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Zabuye Salt Lake in Tibet, China is a carbonate-type salt lake, which has some unique characteristics that make it different from other types of salt lakes. The lake is at the latter period in its evolution and contains liquid and solid resources. Its brine is rich in Li, B, K and other useful minor elements that are of great economic value. We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15°C and 25°C. The crystallization sequence of the primary salts from the brine at 25°C is halite (NaCl) → aphthitalite (3K2SO4·Na2SO4) → zabuyelite (Li2CO3)→ trona (Na2CO3·NaHCO3·2H2O) → thermonatrite (Na2CO3·H2O) → sylvite (KCl), while the sequence is halite (NaCl) → sylvite (KCl) → trona (Na2CO3·NaHCO3·2H2O) → zabuyelite (Li2CO3) → thermonatrite (Na2CO3·H2O) → aphthitalite (3K2SO4·Na2SO4) at 15°C. They are in accordance with the metastable phase diagram of the Na+, K+-Cl?, CO32?, SO42?-H2O quinary system at 25°C, except for Na2CO3·7H2O which is replaced by trona and thermonatrite. In the 25°C experiment, zabuyelite (Li2CO3) was precipitated in the early stage because Li2CO3 is supersaturated in the brine at 25°C, in contrast with that at 15°C, it precipitated in the later stage. Potash was precipitated in the middle and late stages in both experiments, while boron was concentrated in the early and middle stages and precipitated in the late stage.  相似文献   

4.
Carbonate minerals and water (or geofluids) reactions are important for modeling of geochemical processes and have received considerable attention over the past decades. The calcite dissolution rates from 50℃ to 250℃ at 10 MPa in deionized water with a flow rate varying from 0.2 to 5 mL/min were experimentally measured in a continuous flow column pressure vessel reactor. The dissolution began near the equilibrium with c/ceq 〉 0.3 and finally reached the equilibrium at 100℃-250℃, so the corresponding solubility was also determined as 1.87, 2.02, 2.02 and 1.88×10^-4.mol/L at 100℃, 150℃, 200℃ and 250℃ respectively, which was first increasing and then switching to decreasing with temperature and the maximum value might occur between 150℃ and 200℃. The experimental dissolution rate not only increased with temperature, but also had a rapid increase between 150℃ and 200℃ at a constant flow rate of 4 mL/min. The measured dissolution rates can be described using rate equations of R = k(1-c/ceq)n or R = kc-n. In these equations the reaction order n changed with temperature, which indicates that n was a variable rather than a constant, and the activation energy was 13.4 kJ/mol calculated with R = k(1-c/ceq)n or 18.0 kJ/mol with R = kc^-n, which is a little lower than the surface controlled values. The varied reaction order and lower activation energy indicates that calcite dissolution in this study is a complex interplay of diffusion controlled and surface controlled processes.  相似文献   

5.
《Applied Geochemistry》1998,13(7):905-916
Experiments measuring kaolinite and smectite dissolution rates were carried out using batch reactors at 35° and 80°C. No potential catalysts or inhibitors were present in solution. Each reactor was charged with 1 g of clay of the ≤2 μm fraction and 80, 160 or 240 ml of 0.1–4 M KOH solution. An untreated but sized kaolinite from St. Austell and two treated industrial smectites were used in the experiments. One smectite is a nearly pure montmorillonite, while the second has a significant component of beidellitic charge (35%). The change in solution composition and mineralogy was monitored as a function of time. Initially, the 3 clays dissolved congruently. No new formed phases were observed by XRD and SEM during the pure dissolution stage. The kaolinite dissolution is characterized by a linear release of silica and Al as a function of the log of time. This relationship can be explained by a reaction affinity effect which is controlled by the octahedral layer dissolution. Far from equilibrium, dissolution rates are proportional to a0.56±0.12OH at 35°C and to a0.81±0.12OH at 80°C. The activation energy of kaolinite dissolution increases from 33±8 kJ/mol in 0.1 M KOH solutions to 51±8 kJ/mol in 3 M KOH solutions. In contrast to kaolinite, the smectites dissolve at much lower rates and independently of the aqueous silica or Al concentrations. The proportionality of the smectite dissolution rate constant at 35 and 80°C was a0.15±0.06OH. The activation energy of dissolution appears to be independent of pH for smectite and is found to be 52±4 kJ/mol. The differences in behavior between the two kinds of minerals can be explained by structural differences. The hydrolysis of the tetrahedral and the octahedral layer appears as parallel reactions for kaolinite dissolution and as serial reactions for smectite dissolution. The rate limiting step is the dissolution of the octahedral layer in the case of kaolinite, and the tetrahedral layer in the case of smectite.  相似文献   

