputs, turbidity, river flow, and biological production. In the river, DRP was 2–4 μM (51–65% of TP) and inversely related to river flow. PP, although enriched in the river (1–3 μM), was highest (>4 μM) in the turbidity maximum at low salinity. In the bay, distributions of DRP, PP, and DOP were all linked, in different ways, to biological production. The dependence of DOP on production was, however, complex and affected by DRP concentrations. During the past 30 yr, there has been a fourfold decrease in TP concentrations in the tidal river of the Delaware Estuary. This dramatic decrease in TP, however, is contrasted by an apparent increase in DRP concentration over the past 12 yr. This apparent increase in DRP may be linked to improved water quality (e.g., higher pH) in the river over the past decade. 相似文献
278.
279.
Zoning of phosphorus in igneous olivine 总被引:2,自引:2,他引:0
Margaret S. Milman-Barris John R. Beckett Michael B. Baker Amy E. Hofmann Zachary Morgan Meghan R. Crowley Daniel Vielzeuf Edward Stolper 《Contributions to Mineralogy and Petrology》2008,155(6):739-765
We describe P zoning in olivines from terrestrial basalts, andesites, dacites, and komatiites and from a martian meteorite.
P2O5 contents of olivines vary from below the detection limit (≤0.01 wt%) to 0.2–0.4 wt% over a few microns, with no correlated
variations in Fo content. Zoning patterns include P-rich crystal cores with skeletal, hopper, or euhedral shapes; oscillatory
zoning; structures suggesting replacement of P-rich zones by P-poor olivine; and sector zoning. Melt inclusions in olivines
are usually located near P-rich regions but in direct contact with low-P olivine. Crystallization experiments on basaltic
compositions at constant cooling rates (15–30°C/h) reproduce many of these features. We infer that P-rich zones in experimental
and natural olivines reflect incorporation of P in excess of equilibrium partitioning during rapid growth, and zoning patterns
primarily record crystal-growth-rate variations. Occurrences of high-P phenocryst cores may reflect pulses of rapid crystal
growth following delayed nucleation due to undercooling. Most cases of oscillatory zoning in P likely reflect internal factors
whereby oscillating growth rates occur without external forcings, but some P zoning in natural olivines may reflect external
forcings (e.g., magma mixing events, eruption) that result in variable crystal growth rates and/or P contents in the magma.
In experimental and some natural olivines, Al, Cr, and P concentrations are roughly linearly and positively correlated, suggesting
coupled substitutions, but in natural phenocrysts, Cr zoning is usually less intense than P zoning, and Al zoning weak to
absent. We propose that olivines grow from basic and ultrabasic magmas with correlated zoning in P, Cr, and Al superimposed
on normal zoning in Fe/Mg; rapidly diffusing divalent cations homogenize during residence in hot magma; Al and Cr only partially
homogenize; and delicate P zoning is preserved because P diffuses very slowly. This interpretation is consistent with the
fact that zoning is largely preserved not only in P but also in Al, Cr, and divalent cations in olivines with short residence
times at high temperature (e.g., experimentally grown olivines, komatiitic olivines, groundmass olivines, and the rims of
olivine phenocrysts grown during eruption). P zoning is widespread in magmatic olivine, revealing details of crystal growth
and intra-crystal stratigraphy in what otherwise appear to be relatively featureless crystals. Since it is preserved in early-formed
olivines with prolonged residence times in magmas at high temperatures, P zoning has promise as an archive of information
about an otherwise largely inaccessible stage of a magma’s history. Study of such features should be a valuable supplement
to routine petrographic investigations of basic and ultrabasic rocks, especially because these features can be observed with
standard electron microprobe techniques. 相似文献
280.
Late syn‐rift evolution of the Vingleia Fault Complex,Halten Terrace,offshore Mid‐Norway; a test of rift basin tectono‐stratigraphic models
下载免费PDF全文
![点击此处可从《Basin Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gavin M. Elliott Christopher A.‐L. Jackson Robert L. Gawthorpe Paul Wilson Ian R. Sharp Lisa Michelsen 《Basin Research》2017,29(Z1):465-487
Rift basin tectono‐stratigraphic models indicate that normal fault growth controls the sedimentology and stratigraphic architecture of syn‐rift deposits. However, such models have rarely been tested by observations from natural examples and thus remain largely conceptual. In this study we integrate 3D seismic reflection, and biostratigraphically constrained core and wireline log data from the Vingleia Fault Complex, Halten Terrace, offshore Mid‐Norway to test rift basin tectono‐stratigraphic models. The geometry of the basin‐bounding fault and its hangingwall, and the syn‐rift stratal architecture, vary along strike. The fault is planar along a much of its length, bounding a half‐graben containing a faultward‐thickening syn‐rift wedge. Locally, however, the fault has a ramp‐flat‐ramp geometry, with the hangingwall defined by a fault‐parallel anticline‐syncline pair. Here, an unusual bipartite syn‐rift architecture is observed, comprising a lower faultward‐expanding and an upper faultward‐thinning wedge. Fine‐grained basinfloor deposits dominate the syn‐rift succession, although isolated coarse clastics occur. The spatial and temporal distribution of these coarse clastics is complex due to syn‐depositional movement on the Vingleia Fault Complex. High rates of accommodation generation in the fault hangingwall led to aggradational stacking of fan deltas that rapidly (<5 km) pinch out basinward into offshore mudstone. In the south of the basin, rapid strain localization meant that relay ramps were short‐lived and did not represent major, long‐lived sediment entry points. In contrast, in the north, strain localization occurred later in the rift event, thus progradational shorefaces developed and persisted for a relatively long time in relay ramps developed between unlinked fault segments. The footwall of the Vingleia Fault Complex was characterized by relatively low rates of accommodation generation, with relatively thin, progradational hangingwall shorelines developed downdip of the fault block apex, sometime after the onset of sediment supply to the hangingwall. We show that rift basin tectono‐stratigraphic models need modifying to take into account along‐strike variability in fault structure and basin physiography, and the timing and style of syn‐rift sediment dispersal and facies, in both hangingwall and footwall locations. 相似文献