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81.
82.
M. Gordon Wolman 《地球表面变化过程与地形》1995,20(7):585-591
The natural habitat of geomorphologists is at play in the fields of the Lord. Picnics, not the work ethic, often motivate the most productive. As in the field, so too in the mind, creative insights derive from the play of ideas. As in much of science today, Earth scientists are called upon to ‘solve’ immediate problems, but problems whose solutions lie at the cutting edge of the research frontier. The impact of anthropogenic activities in the context of natural processes, the playground where many geomorphologists work, requires continuous reciprocal exchange between research and application. Apologies are not needed for choices of orientation, but only for destructive separation. 相似文献
83.
84.
Behavior and effects of phosphorus in the system Na2O−K2O−Al2O3−SiO2−P2O5−H2O at 200 MPa(H2O) 总被引:1,自引:1,他引:1
David London George B. Morgan VI Harold A. Babb Jennifer L. Loomis 《Contributions to Mineralogy and Petrology》1993,113(4):450-465
The addition of phosphorus to H2O-saturated and initially subaluminous haplogranitic (Qz–Ab–Or) compositions at 200 MPa(H2O) promotes expansion of the liquidus field of quartz, a marked decrease of the solidus temperature, increased solubility limits of H2O in melt at low phosphorus concentrations, and fractionation of melt out of the haplogranite plane (projected along an Or28 isopleth) toward a peralkaline, silica-poor but quartz-saturated minimum composition. The partition coefficient for P2O5 between aqueous vapor and melt with an ASI (aluminum saturation index, mol Al/[mol Na+K])=1 is negligible (0.06), and consequently so are the effects of phosphorus on other melt-vapor relations involving major components. Phosphorus becomes more soluble in vapor, however, as the concentration of a NaPO3 component increases via the fractionation of melt by crystallization of quartz and feldspar. The experimental results here corroborate existing concepts regarding the interaction of phosphorus with alkali aluminosilicate melt: phosphorus has an affinity for alkalis and Al, but not Si. Phosphorus is incorporated into alkali feldspars by the exchange component AlPSi-2. For subaluminous compositions (ASI=1), the distribution coefficient of phosphorus between alkali feldspar and melt, D[P]Af/m, is 0.3. This value increases to D[P]Af/m=1.0 at a melt ASI value of 1.3. The increase in D[P]Af/m with ASI is expected from the fact that excess Al promotes the AlPSi-2 exchange. With this experimental data, the P2O5 content of feldspars and whole rocks can reveal important facets of crystallization and phosphorus geochemistry in subaluminous to peraluminous granitic systems. 相似文献
85.
Albert Eggers Jeffery Krausse Harold Rush James Ward 《Journal of Volcanology and Geothermal Research》1976,1(3):229-236
Gravity changes of up to 1.2 ± 0.1 mgal (1 standard deviation) were measured at three points within 400 m of an active vent on Pacaya volcano, Guatemala during eleven days of January, 1975. For five continuous days gravity varied inversely with the average muzzle velocity of ejecta, the frequency of volcanic explosions, and the frequency of volcanic earthquakes. The gravity changes are most reasonably interpreted as the product of intravolcanic movements of magma with masses one to two orders of magnitude larger than any flow ever erupted from the volcano. However, elevation changes and/or combination of elevation and mass distribution changes could also have been an important factor in effecting the observed gravity variations. Because we lack elevation control on the gravity stations, we are unable to unequivocally conclude which factor or which combination of factors produced the gravity changes. The study indicates the possibility of gravity monitoring of hazardous volcanoes as a predictive tool, and as an added means for investigating the internal mechanism of volcanic eruptions. 相似文献
86.
