全文获取类型
收费全文 | 136篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 19篇 |
地球物理 | 42篇 |
地质学 | 57篇 |
海洋学 | 11篇 |
天文学 | 9篇 |
综合类 | 1篇 |
自然地理 | 1篇 |
出版年
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 8篇 |
2012年 | 10篇 |
2011年 | 10篇 |
2010年 | 10篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1994年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1953年 | 2篇 |
1952年 | 3篇 |
1950年 | 2篇 |
1948年 | 1篇 |
1947年 | 2篇 |
1946年 | 2篇 |
1945年 | 1篇 |
1943年 | 2篇 |
排序方式: 共有141条查询结果,搜索用时 15 毫秒
31.
Heatwaves in Europe: areas of homogeneous variability and links with the regional to large-scale atmospheric and SSTs anomalies 总被引:1,自引:1,他引:0
This work presents a methodology to study the interannual variability associated with summertime months in which extremely
hot temperatures are frequent. Daily time series of maximum and minimum temperature fields (T
max and T
min, respectively) are used to define indexes of extreme months based on the number of days crossing thresholds. An empirical
orthogonal function (EOF) analysis is applied to the monthly indexes. EOF loadings give information about the geographical
areas where the number of days per month with extreme temperatures has the largest variability. Correlations between the EOF
principal components and the time series of other fields allow plotting maps highlighting the anomalies in the large scale
circulation and in the SSTs that are associated with the occurrence of extreme events. The methodology is used to construct
the “climatology” of the extremely hot summertime months over Europe. In terms of both interannual and intraseasonal variability,
there are three regions in which the frequency of the extremely hot days per month homogeneously varies: north-west Europe,
Euro-Mediterranean and Eurasia region. Although extremes over those regions occur during the whole summer (June to August),
the anomalous climatic conditions associated with frequent heatwaves present some intraseasonal variability. Extreme climate
events over the north-west Europe and Eurasia are typically related to the occurrence of blocking situations. The intraseasonal
variability of those patterns is related to the amplitude of the blocking, the relative location of the action centre and
the wavetrain of anomalies downstream or upstream of the blocking. During June and July, blocking situations which give extremely
hot climate conditions over north-west Europe are also associated with cold conditions over the eastern Mediterranean sector.
The Euro-Mediterranean region is a transition area in which extratropical and tropical systems compete, influencing the occurrence
of climate events: blockings tend to be related to extremely hot months during June while baroclinic anomalies dominate the
variability of the climate events in July and August. We highlight that our method could be easily applied to other regions
of the world, to other fields as well as to model outputs to assess, e.g. the potential change of extreme climate events in
a warmer climate. 相似文献
32.
Denudation history of the Bocaina Plateau, Serra do Mar, southeastern Brazil: Relationships to Gondwana breakup and passive margin development 总被引:1,自引:0,他引:1
Silvio T. Hiruma Claudio Riccomini May C. Modenesi-Gauttieri Peter C. Hackspacher Julio C. Hadler Neto Ana O.B. Franco-Magalhes 《Gondwana Research》2010,18(4):674-687
The Bocaina Plateau, which is situated on the eastern flank of the continental rift of southeastern Brazil, is the highest part of the Serra do Mar. Topographic relief in this area is suggested to be closely related to its complex tectono-magmatic evolution since the breakup of Western Gondwana and opening of the South Atlantic Ocean. Apatite fission track ages and track length distributions from 27 basement outcrops were determined to assess these hypotheses and reconstruct the denudation history of the Bocaina Plateau. The ages range between 303 ± 32 and 46 ± 5 Ma, and are significantly younger than the stratigraphic ages. Mean track lengths vary from 13.44 ± 1.51 to 11.1 ± 1.48 μm, with standard deviations between 1.16 and 1.83 μm. Contrasting ages within a single plateau and similar ages at different altitudes indicate a complex regional tectonothermal evolution. The thermal histories inferred from these data imply three periods of accelerated cooling related to the Early Cretaceous continental breakup, Early Cretaceous alkaline magmatism, and the Paleogene evolution of the continental rift of southeastern Brazil. The oldest fission track ages (> 200 Ma) were obtained in the Serra do Mar region, suggesting that these areas were a long-lived source of sediments for the Paraná, Bauru, and Santos basins. 相似文献
33.
Claudia Foti Antonio Gianguzza Frank J. Millero Silvio Sammartano 《Aquatic Geochemistry》1999,5(4):381-398
Hydrolysis constants of dimethyltin(IV) cation, in different salt solutions (CaCl2: 0.15 I 0.90; MgCl2: 0.30 I 0.60; NaCl-–NaClO4, NaCl-–NaNO3 mixtures: I = 3; NaCl-–Na2SO4 mixtures: I = 1 mol dm-3) were determined by potentiometric ([H+]-glass electrode) measurements. These data, together with previous data (De Stefano et al., 1996b) were interpreted in terms of DHT (Debye–Hückel type) and Pitzer equations. The mixed electrolyte solution results also allowed us to obtain and parameters for the Pitzer equation. Calorimetric measurements were made at different ionic strengths in order to find the temperature dependence of hydrolysis constants and of the relative interaction parameters. The body of results allows us to determine the speciation of natural waters in a wide range of ionic strengths and temperatures. 相似文献
34.
