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81.
Fulu Men 《地震工程与工程振动(英文版)》2002,1(2):281-291
In this paper, mantle circulation flow, continental drift, earthquake origin and other mechanical principles are examined
as they apply to earthquake engineering, seismology and dynamics of fluid saturated porous medium. The relationship of mantle
flow to earthquakes is examined and clarified, and a new model, different from Haskell’s, is proposed for the earthquake mechanism.
The proposed new model is based on the discovery that two pairs of jump stress and jump velocity will start to act from the
fault plane. Records obtained directly from recent earthquakes nearby and right on the fault break show a very large velocity
impulse, which verify, indirectly, the new mechanism proposed by the author. Further, at least two physical parameters that
characterize the seismic intensity must be specified, because according to the discontinuous (jump) wave theory, at the earthquake
source, the stress jump and the velocity jump of particle motion should act simultaneously when a sudden break occurs. The
third key parameter is shown to be the break (fracture) propagation speed together with the break plane area. This parameter
influences the form of the unloading time function at the source. The maximum seismic stress in and displacement of a building
are estimated for two unfavorable combinations of the building and its base ground in terms of their relative rigidity. Finally,
it is shown that Biot’s theory of wave propagation in fluid saturated porous media is valid only when fluid flow cannot occur. 相似文献
82.
门可佩 《地震地磁观测与研究》1993,(2)
江苏-南黄海地区自16世纪以来已发生17次6级以上强震,经研究发现它们存在着时间间隔为74年、57年、26年、7年的有序性结构,利用这种强震活动的有序性和可公度性理论相结合,试对该区6级以上强震进行预测探索,结论是1995-1996年、2001-2002年前后该区有发生6级以上强震的可能。 相似文献
83.
新疆及其邻近地区M≥7强震活动在时间分布上具有明显的有序性。自1716年以来的21次M≥7强震存在着时间间隔为11、25、30、41和60年的有序值。利用强震活动时间的有序性结构,可对该区7级强震进行预测探索。本文同时还应用熵和经验分布函数,讨论了下次强震发生的地点和概率。 相似文献
84.
85.
Melisa C. Wong 《Estuaries and Coasts》2018,41(2):536-548
In nearshore ecosystems, habitats with emergent structure are often assumed to have higher ecosystem functioning than habitats lacking structure. However, such habitat-specific differences may depend on the surrounding environment. In this study, I examine the robustness of habitat-specific differences in ecosystem functioning for seagrass (Zostera marina) and adjacent bare soft sediments across varying environmental conditions on the Atlantic Coast of Nova Scotia, Canada, using secondary production as a metric. I also examine relationships of community secondary production and faunal structure with measured environmental variables (water depth, temperature, exposure, sediment, and plant properties). Benthic secondary production (invertebrates ≥500 μm) was higher in seagrass compared to bare sediments only at exposed sites with sandy sediments low in organic content, deep and cool water, and high belowground plant biomass. A regression relating community secondary production to the environmental variables explained 56% of the variance, while a constrained ordination explained 16% of the community structure. Important environmental determinants of community production were shoot density, temperature, depth, exposure, sediment organic content, and belowground plant biomass. Community structure was influenced by these variables plus sediment sand content and canopy height. This study shows that habitat-specific differences in secondary production may not be consistent across varying environmental conditions. Furthermore, seagrass beds are not always associated with higher ecosystem functioning than adjacent bare sediment. Both the surrounding environmental conditions and the presence of habitat structure should be considered for optimal management of nearshore ecosystems. 相似文献
86.
Jens M. Turowski Niels Hovius Hsieh Meng‐Long Dimitri Lague Chen Men‐Chiang 《地球表面变化过程与地形》2008,33(3):353-363
Lateral erosion in bedrock rivers is an important control on the shape of channel cross‐sections, and the coupling of channels and hillslopes. Recent observations link lateral erosion to the variability of flow. We propose two mechanisms to explain this. One is based on changing shear stress distributions within the channel with varying flood level, the other on the competition between cover and tool effects in fluvial bedrock erosion. We assess these processes for the Liwu River, Taiwan, and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
87.
