全文获取类型
收费全文 | 832篇 |
免费 | 37篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 48篇 |
地球物理 | 215篇 |
地质学 | 223篇 |
海洋学 | 129篇 |
天文学 | 174篇 |
综合类 | 5篇 |
自然地理 | 48篇 |
出版年
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 5篇 |
2018年 | 15篇 |
2017年 | 17篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 19篇 |
2011年 | 30篇 |
2010年 | 31篇 |
2009年 | 40篇 |
2008年 | 32篇 |
2007年 | 32篇 |
2006年 | 39篇 |
2005年 | 19篇 |
2004年 | 27篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 21篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1974年 | 7篇 |
1973年 | 11篇 |
1971年 | 5篇 |
排序方式: 共有872条查询结果,搜索用时 156 毫秒
531.
Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH 总被引:2,自引:0,他引:2
Carlos M. Duarte Iris E. Hendriks Tommy S. Moore Ylva S. Olsen Alexandra Steckbauer Laura Ramajo Jacob Carstensen Julie A. Trotter Malcolm McCulloch 《Estuaries and Coasts》2013,36(2):221-236
Ocean acidification due to anthropogenic CO2 emissions is a dominant driver of long-term changes in pH in the open ocean, raising concern for the future of calcifying organisms, many of which are present in coastal habitats. However, changes in pH in coastal ecosystems result from a multitude of drivers, including impacts from watershed processes, nutrient inputs, and changes in ecosystem structure and metabolism. Interaction between ocean acidification due to anthropogenic CO2 emissions and the dynamic regional to local drivers of coastal ecosystems have resulted in complex regulation of pH in coastal waters. Changes in the watershed can, for example, lead to changes in alkalinity and CO2 fluxes that, together with metabolic processes and oceanic dynamics, yield high-magnitude decadal changes of up to 0.5 units in coastal pH. Metabolism results in strong diel to seasonal fluctuations in pH, with characteristic ranges of 0.3 pH units, with metabolically intense habitats exceeding this range on a daily basis. The intense variability and multiple, complex controls on pH implies that the concept of ocean acidification due to anthropogenic CO2 emissions cannot be transposed to coastal ecosystems directly. Furthermore, in coastal ecosystems, the detection of trends towards acidification is not trivial and the attribution of these changes to anthropogenic CO2 emissions is even more problematic. Coastal ecosystems may show acidification or basification, depending on the balance between the invasion of coastal waters by anthropogenic CO2, watershed export of alkalinity, organic matter and CO2, and changes in the balance between primary production, respiration and calcification rates in response to changes in nutrient inputs and losses of ecosystem components. Hence, we contend that ocean acidification from anthropogenic CO2 is largely an open-ocean syndrome and that a concept of anthropogenic impacts on marine pH, which is applicable across the entire ocean, from coastal to open-ocean environments, provides a superior framework to consider the multiple components of the anthropogenic perturbation of marine pH trajectories. The concept of anthropogenic impacts on seawater pH acknowledges that a regional focus is necessary to predict future trajectories in the pH of coastal waters and points at opportunities to manage these trajectories locally to conserve coastal organisms vulnerable to ocean acidification. 相似文献
532.
The role of feeds and feeding in aquatic animal production 总被引:1,自引:0,他引:1
Lori Barck Moore Ph. D. 《GeoJournal》1985,10(3):245-251
The goal in aquaculture systems is to maximize the efficiency of the flow of energy and nutrients toward the animal output. This is more complex than in terrestrial animal agriculture since the cultured organism is immersed in its aquatic environment and is often only one member of a food web system. The organic and inorganic inputs into the system are critical not only to the extent that they feed the cultured species directly, but they may also positively or negatively affect the environment supporting the animal, as well as fertilize other aspects of autotrophic and heterotrophic food webs within the system. Aquaculture systems are characterized by the density of animal biomass in a given area of water, which determines the intensity of management inputs required. Extensive systems rely on natural productivity for food; intensive systems require a high degree of management inputs including a complete diet for the species; systems between the two extremes are optimized by balancing applied feed with natural productivity. Balanced nutrient delivery remains an indispensable requirement, regardless of source, for growth of adults as well as larvae, for reproductive success and for generation of a high quality product. 相似文献
533.
