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191.
The air–sea ice CO2 flux was measured over landfast sea ice in the Chukchi Sea, off Barrow, Alaska in late May 2008 with a chamber technique. The ice cover transitioned from a cold early spring to a warm late spring state, with an increase in air temperature and incipient surface melt. During melt, brine salinity and brine dissolved inorganic carbon concentration (DIC) decreased from 67.3 to 18.7 and 3977.6 to 1163.5 μmol kg−1, respectively. In contrast, the salinity and DIC of under-ice water at depths of 3 and 5 m below the ice surface remained almost constant with average values of 32.4±0.3 (standard deviation) and 2163.1±16.8 μmol kg−1, respectively. The air–sea ice CO2 flux decreased from +0.7 to −1.0 mmol m−2 day−1 (where a positive value indicates CO2 being released to the atmosphere from the ice surface). During this early to late spring transition, brought on by surface melt, sea ice shifted from a source to a sink for atmospheric CO2, with a rapid decrease of brine DIC likely associated with a decrease in the partial pressure of CO2 of brine from a supersaturated to an undersaturated state compared to the atmosphere. Formation of superimposed ice coincident with melt was not sufficient to shut down ice–air gas exchange. 相似文献
192.
In this paper, we look into the theory of designing geoservice systems, i.e., SDI networks and their constituent SDI nodes.
As the field of SDI is strongly about bridging between geoservice systems, interoperability and harmonisation, it is not surprising
that standardisation efforts are of crucial importance in it. These efforts have historically addressed abstract and concrete
content models for data and metadata exchange, as well as abstract and concrete behavioural models for computational processes.
The list of standards that are in use in the SDI field continues to expand, and reaches out to neighbouring fields such as
sensor nets. We argue that given these trends, the resulting levels of standardisation in actual systems, and the complexity
of geoservice systems in general, it appears only natural to look into the possibility to define a standardised design theory for SDI and its nodes, which addresses the function base and the communication base. Specifically, we provide an overview
of those components that need to be designed, and what are their relationships. We do so in an abstract way, focussing on
the concern of information content in this paper, and only hinting at an appropriate theory of realisation based on our skeleton
theory. 相似文献
193.
Daniela Sauer Isabelle Schülli-Maurer Ragnhild Sperstad Rolf Srensen Karl Stahr 《Quaternary International》2009,209(1-2):31
This paper reports a study on soil development in loamy marine sediments on both sides of the Oslofjord (Vestfold, Østfold). This region has been subject to steady glacio-isostatic uplift during the whole Holocene. Hence, land surface age continuously increases from the coast inland. Several sea level curves, based on radiocarbon datings, enable estimation of land surface age for all locations. Clay illuviation starts in less than 1650 years. E horizons become lighter with age, but their lower boundary stays around 40 cm for more than 10 000 years. Albeluvic tongues develop between 4600 and 6200 years. Initially, they form along intersections of cracks. As preferential flow and leaching along the cracks continues, the tongues increase in length and width, progressively consuming the prisms between the cracks in the upper Bt horizon. The Fed/Fet ratios (weighted means of the upper meter) show a clear linear increase with soil age and may be used for “pedo-dating”, i.e. for estimating the ages of non-dated land surfaces covered with similar sediments. In contrast, the logarithmic decrease of base saturation and pH, with rapid changes in the first time but only very slight changes between 2000 and 10 000 years, makes these parameters unsuitable for “pedo-dating”. 相似文献
194.
The sharp concentration peak of the metals Cu, Cd and Zn at the redoxcline of the Framvaren Fjord, Norway, is described as an effect of chelation/complexation with organic ligands. The most dominating ligand is 2-mercaptobenzothiazole (MBT), which binds with a 2 : 1 ligand to metal stoichiometric ratio. MBT has the highest concentrations at the vicinity of the redoxcline where the oxidation of sulfide to elemental sulfur and sulfate is most extensive. We suggest the production being caused by sulfide oxidizing bacteria as we have not been able to detect MBT in pure cultures of sulfate reducing bacteria. Ni does not exhibit the same distribution as the other three metals due to lower preference for coordination with S and N donor atoms and a much lower rate for loss of water than Cu, Cd and Zn. 相似文献
195.
