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81.
Marina A. Ivanova Michail I. Petaev Glenn J. Macpherson Michail A. Nazarov Lawrence A. Taylor John A. Wood 《Meteoritics & planetary science》2002,37(10):1337-1344
Abstract— Natural calcium monoaluminate, CaAl2O4, has been found in a grossite‐rich calcium‐aluminum‐rich inclusion (CAI) from the CH chondrite Northwest Africa 470. The calcium monoaluminate occurs as colorless ~10 μm subhedral grains intergrown with grossite, perovskite, and melilite. Nebular condensation is the most likely origin for the precursor materials of this CAI, but calculations suggest that dust/gas ratios substantially enhanced over solar are required to stabilize CaAl2O4. 相似文献
82.
Marina Manca Claudio Ramoni Patrizia Comoli 《Aquatic Sciences - Research Across Boundaries》2000,62(2):142-153
We reconstruct the impact of different environmental cues on Daphnia seasonal dynamics by means of an analysis of demographic and reproductive parameters, as well as of the size structure of the population. Data from 1996, indicative of the most recent productivity of the lake, with those from 1973, when the lake was meso-eutrophic, allow a discussion of the relevance of the observed changes for the structure of the pelagic food web of Lago Maggiore. Daphnia summer dynamics is mainly controlled by Bythotrephes longimanus. This is quite a different situation from that of the past, when Leptodora kindtii was the prevalent predatory cladocera. The size structure of Daphnia population revealed a depletion of small ovigerous females with increases in the predator. Our data allow a discussion of the idea, recently proposed, of Bythotrephes longimanus as a visual sit- and -wait predator. 相似文献
83.
84.
This study presents results of the first comprehensive research on ecotoxic trace metals (Cd, Pb, Cu and Zn) in aquatic anchialine ecosystems. Data show the influence of hydrological and geological characteristics on trace metals in highly stratified anchialine water columns. 相似文献
85.
Marina Gibilisco 《Astrophysics and Space Science》1997,249(2):189-210
In this paper, I investigate a local effect of polarization of the Cosmic Microwave Background (CMB) in clusters of galaxies,
induced by the Thomson scattering of an anisotropic radiation. A local anisotropy of the CMB is produced by some scattering
and gravitational effects, as, for instance, the Sunyaev Zel‘dovich effect, the Doppler shift due to the cluster motion and
the gravitational lensing. The resulting anisotropy ΔI/I depends on the physical properties of the clusters, in particular
on their emissivity in the X band on their size, on their gravitational potential and on the peculiar conditions characterizing
the gas they contain. By solving the Boltzmann radiative transfer equation in presence of such anisotropies I calculate the
average polarization at the centre of some clusters, namelyA2218, A576 and A2163, whose properties are quite well known. I
prove that the gravitational effects due to the contraction or to the expansion have some importance, particularly for high
density structures; moreover, the peculiar motion of the cluster, considered as a gravitational lens, influences the propagation
of the CMB photons by introducing a particular angular dependence in the gravitational anisotropy and in the scattering integrals.
Thus, the gravitational and the scattering effects overally produce an appreciable local average polarization of the CMB,
may be observable through a careful polarization measurements towards the centres of the galaxy clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
86.
Astrid Holzheid Marina V. Charykova Vladimir G. Krivovichev Brendan Ledwig Elena L. Fokina Ksenia L. Poroshina Natalia V. Platonova Vladislav V. Gurzhiy 《Chemie der Erde / Geochemistry》2018,78(2):228-240
Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87?°C and ends at 226–237?°C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180?°C) and the remaining two molecules of water will be lost in the second stage (>180?°C) or (b) four molecules of water will be lost in the first stage up to 180?°C and the last molecule of water will be lost at a temperature above 180?°C. Based on XRD measurements and thermal analyses we were able to deduce Fe2(SeO3)3·(6-x)H2O (x?=?0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected. 相似文献
87.
Oleg M. Barbakov Marina L. Belonozhko Anatoly N. Silin Alexander S. Gyurdzhinyan 《Journal of the Geological Society of India》2018,92(6):764-766
The article dwells on the problems associated with the development of oil and gas Arctic region of Russia. It also suggests possibilities of their solution based on sociological studies conducted by the authors of representative samples in 2005, 2010 and 2015. Stressing the role and significance of sociological research in the general problem of the circumpolar regions by scientific study, the authors show the need for a sociological diagnosis in the context of different social groups. By doing so, characteristics of social problems inherent to the arctic region and requirements for scientific support of possible technologies is identified. 相似文献
88.
Sousani Marina Eshiet Kenneth Imo-Imo Ingham Derek Pourkashanian Mohamed Sheng Yong 《Environmental Earth Sciences》2014,72(9):3383-3399
A three-dimensional model is presented and used to reproduce the laboratory hydraulic fracturing test performed on a thick-walled hollow cylinder limestone sample. This work aims to investigate the implications of the fluid flow on the behaviour of the micro-structure of the rock sample, including the material strength, its elastic constants and the initialisation and propagation of fractures. The replication of the laboratory test conditions has been performed based on the coupled Discrete Element Method (DEM) and Computational Fluid Dynamics scheme. The numerical results are in good agreement with the experimental data, both qualitatively and quantitatively. The developed model closely validates the overall behaviour of the laboratory sample, providing a realistic overview of the cracking propagation towards total collapse as well as complying with Lame’s theory for thick-walled cylinders. This research aims to provide some insight into designing an accurate DEM model of a fracturing rock that can be used to predict its geo-mechanical behaviour during Enhanced Oil Recovery applications. 相似文献
89.
Marina KOLPAKOVA Stepan SHVARTSEV Vitalyi ISUPOV Sodov ARIUNBILEG Alexander VLADIMIROV Olga GASKOVA 《《地质学报》英文版》2014,88(Z1):142-144
正All the lakes are accumulative systems for the various chemical elements.However,the ratios of the elements in different lake types are very different.It is generally accepted that the composition of lake water determined by 相似文献
90.
Marina A. Ivanova Cyril A. Lorenz Ian A. Franchi Andrei Y. Bychkov Jeffrey E. Post 《Meteoritics & planetary science》2013,48(10):2059-2070
We have conducted hydration–dehydration experiments on terrestrial olivine to investigate the behavior of oxygen isotopic fractionation to test the hypothesis that multiple cycles of aqueous and thermal processing on a parent asteroid comprise a genetic relationship between CM2s and metamorphosed carbonaceous chondrites (MCCs). Two experiments were undertaken. In the first experiment, serpentine was obtained by hydrating terrestrial olivine (Fo90.9) in the laboratory. During this experiment, olivine was reacted with isotopically heavy water (δ18O 21.5‰) at T = 300 °C, = 300 bar, for 100 days. The oxygen isotopic composition of the experimental serpentine was enriched in 18O (by 10 ‰ in δ18O) due to exchange of oxygen isotopes between olivine and the 18O‐rich water. Dehydrated serpentine was then produced during laboratory heating experiment in vacuum, at T = 930 °C, for 1 h. The oxygen isotopic composition of the dehydrated serpentine was enriched in 18O by a further 7 ‰. The net result of the hydration–dehydration process was an enrichment of 18O in the final material by approximately 17‰. The new experimental results suggest that the oxygen isotopic compositions of MCCs of the Belgica‐like group, including Dhofar 225 and Dhofar 725, could be derived from those of typical CM2 chondrites via several cycles of hydration–dehydration caused by aqueous alteration and subsequent thermal metamorphism within their parent asteroids. 相似文献