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101.
102.
T. L. Grove 《Contributions to Mineralogy and Petrology》1982,78(3):298-304
Theoretical and practical considerations are combined to place limits on the iron content of an FePt alloy that is in equilibrium with silicate melt, olivine and a gas phase of known \(f_{{\text{O}}_{\text{2}} }\) . Equilibrium constants are calculated for the reactions: (1) $$2{\text{Fe}}^{\text{o}} + {\text{SiO}}_{\text{2}} + {\text{O}}_{\text{2}} \rightleftharpoons {\text{Fe}}_{\text{2}} {\text{SiO}}_{\text{4}}$$ (2) $${\text{Fe}}^{\text{o}} + \frac{1}{2}{\text{O}}_{\text{2}} \rightleftharpoons {\text{FeO}}$$ . These equilibria may be used to choose an appropriate iron activity for the FePt alloy of an experiment. The temperature dependence of the equilibrium constants is calculated from experimental data. The Gibbs free energy of reaction (1) obtained using thermochemical data is in close agreement with ΔGrxn calculated from the experimental data. Reaction (1) has the advantage that it is independent of the Fe2+/Fe3+ ratio of the melt, but is limited to applications where olivine is a crystallizing phase and requires a formulation for \(a_{{\text{SiO}}_{\text{2}} }^{{\text{liq}}}\) . Reaction (2) uses an empirical approximation for the FeO/Fe2O3 ratio of the liquid, and is independent of olivine saturation. However, it requires a formulation for a FeO liq . Either equilibrium constant may be used to calculate the appropriate FePt alloy in equilibrium with a silicate melt. If experiments are conducted at an \(f_{{\text{O}}_{\text{2}} }\) parallel that of a buffer assemblage, a small range of FePt alloys may be used over a large temperature interval. For example, an alloy containing from 6 % to 9 % Fe by weight is in equilibrium with olivine-saturated tholeiites and komatiites at the quartzfayalite-magnetite buffer over the temperature interval 1,400° C to 1,100° C. Lunar basalt liquids in equilibrium with olivine at 1/2 log unit below the iron-wüstite buffer require an FePt alloy that contains 30–50 wt. % iron over a similar temperature interval. 相似文献
103.
104.
Lavas from Medicine Lake volcano, Northern California have been examined for evidence of magma mixing. Mixing of magmas has
produced basaltic andesite, andesite, dacite and rhyolite lavas at the volcano. We are able to identify the compositional
characteristics of the components that were mixed and to estimate the time lag between the mixing event and eruption of the
mixed magma. Compositional data from pairs of phenocrysts identify a high alumina basalt (HAB) and a silicic rhyolite as endmembers
of mixing. Mg-rich olivine or augite and Ca-rich plagioclase are associated with the HAB component, and Fe-rich orthopyroxene
and Na-rich plagioclase are associated with the rhyolitic component. Some lavas contain multiple phenocryst assemblages suggesting
the incorporation of several magmas intermediate between the HAB and silicic components. Glass inclusions trapped in Mg-rich
olivine and Na-rich plagioclase are similar in composition to the proposed HAB and rhyolite end members and provide supportive
evidence for mixing. Textural criteria are also consistent with magma mixing. Thermal curvature of the liquidus surfaces in
the basalt-andesite-rhyolite system allows magmas produced by mixing to be either supercooled or superheated. Intergranular
textures of basaltic andesites and andesites result from cooling initiated below the liquidus. The trachytic textures of silicic
andesites form from cooling initiated above the liquidus. Reversed compositional zoning profiles in olivine crystals were
produced by the mixing event, and the homogenization of the compositional zoning has been used to estimate the time interval
between magma mixing and eruption. Time estimates are on the order of 80 to 90 h, suggesting that the mixing event triggered
eruption. 相似文献
105.
