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91.
Isothermal (670–700°C) solubility of corundum in supercritical water, within the stability range of corundum as a phase of the system Al2O3-H2O, has been determined by the weight loss method. Experiments were performed in the pressure range 2.5 to 6 kbar in cold seal hydrothermal equipment at 670 ± 5°C using gold tubing. The overall uncertainty of the solubility values obtained was 8%. Experiments in the pressure range 10 to 20 kbar were performed in a piston cylinder apparatus at 700°C using sealed gold capsules held by supporting steel containers. The overall uncertainty of the solubility values obtained was estimated to be 10%.All data could be fitted by the linear equation S[ppmAl2O3] = ?12.37 + 7.24 · p[kbar] with correlation coefficient r = 0.9963. Separate fits of hydrothermal and piston cylinder results yielded a small difference between the two data sets, which is due rather to the experimental uncertainty than to the small temperature difference. 相似文献
92.
Sinnhuber B.-M. Müller R. Langer J. Bovensmann H. Eyring V. Klein U. Trentmann J. Burrows J. P. Künzi K. F. 《Journal of Atmospheric Chemistry》1999,34(3):281-290
In this study measurements of mid-stratospheric Arctic ozone are compared with model simulations. The measurements obtained at Spitsbergen (79°N, 12°E) by ground based millimeter-wave radiometry exhibit large day to day variabilities as well as periods with low ozone. To interpret these measurements, calculations were made using the new photochemical box-trajectory model BRAPHO, with air parcel trajectories calculated from analyzed wind fields. Using a relatively simple approach, the model reproduces the observed ozone variability well, including inter-annual variations. The explanation for the observed ozone behavior is that at these altitudes ozone is determined by what we call dynamically controlled photochemistry. This means that the photochemical evolution of the ozone volume mixing ratio is mainly controlled by the atmospheric dynamics, in particular the solar zenith angle the air parcel has experienced. 相似文献
93.
William H. Langer 《Natural Resources Research》1995,4(4):303-309
Crushed stone and sand and gravel are the two main sources of natural aggregate, and together comprise approximately half the volume and tonnage of mined material in the United States. Natural aggregate is a bulky, heavy material without special or unique properties, and it is commonly used near its source of production to minimize haulage cost. However, remoteness is no longer an absolute disqualifier for the production of aggregate. Today interstate aggregate routinely is shipped hundreds of kilometers by rail and barge. In addition, during 1992, the United States imported 1,317,000 metric tons of aggregate from Canada and 1,531,000 metric tons from Mexico. A number of ports on the Atlantic Coast and Gulf Coast of the United States receive imports of crushed stone from foreign sources for transport to various parts of the eastern United States. These areas either lack adequate supplies of aggregate or are augmenting their supplies because they have difficulties meeting current demand. These difficulties may include poor stone quality, environmental permitting problems, or transportation. Certain societal and geologic conditions of New York City and Philadelphia along the Atlantic Coast, and Tampa and New Orleans along the Gulf Coast, are discussed to demonstrate the different combinations of issues that contribute to the economic viability of importing crushed stone. 相似文献
94.
Alexej N. Platonov Klaus Langer Stanislav S. Matsyuk 《Physics and Chemistry of Minerals》2008,35(6):331-337
In the course of a thorough study of the influences of the second coordination sphere on the crystal field parameters of the
3d
N
-ions and the character of 3d
N
–O bonds in oxygen based minerals, 19 natural Cr3+-bearing (Mg,Ca)-garnets from upper mantle rocks were analysed and studied by electronic absorption spectroscopy, EAS. The
garnets had compositions with populations of the [8]
X-sites by 0.881 ± 0.053 (Ca + Mg) and changing Ca-fractions in the range 0.020 ≤ w
Ca[8] ≤ 0.745, while the [6]
Y-site fraction was constant with x
Cr3+
[6] = 0.335 ± 0.023. The garnets had colours from deeply violet-red for low Ca-contents (up to x
Ca = 0.28), grey with 0.28 ≤ x
Ca ≤ 0.4 and green with 0.4 ≤ x
Ca. The crystal field parameter of octahedral Cr3+ 10Dq decreases strongly on increasing Ca-fraction from 17,850 cm−1 at x
Ca[8] = 0.020 to 16,580 cm−1 at x
Ca[8] = 0.745. The data could be fit with two model which do statistically not differ: (1) two linear functions with a discontinuity
close to x
Ca[8] ≈ 0.3,
(2) one continuous second order function,
The behaviour of the crystal field parameter 10Dq and band widths on changing Ca-contents favour the first model, which is
interpreted tentatively by different influences of Ca in the structure above and below x
Ca[8] ≈ 0.3. The covalency of the Cr–O bond as reflected in the behaviour of the nephelauxetic ratio
decreases on increasing Ca-contents. 相似文献
95.
