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31.
To understand the behavior of manganese in diagenetic processes in sediments of an enclosed bay which is similar to those
of an estuary, chemical analyses have been carried out on both sediment and interstitial water of a core sample collected
from Tokyo Bay. The results suggest that redistribution of manganese takes place within the sediment as a result of the dissolution
of buried manganese oxides and hydroxides under reducing condition, the downward diffusion of Mn2+ through the interstitial water toward lower layers and then the precipitation of carbonate. The carbonate formed in the sediment
contains managanese carbonate probably as a solid solution between calcitic calcium carbonate and manganese carbonate. 相似文献
32.
The Mackenzie River estuary serves as an avenue for suspended particles to pass seaward. The horizontal distribution of surface suspended particles is compartible with the distribution of low-salinity surface waters. The water structure in the shelf area is highly stratified in summer due to a thin upper layer of low-salinity which has a high concentration of suspended particles. The concentration of suspended particles decreases with depth, but near the bottom a turbid layer had often been observed. It is likely that bottom current energy high enough to erode and maintain in suspension the bottom sediments below 15m in diameter does occur over this shelf area. 相似文献
33.
Observations were made of time variations of carbon dioxide in seawater, pCO2, and in the atmosphere, PCO2, in the Seto Inland Sea of Japan. The pCO2 data showed well defined diurnal variation; high values at nighttime and low values during daylight hours. The pCO2 correlated negatively with dissolved oxygen. These results denote that the diurnal variation of pCO2 is associated with effects of photoplankton's activity in seawater. The pCO2 measured in the Seto Inland Sea showed higher values than the PCO2 during June to November, denoting transport of carbon dioxide from the sea surface to the atmosphere, and lower values during December to May, denoting transport of carbon dioxide from the atmosphere to the sea surface. The exchange rates of carbon dioxide were calculated using working formula given by Andriéet al. (1986). The results showed that the Seto Inland Sea gained carbon dioxide of 1.0 m-mol m–2 d–1 from the atmosphere in March and lost 1.7 m-mol m–2 d–1 to the atmosphere in August. 相似文献
34.
35.
Shin Ozawa Eiji Ohtani Masaaki Miyahara Akio Suzuki Makoto Kimura Yoshinori Ito 《Meteoritics & planetary science》2009,44(11):1771-1786
Abstract— The high‐pressure polymorphs of olivine, pyroxene, and plagioclase in or adjacent to shock melt veins (SMVs) in two L6 chondrites (Sahara 98222 and Yamato 74445) were investigated to clarify the related transformation mechanisms and to estimate the pressure‐temperature conditions of the shock events. Wadsleyite and jadeite were identified in Sahara 98222. Wadsleyite, ringwoodite, majorite, akimotoite, jadeite, and lingunite (NaAlSi3O8‐hollandite) were identified in Yamato 74445. Wadsleyite nucleated along the grain boundaries and fractures of original olivine. The nucleation and growth of ringwoodite occurred along the grain boundaries of original olivine, and as intracrystalline ringwoodite lamellae within original olivine. The nucleation and growth of majorite took place along the grain boundaries or fractures in original enstatite. Jadeite‐containing assemblages have complicated textures containing “particle‐like,” “stringer‐like,” and “polycrystalline‐like” phases. Coexistence of lingunite and jadeite‐containing assemblages shows a vein‐like texture. We discuss these transformation mechanisms based on our textural observations and chemical composition analyses. The shock pressure and temperature conditions in the SMVs of these meteorites were also estimated based on the mineral assemblages in the SMVs and in comparison with static high‐pressure experimental results as follows: 13–16 GPa, >1900 °C for Sahara 98222 and 17–24 GPa, >2100 °C for Yamato 74445. 相似文献
36.
Hidetoshi Asanuma Eiji Ohtani Takeshi Sakai Hidenori Terasaki Seiji Kamada Tadashi Kondo Takumi Kikegawa 《Physics and Chemistry of Minerals》2010,37(6):353-359
The melting temperature of Fe–18 wt% Si alloy was determined up to 119 GPa based on a change of laser heating efficiency and
the texture of the recovered samples in the laser-heated diamond anvil cell experiments. We have also investigated the subsolidus
phase relations of Fe–18 wt% Si alloy by the in-situ X-ray diffraction method and confirmed that the bcc phase is stable at
least up to 57 GPa and high temperature. The melting curve of the alloy was fitted by the Simon’s equation, P(GPa)/a = (T
m(K)/T
0)
c
, with parameters, T
0 = 1,473 K, a = 3.5 ± 1.1 GPa, and c = 4.5 ± 0.4. The melting temperature of bcc Fe–18 wt% Si alloy is comparable with that of pure iron in the pressure range
of this work. The melting temperature of Fe–18 wt% Si alloy is estimated to be 3,300–3,500 K at 135 GPa, and 4,000–4,200 K
at around 330 GPa, which may provide the lower bound of the temperatures at the core–mantle boundary and the inner core–outer
core boundary if the light element in the core is silicon. 相似文献
37.