The Xiaoxinancha Au-rich copper deposit is one of important Au-Cu deposits along the continental margin in Eastern China. The deposit consists of two sections: the Beishan mine (North), composed of altered rocks with veinlet-dissemination sulfides and melnicovite-dominated sulfide-quartz veins, and the Nanshan mine (South), composed of pyrrhotite-dominated sulfide-quartz veins and pure sulfide veins. The isotope compositions of noble gases extracted from fluid inclusions in ore minerals, i.e. ratios of 3He/4He, 20Ne/22Ne and40Ar/36Ar are in the ranges of 4.45―0.08 Ra, 10.2―8.8 and 306―430, respectively. Fluid inclusions in minerals from the Nanshan mine have higher 3He/4He and 20Ne/22Ne ratios whereas those from the Beishan mine have lower 3He/4He ratios. The analysis of origin, and evolution of the ore fluids and its relations with the ore-forming stages and the ages of mineralization suggests that the initial hydrothermal fluids probably come from the melts generated by partial melting of oceanic crust with the participation of fluids from the mantle (mantle-plume type)/aesthenosphere. This also corresponds to the continental margin settings during the subduction of Izanagi ocaneic plate towards the palaeo-Asian continent (123―102 Ma). The veinlet-dissemination ore bodies of the Beishan mine were formed through replacement and crystallization of the mixed fluids generated by mixing of the ascending high-temperature boiling fluid with young crustal fluid whereas the melnicovite-dominated sulfide-quartz veins were formed subsequently by filling of the high-temperature ore fluid in fissures. Pyrrhotite-dominated sulfide-quartz veins in the Nanshan mine were formed by filling-deposition-crystallization of the moderate-temperature ore fluids and the pure sulfide veins were formed later by filling-deposition-crystallization of ore substance-rich fluids after boiling of the moderate-temperature ore fluids. The metallogenic dynamic processes can be summarized as: (1) formation of fluidand ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success-sive ascending of the ore fluids and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling. 相似文献
88.
89.
The effect of sea-ice on various aspects of the Southern Hemisphere (SH) extratropical climate is examined. Two simulations using the LMD GCM are performed: a control run with the observed sea-ice distribution and an anomaly run in which all SH sea-ice is replaced by open ocean. When sea-ice is removed, the mean sea level pressure displays anomalies predominantly negatives near the Antarctic coast. In general, the meridional temperature gradient is reduced over most of the Southern Ocean, the polar jet is weaker and the sea level pressure rises equatorward of the control ice edge. The high frequency filtered standard deviation of both the sea level pressure and the 300-hPa geopotential height decreases over the southern Pacific and southwestern Atlantic oceans, especially to the north of the ice edge (as prescribed in the control). In contrast, over the Indian Ocean the perturbed simulation exhibits less variability equatorward of about 50°S and increased variability to the south. The zonal averages of the zonal and eddy potential and kinetic energies were evaluated. The effect of removing sea-ice is to diminish the available potential energy of the mean zonal flow, the available potential energy of the perturbations, the kinetic energy of the growing disturbances and the kinetic energy of the mean zonal flow over most of the Southern Ocean. The zonally averaged intensity of the subpolar trough and the rate of the baroclinic energy conversions are also weaker. 相似文献
90.
Anabela A. Berasategui Mónica S. HoffmeyerFlorencia Biancalana Melisa Fernandez SeveriniMaría C. Menendez 《Estuarine, Coastal and Shelf Science》2009
Eurytemora americana has been only reported as invader in Bahía Blanca Estuary, Argentina within the South Hemisphere. There are a few experimental researches under laboratory conditions done with this species and its reproductive behaviour around the world is very scarce. Consequently, it is still not possible to completely understand its population dynamics. In the present study, E. americana reproductive temporal behaviour and relationships among abundance, female size, egg production and hatching success were examined in the Bahía Blanca Estuary, during 2007 pulse. In order to determine the potential relationships between these variables and the environmental variables, experimental incubations were conducted in the laboratory simulating natural conditions. Spearman’s rank correlation was used to analyze the relationships among all variables. Temporal change of biotic and environmental variables was corroborated by a Mann–Whitney/Kruskal–Wallis non-parametric tests, with significant differences (p ? 0.01) in all variables throughout the study. Abundance population results showed very high values in relation to those recorded in recent years in Bahía Blanca Estuary. This response could be due to the unusual combination of environmental factors (polar wave with temperatures ≤6 °C and a drought period with high salinities, 32.7–36.6) recorded during the studied winter period. Significant positive correlations between abundance and salinity (p < 0.01, n = 226), and hatching success (p < 0.01, n = 25) as well as a significant negative correlation between abundance and chlorophyll a (p < 0.01, n = 226) were found. Although E. americana shows a k-strategy within its annual pulse, it presented two markedly distinct behaviours depending on temporal environmental variability. From July to early september, when the estuary evidenced high salinity, low temperature and high food availability, E. Americana showed large females, large clutch size and high hatching success. When environmental conditions became unfavorable from September to October, small females, small clutch size and very low hatching success were observed. The latter is associated with diapause egg laying which ensures population recruitment. According to our findings the particular combination of low temperatures, high salinities and high available food (i.e. variables which each year modulate its pulse) during 2007 winter–spring, favored the great development of E. americana. This invading species in its opportunistic role has managed to exploit a vacant niche in the estuary, developing two different behaviours within the k-strategy depending on change in environmental conditions. 相似文献