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91.
Chemical and isotopic (Pb,Sr) zonation in a peraluminous granite pluton: role of fluid fractionation
J.?DostalEmail author A.?K.?Chatterjee D.?J.?Kontak 《Contributions to Mineralogy and Petrology》2004,147(1):74-90
The Davis Lake pluton (DLP, ~800 km2) of southwestern Nova Scotia, Canada, part of the large peraluminous South Mountain batholith of ca. 380 Ma (U/Pb zircon, Ar/Ar mica), consists of granite and subordinate topaz–muscovite leucogranite that hosts greisen tin-base metal mineralization. A new Pb–Pb isochron age for leucogranite from the most evolved part of the DLP indicates a crystallization age of 378±3.6 Ma, coincident with other radiometric ages of the DLP (Rb–Sr, Re–Os, Pb–Pb). The intrusion displays a compositional zonation defined by lead and strontium isotopic ratios, as well as some major elements (e.g., Si, F), incompatible trace elements (e.g., Li, Rb, Ta, U, Sn), and elemental ratios (e.g., K/Rb and Nb/Ta). The greisens and the leucogranites that host them are characterized by extreme radiogenic compositions for Pb and Sr, and their chemical-isotopic trends are extensions of the trends displayed by the less evolved granites. The covariations of the isotopic ratios with several major and trace elements and elemental ratios as well as the Pb–Pb and Rb–Sr isochrones indicate that all phases of the intrusion originated from a homogeneous parental magma. The granitoid magma underwent extensive fractional crystallization of feldspars, minor biotite and accessory minerals (monazite, apatite and zircon) in a compositionally zoned magma chamber that was subsequently accompanied by fluid fractionation, during which time the internally derived fluorine-rich fluids modified the Rb/Sr, U/Pb and Th/Pb ratios, leading to distinct variations of 87Sr/86Sr, 206Pb/204Pb, 238U/204Pb and 232Th/204Pb isotopic ratios. These data therefore document the evolution of a granitic magma through magmatic (i.e., crystal fractionation), orthomagmatic (i.e., crystal-fluid fractionation) and hydrothermal (i.e., fluid fractionation) stages that culminated in the formation of a tin-base metal deposit. The Pb isotope data also constrain the source region for the DLP as being Avalonian basement that, by inference, must underlie much of the Meguma Terrane.Editorial responsibility: T.L. Grove 相似文献
92.
Niranjan D. Chatterjee 《Contributions to Mineralogy and Petrology》1970,27(3):244-257
The mineral paragonite, NaAl2[AlSi3O10 (OH)]2, has been synthesized on its own composition starting from a variety of different materials. Indexed powder data and refined cell parameters are given for both the 1M and 2M1 polymorphs obtained. The upper stability limit of paragonite is marked by its breakdown to albite + corundum + vapour. The univariant equilibria pertaining to this reaction have been established by reversing the reaction at six different pressures, the equilibrium curve running through the following
intervals: 1 kb: 530°–550° C 2 kb: 555°–575° C 3 kb: 580°–600° C 5kb: 625°–640° C 6 kb: 620°–650° C 7 kb: 650°–670° C.Comparison with the upper stability limit of muscovite (Velde, 1966) shows that paragonite has a notably lower thermal stability thus explaining the field observation that paragonite is absent in many higher grade metamorphic rocks in which muscovite is still stable.The enthalpy and entropy of the paragonite breakdown reaction have been estimated. Since intermediate albites of varying structural states are in equilibrium with paragonite, corundum and H2O along the univariant equilibrium curve, two sets of data pertaining to the entropy of paragonite (S
298
0
) as well as the enthalpy ( H
f,298
0
) and Gibbs free energy ( G
f,298
0
) of its formation were computed, assuming (1) high albite and (2) low albite as the equilibrium phase. The values are: (1) (2) S
298
0
67.8±3.9 cal deg–1 gfw–1 63.7±3.9 cal deg–1 gfw–1
H
f,298
0
–1417.9±2.7 kcal gfw–1 –1420.2±2.6 kcal gfw–1
G
f,298
0
–1327.4±4.0 kcal gfw–1 –1328.5±4.0 kcal gfw–1.Adapted from a part of the author's Habilitationsschrift accepted by the Ruhr University, Bochum (Chatterjee, 1968). 相似文献
93.
D. Chatterjee 《Pure and Applied Geophysics》1970,82(1):34-40
Summary The expressions for stresses and extension have been obtained in an isotropic circular cylinder in a state of plane strain, the elastic constants and the density of the material varying exponentially and the results have been compared with those in the homogeneous case. 相似文献
94.
Dr. Niranjan D. Chatterjee 《International Journal of Earth Sciences》1964,53(2):536-550
Tectonic analysis within the Mesozoic sequence of the Pennine belt in the vicinity of the northern Dora-Maira massif resulted in the discovery of three different B-axes of Alpine age:
- 1.The oldest one with NNW-trending axes is found to have been developed exclusively to the south and west of the Ambin massif, followed by 相似文献
95.
96.