Eiji Ohtani 《Physics of the Earth and Planetary Interiors》1983,33(1):12-25
The melting curve of perovskite MgSiO3 and the liquidus and solidus curves of the lower mantle were estimated from thermodynamic data and the results of experiments on phase changes and melting in silicates.The initial slope of the melting curve of perovskite MgSiO3 was obtained as at 23 GPa. The melting curve of perovskite was expressed by the Kraut-Kennedy equation as , where Tm?2900 K and P?23 GPa; and by the Simon equation, .The liquidus curve of the lower mantle was estimated as (perovskite) and this gives the liquidus temperature Tliq=7000 ±500 K at the mantle-core boundary. The solidus curve of the lower mantle was also estimated by extrapolating the solidus curve of dry peridotite using the slope of the solidus curve of magnesiowüstite at high pressures. The solidus temperature is ~ 5000 K at the base of the lower mantle. If the temperature distribution of the mantle was 1.5 times higher than that given by the present geotherm in the early stage of the Earth's history, partial melting would have proceeded into the deep interior of the lower mantle.Estimation of the density of melts in the MgOFeOSiO2 system for lower mantle conditions indicates that the initial melt formed by partial fusion of the lower mantle would be denser than the residual solid because of high concentration of iron into the melt. Thus, the melt generated in the lower mantle would tend to move downward toward the mantle-core boundary. This downward transportation of the melt in the lower mantle might have affected the chemistry of the lower mantle, such as in the D″ layer, and the distribution of the radioactive elements between mantle and core. 相似文献
38.
High-pressure phase transformations were investigated for two silicates, MgSiO3 and ZnSiO3; six germanates, MGeO3 and six titanates, MTiO3 (M=Ni, Mg, Co, Zn, Fe, and Mn) at about 1,000°C and pressures up to ca. 30 GPa. CoGeO3 was found to assume the ilmenite form. The ilmenite phases were confirmed to transform in the following schemes: to perovskite in MgSiO3 and MnGeO3, to corundum in MgGeO3 and ZnGeO3, to rocksalt plus rutile in ZnSiO3 and CoGeO3 and to rocksalt plus TiO2 (possibly of some denser structure) in NiTiO3, MgTiO3, CoTiO3, ZnTiO3 and FeTiO3. In the case of FeTiO3, the corundum form appeared as an intermediate phase. The possibility that the corundum type MnTiO3 might transform to some denser modification could not be excluded. The compound NiGeO3 was nonexistent throughout the pressure range studied. High-pressure phases of ABO3 (A=Ni, Mg, Co, Zn, Fe, and Mn; B=Si, Ge and Ti) are summarized, and those stabilized at pressures higher than 20 GPa are discussed. 相似文献
39.
Eiji Ito 《Physics of the Earth and Planetary Interiors》1975,10(1):88-93
High-pressure stability relations in cobalt and nickel silicates have been studied over the pressure range 130–330 kbar employing a double-staged split-sphere-type high-pressure apparatus.γ-Co2SiO4 and γ-Ni2SiO4 decompose directly into their constituent oxide mixtures (rocksalt plus stishovite) 175 kbar and 280 kbar, respectively. The result that γ-Ni2SiO4 has a wider stability field in pressure than γ-Co2SiO4, is consistent with simple crystal-field theory.The experimental precision is high enough to show that the decomposition boundary of γ-Co2SiO4 has a positive slope (dP/dT > 0) and a preliminary determination of the boundary curve is P(kbar) = 0.065 T (°C) + 110.No positive evidence for the existence of high-pressure forms of CoSiO3 and NiSiO3 has been obtained in these quenching experiments, and they finally decompose into constituent oxide mixtures as in the cases of orthosilicates. 相似文献
40.
Eiji Ito Yoshito Matsui Kaichi Suito Naoto Kawai 《Physics of the Earth and Planetary Interiors》1974,8(4):342-344
Magnesium orthosilicate with spinel structure (γ-Mg2SiO4) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001Å. X-ray powder diffraction pattern revealed a significant difference between γ-Mg2SiO4 and other γ-M2SiO4 spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg2SiO4 spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels. 相似文献