6.
《Geochimica et cosmochimica acta》1999,63(19-20):3247-3259
The rate of Si release from dissolving bytownite feldspar in abiotic batch reactors increased as temperatures increased from 5° to 35°C. Metabolically inert subsurface bacteria (bacteria in solution with no organic substrate) had no apparent effect on dissolution rates over this temperature range. When glucose was added to the microbial cultures, the bacteria responded by producing gluconic acid, which catalyzed the dissolution reaction by both proton- and ligand-promoted mechanisms. The metabolic production, excretion, and consumption of gluconic acid in the course of glucose oxidation, and therefore, the degree of microbial enhancement of mineral dissolution, depend on temperature. There was little accumulation of gluconic acid and therefore, no significant enhancement of mineral dissolution rates at 35°C compared to the abiotic controls. At 20°C, gluconate accumulated in the experimental solutions only at the beginning of the experiment and led to a twofold increase in dissolved Si release compared to the controls, primarily by the ligand-promoted dissolution mechanism. There was significant accumulation of gluconic acid in the 5°C experiment, which is reflected in a significant reduction in pH, leading to 20-fold increase in Si release, primarily attributable to the proton-promoted dissolution mechanism. These results indicate that bacteria and microbial metabolism can affect mineral dissolution rates in organic-rich, nutrient-poor environments; the impact of microbial metabolism on aluminum silicate dissolution rates may be greater at lower rather than at higher temperatures due to the metabolic accumulation of dissolution-enhancing protons and ligands in solution.  相似文献   

7.
Dolomitic marble on the island of Naxos was deformed at variable temperatures ranging from 390 °C to >700 °C. Microstructural investigations indicate two end-member of deformation mechanisms: (1) Diffusion creep processes associated with small grain sizes and weak or no CPO (crystallographic preferred orientation), whereas (2) dislocation creep processes are related with larger grain sizes and strong CPO. The change between these mechanisms depends on grain size and temperature. Therefore, sample with dislocation and diffusion creep microstructures and CPO occur at intermediate temperatures in relative pure dolomite samples. The measured dolomite grain size ranges from 3 to 940 μm. Grain sizes at Tmax >450 °C show an Arrhenius type evolution reflecting the stabilized grain size in deformed and relative pure dolomite. The stabilized grain size is five times smaller than that of calcite at the same temperature and shows the same Arrhenius-type evolution. In addition, the effect of second phase particle influences the grain size evolution, comparable with calcite. Calcite/dolomite mixtures are also characterized by the same difference in grain size, but recrystallization mechanism including chemical recrystallization induced by deformation may contribute to apparent non-temperature equilibrated Mg-content in calcite.  相似文献   

8.
The thermally induced reductive decomposition of a natural near end-member almandine [VIII(Fe2.85Mg0.11Ca0.05Mn0.02)VI(Al1.99)IV(Si2.99)O12] and possible hydrogen diffusion into its structure have been carried out at temperatures up to 1,200°C, monitored by simultaneous thermogravimetric analysis and differential scanning calorimetry (DSC), infrared and 57Fe Mössbauer spectroscopy and X-ray powder diffraction. Below 1,000°C, evidence for hydrogen diffusion into almandine structure was not observed. At temperatures above 1,000°C, reductive decomposition sets in, as displayed by a sharp endothermic peak at 1,055°C on the DSC curve accompanied by a total mass loss of 3.51%. We observe the following decomposition mechanism: almandine + hydrogen → α-Fe + cristobalite + hercynite + water. At higher temperatures, fayalite and sekaninaite are formed by consecutive reaction of α-Fe with cristobalite and water, and cristobalite with hercynite, respectively. The metallic α-Fe phase forms spherical and isolated particles (~1 μm).  相似文献   

