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991.
Rosales José J. Jorba Àngel Jorba-Cuscó Marc 《Celestial Mechanics and Dynamical Astronomy》2021,133(11-12):1-25
Celestial Mechanics and Dynamical Astronomy - The Cassini spacecraft discovered many close-in small satellites in Saturnian system, and several of them exhibit exotic orbital states due to... 相似文献
992.
Michael E. Zolensky Atsushi Takenouchi Takashi Mikouchi Timothy Gregory Kunihiko Nishiizumi Marc W. Caffee Michael A. Velbel Daniel K. Ross Andrew Zolensky Loan Le Naoya Imae Akira Yamaguchi 《Meteoritics & planetary science》2021,56(1):49-55
Cosmic ray exposure (CRE) ages of CM chondrites have been found to have multiple peaks (as many as four), in stark contrast to other groups of chondrites (Nishiizumi and Caffee 2012; Herzog and Caffee 2014). In this study, we sought correlations between the CRE ages and petrography of CM chondrites, and we conclude that the degree of aqueous alteration does appear to vary with the CRE ages—the CMs displaying the most aqueous alteration all have relatively short exposure ages. However, some CMs with low degrees of alteration also have short exposure ages—thus, this apparent correlation is not exclusive. We also found a definite inverse relation between the number of distinctive lithologies in a CM and its exposure age, which could indicate different responses of homogeneous and heterogeneous meteoroids to the space environment between their onset of exposure (exhumation and ejection from the parent body) and arrival at Earth. Breccias have more internal surfaces of lithologic discontinuity, possibly resulting in weaker meteoroids that disintegrate more readily than their more homogeneous counterparts. Our results suggest that CM chondrite regoliths consist of numerous genomict lithologies in a breccia with millimeter‐ to decimeter‐scale clasts, with varying degree of heating/metamorphism. 相似文献
993.
Reynier F. Peletier Marc Balcells Roger L. Davies Y. Andredakis A. Vazdekis A. Burkert F. Prada 《Monthly notices of the Royal Astronomical Society》1999,310(3):703-716
We present optical and near-infrared colour maps of the central regions of bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the Hubble Space Telescope ( HST ). By combined use of HST and ground-based data, the colour information spans a region from a few tens of pc to a few kpc. In almost all galaxies, the colour profiles in the central 100–200 pc become more rapidly redder. We attribute the high central colour indices to a central concentration of dust. We infer an average extinction at the centre of A V =0.6–1.0 mag. Several objects show central dust rings or discs at subkpc scales similar to those found by others in giant ellipticals. For galactic bulges of types S0 to Sb, the tightness of the B − I versus I − H relation suggests that the age spread among bulges of early-type galaxies is small, at most 2 Gyr. Colours at 1 R eff , where we expect extinction to be negligible, are similar to those of elliptical galaxies in the Coma cluster, suggesting that these bulges formed at the same time as the bright galaxies in Coma. Furthermore, the galaxy ages are found to be independent of their environment. As it is likely that Coma was formed at redshift z >3, our bulges, which are in groups and in the field, must also have been formed at this epoch. Bulges of early-type spirals cannot be formed by secular evolution of bars at recent epochs, because such bulges would be much younger. There are three galaxies of type Sbc and later; their bulges are younger and could perhaps arise from secular evolution of transient bars. Our results are in good agreement with semi-analytic predictions, which also predict that bulges, in clusters and in the field, are as old as giant ellipticals in clusters. 相似文献
994.
Michel Ritz Henri Robain Evgeni Pervago Yves Albouy Christian Camerlynck Marc Descloitres Adama Mariko 《Geophysical Prospecting》1999,47(2):85-101
Near-surface inhomogeneities (NSIs) can lead to severe problems in the interpretation of apparent resistivity pseudosections because their effects significantly complicate the image aspect. In order to carry out a more efficient and reliable interpretation process, these problematic features should be removed from field data. We describe a filtering scheme using two-sided half-Schlumberger array data. The scheme was tested on synthetic data, generated from a simple 2D resistivity model contaminated by NSIs, and is shown to be suitable for eliminating such contaminations from apparent resistivity data. Furthermore, the original model without NSIs can be recovered satisfactorily from the inversion of filtered apparent resistivity data. The algorithm is also applied efficiently to a real data set collected at Nsimi, in southern Cameroon, along a 200-m shallow depth profile crossing a complex transitional zone. For this case, the filtering scheme provides accurate structural and behavioural interpretations of both the geometry of the major soil constituents and the groundwater partitioning. 相似文献
995.