Gaby Becker Jens-Uwe Grooss Daniel S. McKenna Rolf Müller 《Journal of Atmospheric Chemistry》2000,37(3):217-229
Numerical schemes for the calculation of photolysis rates are usually employed in simulations of stratospheric chemistry. Here, we present an improvement of the treatment of the diffuse actinic flux in a widely used stratospheric photolysis scheme (Lary and Pyle, 1991). We discuss both the consequences of this improvement and the correction of an error present in earlier applications of this scheme on the calculation of stratospheric photolysis frequencies. The strongest impact of both changes to the scheme is for small solar zenith angles. The effect of the improved treatment of the diffuse flux is most pronounced in the lower stratosphere and in the troposphere. Overall, the change in the calculated photolysis frequencies in the region of interest in the stratosphere is below about 20%, although larger deviations are found for H2O, O2, NO, N2O, and HCl. 相似文献
196.
An ice breeze mechanism for boundary-layer jets 总被引:1,自引:0,他引:1
The existence of a low-level (z=~1000 m) jet adjacent to a sea-ice boundary is investigated with a two-dimensional numerical model. A thermally-direct ice breeze circulation is induced by specifying an ice-sea surface temperature gradient, with the mean geostrophic wind parallel to the ice edge. Pressure changes associated with over-water mixed-layer development create an increase in geostrophic velocity that accounts for most of the increase in wind speed. A change in initial geostrophic wind direction has significant effects on location and intensity of the low-level jet; geostrophic winds parallel to the ice edge result in stronger jets than occur with cross-ice geostrophic winds. An inertial oscillation simulated by the model in 1-D makes a negligible contribution to the low-level jet. 相似文献
197.
198.
Snow disappearance timing is dominated by forest effects on snow accumulation in warm winter climates of the Pacific Northwest,United States
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Susan E. Dickerson‐Lange Rolf F. Gersonde Jason A. Hubbart Timothy E. Link Anne W. Nolin Gwyneth H. Perry Travis R. Roth Nicholas E. Wayand Jessica D. Lundquist 《水文研究》2017,31(10):1846-1862
Forests modify snow processes and affect snow water storage as well as snow disappearance timing. However, forest influences on snow accumulation and ablation vary with climate and topography and are therefore subject to temporal and spatial variability. We utilize multiple years of snow observations from across the Pacific Northwest, United States, to assess forest–snow interactions in the relatively warm winter conditions characteristic of maritime and transitional maritime–continental climates. We (a) quantify the difference in snow magnitude and disappearance timing between forests and open areas and (b) assess how forest modifications of snow accumulation and ablation combine to determine whether snow disappears later in the forest or in the open. We find that snow disappearance timing at 12 (out of 14) sites ranges from synchronous in the forest and open to snow persisting up to 13 weeks longer in the open relative to a forested area. By analyzing accumulation and ablation rates up to the day when snow first disappears from the forest, we find that the difference between accumulation rates in the open and forest is larger than the difference between ablation rates. Thus, canopy snow interception and subsequent loss, rather than ablation, set up longer snow duration in the open. However, at two relatively windy sites (hourly average wind speeds up to 8 and 17 m/s), differential snow disappearance timing is reversed: Snow persists 2–5 weeks longer in the forest. At the windiest sites, accumulation rates in the forest and open are similar. Ablation rates are higher in the open, but the difference between ablation rates in the forest and open at these sites is approximately equivalent to the difference at less windy sites. Thus, longer snow retention in the forest at the windiest sites is controlled by depositional differences rather than by reduced ablation rates. These findings suggest that improved quantification of forest effects on snow accumulation processes is needed to accurately predict the effect of forest management or natural disturbance on snow water resources. 相似文献
199.
Rolf Dauskardt 《GeoJournal》1993,30(1):9-20
In the 1990s, South Africa and its cities have entered an unprecedented era of change. This transition has been characterised by a burgeoning of civil society and negotiation processes around the key policy and development challenges facing the country. Within this context, the beginnings of a new post-apartheid urban reconstruction era has been marked by the dual challenges of neutralising the damaging anomalies created in cities by apartheid urban engineering, and of shaping efficient, functional and well-managed cities for the future. The core areas or central city zones of the major metropolitan complexes — comprising inner city residential components and central business district economic sectors — are now emerging as a priority area in urban reconstruction. This paper briefly outlines the evolution of the South African central city within the context of overall metropolitan morphology, before considering several of the key issues and processes currently shaping inner city and CBD zones. 相似文献
200.