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51.
Yu. I. Troitskaya D. A. Sergeev O. S. Ermakova G. N. Balandina 《Doklady Earth Sciences》2010,433(1):922-926
A new method of digital optical anemometry (Particle Image Velocimetry, PIV) of turbulent flows is suggested and implemented
in the laboratory; it is based on the use of continuous laser radiation and high-speed video photography, providing continuous
statistical ensembles of flow velocity fields. Application of the method to the study of wind field over waves has allowed
us to perform, for the first time, direct measurements of velocity fields, averaged over turbulent pulsations induced by waves
in the air flow. The experiments demonstrated that the velocity fields, averaged over the turbulent pulsations, are nonseparated
even in the case of steep and breaking waves, when separation of the flow from the wave crests in the instantaneous fields
is observed. Based on comparison with the experimental data, it is shown that the average wind fields over waves are described
well quantitatively in the framework of semiempirical closure models of turbulence. 相似文献
52.
Ryszard Kryza Jan Zalasiewicz Stanisław Mazur Paweł Aleksandrowski Sergey Sergeev Alexander Larionov 《International Journal of Earth Sciences》2007,96(6):1153-1162
SHRIMP dating of detrital zircons from sandstones of the Gackowa Formation (Kaczawa Complex, Sudetes, SW Poland) indicates
input from late (550–750 Ma) and early Proterozoic to Archaean sources (∼2.0–3.4 Ga, the latter being the oldest recorded
age from the Sudetic region). These dates preclude within-terrane derivation from seemingly correlatory acid volcanic rocks
of early Palaeozoic age. Rather, they indicate provenance from Cadomian and older rocks that currently form part of other,
geographically distant terranes; the most likely source identified to date is the Lusatian Block in the Saxothuringian Zone.
Hence, the Gackowa Formation may be late Proterozoic rather than early Palaeozoic in depositional age, possibly coeval with
the late Proterozoic (pre-Cadomian) greywackes of Lusatia, being subsequently tectonically interleaved with early Palaeozoic
volcanic rocks into the Kaczawa accretionary prism during the Variscan orogeny. However, correlation with the lithologically
similar early Ordovician Dubrau Quartzite of Saxothuringia, and so assignation to the early Paleozoic (post-Cadomian) rift
succession deposited at the northern margin of Gondwana, cannot yet be precluded. 相似文献
53.
54.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev N. Ya. Sotnikova T. V. Demidova 《Astronomy Letters》2006,32(12):827-831
We present our photometric observations of the T Tauri star H 187. They confirm our conclusion that a new extended eclipse has begun in this young object. By the end of 2005, H 187 reached its minimum light following which its brightness began to slowly increase. Comparison with the previous ~3.5-yr-long eclipse observed by Cohen et al. shows that the new eclipse follows the previous eclipse fairly closely and, hence, it was caused by a second passage of the same extended dust or gas-dust cloud around the object. We have estimated the period between these events to be 4.7 yr. The object reddened during the eclipse, suggesting that the extinction was produced by small grains ~0.1μm in size. Possible mechanisms of such unusual eclipses are discussed. We draw an analogy between these eclipses and the cycles of photometric activity observed in UX Ori stars. Light curves similar to those observed for H 187 are shown to be obtained in the model of a young binary system with a low-mass companion accreting matter from the remnants of a protostellar cloud at a rate of ~10?9 M ⊙ yr?1. 相似文献
55.
In the course of the expedition of the Pacific Oceanological Institute in August 2007, extensive hypoxia was found in the
near-bottom layer of the Amur Bay water mass. The hypoxia’s formation was immediately reflected in the values and distribution
of the carbonate parameters in the near-bottom waters of the bay. The maximum values of the carbon dioxide partial pressure,
the dissolved inorganic carbon, and the total alkalinity were associated with the areas of the minimum oxygen content. The
microbial destruction of the dead phytoplankton greatly increased the partial pressure of carbon dioxide, which was over 2000
μatm in the hypoxia centers at a depth of about 20 m. At the same time, the carbon dioxide partial pressure in the surface
waters of Amur Bay was considerably lower than that in the atmosphere. Hence, the bay’s aquatic area was a sink for the atmospheric
CO2 despite its high content in the near-bottom waters. It was shown that the excess alkalinity associated with the hypoxia sites
in the near-bottom layer of water was caused by the sulfate reduction proceeding in the upper layer of the sediment. 相似文献
56.
O. S. Ermakova Yu. A. Mal’kov D. A. Sergeev Yu. I. Troitskaya 《Izvestiya Atmospheric and Oceanic Physics》2009,45(6):791-798
This is an experimental study of the mixing induced by coincident surface waves in a liquid. The main mechanism leading to
the emergence of mixing was shown to be the middle currents generated by coincident waves. The regime of these currents strongly
depends on the amplitude of surface waves. For waves of near-critical amplitudes, an intense turbulization of middle currents
is observed. Patterns of the velocity field were obtained using the Particle Imaging Velocimetry (PIV) technique for different
amplitudes of surface waves. The results obtained can be used to estimate mixing in the near-surface oceanic layer. 相似文献
57.
N.V. Rodionov E.N. Lepekhina A.V. Antonov I.N. Kapitonov Yu.S. Balashova B.V. Belyatsky A.A. Arzamastsev S.A. Sergeev 《Russian Geology and Geophysics》2018,59(8):962-974
Results of this study of titanite samples collected from silicate rocks and apatite-nepheline-(sphene) ores from Paleozoic polyphase alkaline nepheline syenite complexes of the Khibiny and Lovozero massifs revealed the possibility of their in-situ U-Pb dating using sensitive high-resolution ion microprobe SHRIMP-II with an accuracy of 1.0-1.5%, which is comparable with that of U-Pb zircon analysis. Employing different approaches to age determination of the formation of the U-Pb system of titanites, the combined isochrons and mixing lines were plotted from the data obtained from the differentiated complex samples (121 analyses of five Khibiny samples and 52 analyses of one Lovozero sample) and apatite-nepheline ores (120 analyses of five Khibiny samples and 88 analyses of three Lovozero samples). They indicate synchronous crystallization of titanite in silicate rocks throughout the complexes: 374.1 ± 3.7 Ma for the Khibiny massif and 380.9 ± 4.5 Ma for the Lovozero massif, and attest to the later formation of phosphate-rare-metal ores: 371.0 ± 4.2 and 361.4 ± 3.2 Ma, respectively. The relatively delayed ore mineralization specific to the Lovozero massif can be accounted for the significantly lower volumes of magmatic melt and ore fluid involved, different thermal conditions, and the pattern of the investigated mineralization. As such, the obtained U-Pb data from titanite make it possible to limit significantly the time interval (most likely, not exceeding 15-20 Ma) comprising the evolution and activity of the ore-magmatic system of major agpaitic complexes, which is probably associated with plume magmatism. 相似文献
58.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev A. A. Arkharov S. Yu. Shugarov A. O. Semenov N. V. Efimova 《Astronomy Reports》2018,62(10):677-688
The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005–2011). The amplitude of these variations increasedmonotonically, reaching approximately 1m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight. 相似文献
59.