全文获取类型
收费全文 | 1014篇 |
免费 | 30篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 54篇 |
地球物理 | 194篇 |
地质学 | 327篇 |
海洋学 | 65篇 |
天文学 | 285篇 |
综合类 | 1篇 |
自然地理 | 108篇 |
出版年
2021年 | 12篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 18篇 |
2016年 | 31篇 |
2015年 | 14篇 |
2014年 | 24篇 |
2013年 | 56篇 |
2012年 | 15篇 |
2011年 | 38篇 |
2010年 | 37篇 |
2009年 | 53篇 |
2008年 | 53篇 |
2007年 | 54篇 |
2006年 | 56篇 |
2005年 | 40篇 |
2004年 | 37篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 25篇 |
1998年 | 36篇 |
1997年 | 18篇 |
1996年 | 9篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1973年 | 6篇 |
1972年 | 12篇 |
1971年 | 6篇 |
排序方式: 共有1049条查询结果,搜索用时 15 毫秒
91.
S.D.M. White 《Astrophysics and Space Science》1999,267(1-4):355-355
92.
We find statistically significant correlations in the cosmological matter power spectrum over the full range of observable scales. While the correlations between individual modes are weak, the band-averaged power spectrum shows strong non-trivial correlations. The correlations are significant when the modes in either one or both bands are in the non-linear regime, and approach 100 per cent for pairs of bands in which all the modes are non-linear. The correlations are weaker, but not absent, when computed in redshift space. As estimates of the power spectrum from galaxy surveys require band-averaging, the correlations must be taken into account when comparing a measured power spectrum with theoretical models. 相似文献
93.
C. C. White R. Smart M. Stutter M. S. Cresser M. F. Billett E. A. Elias C. Soulsby S. Langan A. C. Edwards A. Wade R. Ferrier C. Neal H. Jarvie R. Owen 《Applied Geochemistry》1999,14(8):369
A simple, unifying approach to classifying quantitatively the susceptibility of catchment soils and surface waters to acidification is suggested. In areas subject to a strong maritime influence, such as the UK and substantial parts of NW Europe, wherever soil mineral weathering rates are low and soils are unfertilised, atmospherically derived base cations of maritime origins have a greater effect than those derived from biogeochemical weathering on the exchangeable soil base cations. This is directly reflected in the relative base cation concentrations of the associated drainage waters, which become increasingly Na-dominated. Using 10 sub-catchments of the River Dee in north-eastern Scotland, it is shown here that the extent of Na dominance, the ratio of Na+ to ΣNa++Ca2++Mg2+, at any point in a river provides a quantitative index of the upstream weathering rate and thus of the susceptibility of the river concerned to acidification under diverse flow conditions. Data from a further 58 sub-catchments from the same river system, and from 4 other catchments from around Scotland, were used to validate this theory. 相似文献
94.
MacQueen R. M. Blankner J. G. Elmore D. F. Lecinski A. R. White O. R. 《Solar physics》1998,182(1):97-105
A new instrument capable of 3-min time resolution full-disk and limb observations in the Hei 1083 nm spectral line has been
in operation at the High Altitude Observatory's Mauna Loa Solar Observatory (MLSO) since April 1996. We discuss instrument
capabilities and performance and present some initial observations of limb activity from the first year of instrument operation.
We compare limb Hei and Hα observations of quiescent and active prominences, comment on the role of Doppler shifts in interpreting
the Hei observations, and illustrate the use of disk/limb Hei observations of a CME-associated eruptive filament in mass-ejection
studies. 相似文献
95.
96.
Minor and trace elements in HF-soluble zircons 总被引:2,自引:0,他引:2
Electron probe analysis of a group of HF-soluble zircons from porphyroids of the Thuringian Forest, Germany, established yttrium, phosphorus, and iron to be the significant minor constituents. It is believed that these elements render the zircon structure HF-soluble. The Y content varies from about 6500–48000 ppm=0.83–6.10% Y2O3; the P concentrations range from a low of about 790 to a maximum of 4000 ppm=0.18–0.92% P2O5; the Fe content varies from about 400–15000 ppm=0.06–2.10% Fe2O3. Although both Y and P are distributed throughout each given grain, they are sometimes mutually enriched in growth zones. These zones are also resolved in reflected light micrographs and the electron images. 相似文献
97.
Ellen?K.?HermanEmail author Jennifer?H.?Tancredi Laura?Toran William?B.?White 《Hydrogeology Journal》2007,15(2):255-266
Springs in karstic carbonate rocks frequently carry a sediment load as well as a dissolved load. Analysis of morphology and
mineralogy of suspended sediment from three contrasting karst springs reveals a suite of clastic particles that reflect both
source areas and processes that take place within the aquifer. Nolte Spring in Lancaster County, Pennsylvania, USA, discharges
sediment of apparently precipitated calcite, indicating that at some point in the aquifer or vadose zone, water exceeds saturation
with respect to calcite. Sediment morphologies and chemical conditions in the aquifer point to two different scenarios for
this precipitation. The other two springs, Arch Spring in Blair County, Pennsylvania and Bushkill Spring in Northampton County,
Pennsylvania, show no evidence of calcite precipitation. Arch Spring discharges mainly layer silicates, while Bushkill Spring
discharges mainly silica.