Polarized electronic absorption spectra, E∥a(∥X), E∥b(∥Y) and E∥c(∥Z), in the energy range 3000–5000?cm–1 were obtained for the orthorhombic thenardite-type phase Cr2SiO4, unique in its Cr2+-allocation suggesting some metal-metal bonding in Cr2+Cr2+ pairs with Cr-Cr distance 2.75?Å along [001]. The spectra were scanned at 273 and 120?K on single crystal platelets ∥(100), containing optical Y and Z, and ∥(010), containing optical X and Z, with thicknesses 12.3 and 15.6?μm, respectively. Microscope-spectrometric techniques with a spatial resolution of 20?μm and 1?nm spectral resolution were used. The orientations were obtained by means of X-ray precession photographs. The xenomorphic, strongly pleochroic crystal fragments (X deeply greenish-blue, Y faint blue almost colourless, Z deeply purple almost opaque) were extracted from polycrystalline Cr2SiO4, synthesized at 35?kbar, above 1440?°C from high purity Cr2O3, Cr (10% excess) and SiO2 in chromium capsules. The Cr2SiO4-phase was identified by X-ray diffraction (XRD). Four strongly polarized bands, at about 13500 (I), 15700 (II), 18700 (III) and 19700 (IV) cm–1, in the absorption spectra of Cr2SiO4 single crystals show properties (temperature behaviour of linear and integral absorption coefficients, polarization behaviour, molar absorptivities) which are compatible with an assignment to localized spin-allowed transitions of Cr2+ in a distorted square planar coordination of point symmetry C2. The crystal field parameter of Cr2+ is estimated to be 10?Dq?10700?cm–1. A relatively intense, sharp band at 18400?cm–1 and three other minor features can, from their small half widths, be assigned to spin-forbidden dd-transitions of Cr2+. The intensity of such bands strongly decreases on decreasing temperature. The large half widths, near 5000?cm–1 of band III are indicative of some Cr-Cr interactions, i.e. δ-δ* transitions of Cr2 4+, whereas the latter alone would be in conflict with the strong polarization of bands I and II parallel [100]. Therefore, it is concluded that the spectra obtained can best be interpreted assuming both dd-transitions of localized d-electrons at Cr2+ as well as δ-δ* transitions of Cr2 4+ pairs with metal-metal interaction. To explain this, a dynamic exchange process 2 Crloc 2+?Cr2, cpl 4+ is suggested wherein the half life times of the ground states of both exchanging species are significantly longer than those of the respective optically excited states, such that the spectra show both dd- and δ-δ*-transitions. 相似文献
96.
97.
We investigate the production of26Al during hydrogen burning and its ejection by massive single and binary stars. Effects of convection and rotation are studied. We discuss the importance of RSGs, LBVs and WR stars to the total Galactic26Al production, and the detection probability of the26Al decay in individual objects as P Cygni, Velorum and Carinae. 相似文献
98.
Hydroxyl defects in garnets from mantle xenoliths in kimberlites of the Siberian platform 总被引:12,自引:0,他引:12
A suite of more than 200 garnet single crystals, extracted from 150 xenoliths, covering the whole range of types of garnet
parageneses in mantle xenoliths so far known from kimberlites of the Siberian platform and collected from nearly all the kimberlite
pipes known in that tectonic unit, as well as some garnets found as inclusions in diamonds and olivine megacrysts from such
kimberlites, were studied by means of electron microprobe analysis and single-crystal IR absorption spectroscopy in the v
OH vibrational range in search of the occurrence, energy and intensity of the v
OH bands of hydroxyl defects in such garnets and its potential use in an elucidation of the nature of the fluid phase in the
mantle beneath the Siberian platform. The v
OH single-crystal spectra show either one or a combination of two or more of the following major v
OH bands, I 3645–3662 cm−1, II 3561–3583 cm−1, III 3515–3527 cm−1, and minor bands, Ia 3623–3631 cm−1, IIa 3593–3607 cm−1. The type of combination of such bands in the spectrum of a specific garnet depends on the type of the rock series of the
host xenolith, Mg, Mg-Ca, Ca, Mg-Fe, or alkremite, on the xenolith type as well as on the chemical composition of the respective
garnet. Nearly all garnets contain band systems I and II. Band system III occurs in Ti-rich garnets, with wt% TiO2 > ca. 0.4, from xenoliths of the Mg-Ca and Mg-Fe series, only. The v
OH spectra do not correspond to those of OH− defects in synthetic pyropes or natural ultra-high pressure garnets from diamondiferous metamorphics. There were no indications
of v
OH from inclusions of other minerals within the selected 60 × 60 μm measuring areas in the garnets. The v
OH spectra of pyrope-knorringite- and pyrope-knorringite-uvarovite-rich garnets included in diamonds do not show band systems
I to III. Instead, they exhibit one weak, broad band (Δv
OH 200–460 cm−1) near 3570 cm−1, a result that was also obtained on pyrope-knorringite-rich garnets extracted from two olivine megacrysts. The quantitative
evaluation, on the basis of relevant existing calibrational data (Bell et al. 1995), of the sum of integral intensities of
all v
OH bonds of the garnets studied yielded a wide range of “water” concentrations within the set of the different garnets, between
values below the detection limit of our single-crystal IR method, near 2 × 10−4 wt%, up to 163 × 10−4 wt%. The “water” contents vary in a complex manner in garnets from different xenolith types, obviously depending on a large
number of constraints, inherent in the crystal chemistry as well as the formation conditions of the garnets during the crystallization
of their mantle host rocks. Secondary alteration effects during uplift of the kimberlite, play, if any, only a minor role.
