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31.
Sadhana M Chatterjee Manideepa Roy Choudhury Subhrajyoti Das 《Journal of Earth System Science》2016,125(7):1321-1328
Fluid infiltration at great depth during regional metamorphism plays a major role in mass transport and is responsible for significant rheological changes in the rock. Calc-silicate rocks of the Kajalbas area of Delhi Fold Belt, Rajasthan, are characterised by foliation parallel alternate bands of amphibole-rich and clinopyroxene–plagioclase feldspar-rich layers of varying thicknesses (mm to decimetre thick). Textural relation suggests that the amphibole grains formed from clinopyroxene and plagioclase in the late phase of regional deformation. Algebraic analysis of the reaction textures and mineral compositions was performed with the computer program C-Space to obtain the balanced chemical reactions that led to the formation of amphibole-rich bands. The computed balanced reaction is 70.74 Clinopyroxene + 27.23 Plagioclase + 22.018 H2O + 5.51 K++ 1.00 Mg2++ 27.15 Fe2+ = 22.02 Amphibole + 67.86 SiO2 aqueous + 36.42 Ca2++ 8.98 Na+. The constructed reaction suggests that aqueous fluid permeated the calc-silicate rock along mm to decimetre thick channels, metasomatized the clinopyroxene–plagioclase bearing rocks to form the amphibole-rich layers. The regional deformation presumably created the fluid channels thereby allowing the metasomatic fluid to enter the rock system. The above reaction has large negative volume change for solid phases indicating reaction-induced permeability. Thermodynamic calculations suggest that the fluid–rock interaction occurred at 665 ±05°C and 6.6 ±0.25 kbar (corresponding to ~20 km depth). Textural modeling integrating the textural features and balanced chemical reaction of the calc-silicate rocks of Mesoproterozoic Phulad Shear Zone thus indicate that extremely channelled fluid flow was reaction enhanced and caused major change in the rock rheology. 相似文献
32.
Tonkeswar Das Ananya Saikia Banashree Mahanta Rahul Choudhury Binoy K Saikia 《Journal of Earth System Science》2016,125(7):1365-1377
Coal gasification with CO2 has emerged as a cleaner and more efficient way for the production of energy, and it offers the advantages of CO2 mitigation policies through simultaneous CO2 sequestration. In the present investigation, a feasibility study on the gasification of three low-quality, high-sulphur coals from the north-eastern region (NER) of India in a CO2 atmosphere using thermogravimetric analysis (TGA-DTA) has been made in order to have a better understanding of the physical and chemical characteristics in the process of gasification of coal. Model-free kinetics was applied to determine the activation energies (E) and pre-exponential factors (A) of the CO2 gasification process of the coals. Multivariate non-linear regression analyses were performed to find out the formal mechanisms, kinetic model, and the corresponding kinetic triplets. The results revealed that coal gasification with CO2 mainly occurs in the temperature range of 800°–1400°C and a maximum of at around 1100°C. The reaction mechanisms responsible for CO2 gasification of the coals were observed to be of the ‘nth order with autocatalysis (CnB)’ and ‘nth order (Fn) mechanism’. The activation energy of the CO2 gasification was found to be in the range 129.07–146.81 kJ mol?1. 相似文献
33.
R. Nagendra Satish J. Patel Rakesh Deepankar A. N. Reddy 《Journal of the Geological Society of India》2010,76(5):525-532
Well preserved ichnofossils were found in Kulakkalnattam sandstone exposed at Kulakkalnattam stream in Ariyalur area, Cauvery Basin. It consists of infaunal structures of both suspension and deposit feeders. Five ichnofossils are present in a fine to coarse grain sandstone which includes Ophiomorpha, Palaeophycus, Planolites Skolithos, and Thalassinoides. The study infers that ichnofossils Skolithos and Ophiomorpha are infaunal colonization of the suspension feeders in high energy condition in shifting substrate, whereas Thalassinoides and Planolites-Palaeophycus ichnofossils indicate infaunal deposit feeders living at the sediment-sediment interface in low to moderate energy conditions. Furthermore, the abundance and diversity of the trace fossils indicates there was alternatively fluctuations in energy conditions which lead to development of Skolithos and Cruziana ichnofacies type condition during the deposition of Kulkkallanattam sandstone in foreshore-shoreface environments. 相似文献
34.
