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61.
Between 1971 and 2001, the Southeast Crater was the most productive of the four summit craters of Mount Etna, with activity that can be compared, on a global scale, to the opening phases of the Pu‘u ‘Ō‘ō-Kūpaianaha eruption of Kīlauea volcano, Hawai‘i. The period of highest eruptive rate was between 1996 and 2001, when near-continuous activity occurred in five phases. These were characterized by a wide range of eruptive styles and intensities from quiet, non-explosive lava emission to brief, violent lava-fountaining episodes. Much of the cone growth occurred during these fountaining episodes, totaling 105 events. Many showed complex dynamics such as different eruptive styles at multiple vents, and resulted in the growth of minor edifices on the flanks of the Southeast Crater cone. Small pyroclastic flows were produced during some of the eruptive episodes, when oblique tephra jets showered the steep flanks of the cone with hot bombs and scoriae. Fluctuations in the eruptive style and eruption rates were controlled by a complex interplay between changes in the conduit geometry (including the growth of a shallow magma reservoir under the Southeast Crater), magma supply rates, and flank instability. During this period, volume calculations were made with the aid of GIS and image analysis of video footage obtained by a monitoring telecamera. Between 1996 and 2001, the bulk volume of the cone increased by ~36×106 m3, giving a total (1971–2001) volume of ~72×106 m3. At the same time, the cone gained ~105 m in height, reaching an elevation of about 3,300 m. The total DRE volume of the 1996–2001 products was ~90×106m3. This mostly comprised lava flows (72×106 m3) erupted at the summit and onto the flanks of the cone. These values indicate that the productivity of the Southeast Crater increased fourfold during 1996–2001 with respect to the previous 25 years, coinciding with a general increase in the eruptive output rates and eruption intensity at Etna. This phase of intense summit activity has been followed, since the summer of 2001, by a period of increased structural instability of the volcano, marked by a series of important flank eruptions. 相似文献
62.
An analysis of the colour-magnitude diagram of stars in Draco dwarf Galaxy is performed on the basis of Baade and Swope observational results. Some evidence is found for the occurrence of a clump in the luminosity distribution of Red Giants stars. By combining this characteristic with the morphology of Horizontal Branch one obtains — in the frame of present knowledge of star-evolution —a suggestion for accepting high helium content (Y-0.30) with a relatively small age (1–2×109 yr) for the evolving stars.Some correlations among lifetimes of evolutionaries stages are derived.
Sommario Sulla base dei risultati osservativi di Baade e Swope viene eseguita un'analisi del diagramma colore-magnitudine delle stelle della Galassia Nana in Draco. Viene così evidenziata la possibile esistenza di un picco nella distribuzione in luminosità delle Giganti Rosse. Combinando questa caratteristica con l'osservato andamento del Ramo Orizzontale si mostra come — nell'ambito delle attuali conoscenze sull'evoluzione stellare — un simile comportamento conduca a postulare un alto contenuto di elio (Y-0.30) e una età relativamente bassa (1–2×109 anni) per le stelle del sistema.Sono infine ricavate alcune correlazioni, tra le vite medie delle principali fasi evolutive.相似文献
63.
Vittorio Banfi 《Earth, Moon, and Planets》1986,36(1):1-10
A theoretical model, based on simple and fundamental concepts of classical mechanics, is presented. It describes the possible historical evolution of the inclination angles of the planetary axes of rotation, with respect to the normal to orbital planes. Owing to the model structure, reasonable agreement with observational facts is expected, especially for the outer and giant planets. 相似文献
64.
Vittorio Coti Zelati 《Celestial Mechanics and Dynamical Astronomy》1989,46(2):177-186
We prove existence and multiplicity of T-periodic solutions (for any given T) for the N-body problem in
m
(any m 2) where one of the bodies has mass equal to 1 and the others have masses 2,...,
N
, small. We find solutions such that the body of mass 1 moves close to x = 0 while the body of mass i moves close to one of the circular solutions of the two body problem of period T/k
i, where ki is any odd number. No relation has to be satisfied by k
2,...,k
N. 相似文献
65.
Vittorio Scheffer 《Pure and Applied Geophysics》1941,3(1):12-13
Riassunto Sono posti a confronto i risultati del rilevamento gravimetrico della zona di Fontevivo (Parma) eseguiti prima con bilancia di torsione e successivamente con gravimetro (tipc Humble-Truman); ottenendosi un buon accordo fra i due metodi.
Zusammenfassung Vergleich der Ergebnisse der gravimetrischen Aufnahme von der Umgebung von Fontevivo (Parma), zuerst mit der Drehwaage durchgeführt, nachher mit einem Gravimeter nach Humble-Truman; die Übereinstimmung der Ergebnisse ist befriedigend.
Résumé Comparaison des résultats du levé gravimétrique de la zone de Fontevivo (Parme) effectué d'abord avec la balance de torsion, ensuite avec un gravimètre type Humble-Truman; bonne concordance entre les deux méthodes.相似文献
66.
