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31.
32.
Zagami, a well characterized SNC meteorite, represents a reference sample to verify the feasibility of the non-destructive infrared micro-spectroscopy technique to extract spectral signatures from individual mineral phases in a meteorite sample. For the first time individual infrared spectra of the major mineral phases, in the 6000-600 cm−1 (1.67-16.7 μm) spectral interval, whose identification is confirmed by energy dispersive X-ray analysis and backscattered imaging, are measured. The signatures of the main mineral phases we identified in the Zagami chip are: (1) maskelynite characterized by broad and smooth SiO vibrational bands in the 1000 cm−1 spectral region; (2) crystalline pyroxenes showing well defined fine structures; and (3) an oxide mineral phase with an almost featureless and flat spectrum. In the part of the spectrum centered around 2 μm, by analyzing the different positions of the Fe2+ bands, we were able to discern the high-Ca from the low-Ca pyroxene phases. This result demonstrates that by means of the infrared micro-spectroscopy technique it is possible to retrieve directly the composition of pyroxenes in the En-Fs-Wo system, without relying on the use of deconvolution techniques. In addition IR signatures due to water and aliphatic hydrocarbons were observed to be more abundant in the pyroxenes than in maskelynite. This could be an indication that the organic and water signatures are due to indigenous compounds in Zagami rather than laboratory contamination, however, further investigations are necessary before this conclusion can be confirmed. 相似文献
33.
Laura Graziani Andrea Tertulliani Alessandra Maramai Antonio Rossi Luca Arcoraci 《Journal of Seismology》2017,21(5):1219-1227
The aim of this paper is to provide a complete and reliable macroseismic knowledge of the events that stroke a large area in Central Italy on 7 and 11 May 1984. Previous studies, together with original accounts integrated with new and unpublished information, have been gathered and examined in order to re-evaluate macroseismic intensities in terms of the European Macroseismic Scale (EMS98). New intensity maps have been compiled; the total number of localities with available information for both the shocks increases from 1254 of the previous study to 1576. On the basis of the new dataset, the macroseismic magnitude of the first shock is MW 5.6 which is lower than the previous macroseismic computation (MW 5.7). Moreover, the topic of assessing macroseismic intensity in the presence of multiple shocks has been also investigated, proposing an unconventional approach to presenting the macroseismic data: an overall picture of the cumulative effects produced by all the seismic sequence is given to support a partial but faithful reconstruction of the second shock. This approach is inspired by the common experience in interpreting historical seismic sequences and gives a picture of the impact of the 1984 events on the territory. 相似文献
34.
Zelia Dionnet Rosario Brunetto Alice Alon‐Toppani Stefano Rubino Donia Baklouti Ferenc Borondics Anne‐Ccile Buellet Zahia Djouadi Andrew King Tomoki Nakamura Alessandra Rotundi Christophe Sandt David Troadec Akira Tsuchiyama 《Meteoritics & planetary science》2020,55(7):1645-1664
In the near future, a new generation of sample return missions (Hayabusa2, OSIRIS‐REx, MMX, etc.) will collect samples from small solar system bodies. To maximize the scientific outcome of laboratory studies and minimize the loss of precious extraterrestrial samples, an analytical sequence from less destructive to more destructive techniques needs to be established. In this work, we present a combined X‐ray and IR microtomography applied to five Itokawa particles and one fragment of the primitive carbonaceous chondrite Paris. We show that this analytical approach is able to provide a 3‐D physical and chemical characterization of individual extraterrestrial particles, using the measurement of their 3‐D structure and porosity, and the detection of mineral and organic phases, and their spatial co‐localization in 3‐D. We propose these techniques as an efficient first step in a multitechnique analytical sequence on microscopic samples collected by space missions. 相似文献
35.
Alessandra Celletti Corrado Falcolini 《Celestial Mechanics and Dynamical Astronomy》1992,53(2):113-127
The stability of spin-orbit resonances, namely commensurabilities between the periods of rotation and revolution of an oblate satellite orbiting around a primary body, is investigated using perturbation theory. We reduce the system to a model described by a one-dimensional, time-dependent Hamiltonian function. By means of KAM theory we rigorously construct bidimensional invariant surfaces, which separate the three dimensional phase space. In particular with a suitable choice of the rotation numbers of the invariant tori we are able to trap the periodic orbit associated with a given resonance in a finite region of the phase space. This technique is applied to the Mercury-Sun system. A connection with the probability of capture in a resonance is also provided. 相似文献
36.
Francesca Sangiorgi Lucilla Capotondi Nathalie Combourieu Nebout Luigi Vigliotti Henk Brinkhuis Simona Giunta Andr F. Lotter Caterina Morigi Alessandra Negri Gert‐Jan Reichart 《第四纪科学杂志》2003,18(8):723-732
Holocene cooling events have been reconstructed for the southern Adriatic Sea (central Mediterranean) by means of analyses of organic walled dinoflagellate cysts, planktonic foraminifera, oxygen isotopes, calcareous nanoplankton, alkenones and pollen from a sediment core. Two cooling events have been detected, during which sea‐surface temperatures (SSTs) were ca. 2°C lower. Unravelling the SST signal into dominant seasonal components suggests maximum winter cooling of 2°C at around 6.0 ka, whereas the cooling at ca. 3.0 ka might be the result of a spring temperature cooling of 2–3°C. The events, lasting several hundred years, are apparently synchronous with those in the Aegean Sea, where they have been related to known cooling events from the Greenland ice‐core record. A distinct interruption in Adriatic Sea sapropel S1 is not clearly accompanied by a local drop in winter temperatures, but seems to be forced by ventilation, which probably occurred earlier in the Aegean Sea and was subsequently transmitted to the Adriatic Sea. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
37.