Locally recorded data for eighteen aftershocks of a magnitude(mb) 4.6 earthquake occurring near Ukhimath in the Garhwal Himalaya were analysed. A master event technique was adopted to locate
seventeen individual aftershock hypocentres relative to the hypocentre of the eighteenth aftershock chosen as the master event.
The aftershock epicentres define an approximately 30 km2 rupture zone commensurate with the magnitude of the earthquake. The distribution of epicentres within this zone and the limited
amount of first motion data support the view that a group of parallel, sub-vertical, sinistral strike-slip faults oriented
N46°, transverse to the regional NW-SE trend of the Garhwal Himalaya, was involved in this seismic episode. Since the estimated
focal depth range for aftershocks of this sequence is 3–14 km, we infer that this transverse fault zone extends through the
upper crustal layer to a depth of 14 km at least. 相似文献
97.
In this paper, we have attempted a diagnostic study of the turbulence characteristics of the ABL by means of two one-dimensional models. The first model uses a first order non-local closure, based on the Transilient Turbulence Theory, for parameterizing turbulent fluxes. while the second model uses second order local closure for parameterizing these. The models have been applied to conduct case studies using the Kytoon data taken at Kharagpur, during 17th–21st June, 1990, as part of the MONTBLEX programme. Our findings bring out various interesting features regarding the non-local and local turbulent statistics such as kinematic fluxes, turbulence kinetic energy, vertical velocity variance, the contribution of the eddies of various sizes to the fluxes at different level and the mixing lengths. The one-dimensional anisotropy of the turbulent eddies has been revealed by the findings from the transilient model. The vertical variation of the turbulence kinetic energy, as computed directly by the second order model, is found to be strongly correlated with the vertical velocity variance. In particular, for stably stratified boundary layers, identification of two distinct zones of the turbulence kinetic energy and corresponding vertical velocity maxima is possible, which has been interpreted as positive evidence of patchy turbulence in the boundary layer. 相似文献
98.
B. H. Subbaraya K. S. Appu K. P. Chatterjee A. F. Chizhov V. D. Grinchinkov A. Jayaraman G. A. Khokin V. A. Kononkov I. S. Moshnikov V. Narayanan S. P. Perov O. V. Shtrikov Y. V. Somayajulu C. R. Sreedharan K. S. Zalpuri 《Journal of Earth System Science》1987,96(1):25-40
A total of seventeen vertical profiles of ozone were obtained during an Indo-USSR collaborative experiment on ozonesonde intercomparison conducted at Thumba during March 1983. The vertical distribution of ozone was measured using rocket-borne, balloon-borne as well as ground-based instruments. Four different rocket ozonesondes from India and USSR and the balloon ozonesonde were used to makein situ observations of ozone concentrations in addition to the Dobson spectrophotometric observations of total ozone and Umkehr. The rocket and the balloon launchings were effected in three salvos and measurements were made at different times of the day as well as during night. The results of all these measurements are used to obtain a mean ozone vertical distribution over Thumba foT the spring equinoxial period. The mean profile shows the maximum ozone concentration at 27 km with a value of (3.86±0-52)×1012 molecules per cc. Comparison of this mean profile with available satellite data for the equatorial regions shows that, in general, the Thumba values are lower by 10–15% at altitudes below 40 km and larger at altitudes above 50 km compared to the satellite results. The data also show evidence for a day-to-day variability and a possible day-to-night variability in the ozone vertical distribution with the night-time values higher than the daytime values at all altitudes above 35 km and the difference is found to increase with the increasing altitude. 相似文献
99.
GeoJournal - Application of geospatial technologies in criminological study is most relevant in present day context. Crime mapping with the help of Geographical Information System is being a very... 相似文献
100.
Accurate knowledge of pore pressure is fundamental to any safe and economic well construction. Here, we present results that
are indicative of over pressure zones (OPZ) for five wells drilled under the Krishna–Godavari offshore basin (KGOB) at the
Eastern Continental Margin of India (ECMI). OPZ in areas of crustal flexuring can act as potential geohazard while drilling.
These wells locate at water depths of 515–1,265 m, where their penetrated-vertical-depth reaches up to 3,960 m in clastic
sediments. pore pressure gradient (PPG) and fracture pressure gradient (FPG) are estimated from acoustic log for all five
wells, while the Normal Compaction Trend (NCT) and pore pressure are calculated from Miller’s sonic equation. Top of OPZ is
indicated by values that are higher than the NCT; departure from NCT is observed at depth intervals of 1,320–2,180 m, 1,700–3,960 m,
1,600–1,880 m, 1,420–2,609 m and 2,080–2,200 m for the respective Wells 1 through 5. The pressure data from Modular Dynamic
Tester (MDT) agree well with the pore pressure values obtained from the logs. The Overburden Gradient (OBG), PPG and FPG values
increase rather slowly with total depth in deeper-water of KGOB when compared to the wells located in shallow water depth.
Consequently, the operating safety margin between PPG and FPG decreases as the water depth increases, and this clearly leads
to an increase in the number of casing strings to reach the target depth. Certain basic conclusions on the potentiality of
natural hazard for drilling operations are drawn on the basis of these results, but evidently, further studies are warranted
to present a more composite picture of OPZ under KGOB. 相似文献