9.
Oxygen isotopic exchange between quartz and water, using a novel technique in which both 18O/16O and 17O/16O fractionations were measured, yielded an equilibrium fractionation Δ18 = 9.0 at 250°C and 15 kbar. The reaction proceeds predominantly by solution of fine grains and growth of larger grains. Exchange by solid-state diffusion is immeasurably slow at this temperature. Under the same experimental conditions, cristobalite behaves quite differently, becoming transformed to sub-micron quartz crystals in a few minutes. The phase transformation is accompanied by a kinetic isotope effect yielding quartz in isotopic disequilibrium with water. It is possible that such disequilibrium products are also formed in other experiments involving phase transitions or mineral syntheses.  相似文献   

10.
A thermodynamic dataset for arsenic species in As–O–H–S–Fe–Ba system was compiled from the literature. Using this dataset, Eh–pH diagrams for the systems As–O–H, As–O–H–S, As–O–H–S–Fe, As–O–H–Ba, and As–O–H–S–Fe–Ba were constructed at 25°C and 1 bar. The inclusion of thioarsenite species in the systems As–O–H–S and As–O–H–S–Fe results in substantial differences from previously published Eh–pH diagrams. There are considerable differences in the thermodynamic properties for orpiment, realgar, scorodite, arsenopyrite, barium arsenate, and barium hydrogen arsenate, which result in vastly different stability fields when different values are adopted.  相似文献   

11.
Twenty-one energy-dispersive X-ray diffraction spectra for fayalite at 400° C constitute the basis for an elevated-temperature static compression isotherm for this important silicate mineral. A Murnaghan regression of the resulting molar volumes yields 103.8 GPa and 7.1 for the 400° C, room-pressure values of the isothermal bulk modulus (K 0) and its first pressure derivative (K0), respectively. When compared to the room-temperature static compression isotherm of Yagi et al. (1975), our 400° C value for K 0 yields 5.4 ×10–2 GPa/deg for (K/T)00. When combined with literature volume data, our measurements indicate that the fayalite isochores are strongly concave toward the pressure axis [( 2 T/P 2 ) v <>This is publication number 1125 of the School of Earth Sciences, Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA  相似文献   

12.
Zusammenfassung An zwei typischen Basalten der Göttinger Umgebung wird untersucht, wie sich die magnetischen Größen nach Erhitzung verändert haben. Die magnetischen Materialeigenschaften: Sättigungsmagnetisierung, Curie-Punkt und magnetische Anfangssuszeptibilität zeigen systematische Veränderungen. Aus licht- und elektronenoptischen Untersuchungen folgt, daß Entmischungsstrukturen allein nicht als Erklärung hierfür angesehen werden können. Der entscheidende Prozeß scheint die Tieftemperaturoxydation von Fe2+ zu sein, die bei den gewählten Temperaturen 250 und 350° C eine Folge der Abgabe von Kristallwasser ist.Eine bei denselben Temperaturen erzeugte isothermale Remanenz zeigt starke Abhängigkeit von der Dauer der Erhitzung. In einzelnen Fällen ergab sich eine inverse Magnetisierung, die allerdings nicht stabil war.Teilzusammenfassungen, die mehr ins einzelne gehen, finden sich auf den S. 334 und 345.
The magnetic behaviour of two typical basalts of the Göttingen area after heat treatment is studied. The magnetic characteristic properties: saturation magnetization, Curie Point and magnetic susceptibility change systematically. Application of light — and electronoptical methods shows that exsolution structures alone cannot be responsible for these changes. The most important process seems to be the low-temperature-oxidation of Fe2+ which (at the chosen temperatures of 250 °C and 350 °C) is caused by loss of crystal water.An isothermal remanent magnetization (IRM), which is produced at the same temperature, shows a pronounced dependance on the duration of heating. A few experiments produced an inverse IRM which, however, was not stable.More detailed, partial summaries will be found on pages 334 and 345.
  相似文献   

13.
Observations of competitive complexation of NTA by Cu2+ and rare earth element (REE) ions are used to determine REE-NTA stability constants at ionic strengths between 0.1 and 5.0 molar. Although REE stability constants change markedly with ionic strength, differences in the ionic strength dependence of REE-NTA stability constants across the rare earth element series are small. The ionic strength dependence of log1 for Y and REEs with NTA at 25 °C can be described as: log1(M) = log1(M)0 - 9.198 I1/2/(1+B I1/2)+C I + D I3/2, where 1(M) = [MNTA°][M3+]-1[NTA3-]-1, I is ionic strength, B = 1.732, C = 0.1596, D = 0.0816, and log1(M)° is the metal-NTA stability constant at zero ionic strength.  相似文献   

