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61.
By BIRGIT HEESE DIETRICH ALTHAUSEN TILMAN DINTER MICHAEL ESSELBORN THOMAS MÜLLER MATTHIAS TESCHE MATTHIAS WIEGNER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):195-205
Vertical profiles of dust key optical properties are presented from measurements during the Saharan Mineral Dust Experiment (SAMUM) by Raman and depolarization lidar at two ground-based sites and by airborne high spectral resolution lidar. One of the sites, Tinfou, is located close to the border of the Sahara in Southern Morocco and was the main in situ site during SAMUM. The other site was Ouarzazate airport, the main lidar site. From the lidar measurements the spatial distribution of the dust between Tinfou and Ouarzazate was derived for 1 d. The retrieved profiles of backscatter and extinction coefficients and particle depolarization ratios show comparable dust optical properties, a similar vertical structure of the dust layer, and a height of about 4 km asl at both sites. The airborne cross-section of the extinction coefficient at the two sites confirms the low variability in dust properties. Although the general picture of the dust layer was similar, the lidar measurements reveal a higher dust load closer to the dust source. Nevertheless, the observed intensive optical properties were the same. These results indicate that the lidar measurements at two sites close to the dust source are both representative for the SAMUM dust conditions. 相似文献
62.
By KYUNG-SOOK YUN BAOHUA REN KYUNG-JA HA JOHNNY C. L. CHAN JONG-GHAP JHUN 《地球,A辑:动力气象学与海洋学》2009,61(5):565-578
Based on 30–60-day oscillation in the East Asian summer monsoon (EASM), the relationship between its northward propagation and ENSO (El Niño and Southern Oscillation) was investigated. To explicitly describe the 30–60-day monsoonal evolution, an empirical orthogonal function (EOF) analysis was carried out on the temporal-latitude section of the longitudinal average for 115°E–120°E. The principal 30–60-day EASM mode captures a northward propagation of well-organized intraseasonal oscillation (NISO). Using the associated time series of the first mode, we found a significant lagged correlation between interannual variability of the NISO and ENSO. Its lagged correlations with NINO indices have a quasi-biennial (QB) characteristic through the preceding summer and the concurrent summer. Their relationship was found by the regression analysis relating the low-level circulation to the ocean temperature. The western North Pacific anticyclone and the anticyclone-induced easterly vertical wind shear anomalies induce the dynamical linkage between the NISO and QB-type ENSO. It is shown that the NISO is more closely tied with QB-type ENSO in its phase than in its amplitude, and may be connected to the anomalous easterly wind and the eastward evolution of an oceanic Kelvin wave, which is associated with abrupt ENSO transition. The predictability on ENSO and NISO is examined through the canonical correlation analysis. 相似文献
63.
64.
Fine-grained glaciomarine and glacial deposits on the outer Mid Norwegian continental shelf show complex variations in shear strength and degree of consolidation. At the Smørbukk Sør field (approx. 65°N, 7°E) about 80 m of variably overconsolidated clayey till is found on top of normally- or possibly underconsolidated glaciomarine and marine sediments. A high gas content is found below 60 m, and the porewater in the rather soft sediments in the lower part of the borehole may have been partly trapped by gas hydrates when the overlying hard till was deposited. The variations in geotechnical properties of the 80 m thick till section are suggested to result mainly from compaction below grounded ice during the last glaciation, and we interpret the strength variations in the till to reflect shifts between freeze of sediment porewater onto the base of the ice causing highly overconsolidated intervals, and thermal equilibrium or melting at the ice sole resulting in intervals of softer till.A large ridge northwest of Smørbukk (Skjoldryggen) is probably partly formed by ice push during ice flow oscillations at the same time as the described till at Smørbukk was deposited. This ridge retarded the ice flow and hence the frictional heating at the end of surges, creating pulses of net freezing base ice and consolidation of the substratum. The described process has possibly affected a wide area up-ice of Skjoldryggen, and may be common in areas with a complex glacial history and a fine-grained substratum. 相似文献
65.
Depolarization ratio profiling at several wavelengths in pure Saharan dust during SAMUM 2006 总被引:1,自引:0,他引:1
By VOLKER FREUDENTHALER MICHAEL ESSELBORN MATTHIAS WIEGNER BIRGIT HEESE MATTHIAS TESCHE ALBERT ANSMANN DETLEF MÜLLER DIETRICH ALTHAUSEN MARTIN WIRTH REAS FIX GERHARD EHRET PETER KNIPPERTZ CARLOS TOLEDANO JOSEF GASTEIGER MARKUS GARHAMMER MEINHARD SEEFELDNER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):165-179
Vertical profiles of the linear particle depolarization ratio of pure dust clouds were measured during the Saharan Mineral Dust Experiment (SAMUM) at Ouarzazate, Morocco (30.9°N, –6.9°E), close to source regions in May–June 2006, with four lidar systems at four wavelengths (355, 532, 710 and 1064 nm). The intercomparison of the lidar systems is accompanied by a discussion of the different calibration methods, including a new, advanced method, and a detailed error analysis. Over the whole SAMUM periode pure dust layers show a mean linear particle depolarization ratio at 532 nm of 0.31, in the range between 0.27 and 0.35, with a mean Ångström exponent (AE, 440–870 nm) of 0.18 (range 0.04–0.34) and still high mean linear particle depolarization ratio between 0.21 and 0.25 during periods with aerosol optical thickness less than 0.1, with a mean AE of 0.76 (range 0.65–1.00), which represents a negative correlation of the linear particle depolarization ratio with the AE. A slight decrease of the linear particle depolarization ratio with wavelength was found between 532 and 1064 nm from 0.31 ± 0.03 to 0.27 ± 0.04. 相似文献
66.
