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排序方式: 共有263条查询结果,搜索用时 46 毫秒
1.
Yuki Saito Peng K. Hong Takafumi Niihara Hideaki Miyamoto Kenji Fukumizu 《Meteoritics & planetary science》2020,55(1):193-206
The matching of asteroids and meteorites is a significant step toward a better understanding of the origin, structure, and history of the solar system. We propose a data‐driven approach for investigating common taxonomic structure between asteroids and meteorites; C‐, S‐, and V‐type for the former, and carbonaceous chondrite, ordinary chondrite, and howardite‐eucrite‐diogenite (HED) meteorite for the latter. In the numerical experiments, by checking whether the taxonomy information of meteorites improves classification for asteroid data, we examine the existence of common structure over the two domains. For this purpose, we compare the resultant accuracies of two clustering methods which are with/without the guidance of meteorite data. We observe that the guidance of meteorite taxonomy improves the accuracy for classifying asteroids, either with the reflectance spectra or major chemical compositions of meteorites. This fact serves as a piece of evidence that there is a common taxonomic structure and links between meteorites and asteroids, supporting a long‐standing hypothesis. 相似文献
2.
In the Cleaverville area of Western Australia, the Regal, Dixon Island, and Cleaverville Formations preserve a Mesoarchean lower‐greenschist‐facies volcano‐sedimentary succession in the coastal Pilbara Terrane. These formations are distributed in a rhomboidal‐shaped area and are unconformably overlain by two narrowly distributed shallow‐marine sedimentary sequences: the Sixty‐Six Hill and Forty‐Four Hill Members of the Lizard Hills Formation. The former member is preserved within the core of the Cleaverville Syncline and the latter formed along the northeast‐trending Eighty‐Seven Fault. Based on the metamorphic grade and structures, two deformation events are recognized: D1 resulted in folding caused by a collisional event, and D2 resulted in regional sinistral strike‐slip deformation. A previous study reported that the Cleaverville Formation was deposited at 3020 Ma, after the Prinsep Orogeny (3070–3050 Ma). Our SHRIMP U–Pb zircon ages show that: (i) graded volcaniclastic–felsic tuff within the black shale sequence below the banded iron formation in the Cleaverville Formation yields an age of (3 114 ±14) Ma; (ii) the youngest zircons in sandstones of the Sixty‐Six Hill Member, which unconformably overlies pillow basalt of the Regal Formation, yield ages of 3090–3060 Ma; and (iii) zircons in sandstones of the Forty‐Four Hill Member show two age peaks at 3270 Ma and 3020 Ma. In this way, the Cleaverville Formation was deposited at 3114–3060 Ma and was deformed at 3070–3050 Ma (D1). Depositional age of the Cleaverville Formation is at least 40–90 Myr older than that proposed in previous studies and pre‐dates the Prinsep Orogeny (3070–3050 Ma). After 3020 Ma, D2 resulted in the formation of a regional strike‐slip pull‐apart basin in the Cleaverville area. The lower‐greenschist‐facies volcano‐sedimentary rocks are distributed only within this basin structure. This strike‐slip deformation was synchronous with crustal‐scale sinistral shear deformation (3000–2930 Ma) in the Pilbara region. 相似文献
3.
Chemical characteristics of chromian spinel in plutonic rocks: Implications for deep magma processes and discrimination of tectonic setting 总被引:2,自引:0,他引:2
Shoji Arai Hidenobu Okamura Kazuyuki Kadoshima Chima Tanaka Kenji Suzuki Satoko Ishimaru 《Island Arc》2011,20(1):125-137
We summarize chemical characteristics of chromian spinels from ultramafic to mafic plutonic rocks (lherzolites, harzburgites, dunites, wehrlites, troctolites, olivine gabbros) with regard to three tectonic settings (mid‐ocean ridge, arc, oceanic hotspot). The chemical range of spinels is distinguishable between the three settings in terms of Cr# (= Cr/(Cr + Al) atomic ratio) and Ti content. The relationships are almost parallel with those of chromian spinels in volcanic rocks, but the Ti content is slightly lower in plutonics than in volcanics at a given tectonic environment. The Cr# of spinels in plutonic rocks is highly diverse; its ranges overlap between the three settings, but extend to higher values (up to 0.8) in arc and oceanic hotspot environments. The Ti content of spinels in plutonics increases, for a given lithology, from the arc to oceanic hotspot settings by mid‐ocean ridge on average. This chemical diversity is consistent with that of erupted magmas from the three settings. If we systematically know the chemistry of chromian spinels from a series of plutonic rocks, we can estimate their tectonic environments of formation. The spinel chemistry is especially useful in dunitic rocks, in which chromian spinel is the only discriminating mineral. Applying this, discordant dunites cutting mantle peridotites were possibly precipitated from arc‐related magmas in the Oman ophiolite, and from an intraplate tholeiite in the Lizard ophiolite, Cornwall. 相似文献
4.
Influence of flooding on groundwater flow in central Cambodia 总被引:2,自引:1,他引:1
Cambodia is affected by flooding from the Mekong, Tonle Sap and Bassac rivers every year, which harms human populations and
damages property, as well as alters the water quality in aquifer systems. The objective of this paper is to highlight the
effects of river flooding on groundwater flow using numerical simulation. A two-dimensional groundwater flow model coupled
with a groundwater recharge model was applied to the research area in central Cambodia. River level variation was included
in model processes, and flood areas and periods were assigned. The results showed that during flooding periods, floodwater
from the three rivers played an important role in recharging groundwater. During the dry season, Tonle Sap River received
groundwater supply from the northwest, and levels in the Bassac and Mekong River dropped to lower than the groundwater level.
This study improves understanding of the surface water and groundwater flow system in the study area. 相似文献
5.