Resumen Los manantiales en rocas carbonatadas karstficadas tienen frecuentemente una carga de sedimentos y de sólidos disueltos. Los análisis de la morfología y mineralogía de los sedimentos suspendidos de tres manantiales kársticos contrastados revela un conjunto de partículas clásticas que reflejan ambas áreas fuente y los procesos que tienen lugar dentro del acuífero. Nolte Spring en el Condado de Lancaster, Pennsylvania, USA, descarga sedimento de calcita aparentemente precipitada indicando que en cierto punto del acuífero o en la zona vadosa, el agua supera la saturación con respecto a la calcita. La morfología de los sedimentos y las condiciones químicas en el acuífero apuntan a dos escenarios diferentes para esta precipitación. Los otras dos manantiales, Arch Spring en el Condado de Blair, Pennsylvania y Bushkill Spring en el Condado de Norhtampton, Pennsylvania, no muestran evidencia de precitación de calcita. Arch Spring descarga principalmente filosilicatos mientras que Bushkill Spring descarga fundamentalmente Sílice.
Résumé Les sources situées en contexte carbonaté karstique charrient fréquemment, outre les matières dissoutes, une charge solide. La morphologie et la minéralogie des sédiments en suspension issus de trois sources karstiques de caractéristiques distinctes ont été analysées : une série de particules clastiques, reflétant à la fois les secteurs des sources et les processus internes de l’aquifère, en ressort. Les sédiments issus de Nolte Spring (Comté de Lancaster, Pennsylvanie, Etats-Unis) sont constitués de calcite apparemment précipitée: ceci indique que l’eau atteint la sursaturation vis-à-vis de la calcite à un certain point de l’aquifère ou de la zone non-saturée. La morphologie des sédiments et les conditions chimiques au sein de l’aquifère mènent à deux scénarii différents pour expliquer cette précipitation. Les deux autres sources, Arch Spring (Comté de Blair, Pennsylvanie) et Bushkill Spring (Comté de Northampton, Pennsylvanie), ne présentent aucun indice de précipitation de calcite. Arch Spring exporte essentiellement des phyllosilicates, alors que la silice est majoritaire à Bushkill Spring.相似文献
98.
Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP 总被引:2,自引:2,他引:2
The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related
to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless
tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km2). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within
vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country
rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite
and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of
contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris
+ steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the
surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however,
probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached
the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral
quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents.
The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia
beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the
extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water,
as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer
rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water
increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves
no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture,
lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the
complex evolved.
Editorial responsibility: J. Donnelly-Nolan 相似文献
99.
John T. Wilson Cherri Adair Hal White Robert L. Howard 《Ground Water Monitoring & Remediation》2016,36(4):50-61
The risk that benzene and toluene from spills of gasoline will impact drinking water wells is largely controlled by the natural anaerobic biodegradation of benzene and toluene. Benzene and toluene, as well as ethanol and other biofuels, are degraded under anaerobic conditions to the same pool of degradation products. Biodegradation of biofuels may produce concentrations of degradation products that make the thermodynamics for degradation of benzene and toluene infeasible under methanogenic conditions and produce larger plumes of benzene and toluene. This study evaluated the concentrations of fuel alcohols that are necessary to inhibit the anaerobic degradation of benzene and toluene under methanogenic conditions. At two ethanol spill sites, concentrations of ethanol greater ≥42 mg/L inhibited the anaerobic degradation of toluene. The pH and concentrations of acetate, dissolved inorganic carbon, and molecular hydrogen were used to calculate the Gibbs free energy for the biodegradation of toluene. In general, the anaerobic biodegradation of toluene was not thermodynamically feasible in water with ≥42 mg/L ethanol. In a microcosm study, when the concentrations of ethanol were ≥14 mg/L or the concentrations of n‐butanol were ≥16 mg/L, the biodegradation of the alcohols consistently produced concentrations of hydrogen, dissolved inorganic carbon, and acetate that would preclude natural anaerobic biodegradation of benzene and toluene by syntrophic organisms. In contrast, iso‐butanol and n‐propanol only occasionally produced conditions that would preclude the biodegradation of benzene and toluene. 相似文献
100.
Anna Brooks Rehema M. White David C. Paton 《International Journal of Salt Lake Research》1995,4(2):133-163
The hypermarine southern Coorong is threatened by proposals to drain relatively fresh surface water and groundwater from adjacent agricultural areas into the Coorong. These influent waters carry moderate loads of heavy metals. Acute toxicity of heavy metals toDiacypris compacta, an abundant ostracod in the Coorong, was measured in the laboratory at 18°C in a static system using Coorong water (pH 7.8 salinity 50 ppt). At 4 days (96 h) the mean values of LC50 for copper, zinc, lead and, cadmium respectively were 0.8, 2.1, 3.1 and 4.3 mg L–1, and at 8 days the respective mean LC50
s were 0.4, 0.7, 2.2 and 1.1 mgL–1. The effect of two or three metals on mortality was additive in some cases and synergistic in other cases, but generally less than additive. However, in all cases mortality was greater in the presence of two or three metals than in the presence of a single metal. According to ANZECC (1992) guidelines, maximum acceptable concentrations of heavy metals should be no higher than 0.01 x the lowest LC50 value. Using the lowest LC50 values forDiacypris compacta obtained at 8 days, maximum acceptable concentrations in the Coorong would be 4, 5, 9 and 22 gL–1 for copper, zinc, cadmium and lead respectively, the values for zinc and copper failling below those recommended by ANZECC (1992) for marine waters. Reported concentrations of copper and zinc in surface water and groundwater in areas adjacent to the Coorong sometimes exceed these values, hence drainage of these waters into the Coorong represents a significant hazard to the Coorong biota. 相似文献