Edgar L Andreas Reginald J. Hill James R. Gosz Douglas I. Moore William D. Otto Achanta D. Sarma 《Boundary-Layer Meteorology》1998,86(3):379-408
Refuge has patchy vegetation in sandy soil. During midday and at night, the surface sources and sinks for heat and moisture may thus be different. Although the Sevilleta is broad and level, its metre-scale heterogeneity could therefore violate an assumption on which Monin-Obukhov similarity theory (MOST) relies. To test the applicability of MOST in such a setting, we measured the standard deviations of vertical (w) and longitudinal velocity (u), temperature (t), and humidity (q), the temperature-humidity covariance (¯tq), and the temperature skewness (St). Dividing the former five quantities by the appropriate flux scales (u*, *, and q*) yielded the nondimensional statistics w/u*, u/u*, t/|t*|, q/|q*|, and ¯tq/t*q*. w/u*, t/|t*|, and St have magnitudes and variations with stability similar to those reported in the literature and, thus, seem to obey MOST. Though u/u* is often presumed not to obey MOST, our u/u* data also agree with MOST scaling arguments. While q/|q*| has the same dependence on stability as t/|t*|, its magnitude is 28% larger. When we ignore ¯tq/t*q* values measured during sunrise and sunset transitions – when MOST is not expected to apply – this statistic has essentially the same magnitude and stability dependence as (t/t*)2. In a flow that truly obeys MOST, (t/t*)2, (q/q*)2, and ¯tq/t*q* should all have the same functional form. That (q/q*)2 differs from the other two suggests that the Sevilleta has an interesting surface not compatible with MOST. The sources of humidity reflect the patchiness while, despite the patchiness, the sources of heat seem uniformly distributed. 相似文献
534.
Christian Birkel Alicia Correa-Barahona Marco Martinez-Martinez Sebastian Granados-Bolaños Nelson Venegas-Cordero Kenneth Gutiérrez-García Sara Blanco-Ramírez Rafael Quesada-Mora Vanessa Solano-Rivera Jasson Mussio-Mora Andres Chavarría-Palma Katherine Vargas-Arias Georgianne W. Moore Ana Maria Durán-Quesada Javier Vasquez-Morera Chris Soulsby Dörthe Tetzlaff Edgar Espinoza-Cisneros Ricardo Sánchez-Murillo 《水文研究》2020,34(18):3824-3841
Headwaters are generally assumed to contribute the majority of water to downstream users, but how much water, of what quality and where it is generated are rarely known in the humid tropics. Here, using monthly monitoring in the data scarce (2,370 km2) San Carlos catchment in northeastern Costa Rica, we determined runoff-area relationships linked to geochemical and isotope tracers. We established 46 monitoring sites covering the full range of climatic, land use and geological gradients in the catchment. Regression and cluster analysis revealed unique spatial patterns and hydrologically functional landscape units. These units were used for seasonal and annual Bayesian tracer mixing models to assess spatial water source contributions to the outlet. Generally, the Bayesian mixing analysis showed that the chemical and isotopic imprint at the outlet is throughout the year dominated by the adjacent lowland catchments (68%) with much less tracer influence from the headwaters. However, the headwater catchments contributed the bulk of water and tracers to the outlet during the dry season (>50%) despite covering less than half of the total catchment area. Additionally, flow volumes seemed to be linearly scaled by area maintaining a link between the headwaters and the outlet particularly during high flows of the rainy season. Stable isotopes indicated mean recharge elevations above the mean catchment altitude, which further supports that headwaters were the primary source of downstream water. Our spatially detailed “snap-shot” sampling enabled a viable alternative source of large-scale hydrological process knowledge in the humid tropics with limited data availability. 相似文献
535.