Despite the very complex pattern of the “water” contents of the garnets, preventing an evaluation of a straightforward correlation
between “water” contents of the garnets and the composition of the mantle's fluid phase during garnet formation, at least
two general conclusions could be drawn: (1) the wide variation of “water” contents in garnets is not indicative of regional
or local differences in the composition of the mantle's fluid phase; (2) garnets formed in the high-pressure/high-temperature
diamond-pyrope facies invariably contain significantly lower amounts of “water” than garnets formed under the conditions of
the graphite-pyrope facies. This latter result (2) may point to significantly lower f
H2O and f
O2 in the former as compared to the latter facies.
Received: 25 November 1997 / Accepted: 9 March 1998 相似文献
99.
Bridget O'Neill Jay D. Bass George R. Rossman Charles A. Geiger Klaus Langer 《Physics and Chemistry of Minerals》1991,17(7):617-621
Brillouin spectroscopy was used to measure the single crystal elastic properties of a pure synthetic pyrope and a natural garnet containing 89.9 mol% of the pyrope end member (Mg3Al2Si3O12). The elastic moduli, c
ij
, of the two samples are entirely consistent and agree with previous estimates of the elastic properties of pyrope based upon the moduli of solid solutions. Our results indicate that the elastic moduli of pyrope end-member are c
11=296.2±0.5, c
12=111.1±0.6, c
44=91.6±0.3, Ks=172.8±0.3, =92.0±0.2, all in units of GPa. These results differ by several percent from those reported previously for synthetic pyrope, but are based upon a much larger data set. Although the hydrous components of the two samples from the present study are substantially different, representing both dry and saturated samples, we find no discernable effect of structurally bound water on the elastic properties. This is due to the small absolute solubility of water in pyrope, as compared with other garnets such as grossular. 相似文献
100.
In order to explore possible quantitative relations between crystal field stabilization energy, CFSE, and partitioning behaviour
of the 3d 6-configured Fe2+ ion, a suite of 29 paragenetic rock-forming minerals from 12 high-grade metamorphic rock samples of the Ukrainian shield,
including the parageneses garnet/orthopyroxene/clinopyroxene (2x), orthopyroxene/clinopyroxene, garnet/clinopyroxene, garnet/orthopyroxene/biotite,
garnet/biotite, garnet/cordierite, garnet/cordierite/biotite, garnet/orthopyroxene/clinopyroxene/Ca-amphibole, Ca-amphibole/biotite
(retrograde), was studied by electron microprobe analysis to obtain the respective K
D
Fe2+
(Ph1/Ph2) values and by polarized single crystal electronic absorption spectroscopy to evaluate the respective CFSEFe2+ values. Other than in the case of Cr3+, a clear quantitative relation between K
D
(Ph1/Ph2) and the ΔCFSE(Ph1/Ph2) was only observed when geometrical factors, mainly the volume of crystallographic sites and ionic radii of ions competing
in the partitioning process, are similar in the respective two paragenetic phases to within 15–20%. In such cases, the ΔCFSEFe2+ contribution to K
D
(Ph1/Ph2) amounts to 0.1 to 0.2 log K
D
per 100 cm−1ΔCFSE. The conclusion is that ΔCFSEFe2+ plays only a secondary role after geometrical factors, in the partitioning behaviour of Fe2+. The reason for this is seen in the facts that, compared to the 3d
3-configured Cr3+ ion, CFSE of the 3d 6-configured Fe2+ amounts only to 20–25%, and that the former ion enters only octahedral sites with similar geometrical properties in the paragenetic
mineral phases.
Received: 17 November 1998 / Accepted: 28 June 1999 相似文献