Prof. Dr. Silvio Polli 《Pure and Applied Geophysics》1953,25(1):123-129
Riassunto Aderendo alle proposte del Comitato del Livello Medio Marino della Associazione Internazionale di Oceanografia Fisica, sono stati calcolati, col metodo dei minimi quadrati, i valori dellavariazione secolare e dellavariazione standard dei livelli medi marini relativi ad 11 porti italiani. Il valore medio della variazione per i mari italiani corrisponde ad un aumento del livello marino di 16 cm/secolo, quello di tutti i mari della Terra è di 11 cm/secolo. La differenza in più per i mari italiani è dovuta ad un contemporaneo abbassamento delle zone costiere di Napoli e di Venezia.
Comunicazione presentata il 10 Aprile 1953 alla I.a Assemblea Generale della Società Italiana di Geofisica e Meteorologia (Genova, 10–12 Aprile 1953). 相似文献
Summary Complying with the proposals of the Committee on Mean Sea Level of the International Association of Physical Oceanography, they were calculated, by the least square method; the values of the secular variation and of the standard deviation of the mean sea levels of eleven Italian stations. The mean value of the variation for the Italian seas corresponds to an encrease of 16 cm/100 years of the sea level; that of the whole seas of the Earth is of 11 cm/100 years. The highest value for the Italian seas it is due to a contemporaneous sinking of Neaple and Venice coasts.
Comunicazione presentata il 10 Aprile 1953 alla I.a Assemblea Generale della Società Italiana di Geofisica e Meteorologia (Genova, 10–12 Aprile 1953). 相似文献
35.
36.
The Chichontepec volcano is a Plio-Pleistocene composite volcano that erupted lavas ranging from high-alumina basalts to dacites. It experienced a caldera-forming paroxysmal eruption during the early Pleistocene. Pre-caldera lavas are mildly tholeiitic and they evolved mainly by low pressure crystal fractionation, notwithstanding the fact that most mafic lavas (low-MgO high-alumina basalts) retain traces of polybaric evolution. Conversely, post-caldera lavas, which are mainly pyroxene andesites, are clearly calc-alkaline, having evolved by open-system crystal fractionation. Sr–Nd isotopic data and trace elements characteristics indicate that the same mantle source was involved in the petrogenesis of these series. Modelling the AFC process showed that it did not play any role in the petrogenesis of these rocks; a crystal fractionation model is considered to be more relevant. A slight variation in the fractionating assemblage could have caused the transition from an early mildly tholeiitic trend to a late calc-alkaline one. Mineralogical evidence, mass-balance calculations and elemental chemistry support this hypothesis, assuming that the greater amount of pyroxene on the liquidus is at the expense of plagioclase; this would have prevented the trend in iron enrichment. 相似文献
37.
Pablo Diego GonzAlez Ana Maria Sato Eduardo Jorge Llambias Miguel A.S. Basei Silvio R.F. Vlach 《Gondwana Research》2004,7(4):1157-1170
Structural, metamorphic and isotopic data obtained from the Nogoli Metamorphic Complex of western Sierra de San Luis indicate that the Early Paleozoic Famatinian Orogeny overprinted an already structured and metamorphosed older basement. The older geological features are relict NW trending fabric associated with high-grade (amphibolite facies) regional metamorphism preserved within thin strips of schists and paragneisses and in the core of mafic to ultramafic lenses. Arc magmatism, medium P (Barrovian type)/high T (amphibolite to granulite facies) regional metamorphism and penetrative NNE to NE trending foliation are related to the building of the Famatinian orogenic belt. The P-T conditions of the Famatinian prograde metamorphism reached a pressure peak of ca. 8 kb, with a thermal peak from -750°C up to -820°C. U-Pb conventional and chemical dating and Ar-Ar plateau ages constrain the peak of the main orogenic phase related to the Famatinian belt to 470–457 Ma (Early to Mid-Ordovician). Greenschist facies retrograde metamorphism closely associated with shear zones and secondary Ar-Ar plateau and Sm-Nd ages suggest that a late to post-orogenic phase of the Famatinian belt was active at least since -445 Ma. This phase continued during the Silurian to Late Devonian times through multiple reactivation of early shear zones. The Famatinian Orogeny reset a previous thermal history and therefore, the timing of the relict fabric could not be constrained conclusively with radiometric dates. Despite this difficulty, a range of 520 to 490 Ma suggests some inheritance from Pampean events registered by the older NW-SE fabric. The Early to Mid-Ordovician regional metamorphism and ductile deformation of the western Sierra de San Luis is interpreted as the orogenic effects of the collision of the allochthonous Cuyania terrane with the autochthonous proto-Pacific margin of Gondwana during the Famatinian Orogeny. 相似文献
38.