X-ray single crystal diffraction data of natural and heated Al-rich orthopyroxenes were used to study the cation ordering and the geometrical changes induced by Si+R 2+=AlIV+R 3+ substitution. The calculated site populations and the observed bond distances in tetrahedral and octahedral sites suggest a total ordering of AlIV in the TB tetrahedron and of R 3+ cations in the M1 octahedron, even in samples heated at 1000° C. The mismatch between the tetrahedral and octahedral layers along the c axis seems to play a crucial role in determining the limits of Si/AlIV substitution. 相似文献
67.
Kinetic studies of isothermal heating experiments (600–800° C) on aluminous pyroxenes (Mg0.942Fe 0.880 2+ Fe 0.068 3+ Mn0.016Ca0.010Al0.084) (Si1.848Al0.152) permit the determination of rate constant of isothermal disordering as 2.5457 E13(±1.4 E13) min?1. The activation energy is determined as 278 (±23) kJ/mol. Data on two other aluminous pyroxenes at 700° C indicate that the rate constant decreases significantly with increasing amount of trivalent cations. There is a similar but reverse correlation between the concentration of trivalent cations and the Fe2+-Mg equilibrium distribution between sites. The site distribution coefficient increases with increasing concentration of trivalent cations at constant temperature. 相似文献
68.
S. K. Saxena M. C. Domeneghetti G. M. Molin V. Tazzoli 《Physics and Chemistry of Minerals》1989,16(5):421-427
Kinetic rates of Fe2+-Mg disordering in three orthopyroxenes (mean value of XFe = Fe2+/(Fe2++Mg) = 0.175,0.482,0.770 respectively) have been determined employing heating experiments and single crystal X-ray structural refinements. Disordering rate constants \((\vec K)\) (550800° C) for two pyroxenes are given by: ln \((\vec K)\) = 27.107(±5.177)?32062(±783)T?1(XFe = 0.175) ln \((\vec K)\) = 16.142(±0.057)?18227(±423)T?1(XFe = 0.770) The distribution coefficients KD (representing a steady state of disordering FeM2 + MgM1 ? FeM1 + MgM2) are given by: ln KD = 5.016(±0.223)-7033(±1473) T?1(XFe = 0.175) ln KD = 1.988(±0.122)-3809(±913)T?1(XFe = 0.770) These distribution coefficients provide the constraint of the disordering reaction on the value of the equilibrium constant for Fe2+-Mg order-disorder. Until the low temperature dependence of KD is well constrained, the calculation of cooling rates of pyroxenes and host rocks cannot be done reliably. 相似文献
69.
Patrizio Signanini Vittorio D'Intinosante Maurizio Ferrini Mario L. Rainone 《Geotechnical and Geological Engineering》2004,22(2):227-244
In the seismic microzonation the evaluation of the local amplification issue may be solved using different methodological
approaches. Taking the hint from the studies made within VEL project framework, sponsored by Tuscany Region on Fivizzano's
area we are herewith comparing the results of geotechnical and geophysical integrated multidisciplinary studies with the existing
data available from previous studies, mainly using a macroseismic approach, on the same area. This qualitative method does
not seem to be able to make any forecasting on the scale whereas generally microzoning is performed. On the contrary, the
knowledge of the geological-technical model of the investigated area, obtained by punctual multidisciplinary integrated studies,
allows a direct collection of the data to insert in input step of numerical modelling, aimed to local effects evaluation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
Lava balloons—peculiar products of basaltic submarine eruptions 总被引:1,自引:1,他引:0
Ulrich Kueppers Alexander R. L. Nichols Vittorio Zanon Marcel Potuzak Jose M. R. Pacheco 《Bulletin of Volcanology》2012,74(6):1379-1393
Between December 1998 and April 2001, a submarine basaltic eruption occurred west of Terceira Island, Azores (Portugal) in water depths between 300 and 1,000?m. Physical evidence for the eruption was provided by the periodic occurrence of hot lava “balloons” floating on the sea surface. The balloons consisted of a large gas-filled cavity surrounded by a thin shell (a few centimetres thick). The shells of the collected balloons are composed of two layers, termed the outer layer and the inner layer, defined by different bubble number density, bubble sizes and crystal content. The inner layer is further divided into three sublayers defined by more subtle differences in vesicularity. The outer layer is glassy, golden-coloured and highly porous. It shows signs of fluidal deformation and late-stage extension cracks. Interstitial glass contains 0.29?wt% H2O and CO2 is below detection. Melt inclusions contain up to 1.18?wt% H2O and 1,500?ppm CO2 (from different inclusions). Cooling rates of the outermost glass of the outer layer are found to be as high as 1,259?K/s. During ascent of low viscosity magma to the ocean floor, volatiles, dominated by CO2, exsolved from the magma (melt + crystals). The buoyancy of the vapour phase that accumulated below a thin crust on lava ponded at the vent caused bulging and ultimately cracking of the crust. This allowed large bubbles (central cavity) surrounded by a film of vesicular magma (balloon shell) to leak into the water column. On contact with the seawater, the outermost part of the outer layer of the shell hyperquenched. If an entirely closed shell was produced during detachment, the trapped gas inside allowed buoyant rise. Only balloons with the right balance of physical properties (e.g. size and bulk density) rose all the way to the sea surface. 相似文献