We characterized the abundance and species composition of sessile and mobile epifaunal assemblages in the York River, a tributary
of the Chesapeake Bay, U.S., during the summer hypoxia seasons in 1996 and 1997. We collected communities on artificial substrates
in two areas of the river that have historically experienced different exposure to hypoxia. Despite frequent hypoxic stress,
epifauna formed dense communities in both areas. Dominant species comprised a range of phyla and included the polychaetesPolydora cornuta andSabellaria vulgaris, the bryozoansMembranipora tenuis andConopeum tenuissimum, the tunicateMolgula manhattensis, the barnacleBalanus improvisus, the anemoneDiadumene leucolena, and the hydroidsEctopleura dumortieri andObelia bicuspidata. Common mobile species included the nudibranchsCratena kaoruae andDoridella obscura, the amphipodsMelita nitida andParacaprella tenuis, the polychaeteNereis succinea, and the flatwormStylochus ellipticus. We found few differences in species composition between the two areas, even though one area usually experienced lower oxygen
concentrations during hypoxic events, suggesting that hypoxia does not exclude any epifaunal species, in the York River. We
did find differences between the two study areas in percent cover and abundance of some species. While tunicates, hydroids,
and anemones were equally abundant in both areas during both study years, bryozoans and the polychaeteS. vulgaris were more abundant in the area with gereally higher oxygen, suggesting that they may be less tolerant of hypoxic stress.
The polychaeteP. cornuta was more abundant in the area that usually had lower oxygen. These results suggest that many epifaunal species have high
hypoxia tolerance, and most epifaunal species found in the lowr York River are able to survive in hypoxic areas. Epifaunal
species are not necessarily more susceptible to hypoxia than infaunal species in the York River. Epifaunal communities in
areas with brief hypoxic episodes and moderate hypoxia (0.5–2 mg O2 I−1) can persist with little change in species composition, and with few changes in abundance, as oxygen concentrations fall. 相似文献
38.
Anji Seth Sara A. Rauscher Maisa Rojas Alessandra Giannini Suzana J. Camargo 《Climatic change》2011,104(2):403-414
Twenty-first century climate model projections show an amplification of the annual cycle in tropical precipitation with increased
strength in both wet and dry seasons, but uncertainty is large and few studies have examined transition seasons. Here we analyze
coupled climate model projections of global land monsoons and show a redistribution of precipitation from spring to summer
in northern (North America, West Africa and Southeast Asia) and southern (South America, Southern Africa) regions. The annual
cycle changes are global in scale. Two mechanisms, remote (based on tropospheric stability) and local (based on low level
and surface moisture), are evaluated through the annual cycle. Increases in tropospheric stability persist from winter into
spring and are reinforced by a reduction in surface moisture conditions, suggesting that in spring both remote and local mechanisms
act to inhibit convection. This enhanced spring convective barrier leads to reduced early season rainfall; however, once sufficient
increases in moisture (by transport) are achieved, decreases in tropospheric stability result in increased precipitation during
the late rainy season. Further examination of this mechanism is needed in observations and models, as the projected changes
would have substantial implications for agriculture, water management, and disaster preparedness. 相似文献
39.
Here new mineralogical data is presented on the occurrence of K-feldspar in granulite-facies metagabbronorite xenoliths found in recent alkaline lavas from Western Sardinia, Italy. The xenoliths originated from the underplating of variably evolved subduction-related basaltic liquids, which underwent cooling and recrystallisation in the deep crust (T = 850–900 °C, P = 0.8–1.0 GPa). They consist of orthopyroxene + clinopyroxene + plagioclase porphyroclasts (An = 50–66 mol%) in a granoblastic, recrystallised, quartz-free matrix composed of pyroxene + plagioclase (An = 56–72 mol%) + Fe–Ti oxides ± K-feldspar ± biotite ± fluorapatite ± Ti-biotite. Texturally, the K-feldspar occurs in a variety of different modes. These include: (1) rods, blebs, and irregular patches in a random scattering of plagioclase grains in the form of antiperthite; (2) micro-veins along plagioclase–plagioclase and plagioclase–pyroxene grain rims; (3) myrmekite-like intergrowths with Ca-rich plagioclase along plagioclase–plagioclase grain boundaries; and (4) discrete anhedral grains (sometimes microperthitic). The composition of each type of K-feldspar is characterized by relatively high albite contents (16–33 mol%). An increasing anorthite content in the plagioclase towards the contact with the K-feldspar micro-vein and myrmekite-like intergrowths into the K-feldspar along the plagioclase–K-feldspar grain boundary are also observed. Small amounts of biotite (TiO2 = 4.7–6.5 wt.%; F = 0.24–1.19 wt.%; Cl = 0.04–0.20 wt.%) in textural equilibrium with the granulite-facies assemblage is present in both K-feldspar-bearing and K-feldspar-free xenoliths. These K-feldspar textures suggest a likely metasomatic origin due to solid-state infiltration of KCl-rich fluids/melts. The presence of such fluids is supported by the fluorapatite in these xenoliths, which is enriched in Cl (Cl = 6–50% of the total F + Cl + OH). These lines of evidence suggest that formation of K-feldspar in the mafic xenoliths reflects metasomatic processes, requiring an external K-rich fluid source, which operated in the lower crust during and after in-situ high-T recrystallisation of relatively dry rocks. 相似文献
40.
Didkovskyi Oleksandr Ivanov Vladislav Radice Alessio Papini Monica Longoni Laura Menafoglio Alessandra 《Mathematical Geosciences》2022,54(3):467-506
Mathematical Geosciences - The problem of providing data-driven models for sediment transport in a pre-Alpine stream in Italy is addressed. This study is based on a large set of measurements... 相似文献