Marc Constantin 《Contributions to Mineralogy and Petrology》1999,136(1-2):111-130
Mafic and ultramafic rocks sampled in the Garrett transform fault at 13°28′S on the East Pacific Rise (EPR) provide insight
on magmatic processes occurring under a fast-spreading ridge system. Serpentinized harzburgite from Garrett have modal, mineral
and bulk chemical compositions consistent with being mantle residue of a high degree of partial melting. Along with other
EPR localities (Terevaka transform fault and Hess Deep), these harzburgites are among the most residual and depleted in magmatophile
elements of the entire mid-ocean ridge system. Geothermometric calculations using olivine-spinel pairs indicate a mean temperature
of 759 ± 25 °C for Garrett residual harzburgite similar to the average of 755 °C for tectonite peridotites from slow-spreading
ridges. Results of this study show that mid-ocean ridge peridotites are subject to both fractional melting and metasomatic
processes. Evidence for mantle metasomatism is ubiquitous in harzburgite and is likely widespread in the entire Garrett peridotite
massif. Magma-harzburgite interactions are very well preserved as pyroxenite lenses, plagioclase dunite pockets or dunitic
wall rock to intrusive gabbros. Abundant gabbroic rocks are found as intrusive pockets and dikes in harzburgite and have been
injected in the following sequence: olivine-gabbro, gabbro, gabbronorite, and ferrogabbro. The wide variety of magmas that
crystallized into gabbros contrast sharply with present-day intratransform basalts, which have a highly primitive composition.
Ferrogabbro dikes have been intruded at the ridge-transform intersection and as they represent the last event of a succession
of gabbros intrusive into the peridotite, they likely constrain the origin of the entire peridotite massif to the same location.
In peridotite massifs from Pacific transform faults (Garrett and Terevaka), primitive to fractionated basaltic magmas have
flowed and crystallized variable amounts of dunite (±plagioclase) and minor pyroxenite, followed by a succession of cumulate
gabbroic dikes which have extensively intruded and modified the host harzburgitic rocks. The lithosphere and style of magmatic
activity within a fast-slipping transform fault (outcrops of ultramafic massif, discontinuous gabbro pockets intrusive in
peridotite, magnesian and phyric basalts) are more analogous to slow-spreading Mid-Atlantic Ridge type than the East Pacific
Rise.
Received: 13 October 1997 / Accepted: 5 February 1999 相似文献
996.
Jérôme Korona Etienne Berthier Marc Bernard Frédérique Rémy Eric Thouvenot 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(2):204-212
Monitoring the evolution of polar glaciers, ice caps and ice streams is of utmost importance because they constitute a good indicator of global climate change and contribute significantly to ongoing sea level rise. Accurate topographic surveys are particularly relevant as they reflect the geometric evolution of ice masses. Unfortunately, the precision and/or spatial coverage of current satellite missions (radar altimetry, ICESat) or field surveys are generally insufficient. Improving our knowledge of the topography of Polar Regions is the goal of the SPIRIT (SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies) international polar year (IPY) project. SPIRIT will allow (1) the acquisition of a large archive of SPOT 5 stereoscopic images covering most polar ice masses and, (2) the delivery of digital terrain models (DTM) to the scientific community.Here, we present the architecture of this project and the coverage achieved over northern and southern polar areas during the first year of IPY (July 2007 to April 2008). We also provide the first accuracy assessments of the SPIRIT DTMs. Over Jakobshavn Isbrae (West Greenland), SPIRIT elevations are within ±6 m of ICESat elevations for 90% of the data. Some comparisons with ICESat profiles over Devon ice cap (Canada), St Elias Mountains (Alaska) and west Svalbard confirm the good overall quality of the SPIRIT DTMs although large errors are observed in the flat accumulation area of Devon ice cap. We then demonstrate the potential of SPIRIT DTMs for mapping glacier elevation changes. The comparison of summer-2007 SPIRIT DTMs with October-2003 ICESat profiles shows that the thinning of Jakobshavn Isbrae (by 30–40 m in 4 years) is restricted to the fast glacier trunk. The thinning of the coastal part of the ice stream (by over 100 m) and the retreat of its calving front (by up to 10 km) are clearly depicted by comparing the SPIRIT DTM to an ASTER April-2003 DTM. 相似文献
997.
The importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs 总被引:14,自引:0,他引:14
The effect of shale composition and fabric upon pore structure and CH4 sorption is investigated for potential shale gas reservoirs in the Western Canadian Sedimentary Basin (WCSB). Devonian–Mississippian (D–M) and Jurassic shales have complex, heterogeneous pore volume distributions as identified by low pressure CO2 and N2 sorption, and high pressure Hg porosimetry. Thermally mature D–M shales (1.6–2.5% VRo) have Dubinin–Radushkevich (D–R) CO2 micropore volumes ranging between 0.3 and 1.2 cc/100 g and N2 BET surface areas of 5–31 m2/g. Jurassic shales, which are invariably of lower thermal maturity ranging from 0.9 to 1.3% VRo, than D–M shales have smaller D–R CO2 micropore volumes and N2 BET surface areas, typically in the range of 0.23–0.63 cc/100 g (CO2) and 1–9 m2/g (N2). 相似文献
998.
Peter Jenniskens Nick Moskovitz Laurence A. J. Garvie Qing‐Zhu Yin J. Andreas Howell Dwayne L. Free Jim Albers David Samuels Marc D. Fries Prajkta Mane Daniel R. Dunlap Karen Ziegler Matthew E. Sanborn Qin Zhou Qiu‐Li Li Xian‐Hua Li Yu Liu Guo‐Qiang Tang Kees C. Welten Marc W. Caffee Henner Busemann Matthias M. M. Meier David Nesvorny 《Meteoritics & planetary science》2020,55(3):535-557
The trajectory and orbit of the LL7 ordinary chondrite Dishchii'bikoh are derived from low‐light video observations of a fireball first detected at 10:56:26 UTC on June 2, 2016. Results show a relatively steep ~21° inclined orbit and a short 1.13 AU semimajor axis. Following entry in Earth's atmosphere, the meteor luminosity oscillated corresponding to a meteoroid spin rate of 2.28 ± 0.02 rotations per second. A large fragment broke off at 44 km altitude. Further down, mass was lost to dust during flares at altitudes of 34, 29, and 25 km. Surviving meteorites were detected by Doppler weather radar and several small 0.9–29 g meteorites were recovered under the radar reflection footprint. Based on cosmogenic radionuclides and ground‐based radiometric observations, the Dishchii'bikoh meteoroid was 80 ± 20 cm in diameter assuming the density was 3.5 g/cm3. The meteoroid's collisional history confirms that the unusual petrologic class of LL7 does not require a different parent body than three previously observed LL chondrite falls. Dishchii'bikoh was ejected 11 Ma ago from parent body material that has a 4471 ± 6 Ma U‐Pb age, the same as that of Chelyabinsk (4452 ± 21 Ma). The distribution of the four known pre‐impact LL chondrite orbits is best matched by dynamical modeling if the source of LL chondrites is in the inner asteroid belt in a low inclined orbit, with the highly inclined Dishchii'bikoh being the result of interactions with Earth before impacting. 相似文献
999.
Defining the spatial extent of mountain areas has long been a challenge. In the present century, the availability of digital elevation models(DEMs) incorporated into geographic information systems(GIS) has allowed the definition of mountain areas based on topographic and other criteria. This paper presents the various delineations of mountains that have been prepared at three scales – global, regional(Europe), and national – and explores the reasons and processes leading to these delineations, and how they have been used. A detailed case study is then presented for Norway. Overall, two types of approaches to mapping mountains have been taken: first, considering mountains per se, based on elevation and/or topography; second, considering them among other categories, e.g., landforms or biogeographical, environmental or landscape zones. All attempts to map mountain areas derive essentially from the objectives of those commissioning and/or undertaking the work; a unitary definition remains unlikely. 相似文献
1000.
Annama H chondrite—Mineralogy,physical properties,cosmic ray exposure,and parent body history
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Tomáš Kohout Jakub Haloda Patricie Halodová Matthias M. M. Meier Colin Maden Henner Busemann Matthias Laubenstein Marc. W. Caffee Kees C. Welten Jens Hopp Mario Trieloff Ramakant R. Mahajan Sekhar Naik Josep M. Trigo‐Rodriguez Carles E. Moyano‐Cambero Michael I. Oshtrakh Alevtina A. Maksimova Andrey V. Chukin Vladimir A. Semionkin Maksim S. Karabanalov Israel Felner Evgeniya V. Petrova Evgeniia V. Brusnitsyna Victor I. Grokhovsky Grigoriy A. Yakovlev Maria Gritsevich Esko Lyytinen Jarmo Moilanen Nikolai A. Kruglikov Aleksey V. Ishchenko 《Meteoritics & planetary science》2017,52(8):1525-1541
The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar‐Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7–8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 ± 4 Ma. The results from short‐lived radionuclides are compatible with an atmospheric pre‐entry radius of 30–40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The 10Be concentration indicates a recent (3–5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30–35 cm pre‐entry radius. 相似文献