Mineral/melt partitioning of trace elements during hydrous peridotite partial melting 总被引:6,自引:4,他引:2
Glenn?A.?GaetaniEmail author Adam?J.?R.?Kent Timothy?L.?Grove Ian?D.?Hutcheon Edward?M.?Stolper 《Contributions to Mineralogy and Petrology》2003,145(4):391-405
This experimental study examines the mineral/melt partitioning of incompatible trace elements among high-Ca clinopyroxene, garnet, and hydrous silicate melt at upper mantle pressure and temperature conditions. Experiments were performed at pressures of 1.2 and 1.6 GPa and temperatures of 1,185 to 1,370 °C. Experimentally produced silicate melts contain up to 6.3 wt% dissolved H 2O, and are saturated with an upper mantle peridotite mineral assemblage of olivine+orthopyroxene+clinopyroxene+spinel or garnet. Clinopyroxene/melt and garnet/melt partition coefficients were measured for Li, B, K, Sr, Y, Zr, Nb, and select rare earth elements by secondary ion mass spectrometry. A comparison of our experimental results for trivalent cations (REEs and Y) with the results from calculations carried out using the Wood-Blundy partitioning model indicates that H 2O dissolved in the silicate melt has a discernible effect on trace element partitioning. Experiments carried out at 1.2 GPa, 1,315 °C and 1.6 GPa, 1,370 °C produced clinopyroxene containing 15.0 and 13.9 wt% CaO, respectively, coexisting with silicate melts containing ~1–2 wt% H 2O. Partition coefficients measured in these experiments are consistent with the Wood-Blundy model. However, partition coefficients determined in an experiment carried out at 1.2 GPa and 1,185 °C, which produced clinopyroxene containing 19.3 wt% CaO coexisting with a high-H 2O (6.26±0.10 wt%) silicate melt, are significantly smaller than predicted by the Wood-Blundy model. Accounting for the depolymerized structure of the H 2O-rich melt eliminates the mismatch between experimental result and model prediction. Therefore, the increased Ca 2+ content of clinopyroxene at low-temperature, hydrous conditions does not enhance compatibility to the extent indicated by results from anhydrous experiments, and models used to predict mineral/melt partition coefficients during hydrous peridotite partial melting in the sub-arc mantle must take into account the effects of H 2O on the structure of silicate melts. 相似文献
106.
We have developed a method to calculate site and path effects for complex heterogeneous media using synthetic Green’s functions. The Green’s functions are calculated numerically by imposing body forces at the site of interest and then storing the reciprocal Green’s functions along arbitrary finite-fault surfaces. By using reciprocal Green’s functions, we can then simulate many source scenarios for those faults because the primary numerical calculations need be done only once. The advantage of the proposed method is shown by evaluation of the site and path effects for three sites in the vicinity of the Los Angeles basin using the Southern California Velocity Model (version 2.2, Magistrale et al., 2000). In this example, we have simulated 300 source scenarios for 5 major southern California faults and compared their responses for period longer then 3 seconds at the selected sites. However, a more detailed comparison with strong motion records will be necessary before a particular hazard assessment can be made. For the tested source scenarios the results show that the variations in the peak velocity amplitudes and durations due to a source scenarios are as large as variations due to a heterogeneous velocity model. 相似文献
107.
Quaternary sedimentary deposits along the structural depression of the San Andreas fault (SAF) zone north of San Francisco in Marin County provide an excellent record of rates and styles of neotectonic deformation in a location near where the greatest amount of horizontal offset was measured after the great 1906 San Francisco earthquake. A high-resolution gravity survey in the Olema Valley was used to determine the depth to bedrock and the thickness of sediment fill along and across the SAF valley. In the gravity profile across the SAF zone, Quaternary deposits are offset across the 1906 fault trace and truncated by the Western and Eastern Boundary faults, whose youthful activity was previously unknown. The gravity profile parallel to the fault valley shows a basement surface that slopes northward toward an area of present-day subsidence near the head of Tomales Bay. Surface and subsurface investigations of the late Pleistocene Olema Creek Formation (Qoc) indicate that this area of subsidence was located further south during deposition of the Qoc and that it has migrated northward since then. Localized subsidence has been replaced by localized contraction that has produced folding and uplift of the Qoc. This apparent alternation between transtension and transpression may be the result of a northward-diverging fault geometry of fault strands that includes the valley-bounding faults as well as the 1906 SAF trace. The Vedanta marsh is a smaller example of localized subsidence in the fault zone, between the 1906 SAF trace and the Western Boundary