Djamel Bengora Lotfi Khiari Jacques Gallichand Noureddine Dechemi Silvio José Gumiere 《国际泥沙研究》2018,33(4):518-524
The capacity of water reservoirs may be considerably reduced by sediment transport and accumulation. This phenomenon may occur quickly in regions prone to erosion, such as Hammam Debagh Dam region in Algeria. For better management of water resources, it is important to estimate the volume of a reservoir by regular and frequent topo-bathymetric surveys. Topo-bathymetric surveys with a high point measurement density are expensive and time-consuming. To reduce this expense and to increase the frequency of topo-bathymetric surveys, it is required to optimize their size and density. The complete survey of the reservoir created by the Hammam Debagh Dam in Algeria was examined in comparison with 19 reduction subsets using geostatistics. The study showed that the complete dataset of 32,164 points, corresponding to a density of 42 points ha-1 could be reduced to 10,000 points, i.e. 13 points ha-1, without affecting the estimation of the water volume in the reservoir. This reduction could considerably simplify the work load, reduce the expenses to do these surveys, and, therefore, allow for an increased frequency of topo-bathymetric surveys. 相似文献
39.
The dual isotopes of deep nitrate as a constraint on the cycle and budget of oceanic fixed nitrogen 总被引:1,自引:0,他引:1
Daniel M. Sigman Peter J. DiFiore Mathis P. Hain Curtis Deutsch Yi Wang David M. Karl Angela N. Knapp Moritz F. Lehmann Silvio Pantoja 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1419-1439
We compare the output of an 18-box geochemical model of the ocean with measurements to investigate the controls on both the mean values and variation of nitrate δ15N and δ18O in the ocean interior. The δ18O of nitrate is our focus because it has been explored less in previous work. Denitrification raises the δ15N and δ18O of mean ocean nitrate by equal amounts above their input values for N2 fixation (for δ15N) and nitrification (for δ18O), generating parallel gradients in the δ15N and δ18O of deep ocean nitrate. Partial nitrate assimilation in the photic zone also causes equivalent increases in the δ15N and δ18O of the residual nitrate that can be transported into the interior. However, the regeneration and nitrification of sinking N can be said to decouple the N and O isotopes of deep ocean nitrate, especially when the sinking N is produced in a low latitude region, where nitrate consumption is effectively complete. The δ15N of the regenerated nitrate is equivalent to that originally consumed, whereas the regeneration replaces nitrate previously elevated in δ18O due to denitrification or nitrate assimilation with nitrate having the δ18O of nitrification. This lowers the δ18O of mean ocean nitrate and weakens nitrate δ18O gradients in the interior relative to those in δ15N. This decoupling is characterized and quantified in the box model, and agreement with data shows its clear importance in the real ocean. At the same time, the model appears to generate overly strong gradients in both δ18O and δ15N within the ocean interior and a mean ocean nitrate δ18O that is higher than measured. This may be due to, in the model, too strong an impact of partial nitrate assimilation in the Southern Ocean on the δ15N and δ18O of preformed nitrate and/or too little cycling of intermediate-depth nitrate through the low latitude photic zone. 相似文献
40.
Mt. Veniaminof, Alaska Peninsula, is a stratovolcano with a summit ice-filled caldera containing a small intracaldera cone
and active vent. From January 2 to February 21, 2005, Mt. Veniaminof erupted. The eruption was characterized by numerous small
ash emissions (VEI 0 to 1) and accompanied by low-frequency earthquake activity and volcanic tremor. We have performed spectral
analyses of the seismic signals in order to characterize them and to constrain their source. Continuous tremor has durations
of minutes to hours with dominant energy in the band 0.5–4.0 Hz, and spectra characterized by narrow peaks either irregularly
(non-harmonic tremor) or regularly spaced (harmonic tremor). The spectra of non-harmonic tremor resemble those of low-frequency
events recorded simultaneously with surface ash explosions, suggesting that the source mechanisms might be similar or related.
We propose that non-harmonic tremor at Mt. Veniaminof results from the coalescence of gas bubbles while low-frequency events
are related to the disruption of large gas pockets within the conduit. Harmonic tremor, characterized by regular and quasi-sinusoidal
waveforms, has duration of hours. Spectra containing up to five harmonics suggest the presence of a resonating source volume
that vibrates in a longitudinal acoustic mode. An interesting feature of harmonic tremor is that frequency is observed to
change over time; spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained.
Factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and
variations of the effective size of the resonator. 相似文献