Wook-Hyun Nahm Gyoo Ho Lee Dong-Yoon Yang Ju-Yong Kim Kenji Kashiwaya Masayoshi Yamamoto Aya Sakaguchi 《Journal of Paleolimnology》2010,43(3):489-498
This paper describes mean grain-size data from the 137Cs- and 210Pb-dated sediment core BS-3 (33-cm long) recovered from Jinheung Pond, located in the southwestern part of the Korean Peninsula.
Grain-size analysis of the Jinheung Pond sediments shows a clear signal for changes in annual precipitation over the past
60 years. Instrumental records of annual precipitation (AP) and the annual summation of the precipitation of >50 mm per day
(AP50), which reflects the energy available for sediment transport, correlate well with the mean grain-size distributions
measured in the core. The most plausible mechanism for this response in mean grain size is variations in the annual amount
and intensity of precipitation. Heavy precipitation enhances soil erosion over the catchment area and increases the transport
capacity of streams and rivers. Thus, coarser mean grain size should reflect higher precipitation, and smaller mean grain
size should reflect lower rainfall. In the data from core BS-3, however, grain-size peaks attributed to increased annual precipitation
are not prominent. This is because a dam prevents removal of fine particles from the pond via the outflow. Therefore, the
mean grain-size value represents somewhat larger sediments together with fine clays. The results of this study show that sediments
of dammed lakes and ponds are well suited for high-resolution environmental investigations, especially for records of changes
in precipitation over time. 相似文献
6.
Kenji Hirata Kenji Satake Yuichiro Tanioka Yohei Hasegawa 《Pure and Applied Geophysics》2009,166(1-2):77-96
In the southernmost Kuril Trench, the tsunami source regions vary their along-trench extent even among earthquakes occurring within the same segment. Recent studies suggest that the tsunami source of the 1952 Tokachi-oki earthquake (M 8.1) differs from but partially overlaps with that of the 2003 Tokach-oki earthquake (M 8.0). Furthermore, the along-trench extent among the earthquakes seems to differ between deep and shallow portions of the subduction interface. A seismic gap has been recognized along the deep subduction interface between the sources of the 1952 and 1973 earthquakes. We propose that the gap is now larger, including both shallow to deep portions of the interface between the 1973 and 2003 earthquakes. Variability in spatial extent of large subduction earthquakes in both along-trench direction and trench-normal direction makes it difficult to forecast future earthquakes in the southernmost Kuril Trench. 相似文献
7.
We study the effects of structural inhomogeneity on the quasi-static growth of strike-slip faults. A layered medium is considered, made up of an upper layer bounded by a free surface and welded to a lower half-space with different elastic property. Mode III crack is employed as a mathematical model of strike-slip fault, which is nucleated in the lower half-space and then propagates towards the interface. We adopt FEM-β, newly proposed analysis method for failure, to simulate the quasi-statistic crack growth governed by the stress distribution in layered media. Our results show that along planar traces across interfaces a compliant upper layer has significant effects on promoting/suppressing crack growth before/after its extension into the layer and vice versa for a rigid one. This proposes a possibility that surface breaks due to strike-slip faulting could be arrested by deposit layers at the topmost part of the Earth's crust. 相似文献
8.
Haruko Sekiguchi Masayuki Yoshimi Haruo Horikawa Kunikazu Yoshida Sunao Kunimatsu Kenji Satake 《Journal of Seismology》2008,12(2):185-195
We studied the long-period ground motions in the Osaka sedimentary basin, Japan, which contains a 1- to 3-km thickness of
sediments and is the site of many buildings or construction structures with long-natural period. We simulated the broadband
ground motions likely to be produced by the hypothetical Nankai earthquake: the earthquake expected to give rise to the most
severe long-period ground motion within the basin. For the simulation, we constructed multiscale heterogeneous source models
based on the Central Disaster Management Council of Japan (CDMC) source model and adopted a hybrid computation method in which
long-period motion and short-period motion are computed using a 3-D finite difference method and the stochastic Green’s function
method, respectively. In computing long-period motions, we used a 3-D structure model of the crust and the Osaka sedimentary
basin. The ground motions are estimated to have peak velocities of 50–90 cm/s, prolonged durations exceeding 300 s, and long
predominant periods of 5–10 s in the area with great thickness of sediments. The predominant periods are in agreement with
an approximate evaluation by 4 H/V
s where H and V
s are the thickness of the sediment and the average S wave velocity, respectively. 相似文献
9.
Nguyen Ba Thuy Katsutoshi Tanimoto Norio Tanaka Kenji Harada Kosuke Iimura 《Ocean Engineering》2009,36(15-16):1258-1269
The objective of this study is to investigate the effects of an open gap, such as a road, in a coastal forest on tsunami run-up. A numerical model based on two-dimensional nonlinear long-wave equations was developed to account for the effects of drag and turbulence induced shear forces due to the presence of vegetation. Experiments were conducted on a forest simulated with vertical cylinders by changing the gap width. The numerical model was validated in good agreement with the experimental results. The numerical model was then applied to a wide forest of Pandanus odoratissimus, a tree species that is a dominant coastal vegetation on a sand dune in South and Southeast Asia. The effect of vertical stand characteristics of P. odoratissimus with aerial roots was considered on the drag resistance. A straight open gap perpendicular to the shoreline was used to investigate the effect of gap width. As the gap width increases, the flow velocity at the end of the open gap first increases, reaches a maximum, and then decreases, while the run-up height increases monotonously. The maximum velocity in the present condition is 1.7 times the maximum velocity without a coastal forest. The effects of different gap arrangements in the forest on tsunami run-up were also investigated in this paper. The flow velocity at the end of an open gap can be reduced by a staggered arrangement. 相似文献
10.