fault. Analyses of Holocene marsh sediments in cores and a paleoseismic trench indicate thickening, and probably tilting, toward the 1906 trace, consistent with coseismic deformation observed at the site following the 1906 earthquake.New age data and offset sedimentary and geomorphic features were used to calculate four late Quaternary slip rate estimates for the SAF at this latitude. Luminescence dates of 112–186 ka for the middle part of the Olema Creek Formation (Qoc), the oldest Quaternary deposit in this part of the valley, suggest a late Pleistocene slip rate of 17–35 mm/year, which replaces the unit to a position adjacent to its sediment source area. A younger alluvial fan deposit (Qqf; basal age 30 ka) is exposed in a quarry along the medial ridge of the fault valley. This fan deposit has been truncated on its western side by dextral SAF movement, and west-side-down vertical movement that has created the Vedanta marsh. Paleocurrent measurements, clast compositions, sediment facies distributions, and soil characteristics show that the Bear Valley Creek drainage, now located northwest of the site, supplied sediment to the fan, which is now being eroded. Restoration of the drainage to its previous location provides an estimated slip rate of 25 mm/year. Furthermore, the Bear Valley Creek drainage probably created a water gap located north of the Qqf deposit during the last glacial maximum 18 ka. The amount of offset between the drainage and the water gap yields an average slip rate of 21–30 mm/year. Finally, displacement of a 1000-year-old debris lobe approximately 20 m from its hillside hollow along the medial ridge indicates a minimum late Holocene slip rate of 21–25 mm/year. Similarity of the late Pleistocene rates to the Holocene slip rate, and to previous rates obtained in paleoseismic trenches in the area, indicates that the rates may not have changed over the past 30 ka, and perhaps the past 200–400 ka. Stratigraphic and structural observations also indicate that valley-bounding faults were active in the late Pleistocene and suggest the need for further study to evaluate their continued seismic potential. 相似文献
108.
Weishan Ren Jason A. Mclennan Oy Leuangthong Clayton V. Deutsch 《Natural Resources Research》2006,15(2):111-117
There is a need to estimate reserve uncertainty for large lease areas. Detailed 3D models of heterogeneity are not necessarily
required, but there is a need to integrate all available data into an in-situ reserve estimate with uncertainty. A 2D mapping
approach is presented to appraise reserves accounting for multiple variables, multiple data sources, and uncertainty. The
approach can be considered in three primary steps: (1) Bayesian updating is used to determine local distributions of uncertainty
for each primary variable while integrating multiple secondary information, (2) matrix simulation is employed to jointly and
simultaneously simulate multiple collocated variables to determine a derived variable such as OOIP, and (3) probability field
simulation then is applied to permit joint simulation of multiple locations. This methodology permits local and global uncertainty
assessment while integrating multiple sources of information. An application to the McMurray Formation in Alberta, Canada
is demonstrated. 相似文献
109.
The influence of water on melting of mantle peridotite 总被引:47,自引:8,他引:39
This experimental study examines the effects of variable concentrations of dissolved H2O on the compositions of silicate melts and their coexisting mineral assemblage of olivine + orthopyroxene ± clinopyroxene ± spinel ± garnet.
Experiments were performed at pressures of 1.2 to 2.0 GPa and temperatures of 1100 to 1345 °C, with up to ∼12 wt% H2O dissolved in the liquid. The effects of increasing the concentration of dissolved H2O on the major element compositions of melts in equilibrium with a spinel lherzolite mineral assemblage are to decrease the
concentrations of SiO2, FeO, MgO, and CaO. The concentration of Al2O3 is unaffected. The lower SiO2 contents of the hydrous melts result from an increase in the activity coefficient for SiO2 with increasing dissolved H2O. The lower concentrations of FeO and MgO result from the lower temperatures at which H2O-bearing melts coexist with mantle minerals as compared to anhydrous melts. These compositional changes produce an elevated
SiO2/(MgO + FeO) ratio in hydrous peridotite partial melts, making them relatively SiO2 rich when compared to anhydrous melts on a volatile-free basis. Hydrous peridotite melting reactions are affected primarily
by the lowered mantle solidus. Temperature-induced compositional variations in coexisting pyroxenes lower the proportion of
clinopyroxene entering the melt relative to orthopyroxene. Isobaric batch melting calculations indicate that fluid-undersaturated
peridotite melting is characterized by significantly lower melt productivity than anhydrous peridotite melting, and that the
peridotite melting process in subduction zones is strongly influenced by the composition of the H2O-rich component introduced into the mantle wedge from the subducted slab.
