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Akulichev V. A. Burenin A. V. Voytenko E. A. Lebedev M. S. Morgunov Yu. N. Tagiltsev A. A. 《Doklady Earth Sciences》2021,498(2):498-501
Doklady Earth Sciences - The results of experimental studies on the features of propagation and reception of broadband pulsed signals in an underwater sound channel (USC) at a distance of 300 km... 相似文献
126.
Kaigorodova E. N. Lebedev V. A. Chernyshev I. V. Yakushev A. I. 《Doklady Earth Sciences》2021,496(1):37-44
Doklady Earth Sciences - An isotope-geochronological study for a number of young volcanic localities in the eastern part of Balkaria (North Caucasus, Russia), referred to the... 相似文献
127.
V. A. Lebedev A. V. Parfenov G. T. Vashakidze Q. A. Gabarashvili I. V. Chernyshev M. G. Togonidze 《Petrology》2018,26(1):1-28
The paper presents detailed isotope-geochronological, geological, and petrologic–mineralogical data on lavas of one of the greatest Quaternary magmatic area in the Greater Caucasus, the Kazbek neovolcanic center, including polygenetic Kazbek stratovolcano and a number of subordinate volcanic cones in its vicinities. The research was conducted based on a representative collection of more than 150 geological samples that characterize most of the volcanic cones and lava flows of different age, some of which were known previously, and other were discovered by the authors. The high-precision K–Ar data obtained on these materials make it possible to reproduce the evolutionary history of youngest magmatism at the Kazbek center and evaluate the total duration of this evolution at ~450 ka. The magmatic activity was subdivided into four phases (at 460–380, 310–200, 130–90, and <50 ka) with long-lasting interludes in between. Because the latest eruptions occurred in the Kazbek vicinity in the Holocene, this volcano is regarded as potentially active. The volcanic rocks of the Kazbek center make up a continuous compositional succession of basaltic (trachy)andesite–(trachy)andesite–dacite and mostly belong to the calc–alkaline series. The principal petrographic characteristics of the rocks and the composition of their phenocryst minerals are determined, mineral assemblages of these minerals are distinguished in the lavas of different type, and the temperature of the magmatic melts is evaluated. A principally important role in the petrogenesis of the Kazbek youngest magmas is proved to have been played by fractional crystallization and replenishment of mafic melts in the magmatic chambers beneath the volcano, which resulted in their mixing and mingling with the residual dacite melt and the origin of high-temperature hybrid andesite lavas. The comprehensive geological studies, involving interpretation of high-resolution satellite images, allowed the authors to compile the first detailed (1: 25 000) volcanologic map of the Kazbek center and a geochronologic chart supplemented with a stratigraphic column, which illustrate the origin sequence of the volcanic vents and their lava flows, geological relations between them, as seen in reference geological sections, and variations in the composition of the magmatic products with time. 相似文献
128.
V.?V.?ZharikovEmail author K.?Yu.?Bazarov E.?G.?Egidarev A.?M.?Lebedev 《Oceanology》2018,58(3):487-496
The application of two approaches to radiometric correction of Landsat data and their further classification has made it possible to compile maps of the distribution pattern of sea grass at the East Site of the Far East National Marine Reserve (FEMR). The mapping accuracy, evaluated with the use of field data, has shown that the bottom reflectance index makes it possible to increase the accuracy of maps compared to the depth-invariant index. The areas of aquatic plants have been calculated from 2001, 2013, and 2014 data. It has been shown that the approaches for processing remote data are useful for monitoring nearshore vegetation. 相似文献
129.
G. V. Ledneva B. A. Bazylev V. V. Lebedev N. N. Kononkova A. Ishiwatari 《Geochemistry International》2012,50(1):44-53
The Ust’-Belaya mafic-ultramafic massif is assigned to the Western Koryak fold belt and largely composed of residual spinel
peridotites, layered spinel and plagioclase peridotites, and gabbros. These rocks are crosscut by occasional plagiogranite
and diorite veins and exhibit locally a close spatial association with basalts and carbonate-sedimentary deposits of Late
Devonian and Early Carboniferous age. Based on this evidence, the massif was ascribed to the pre-Late Devonian ophiolite association.
Our study presents new U-Pb SHPIMP II zircon ages and petrographic and mineralogical data on samples of the layered amphibole
gabbro and vein diorite from the Ust’-Belaya massif. The approximate concordant U-Pb age corresponding to a timing of of amphibole
gabbro crystallization is 799 ± 15 Ma, and the concordant U-Pb age reflecting a timing of of vein diorite crystallization
is 575 ± 10 Ma. These ages coupled with geological studies of the massif, petrological and mineralogical investigations of
the dated samples, as well as literature data on the petrology of peridotites and the age of formed plagiogranites suggest
that the peridotites and layered gabbros of the Ust’-Belaya massif were formed by the Late Riphean, whereas the vein diorite
and plagiogranite were resulted from a later (Vendian-Cambrian) magmatic stage. The peridotites and gabbros of the massif
display no genetic relationship with spatially associated basalts and sedimentary rocks and, thus, they cannot be considered
as members the pre-Late Devonian ophiolitic association. The results of this study will inevitably lead to a significant revision
of geological and geodynamic interpretations of the Ust’-Belaya mafic-ultramafic massif. However, uneven study of the Precambrian
complexes of the Koryak and Chukchi areas, their evolution in different structures of the region cannot yet be described by
a single geodynamic scenario. 相似文献
130.
Tourmaline solid solutions containing Fe, Fe+ Ti, Cr, Ni, Cu, Co, Mn chromophoric centers have been grown hydrothermally at 650° C and 1,5 kbar on natural seeding plates close to the elbaite composition. The newly grown tourmalines were characterized by chemical analyses and optical absorption spectroscopy in the range 26316-5000 cm-1 at 297 K and in the range 26316-9090 cm-1 at 77 K. Most characteristic of Fe2+, Fe3+-bearing specimens is the presence of intensive σpolarized absorption bands caused by exchange-coupled Fe2+-Fe3+ pairs in Y- and Z-sites of the tourmaline structure. An additional intensive absorption band 12500 cm-1 (σ-polarisation) appears in some specimens but is not yet found in spectra of natural tourmalines. The colour and spectroscopic properties of the Fe3+, Mn3+ and Cu2+ containing tourmalines are significantly affected by the presence of even the smallest Li-contents. The results suggest that Fe2+, Cu2+, Co2+, Ni2+-ions occupy, predominantly, Y-sites of the tourmaline structure, whereas the Cr3+-ions seem to enter the smaller Z-octachedra. 相似文献