全文获取类型
收费全文 | 133篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 17篇 |
地球物理 | 25篇 |
地质学 | 41篇 |
海洋学 | 15篇 |
天文学 | 23篇 |
自然地理 | 10篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 7篇 |
2011年 | 4篇 |
2010年 | 11篇 |
2009年 | 4篇 |
2008年 | 5篇 |
2007年 | 11篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 31 毫秒
71.
Fundamental differences between SPH and grid methods 总被引:1,自引:0,他引:1
Oscar Agertz Ben Moore Joachim Stadel Doug Potter Francesco Miniati Justin Read Lucio Mayer Artur Gawryszczak rey Kravtsov Åke Nordlund Frazer Pearce Vicent Quilis Douglas Rudd Volker Springel James Stone Elizabeth Tasker Romain Teyssier James Wadsley Rolf Walder 《Monthly notices of the Royal Astronomical Society》2007,380(3):963-978
72.
73.
Doug Burns 《水文研究》2005,19(6):1325-1327
74.
75.
Doug Newcomb 《Transactions in GIS》2012,16(2):161-176
Sunlight can have a significant impact on freshwater aquatic communities. Using 64‐ bit GRASS, a previously generated 18.2 m resolution forest canopy height grid for the State of North Carolina was used as a base elevation layer for calculation of 18.2 m resolution total irradiance (Watt‐hours/square meter/day) grids for 365 days of the year. Daily calculations were aggregated annually and overlaid on rasterized 1:24,000‐scale USGS hydrology with canopy type and seasonal filters to quantify annual solar irradiation input to streams and rivers in North Carolina. Bare earth calculations of solar irradiation for the aquatic habitats were compared to the canopy filtered calculations. There was substantially less solar irradiation in aquatic habitats under the canopy filtered model. Total solar irradiation for subbasins created from point locations of occurrences of Dwarf wedgemussel (Alasmidonta heterodon) were compared with total solar irradiation for watersheds created from locations with no mussels for the full subbasin, 1 km, and 500 m upstream from the sampling point. There was no significant difference in the amount of total solar irradiation modeled for the subbasins with Dwarf wedgemussel and watersheds with no mussels. 相似文献
76.
A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM)
is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in
baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient
eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat
flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between
local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux
of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component
is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity
reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the
LGM, while they only account for half the seasonal range at the present-day. 相似文献
77.
Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis 总被引:2,自引:0,他引:2
P.N. Froelich G.P. Klinkhammer M.L. Bender N.A. Luedtke G.R. Heath Doug Cullen Paul Dauphin Doug Hammond Blayne Hartman Val Maynard 《Geochimica et cosmochimica acta》1979,43(7):1075-1090
Pore water profiles of total-CO2, pH, PO3?4, NO?3 plus NO?2, SO2?4, S2?, Fe2+ and Mn2+ have been obtained in cores from pelagic sediments of the eastern equatorial Atlantic under waters of moderate to high productivity. These profiles reveal that oxidants are consumed in order of decreasing energy production per mole of organic carbon oxidized (O2 > manganese oxides ~ nitrate > iron oxides > sulfate). Total CO2 concentrations reflect organic regeneration and calcite dissolution. Phosphate profiles are consistent with organic regeneration and with the effects of release and uptake during inorganic reactions. Nitrate profiles reflect organic regeneration and nitrate reduction, while dissolved iron and manganese profiles suggest reduction of the solid oxide phases, upward fluxes of dissolved metals and subsequent entrapment in the sediment column. Sulfate values are constant and sulfide is absent, reflecting the absence of strongly anoxic conditions. 相似文献
78.
Olga N. Krankina Mark E. Harmon Warren B. Cohen Doug R. Oetter Zyrina Olga Maureen V. Duane 《Climatic change》2004,67(2):257-272
Forest inventories and remote sensing are the two principal data sources used to estimate carbon (C) stocks and fluxes for large forest regions. National governments have historically relied on forest inventories for assessments but developments in remote sensing technology provide additional opportunities for operational C monitoring. The estimate of total C stock in live forest biomass modeled from Landsat imagery for the St. Petersburg region was consistent with estimates derived from forest inventory data for the early 1990s (272 and 269 TgC, respectively). The estimates of mean C sink in live forest biomass also agreed well (0.36 and 0.34 Mg C ha–1 yr–1). Virtually all forest lands were accumulating C in live biomass, however when the net change in total ecosystem C stock was considered, 19% of the forest area were a net source of C. The average net C sink in total ecosystem biomass is quite weak (0.08 MgC ha–1 yr–1 and could be reversed by minor increases in harvest rates or a small decline in biomass growth rates. 相似文献
79.
Yong Shu Xiahong Feng Doug Anderson Kuilian Tang Gregory J. Ettl 《Geochimica et cosmochimica acta》2005,69(4):791-799
Humidity is one of the fundamental variables controlling the energy balance of the climate, and thus its reconstruction represents a significant aspect of paleoclimate studies. We here report a study of oxygen and hydrogen isotopic compositions of tree-ring cellulose along a precipitation gradient in the Olympic Mountains of Washington, USA, to examine whether and how the relative humidity is recorded in the cellulose. According to the physically-based model described in this paper, the relationship between δD and δ18O of cellulose should have the same slope as that in the relationship between δD and δ18O in the source water (∼8.8 for the local meteoric water) if there is no systematic variation in the mean relative humidity among study sites and no physiologic differences among trees. However, our isotopic analyses of cellulose yielded a slope of 17.4, significantly greater than the slope of the Local Meteoric Water Line. We show that to produce such a slope, a positive covariation between the relative humidity and the δD and δ18O in the source water is required across the precipitation gradient. This work suggests that the δD vs. δ18O relationship in tree rings can be a useful tool for paleohumidity reconstruction. 相似文献
80.
Doug V. Prose 《Environmental Geology》1985,7(3):163-170
Soil compaction and substrate modification produced during large-scale armored military maneuvers in the early 1940s were
examined in 1981 at seven sites in California’s eastern Mojave Desert Recording penetrometer measurements show that tracks
left by a single pass of an M3 “medium” tank have average soil resistance values that are 50% greater than those of the surrounding
untracked soil in the upper 20 cm At one site, measurements made along short segments of track that have been visually eliminated
by erosion and deposition processes show a 73% increase in penetrometer resistance over adjacent, undisturbed soils Dirt roadways
at three former base camp locations could not be penetrated below 5–10 cm because of extreme compaction Soil bulk density
was not as sensitive an indicator of soil compaction as was penetrometer resistance Density values in the upper 10 cm of soil
are not significantly different between tank tracks and undisturbed soils at most sites, and roadways at two base camps show
an average increase in bulk density of only 12% over adjacent soils. Trench excavations across tank tracks show that physical
modifications of the substrate can extend vertically beneath a track to a depth of 25 cm and outward from a track’s edge to
50 cm These soil disturbances are probably major factors that encourage accelerated soil erosion throughout the manuever area
and also retard or prevent the return of vegetation to pre-disturbance conditions 相似文献