14.
The hydrolysis of the Pd2+ ion in HClO4 solutions was examined at 25–70°C, and the thermodynamic constants of equilibrium K (1)0 and K (2)0were determined for the reactions Pd2+ + H2O = PdOH+ + H+ and Pd2+ + 2H2O = Pd(OH)20 + 2H+, respectively. The values of log K (1)0 = −1.66 ± 0.5 (25°C) and −0.65 ± 0.25 (50°C) and log K (2)0 = −4.34 ± 0.3 (25°C) and −3.80 ± 0.3 (50°C) were derived using the solubility technique at 0.95 confidence level. The values of log K (1)0 = −1.9 ± 0.6 (25°C), −1.0 ± 0.4 (50°C), and −0.5 ± 0.3 (70°C) were obtained by spectrophotometric techniques. The palladium ion is significantly hydrolyzed at elevated temperatures (50–70°C) even in strongly acidic solutions (pH 1–1.5), and its hydrolysis is enhanced with increasing temperature.  相似文献   

15.
《Applied Geochemistry》1999,14(1):17-25
The nucleation induction period of CaCO3 in NaCl brines in the absence and presence of scale inhibitors was experimentally measured at temperatures from 25 to 90°C. A semi-empirical mathematical inhibitor model is presented for the CaCO3 scale control in industrial processes based upon nucleation theory and experimental observations. Results show that the minimum inhibitor dosage (Cinh) may be obtained from: Cinh=f(s)/binh log [tinh/t0], where tinh is the inhibition time, e.g., 20 min, t0 is the nucleation induction period in the absence of inhibitors, binh is the inhibitor efficiency, and f(s) is the safety factor, e.g., 2. Important factors for the kinetics of both nucleation and inhibition have been incorporated in this model including the calcite saturation index (SI), temperature (T), and the molar ratio of Ca to HCO3 alkalinity (R). In this paper, model parameters are presented for commonly used inhibitors, including 1-hydroxyethylidene-1,1-diphosphonic-acid (HEDP) and nitrilotri(methylene phosphonic) acid (NTMP). Results show that HEDP and NTMP are the best inhibitors for calcite scaling in the systems examined.  相似文献   

16.
Literature thermodynamic data on species and particles existing in the heterogeneous PdO-H2O system were checked for consistency, and the equilibrium constants for dissolution of palladium oxide and hydroxide in water and for Pd2+ (aq) hydrolysis were recommended. Δ f G 298.15 ° obtained in this work for Pd2+(aq) sharply differs (no less than by 6 kJ/mol) from values that are reported in fundamental thermodynamic reference books and based on experimentally measured palladium electrode potential at 25°C. Detailed examination of literature data on the thermodynamic properties of compounds in the Cl-Pd(aq) system is required to account for revealed inconsistency.  相似文献   