Received: 7 April 1997 / Accepted: 9 January 1998 相似文献
110.
B. L. Beard Kathy N. Fraracci Robert A. Clayton Toshiko K. Mayeda G. A. Snyder N. V. Sobolev L. A. Taylor 《Contributions to Mineralogy and Petrology》1996,125(4):293-310
Diamond-bearing eclogites are an important component of the xenoliths that occur in the Mir kimberlite, Siberian platform,
Russia. We have studied 16 of these eclogite xenoliths, which are characterized by coarse-grained, equigranular garnet and
omphacite. On the basis of compositional variations in garnet and clinopyroxene, this suite of eclogites can be divided into
at least two groups: a high-Ca group and a low-Ca group. The high-Ca group consists of high-Ca garnets in equilibrium with
pyroxenes that have high Ca-ratios [Ca/(Ca+Fe+Mg)] and high jadeite contents. These high-Ca group samples have high modal%
garnet, and garnet grains often are zoned. Garnet patches along rims and along amphibole- and phlogopite-filled veins have
higher Mg and lower Ca contents compared to homogeneous cores. The low-Ca group consists of eclogites with low-Ca garnets
in equilibrium with pyroxenes with a low Ca-ratio, but variable jadeite contents. These low-Ca group samples typically have
low modal% of garnet, and garnets are rarely compositionally zoned. Three samples have mineralogic compositions and modes
transitional to the high- and low-Ca groups. We have arbitrarily designated these samples as the intermediate-Ca group. The
rare-earth-element (REE) contents of garnet and clinopyroxene have been determined by ion microprobe. Garnets from the low-Ca
group have low LREE contents and typically have [Dy/Yb]n < 1. The high-Ca group garnets have higher LREE contents and typically have [Dy/Yb]n > 1. Garnets from the intermediate-Ca group have REE contents between the high- and low-Ca groups. Clinopyroxenes from the
low-Ca group have convex-upward REE patterns with relatively high REE contents (ten times chondrite), whereas those from the
high-Ca group have similar convex-upward shapes, but lower REE contents, approximately chondritic. Reconstructed bulk-rock
REE patterns for the low-Ca group eclogites are relatively flat at approximately ten times chondrite. In contrast, the high-Ca
group samples typically have LREE-depleted patterns and lower REE contents. The δ18O values measured for garnet separates range from 7.2 to 3.1‰. Although there is a broad overlap of δ18O between the low-Ca and high-Ca groups, the low-Ca group samples range from mantle-like to high δ18O values (4.9 to 7.2‰), and the high-Ca group garnets range from mantle-like to low δ18O values (5.3 to 3.1‰). The oxygen isotopic compositions of two of the five high-Ca group samples and four of the eight low-Ca
group eclogites are consistent with seawater alteration of basaltic crust, with the low-Ca group eclogites representative
of low-temperature alteration, and the high-Ca group samples representative of high-temperature hydrothermal seawater alteration.
We interpret the differences between the low- and high-Ca group samples to be primarily a result of differences in the protoliths
of these samples. The high-Ca group eclogites are interpreted to have protoliths similar to the mid to lower sections of an
ophiolite complex. This section of oceanic crust would be dominated by rocks which have a significant cumulate component and
would have experienced high-temperature seawater alteration. Such cumulate rocks probably would be LREE-depleted, and can
be Ca-rich because of plagioclase or clinopyroxene accumulation. The protoliths of the low-Ca group eclogites are interpreted
to be the upper section of an ophiolite complex. This section of oceanic crust would consist mainly of extrusive basalts that
would have been altered by seawater at low temperatures. These basaltic lavas would probably have relatively flat REE patterns,
as seen for the low-Ca group eclogites.
Received: 10 July 1995 / Accepted: 17 May 1996 相似文献