Michael A. Feierberg Larry A. Lebofsky Harold P. Larson 《Geochimica et cosmochimica acta》1981,45(6):971-981
High-resolution IR spectra (0.9–2.5 μm) and narrowband photometry (3.0–3.5 μm) are presented for asteroids 1 Ceres, 2 Pallas and 324 Bamberga. Laboratory experiments with hydrated minerals indicate that the 3 μm absorption feature observed on asteroids is largely due to interlayer water molecules in clay minerals, with a possible contribution from water molecules bound to salts. The depth of the 3 μm band as a function of 2.2 μm albedo is a useful measure of the amount of hydrated mineral present on these asteroids. 1 Ceres must consist mostly of a clay mineral like that in CM chondrites, with some contribution to the strength of the 3 μm band by hydrated salts. These salts, which are products of aqueous alteration, may also be responsible for Ceres' high albedo relative to other C-type asteroids. 2 Pallas must have a low abundance of hydrated minerals relative to 1 Ceres, with the bulk of its composition being spectrally featureless minerals such as the iron-free silicates in CM chondrules. 324 Bamberga probably contains clay minerals, but their abundance cannot be determined at present. The spectrum of Bamberga below 2.5 μm shows evidence for abundant magnetite, which can be a product of aqueous alteration. The presence of magnetite on Bamberga and possibly other C-type asteroids may be responsible for their low albedos. The spectra of C-type asteroids may be reconcilable with those of carbonaceous chondrites if the asteroids surfaces have undergone alteration by aqueous or other analogous processes. 相似文献
87.
Michael A. Feierberg Harold P. Larson Uwe Fink Howard A. Smith 《Geochimica et cosmochimica acta》1980,44(3):513-524
A Fourier spectrometer was used to obtain IR spectra of asteroids 349 Dembowska and 4 Vesta (0.8–2.5μm; 25cm ?1 resolution). The spectrum of Dembowska shows olivine and pyroxene (Fs24 ± 8) with an olivine/pyroxene abundance ratio greater than 2, and possibly as high as 10. This is probably an unsampled achondritic composition, similar to the unique achondrite ALHA 77005. Similar olivine-rich compositions have also been proposed for the mantles of basaltic achondrite parent bodies. Dembowska's mineralogy therefore appears related in some way to the achondrites. but a direct link cannot as yet be made. Our IR observations of Vesta have more complete spectral coverage than those first obtained by Larson and Fink (1975b). Pyroxene (Fs50 ± 5) and plagioclase feldspar are both seen, with a pyroxene/feldspar abundance ratio between 1.5 and 2.0. Vesta's mineralogy is consistent with a mixture of eucrites and howardites on its surface. Time-resolved observations over one-half of the rotation period show no spectral variations at the 2% level, indicating compositional homogeneity. Both 349 Dembowska and 4 Vesta can be considered as candidates for the parent bodies of igneous meteorites. 相似文献
88.
Douglas G. Brookins Joseph K. Register Harold W. Krueger 《Geochimica et cosmochimica acta》1980,44(5):635-637
Polyhalite, K2Ca2Mg (SO4)4-2H2O, is an important mineral in many evaporites. Although its use for K-Ar dating has never been investigated, our results indicate that it is a very useful mineral for dating events ranging from the time of potash mineralization to any younger events which may have affected the evaporite. Five K-Ar dates on pure polyhalite, including two from included material and from beds distorted by the formation of a rubble chimney, yield dates between 198 and 216 Myp, in good agreement with Rb-Sr dates and the diagenetic age of the potash deposits from the same rocks. Two polyhalites mixed with sylvite gave lower dates (154 and 174 Myr) which is to be expected because of radiogenic 40Ar loss from the sylvite phase. One polyhalite, formed after the intrusion of a 31 Myr lamprophyre dike, yielded 21 Myr. Collectively our results indicate that pure polyhalite is satisfactory for K-Ar dating and may provide critical age information in studies of the geologic history of the evaporite sequences. 相似文献
89.
90.
Harold C. Walker 《Pure and Applied Geophysics》1970,81(1):313-322
Summary For the past several years observational studies of the northern hemisphere kinetic energy balance and related subjects have been performed by the Planetary Circulation Project of the Massachusetts Institute of Technology. Numerous integrals required were recently evaluated directly from a five-year period of observations using a network of nearly 800 stations. The stations, however, are concentrated primarily over temperate latitude continents, and the data from maritime and tropical areas were comparatively sparse. The question then arises whether the results are representative. The problem discussed in this paper is to select a subset of more uniformly spaced stations and to recompute the zonal kinetic energy balance. This is accomplished and the results are presented herewith.The research reported in this paper was sponsored by the U.S. National Science Foundation under Grant No. GA-1310X. 相似文献