17.
The thermoelastic behavior of a natural clintonite-1M [with composition: Ca1.01(Mg2.29Al0.59Fe0.12)Σ3.00(Si1.20Al2.80)Σ4.00O10(OH)2] has been investigated up to 10 GPa (at room temperature) and up to 960°C (at room pressure) by means of in situ synchrotron single-crystal and powder diffraction, respectively. No evidence of phase transition has been observed within the pressure and temperature range investigated. PV data fitted with an isothermal third-order Birch–Murnaghan equation of state (BM-EoS) give V 0 = 457.1(2) ?3, K T0 = 76(3)GPa, and K′ = 10.6(15). The evolution of the “Eulerian finite strain” versus “normalized stress” shows a linear positive trend. The linear regression yields Fe(0) = 76(3) GPa as intercept value, and the slope of the regression line leads to a K′ value of 10.6(8). The evolution of the lattice parameters with pressure is significantly anisotropic [β(a) = 1/3K T0(a) = 0.0023(1) GPa−1; β(b) = 1/3K T0(b) = 0.0018(1) GPa−1; β(c) = 1/K T0(c) = 0.0072(3) GPa−1]. The β-angle increases in response to the applied P, with: βP = β0 + 0.033(4)P (P in GPa). The structure refinements of clintonite up to 10.1 GPa show that, under hydrostatic pressure, the structure rearranges by compressing mainly isotropically the inter-layer Ca-polyhedron. The bulk modulus of the Ca-polyhedron, described using a second-order BM-EoS, is K T0(Ca-polyhedron) = 41(2) GPa. The compression of the bond distances between calcium and the basal oxygens of the tetrahedral sheet leads, in turn, to an increase in the ditrigonal distortion of the tetrahedral ring, with ∂α/∂P ≈ 0.1°/GPa within the P-range investigated. The Mg-rich octahedra appear to compress in response to the applied pressure, whereas the tetrahedron appears to behave as a rigid unit. The evolution of axial and volume thermal expansion coefficient α with temperature was described by the polynomial α(T) = α0 + α1 T −1/2. The refined parameters for clintonite are as follows: α0 = 2.78(4) 10−5°C−1 and α1 = −4.4(6) 10−5°C1/2 for the unit-cell volume; α0(a) = 1.01(2) 10−5°C−1 and α1(a) = −1.8(3) 10−5°C1/2 for the a-axis; α0(b) = 1.07(1) 10−5°C−1 and α1(b) = −2.3(2) 10−5°C1/2 for the b-axis; and α0(c) = 0.64(2) 10−5°C−1 and α1(c) = −7.3(30) 10−6°C1/2for the c-axis. The β-angle appears to be almost constant within the given T-range. No structure collapsing in response to the T-induced dehydroxylation was found up to 960°C. The HP- and HT-data of this study show that in clintonite, the most and the less expandable directions do not correspond to the most and the less compressible directions, respectively. A comparison between the thermoelastic parameters of clintonite and those of true micas was carried out.  相似文献   

18.
Shock experiments on quartz single crystals with initial temperatures –170 to +1000°C showed that ambient temperature does not affect the type of defects formed but can lower the pressure of complete amorphization. The amount of glass recovered increases with both pressure and temperature, and the shock-induced phase transformation of quartz is temperature-activated with an apparent activation energy of <60 kj/=" mol.=" the=" phase=" transformation=" is=" localized=" along=" three=" types=" of=" transformation=" lamellae=" (narrow,=" s-shaped,=" and=" wide)=" which=" contain=" fractured=" and/or=" high-pressure=" phases.=" transformation=" lamellae=" are=" inferred=" to=" form=" by=" motion=" of=" linear=" collapse=" zones=" propagating=" near=" the=" shock=" front.=" equilibrium=" phases,=" such=" as=" stishovite,=" were=" not=" recovered=" and=" are=" probably=" not=" formed=" at=" high=" shock=" pressures:=" the=" dominant=" transformation=" mechanism=" is=" inferred=" to=" be=" solid-state=" collapse=" to=" a=" dense,=" disordered=" phase.=" melting=" occurs=" separately=" by=" friction=" along=" microfaults,=" but=" no=" high-pressure=" crystal=" phases=" are=" quenched=" in=" these=" zones.=" shock=" of=" quartz=" thus=" produces=" two=" types=" of=" disordered=" material,=" quenched=" melt=" (along=" microfaults)=" and=" diaplectic=" glass=" (in=" transformation=" lamellae);=" the=" quenched=" melt=" expands=" during=" p-t=" release,=" leaving=" it=" with=" a=" density=" lower=" than=" quartz,=" while=" recovered=" diaplectic=" glass=" has=" a=" density=" closer=" to=" that=" of=" quartz.=" at=" low=" pressures=">< 15=" gpa),=" quartz=" transforms=" mostly=" by=" shear=" melting,=" while=" at=" higher=" pressures=" it=" converts=" mostly=" along=" transformation=" lamellae.=" we=" find=" that=" shock=" paleopiezometers=" using=" microstructures=" are=" nominally=" temperature-invariant,=" so=" that=" features=" observed=" at=" impact=" craters=" and=" the=" k/t=" boundary=" require=" in=" excess=" of=" 10=" gpa=" to=" form,=" regardless=" of=" the=" target=" temperature.=" shock=" comminution=" will=" be=" much=" more=" extensive=" for=" impacts=" on=" cold=" surfaces=" due=" to=" lack=" of=" cementation=" of=" fragments=" by=" melt=" glass;=" shock=" on=" hot=" surfaces=" could=" produce=" much=" more=" glass=" than=" estimated=" from=" room-temperature=" experiments.=" because=" of=" the=" shock-impedance=" mismatch=" between=" quartz=" specimen=" and=" steel=" capsule,=" the=" incident=" shock=" wave=" reverberates=" up=" to=" a=" final=" pressure.=" the=" dynamic=" compression=" process=" is=" quasi-isentropic=" with=" high=" strain=" rates.=" preheating=" and=" precooling=" achieves=" final=" shock=" pressures=" and=" temperatures=" representative=" of=" single-shock=" states=" of=" room=" temperature=" quartz=" and=" of=" quartz=" on=" known=" planetary=" surfaces.=" stress=" histories=" were=" calculated=" by=" detailed=" 1-=" and=" 2-dimensional=" computer=" simulations.=" the=" stress=" history=" throughout=" the=" sample=" is=" relatively=" uniform,=" with=" minor=" variations=" during=" unloading.=" significant=" differences=" between=" impact=" pressures=" calculated=" by=" the=" shock-impedance-match=" method=" and=" specimen=" pressures=" calculated=" by=" computer=" simulations=" indicate=" the=" importance=" of=" modeling=" shock=" recovery=" experiments=">  相似文献   

