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751.
Tine?Derez Tom?Van Der?Donck Oliver?Plümper Philippe?Muchez Gill?Pennock Martyn?R.?Drury Manuel?SintubinEmail author 《Contributions to Mineralogy and Petrology》2017,172(7):56
Fine extinction bands (FEBs) (also known as deformation lamellae) visible with polarized light microscopy in quartz consist of a range of nanostructures, inferring different formation processes. Previous transmission electron microscopy studies have shown that most FEB nanostructures in naturally deformed quartz are elongated subgrains formed by recovery of dislocation slip bands. Here we show that three types of FEB nanostructure occur in naturally deformed vein quartz from the low-grade metamorphic High-Ardenne slate belt (Belgium). Prismatic oriented FEBs are defined by bands of dislocation walls. Dauphiné twin boundaries present along the FEB boundaries probably formed after FEB formation. In an example of two sub-rhombohedral oriented FEBs, developed as two sets in one grain, the finer FEB set consists of elongated subgrains, similar to FEBs described in previous transmission electron microscopy studies. The second wider FEB set consists of bands with different dislocation density and fluid-inclusion content. The wider FEB set is interpreted as bands with different plastic strain associated with the primary growth banding of the vein quartz grain. The nanometre-scale fluid inclusions are interpreted to have formed from structurally bounded hydroxyl groups that moreover facilitated formation of the elongate subgrains. Larger fluid inclusions aligned along FEBs are explained by fluid-inclusion redistribution along dislocation cores. The prismatic FEB nanostructure and the relation between FEBs and growth bands have not been recognized before, although related structures have been reported in experimentally deformed quartz. 相似文献
752.
Merja?H.?T?lleEmail authorView authors OrcID profile Lukas?Schefczyk Oliver?Gutjahr 《Theoretical and Applied Climatology》2018,133(3-4):829-849
A 26-year simulation (1980–2005) was performed with the Weather Research and Forecast (WRF) model over the Volta Basin in West Africa. This was to investigate the ability of a climate version of WRF to reproduce present day temperature and precipitation over the Volta Basin. The ERA-Interim reanalysis and one realization of the ECHAM6 global circulation model (GCM) data were dynamically downscaled using two nested domains within the WRF model. The outer domain had a horizontal resolution of 50 km and covered the whole of West Africa while the inner domain had a horizontal resolution of 10 km. It was observed that biases in the respective forcing data were carried over to the RCM, but also the RCM itself contributed to the mean bias of the model. Also, the biases in the 50-km domain were transferred unchanged, especially in the case of temperature, to the 10-km domain, but, for precipitation, the higher-resolution simulations increased the mean bias in some cases. While in general, WRF underestimated temperature in both the outer (mean biases of ?1.6 and ?2.3 K for ERA-Interim and ECHAM6, respectively) and the inner (mean biases of ?0.9 K for the reanalysis and ?1.8 K for the GCM) domains, WRF slightly underestimated precipitation in the coarser domain but overestimated precipitation in the finer domain over the Volta Basin. The performance of the GCM, in general, is good, particularly for temperature with mean bias of ?0.7 K over the outer domain. However, for precipitation, the added value of the RCM cannot be overlooked, especially over the whole West African region on the annual time scale (mean biases of ?3% for WRF and ?8% for ECHAM6). Over the whole Volta Basin and the Soudano-Sahel for the month of April and spring (MAM) rainfall, respectively, mean bias close to 0% was simulated. Biases in the interannual variability in both temperature and precipitation over the basin were smaller in the WRF than the ECHAM6. High spatial pattern correlations between 0.7 and 0.8 were achieved for the autumn precipitation and low spatial correlation in the range of 0.0 and 0.2 for the winter season precipitation over the whole basin and all the three belts over the basin. 相似文献
753.
Carleton R. Bern Mark A. Brzezinski Charlotte Beucher Oliver A. Chadwick 《Geochimica et cosmochimica acta》2010,74(3):876-5891
Silicon isotope ratios (δ30Si) of bulk mineral materials in soil integrate effects from both silicon sources and processing. Here we report δ30Si values from a climate gradient of Hawaiian soils developed on 170 ka basalt and relate them to patterns of soil chemistry and mineralogy. The results demonstrate informative relationships between the mass fraction of soil Si depletion and δ30Si. In upper (<1 m deep) soil horizons along the climate gradient, Si depletion correlates with decreases of residual δ30Si values in low rainfall soils and increases in high rainfall soils. Strong positive correlation between soil δ30Si and dust-derived quartz and mica content show that both trends are largely controlled by the abundance of these weathering-resistant minerals. The data also lend support to the idea that fractionation of Si isotopes in secondary phases is controlled by partitioning of silicon between dissolved and precipitated products during the initial weathering of primary basalt. Secondary mineral δ30Si values from lower (>1 m deep) soil horizons generally correlate with the isotope fractionation predicted by a study of dissolved Si in basalt-watershed rivers and driven by preferential 28Si removal from the dissolved phase during precipitation. In contrast, after correcting for the influence of dust, secondary mineral Si depletion and δ30Si values in shallow (<1 m deep) soil horizons showed evidence of biocycling induced Si redistribution and substantially lower δ30Si values than predicted. Low δ30Si values in shallow soil horizons compared to predictions can be attributed to repeated fractionation as secondary minerals undergo additional cycles of dissolution and precipitation. Primary mineral weathering, secondary mineral weathering, dust accumulation, and biocycling are major processes in terrestrial Si cycling and these results demonstrate that each can be traced by δ30Si values interpreted in conjunction with mineralogy and measures of Si depletion. 相似文献
754.
Degradation of chlorinated ethylenes by Fe0: inhibition processes and mineral precipitation 总被引:2,自引:0,他引:2
755.
756.