We describe a parallel hybrid symplectic integrator for planetary system integration that runs on a graphics processing unit (GPU). The integrator identifies close approaches between particles and switches from symplectic to Hermite algorithms for particles that require higher resolution integrations. The integrator is approximately as accurate as other hybrid symplectic integrators but is GPU accelerated. 相似文献
536.
Kimberlitic olivines typically show a continuous range in size and texture rather than two discrete populations. The cores of small euhedral olivines commonly provide the template for the final crystal shape, which in turn closely matches morphologies produced by crystallization from a moderately under-cooled magma. Cores and edges of the majority of all olivines define a continuous compositional field, which can be interpreted in terms of Raleigh crystallization. Marked chemical gradients at the olivine margins are linked to rapid physico-chemical changes to the magma associated with loss of volatiles during the late stages of emplacement. Thus, rapid crystallization of groundmass olivines would deplete the magma in Ni, but increase Ca activity. The latter would be enhanced by decreasing pressure coupled with loss of CO2 from the carbonate-bearing kimberlite magma.For mantle olivines and the most refractory olivines in kimberlites (~ Fo94) to be in equilibrium with bulk rock compositions matching those of Mg-rich macrocrystic and aphanitic kimberlites (Mg# ~ 88) requires a mineral-melt Mg–Fe distribution coefficient of 0.47. This is well within the experimentally determined range for this distribution coefficient in carbonate-bearing systems. In southern African post-Gondwana alkaline pipe clusters, the average bulk rock Mg# and composition of the associated most Mg-rich olivine both decrease sympathetically from the interior to the continental margin, which is also consistent with a cognate origin for the olivines.A kimberlite magma following a plausible P-T trajectory relative to the CO2/H2O peridotite solidus would initially experience superheating, resulting in partial resorption of early-formed olivines that crystallized on the cool conduit walls. It would become supersaturated as it crossed the carbonated peridotite “ledge”, resulting in tabular and hopper growth forms typical of euhedral olivine cores. With further ascent, the magma would once again become superheated, resulting in partial resorption of these cores. Thus, apparently complex textures and internal zonation patterns of kimberlitic olivines are predicted by a plausible magma P-T trajectory. 相似文献
537.
K. Vozoff D. Kerr R. F. Moore D. L. B. Jupp R. J. G. Lewis 《Australian Journal of Earth Sciences》2013,60(3):361-375
The Murray Basin is geologically featureless, has been sparsely covered by geophysics, and is penetrated by a few scattered wells. Only drilling and reflection seismic work have provided consistently reliable depth information. They have indicated the presence of narrow troughs, which contain more than 3 km of Palaeozoic sediment, covered by basement highs with less than 300 m of Mesozoic and Cainozoic cover. Six widely spaced magnetotelluric (MT) sites were occupied in the north central Murray Basin. Results showed a 5 km thick horizontal section at Pooncarie, with a probably average porosity of 10%. Higher porosities, and probably a thicker section, were indicated near Little Topar, but the structural complexity there requires that additional data be acquired for positive interpretation. A persistent conductivity increase near 100 km suggests that the method may respond well to the base of the tectonic plate. The MT method appears well suited to the onshore exploration problems currently faced in Australia. 相似文献
538.