Seasonal variation of the molecular hydrogen uptake by soils inferred from continuous atmospheric observations in Heidelberg, southwest Germany 总被引:1,自引:0,他引:1
By SAMUEL HAMMER INGEBORG LEVIN 《Tellus. Series B, Chemical and physical meteorology》2009,61(3):556-565
The dominant sink of atmospheric molecular hydrogen (H2 ) is its enzymatic destruction in soils. Quantitative estimates of the global sink strength, as derived from bottom-up process studies, are, however, still associated to large uncertainties. Here we present an alternative way to estimate atmosphere-to-soil flux densities, respectively deposition velocities of H2 , based on atmospheric H2 and 222 Rn observations in the boundary layer. Two and a half years of continuous measurements from a polluted site in the Rhine-Neckar area have been evaluated and night-time flux densities were calculated for situations of strong nocturnal boundary layer inversions using the Radon-Tracer Method. The influences from local anthropogenic combustion sources could be detected and successfully separated by parallel measurements of carbon monoxide. Inferred daily uptake fluxes in the Heidelberg catchment area range from 0.5 to 3 × 10−8 g H2 m−2 s−1 with a mean value of (1.28 ± 0.31) × 10−8 g H2 m−2 s−1 . Uptake rates are about 25% larger during summer than during winter, when soil moisture is high, and diffusive transport of H2 into the soil is inhibited. The mean deposition velocity is 3.0 ± 0.7 × 10−2 cm s−1 , which is very well in line with direct measurements on similar soil types in Europe and elsewhere. 相似文献
67.
68.
Characterizing the capacity of the terrestrial biome to absorb CO2 is one of the most pressing topics in climate science. One of the key players in this arena is also one of the most poorly understood: the role of nitrogen deposition. While N deposition seems to fertilize some forests, in others it has been blamed for forest decline and tree mortality. In order to further understand the role of N deposition in forest primary productivity, an in situ N-amendment study was conducted in a relatively high N deposition region of the CO Rocky Mountains over 3 yr.
Chlorophyll fluorometry is a non-invasive technique that allows for the characterization of photosynthetic efficiency and photoinhibition in plants. Analysis of chlorophyll fluorometry data showed that in this tree line forest, moderate amounts of additional N significantly lower the photosynthetic efficiency of individual branches when compared to control branches, while significantly improving the non-photochemical dissipation of excess absorbed energy. This suggests that in high-altitude spruce forests receiving relatively high N inputs, GPP may be impaired by continued chronic additions of N. One potential cause of this is an increase in the light harvesting capacity of N amended branches without a concurrent increase in photosynthesis. 相似文献
Chlorophyll fluorometry is a non-invasive technique that allows for the characterization of photosynthetic efficiency and photoinhibition in plants. Analysis of chlorophyll fluorometry data showed that in this tree line forest, moderate amounts of additional N significantly lower the photosynthetic efficiency of individual branches when compared to control branches, while significantly improving the non-photochemical dissipation of excess absorbed energy. This suggests that in high-altitude spruce forests receiving relatively high N inputs, GPP may be impaired by continued chronic additions of N. One potential cause of this is an increase in the light harvesting capacity of N amended branches without a concurrent increase in photosynthesis. 相似文献
69.
Barend Köbben Rolf De By Theodor Foerster Otto Huisman Rob Lemmens Javier Morales 《Transactions in GIS》2010,14(Z1):25-37
ITC, the Faculty of Geo–Information Science and Earth Observation of the University of Twente, is an institute that aims at capacity building and institutional development, specifically in developing countries. In our Geoinformatics curriculum, we emphasise two principles. The first addresses the systematics of purposeful spatial data production and uptake into computerised systems; the second addresses the methodical construction of these computerised systems, applying principles of model – driven architecture, formal specification and transformational design of SDI nodes. The term Spatial Data Infrastructure (SDI) usually denotes large, complex systems, but its principles can also be applied in simple and cost–effective ways. This approach we have called SDIlight and it is of particular interest to our students that come from developing countries. We work with and build a software stack consisting of free and open source components. To achieve interoperability, we emphasise the use of open standards from the Open Geospatial Consortium and others. In this paper, we explain how our students apply the SDIlight approach in the GeoinformaticsMaster degree course. An important part of that course is a Case Study Application Building & Programming, in which students apply their knowledge in a ‘real–world’ project, with a focus on geo–information engineering skills. We conclude with a section that evaluates the effectiveness of using the SDIlight concept in teaching our Geoinformatics Master, and on the more general applicability of the methodology. 相似文献
70.
The generation of internal waves from barotropic tides can be quantified in terms of the conversion rates. These have often been obtained by applying the WKB approximation, which yields an expression for the conversion rates which is proportional to the seabed buoyancy frequency N B . For small values of N B or strong variations of the buoyancy profile N ( z ) , this gives unreliable results. Using homogenization theory it is here shown that the conversion rate instead depends on the value of N ( z ) averaged over a vertical region at the bottom of the same magnitude as the vertical length-scale of the internal wave, which for the lowest modes is of the same order as the entire ocean depth. This gives a substantially larger conversion rate. 相似文献