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131.
The role of wood as a driver of landform development appears to have been overlooked in the interpretation of palaeo‐landscape change along river corridors. Deforested river corridors and wood‐free rivers characterize ‘modern’, managed landscapes, but along natural river corridors both driftwood dynamics and tree reproductive strategies can have a dramatic impact on the style and rate of channel and floodplain development. Therefore, we believe that interpretations of the post‐glacial history of river valleys across the northern temperate climatic zone could be usefully reassessed, incorporating the roles of riparian trees. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
132.
Peter Francis Coleman 《Journal of Atmospheric and Solar》2009,71(8-9):1001-1002
Comments are made on the ball lightning paper of Stephan and Massey [Stefan, K.D., Massey, N., 2008. Burning molten metallic sphere: One class of ball lightning? Journal of Atmospheric and Solar–Terrestrial Physics 70, 1589–1596] that describes their ‘welding drop’ theory. An alternative theory is offered based on combustion inside an atmospheric vortex. The ‘vortex fireball’ hypothesis has good explanatory capability in regard to published ball lightning properties. 相似文献
133.
In this study we validate the raw ensemble mean forecasts of the CCCma's GCM2 modelagainst surface temperature and precipitation data obtained from 160 Chinese stations.It is foundthat despite the lagre biases,the model was able to produce seasonal anomalies that haveproperties that are reasonably close to those that are observed.This anomaly is the quantity ofinterest when forecasting seasonal climatic conditions.The root mean squared difference(RMSD)between the forecast and observed anomaly leads us to be modestly optimistic about the prospectsfor using dynamical models to forecast the interannual variability of some meteorological elements.The correlation analysis of the forecast and observation also supports the result given by theRMSD analysis and provides a tool for identify the forecast confidence level in various regions, 相似文献
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Ferric iron in mantle-derived garnets 总被引:4,自引:0,他引:4
Robert W. Luth David Virgo Francis R. Boyd Bernard J. Wood 《Contributions to Mineralogy and Petrology》1990,104(1):56-72
The oxidation state of a mantle assemblage may be defined by heterogeneous reactions between oxygen and iron-bearing minerals. In spinel lherzolites, the presence of Fe3+ in spinel allows use of the assemblage olivine-orthopyroxene-spinel to define f
O
2 at fixed T and P. As a first step towards establishing an analogous reaction for garnet lherzolites, garnets from mantle-derived xenoliths from South Africa and the USSR have been analyzed with 57Fe Mössbauer spectroscopy at 298 and 77K to determine Fe3+/Fe2+ and the coordination state of iron. Garnets from South African alkremites (pyrope+Mg-spinel) and eclogites, as well as garnet-spinel and low-temperature garnet lherzolites from both South Afica and the USSR, have Fe3+/Fe<0.07. In contrast, garnets from high-temperature garnet lherzolites from within the Kaapvaal craton of South Africa have Fe3+/Fe>0.10. Ferric iron is octahedrally coordinated, and ferrous iron is present in the dodecahedral site in all samples. The occurrence of significant Fe3+ in these garnets necessitates caution in the use of geothermometers and geobarometers that are applied to mantle samples. For example, the presence of 12% of the Fe as Fe3+ in garnets can increase temperatures calculated from existing Fe/Mg geothermometers by>200°C. The concomitant increase in pressures calculated from geobarometers that use the Al content in orthopyroxene coexisting with garnet are 10–15 kbar. Results of calculations based on heterogeneous equilibria between garnet, olivine, and pyroxene are consistent with the derivation of the peridotite samples from source regions that are relatively oxidized, between the f
O
2 of the FMQ (quartz-fayalite-magnetite) buffer and that of the WM buffer. No samples yield values of f
O
2 as reduced as IW (iron-wüstite buffer). 相似文献
136.
Vincent Balter Philippe Telouk José Braga Francis Albarède 《Geochimica et cosmochimica acta》2008,72(16):3980-3990
We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and 87Sr/86Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST “SRM1400 Bone Ash” with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and 87Sr/86Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas 87Sr/86Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the 87Sr/86Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating. 相似文献
137.
Optimum data weighting and error calibration for estimation of gravitational parameters 总被引:1,自引:0,他引:1
Francis J. Lerch 《Journal of Geodesy》1991,65(1):44-52
Summary A new approach has been developed for determining consistent satellite-tracking data weights in solutions for the satellite-only gravitational models. The method employs subset least-squares solutions of the satellite data contained within the complete solution and requires that the differences of the parameters of subset solutions and the complete solution to be in agreement with their error estimates by adjusting the data weights. GEM-T2 model was recently computed and adjusted through a direct application of this method. The estimated data weights are markedly smaller than the weights implied by the formal uncertainties of the measurements. Orbital arc tests as well as surface gravity comparisons show significant improvements for solutions when more realistic data weighting is achieved. 相似文献
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