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91.
92.
We present photometric observations of Centaur (60558) 2000 EC98 and trans-neptunian object (55637) 2002 UX25 at different phase angles and with different filters (mainly R but also V and B for some data). Results for 2000 EC98 are: (i) a rotation period of 26.802±0.042 h if a double-peaked lightcurve is assumed, (ii) a lightcurve amplitude of 0.24±0.06 for the R band, (iii) a phase curve with H=9.03±0.01 and G=−0.39±0.08 (R filter) and H=9.55±0.04 and G=−0.50±0.35 (V filter) or a slope of (R filter) and 0.22±0.06 (V filter), (iv) the color indices B-V=0.76±0.15 and V-R=0.51±0.09 (for α=0.1-0.5°) and 0.55±0.08 (for α=1.4-1.5°). The rotation period is amongst the longest ever measured for Centaurs and TNOs. We also show that our photometry was not contaminated by any cometary activity down to magnitude ?27/arcsec2. For 2002 UX25 the results are: (i) a rotation period of 14.382±0.001 h or 16.782±0.003 h (if a double-peaked lightcurve is assumed) (ii) a lightcurve amplitude of 0.21±0.06 for the R band (and the 16.782 h period), (iii) a phase curve with H=3.32±0.01 and G=+0.16±0.18 or a slope of (R filter), (iv) the color indices B-V=1.12±0.26 and V-R=0.61±0.12. The phase curve reveals also a possible very narrow and bright opposition surge. Because such a narrow surge appears only for one point it needs to be confirmed. 相似文献
93.
Silicified carbonates of the latest Mesoproterozoic Sukhaya Tunguska Formation, northwestern Siberia, contain abundant and diverse permineralized microfossils. Peritidal environments are dominated by microbial mats built by filamentous cyanobacteria comparable to modern species of Lyngbya and Phormidium. In subtidal to lower intertidal settings, mat-dwelling microbenthos and possible coastal microplankton are abundant. In contrast, densely woven mat populations with few associated taxa characterize more restricted parts of tidal flats; the preservation of vertically oriented sheath bundles and primary fenestrae indicates that in these mats carbonate cementation was commonly penecontemporaneous with mat growth. Eoentophysalis mats are limited to restricted environments where microlaminated carbonate precipitates formed on or just beneath the sediment surface. Most microbenthic populations are cyanobacterial, although eukaryotic microfossils may occur among the simple spheroidal cells interpreted as coastal plankton. Protists are more securely represented by large (up to 320 micrometers in diameter) but poorly preserved acritarchs in basinal facies. The Sukhaya Tunguska assemblage contains 27 species in 18 genera. By virtue of their stratigraphic longevity and their close and predictable association with specific paleoenvironmental conditions, including substrates, Proterozoic cyanobacteria support a model of bacterial evolution in which populations adapt rapidly to novel environments and, thereafter, resist competitive replacement. The resulting evolutionary pattern is one of accumulation and stasis rather than the turnover and replacement characteristic of Phanerozoic plants and animals. 相似文献
94.
E. A. Koptelova B. P. Artamonov V. V. Bruevich O. A. Burkhonov A. V. Sergeev 《Astronomy Reports》2008,52(4):270-277
Results of VRI photometry of two components of the gravitationally lensed quasar UM 673 in 2003–2005 are presented. The observational data were obtained on the 1.5-m telescope of the Maidanak observatory. During the monitoring of the system, considerable brightness variations in components A and B with amplitudes of about 0.2 m were recorded, demonstrating variability of the quasar. The increase in the brightness of the components was accompanied by reddening of their V-R color indices. Analysis of the brightness and color variations of the components shows no variations related to microlensing. 相似文献
95.
96.
T. S. Zaitseva M. A. Semikhatov I. M. Gorokhov V. N. Sergeev A. B. Kuznetsov T. A. Ivanovskaya N. N. Melnikov G. V. Konstantinova 《Stratigraphy and Geological Correlation》2016,24(6):549-574
The structure of Riphean deposits developed on the western slope of the Anabar Massif is described with analysis of their depositional environments, distribution of stromatolite assemblages and organic-walled and silicified microfossils through sections, and evolution of views on stratigraphic significance of some of these assemblages. The investigation included complex mineralogical, geochemical, structural, and isotopic?geochronological study of globular phyllosilicates (GPS) of the glauconite?illite series from paleontologically well substantiated Riphean sequences (Ust’-Il’ya and Yusmastakh formations of the Billyakh Group) of the Anabar Massif in the Kotuikan River basin. Isotopic dating of monomineral size and density fractions of GPS from the Billyakh Group was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mössbauer spectrometry data. The applied approach is based on an assumption that the formation and transformation of Rb?Sr and K?Ar systems in GPS are synchronous with stages in their structural evolution, which are determined by the geological and geochemical processes during depositional history. Such an approach combined with the mineralogical and structural analysis contributes to correct interpretation of stratigraphic significance of isotopic data. The results obtained provide grounds for the conclusion that isotopic dates of GPS from the Ust’-Il’ya (Rb?Sr, 1485 ± 13 Ma; K?Ar, 1459 ± 20 Ma) and Yusmastakh (Rb?Sr, 1401 ± 10 Ma; K?Ar, 1417 ± 44 Ma) formations mark the stage of early diagenesis of sediments and are suitable for estimating the age of formations in question. 相似文献
97.