19.
A new phase of AlOOH (tentatively called δ-AlOOH) was synthesized at 21?GPa and 1000?°C and its crystal structure was identified by a powder X-ray diffraction method. Rietveld refinement revealed that this aluminum oxide hydroxide has an orthorhombic unit cell, a?=?4.7134(1) Å, b?=?4.2241(1) Å, c?=?2.83252(8) Å, V?=?56.395 (5) Å3, and Z?=?2 in the space group of P21?nm. A calculated density is 3.533?g?cm?3, which is about 4.48 and 15.04% denser than that of diaspore and boehmite, respectively. The δ-[Al0.86Mg0.07Si0.07]OOH is also stable at 21?GPa and 1000?°C, coexisting with majorite and phase egg, and its cell parameters are a?=?4.710(1) Å, b?=?4.215(1) Å, c?=?2.839(1) Å, and V?=?56.37(1) Å3.  相似文献   

20.
《Applied Geochemistry》1996,11(4):511-521
It is difficult to measure accurately the natural long-term corrosion rates of highly durable nuclear waste glasses. Care should be taken when using data from high temperature experiments to predict corrosion rates under ambient repository conditions as there are many factors (such as the precipitation of secondary compounds, the chemistry of the water in contact with the glass, or circulation of this water through the repository) that can influence the temperature dependence of aqueous reactions. In this study, some standard leach tests using pure water, in continuous flow and direct sampling autoclaves, were performed on a synthetic medieval glass. Archaeological glass samples of a similar composition and which had suffered several centuries of corrosion in damp soil had been the subject of previous studies. The corrosion of the archaeological samples in damp soil was well understood and the aim was to determine how well standard leach tests would predict the observed corrosion.The experimentally measured long-term corrosion rates were not simply dependent on temperature, therefore they could not be used to predict either the corrosion rates or products found on the archaeological samples. In continuous flow experiments this was largely because the release of some cations (e.g. Mg2+) was proportional to the flow rates used, and so the long-term corrosion was dependent on both flow rate and temperature. In the autoclave experiments, concentrations of dissolved ions climbed rapidly in the small water volume, leading to the precipitation of complex mineral phase assemblages. The experiments did not reach silica saturation, therefore the long-term rates measured were a function of both the temperature and the extent of reaction. The initial release rates of silica and of the network modifying cations showed an Arrhenius temperature dependence with an activation energy of about 78.5 kJmol−1. These results would have predicted the soil corrosion of the archaeological samples to within about 30%, i.e. the initial corrosion rate in pure water was similar to the long-term rate in damp soil. As an explanation of the experimental observations it is suggested that clay minerals in the soil consumed silica as the glass dissolved, maintaining under-saturated conditions and allowing corrosion at a rate similar to the initial rate in pure water.  相似文献   

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