R. A. Cayley R. J. Korsch D. H. Moore R. D. Costelloe A. Nakamura C. E. Willman 《Australian Journal of Earth Sciences》2013,60(2):113-156
A ~400 km long deep crustal reflection seismic survey was acquired in central Victoria, Australia, in 2006. It has provided information on crustal architecture across the western Lachlan Orogen and has greatly added to the understanding of the tectonic evolution. The east-dipping Moyston Fault is confirmed as the suture between the Delamerian and western Lachlan Orogens, and is shown to extend down to the Moho. The Avoca Fault, the boundary between the Stawell and Bendigo Zones, is a west-dipping listric reverse fault that intersects the Moyston Fault at a depth of about 22 km, forming a V-shaped geometry. Both the Stawell and Bendigo Zones can be divided broadly into a lower crustal region of interlayered and imbricated metavolcanic and metasedimentary rocks and an upper crustal region of tightly folded metasedimentary rocks. The Stawell Zone was probably part of a Cambrian accretionary system along the eastern Gondwanaland margin, and mafic rocks may have been partly consumed by Cambrian subduction. Much of the Early Cambrian oceanic crust beneath the Bendigo Zone was not subducted, and is preserved as a crustal-scale imbricate thrust stack. The seismic data have shown that a thin-skinned structural model appears to be valid for much of the Melbourne Zone, whereas the Stawell and Bendigo Zones have a thick-skinned structural style. Internal faults in the Stawell and Bendigo Zones are mostly west-dipping listric faults, which extend from the surface to near the base of the crust. The Heathcote Fault Zone, the boundary between the Bendigo and Melbourne Zones, extends to at least 20 km, and possibly to the Moho. A striking feature in the seismic data is the markedly different seismic character of the mid to lower crust of the Melbourne Zone. The deep seismic reflection data for the Melbourne Zone have revealed a multilayered crustal structure that supports the Selwyn Block model. 相似文献
539.
The northern part of the auriferous Bendigo Zone is obscured by thick Cenozoic sediments of the Murray Basin, and as such remains poorly explored. Consequently, in addition to the 2006 deep seismic line obtained in Central Victoria, a magnetotelluric (MT) survey was completed to provide a signature for the major structures previously defined in the Bendigo area. Based on these correlations a second MT line, which we present here, was completed some 50 km to the north of the original line in an attempt to trace the deep structural trends extending north to the Victorian/NSW border. Extending some 155 km across the central north of the state, data were collected at 52 sites along an east–west profile. The new electrical conductivity model generated correlates well with the results from the southern transect; it confirms previously identified structural trends to the north and identifies additional unknown deep structures, thus adding to the understanding of the geology of the covered region and to its gold-bearing potential. 相似文献
540.
In variably confined carbonate platforms, impermeable confining units collect rainfall over large areas and deliver runoff to rivers or conduits in unconfined portions of platforms. Runoff can increase river stage or conduit heads in unconfined portions of platforms faster than local infiltration of rainfall can increase groundwater heads, causing hydraulic gradients between rivers, conduits and the aquifer to reverse. Gradient reversals cause flood waters to flow from rivers and conduits into the aquifer where they can dissolve limestone. Previous work on impacts of gradient reversals on dissolution has primarily emphasized individual caves and little research has been conducted at basin scales. To address this gap in knowledge, we used legacy data to assess how a gradient of aquifer confinement across the Suwannee River Basin, north‐central Florida affected locations, magnitudes and processes of dissolution during 2005–2007, a period with extreme ranges of discharge. During intense rain events, runoff from the confining unit increased river stage above groundwater heads in unconfined portions of the platform, hydraulically damming inputs of groundwater along a 200 km reach of river. Hydraulic damming allowed allogenic runoff with SICAL < ?4 to fill the entire river channel and flow into the aquifer via reversing springs. Storage of runoff in the aquifer decreased peak river discharges downstream and contributed to dissolution within the aquifer. Temporary storage of allogenic runoff in karst aquifers represents hyporheic exchange at a scale that is larger than found in streams flowing over non‐karst aquifers because conduits in karst aquifers extend the area available for exchange beyond river beds deep into aquifers. Post‐depositional porosity in variably confined carbonate platforms should thus be enhanced along rivers that originate on confining units. This distribution should be considered in models of porosity distribution used to manage water and hydrocarbon resources in carbonate rocks. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献