98.
Marion Tichomirowa Sergey Sergeev Hans-Jürgen Berger Dietmar Leonhardt 《Contributions to Mineralogy and Petrology》2012,164(3):375-396
Protoliths of highly metamorphosed gneisses from the Erzgebirge are deduced from the morphology, age and chemistry of zircons as well as from whole rock geochemistry and are compared with lower-grade rocks of Lusatia. Gneisses with similar structural appearance and/or geochemical pattern may have quite different protoliths. The oldest rocks in the Erzgebirge are paragneisses representing meta-greywackes and meta-conglomerates. The youngest group of zircon of meta-greywackes that did not undergo Pb loss represents the youngest igneous component for source rocks (about 575 Ma). Similar ages and zircon morphology reflect the subordinate formation of new zircon grains or only zircon rims in the augengneiss from Bärenstein and Wolkenstein, which probably represent metamorphic equivalents to Lower Cambrian two-mica granodiorites from Lusatia. Bulk rock chemistry, intense fracturing and high U and Th concentrations of zircons suggest deformation-induced and fluid-enhanced recrystallisation of zircon grains. Temperatures during tectonic overprinting—too low to reset zircon ages—indicate mid- or upper crustal levels for shearing recorded in these augengneisses. Lower Cambrian (~540 Ma) granodiorites are widespread in Lusatia but are exclusively represented by the Freiberg gneiss dome in the Eastern Erzgebirge. Ordovician protolith ages were recorded by zircons from the augengneisses of the Reitzenhain–Catherine dome and the Schwarzenberg dome (Western Erzgebirge) documenting significant regional differences between the eastern and the western Erzgebirge (~540 vs. ~490 Ma). In the Western Erzgebirge, most meta-volcanic rocks (muscovite gneisses) and meta-granites (mainly red augengneisses) yield Ordovician zircon ages, whereas in the Eastern part, similar rocks mainly recorded Lower Cambrian protolith ages. Zircon overprinting was highest within discrete tectonic zones where the combination of fluid infiltration and deformation induced variable degrees of recrystallisation and formation of a new augengneiss structure. Variable degrees of Pb loss caused age shifts that do not correspond to changes in zircon morphology but may be associated with U and Th enrichments. Major changes in bulk rock composition appear to be restricted to discrete zones and to (U)HP nappes, whereas gneisses with a MP–MT metamorphic overprint basically show no geochemical modifications. 相似文献
99.
100.
N. V. Emelyanov M. V. Andreev A. A. Berezhnoi A. S. Bekhteva S. N. Vashkovyak Yu. I. Velikodskii I. A. Vereshchagina D. L. Gorshanov A. V. Devyatkin I. S. Izmailov A. V. Ivanov T. R. Irsmambetova V. A. Kozlov S. V. Karashevich A. N. Kurenya Ya. V. Naiden K. N. Naumov N. A. Parakhin V. N. Raskhozhev S. A. Selyaev A. V. Sergeev E. N. Sokov M. Yu. Khovrichev E. V. Khrutskaya M. M. Chernikov 《Solar System Research》2011,45(3):264-277
In 2009, in five Russian observatories photometric observations of Jupiter’s Galilean satellites during their mutual occultations and eclipses were carried out. Based on these observations, an original method was used to ascertain astrometric results such as the difference between the coordinates of pairs of satellites. Fifty-three phenomena were successfully observed. A total of 94 light curves of satellites were measured. The error in the coordinates of satellites due to random errors in photometry, calculated on all data obtained, was 0.041″ in right ascension and 0.046″ in declination. The discrepancies between the theory and observations in these coordinates was found to be 0.060″ and 0.057″, respectively. The results were uploaded to the common database for all observations of natural satellites of planets at the Natural Satellites Data Center (NSDC), which is available online at http://www.sai.msu.ru/neb/nss/index.htm. For the first time in the practice of photometric observations of satellites in epochs of mutual occultations and eclipses a new method of observation was tested, which eliminates from astrometric results the major systematic errors caused by an inaccurate account of the background level. The tests were conducted in the Terskol Observatory and the observatory of the Crimean laboratory of the Sternberg State Astronomical Institute of the Moscow State University. The application of the new method showed that the elimination of the background level at these observatories was carried out correctly. 相似文献