A method of analysis for the uplift capacity of pile anchors in cohesionless soil is proposed using Kötter’s equation that facilitates computation of the distribution of soil reaction on the axis-symmetric failure surface, which is assumed to be the frustum of a cone with a characteristic angle of inclination with the pile–soil interface. A closed-form solution for the uplift capacity is obtained with no requirement of any charts or tables. Empirical relations using available literature are proposed for expressing critical embedment ratio and computation of net uplift capacity. The results are compared with a set of experimental data for 28 cases, ranging from loose to dense cohesionless soil up to maximum embedment ratio of 40, vis-à-vis available theoretical solutions. The proposed method leads to the predictions that are in good agreement with the experimental results. It further demonstrates the successful application of Kötter’s equation in the estimation of uplift capacity of pile anchors. 相似文献
35.
We show evidence that interannual variations in the net radiation balance at the top-of-atmosphere over North Africa may be linked to variations at the land surface within the Sahelian zone. By utilizing concurrent monthly time series of earth radiation budget and passive microwave measurements obtained from the Nimbus 7 satellite over a five year period from 1979 to 1983, we have examined the spatial distribution of the amplitude of interannual variability of the net radiation at the top of the atmosphere. A strong association is found between the radiation budget anomalies derived from ERB-WFOV measurements and the anomalies of 37 GHz polarized brightness temperature difference derived from SMMR measurements. Previous research has shown that the interannual anomalies in the top-of-atmosphere net radiation balance in the Sahelian zone mostly arise from changes taking place at the surface, not from variations in cloudiness which brings variable rainfall throughout the African Sahel. Since microwave polarization difference is related in part to vegetation cover, we suggest that the main control of the modulation of North Africa's radiation balance may be year to year fluctuations of vegetation cover within the Sahelian zone, likely stemming from fluctuations in the rainfall. This relationship is relevant to the problem of radiation control and feedback on global climate through processes taking place within the biosphere of a semi-arid zone. 相似文献
36.
Deepankar Choudhury Sanjay S. Nimbalkar 《Geotechnical and Geological Engineering》2006,24(5):1103-1113
Knowledge of seismic active earth pressure behind rigid retaining wall is very important in the design of retaining wall in
earthquake prone region. Commonly used Mononobe-Okabe method considers pseudo-static approach, which gives the linear distribution
of seismic earth pressure in an approximate way. In this paper, the pseudo-dynamic method is used to compute the distribution
of seismic active earth pressure on a rigid retaining wall supporting cohesionless backfill in more realistic manner by considering
time and phase difference within the backfill. Planar rupture surface is considered in the analysis. Effects of a wide range
of parameters like wall friction angle, soil friction angle, shear wave velocity, primary wave velocity and horizontal and
vertical seismic accelerations on seismic active earth pressure have been studied. Results are provided in tabular and graphical
non-dimensional form with a comparison to pseudo-static method to highlight the realistic non-linearity of seismic active
earth pressures distribution. 相似文献
37.
K. R. Rao S. L. Chaplot Narayani Choudhury Subrata Ghose J. M. Hastings L. M. Corliss D. L. Price 《Physics and Chemistry of Minerals》1988,16(1):83-97
Magnesium-rich olivine (Mg0.9Fe0.1)2SiO4 is considered to be a major constituent of the Earth's upper mantle. Because of its major geophysical importance, the temperature and pressure dependence of its crystal structure, elastic and dielectric constants, long-wavelength phonon modes and specific heat have been measured using a variety of experimental techniques. Theoretical study of lattice dynamics provides a means of analyzing and understanding a host of such experimental data in a unified manner. A detailed study of the lattice dynamics of forsterite, Mg2SiO4, has been made using a crystal potential function consisting of Coulombic and short-range terms. Quasiharmonic lattice dynamical calculations based on a rigid molecular-ion model have provided theoretical estimates of elastic constants, long-wavelength modes, phonon dispersion relation for external modes along the three high symmetry directions in the Brillouin zone, total and partial density of states and inelastic neutron scattering cross-sections. The neutron cross-sections were used as guides for the coherent inelastic neutron scattering experiment on a large single crystal using a triple axis spectrometer in the constant Q mode. The observed and predicted phonon dispersion relation show excellent agreement. The inelastically scattered neutron spectra from a powder sample have been analyzed on the basis of a phonon density of states calculated from a rigid-ion model, which includes both external and internal modes. The experimental data from a powder sample show good agreement with the calculated spectra, which include a multiphonon contribution in the incoherent approximation. The computed phonon densities of states are used to calculate the specific heat as a function of temperature using both the rigid molecular-ion and rigid ion models. These results are in very good agreement with the calorimetric measurement of the specific heat. The interatomic potential developed here can be used with some confidence to study physical properties of forsterite as a function of pressure and temperature. 相似文献
38.
In the hilly region due to scarcity of the plain area, buildings like set back-step back are more often used and also as a big surge in the telecommunication industries, rooftop tower adaptation is very common story nowadays. In the present study an analogy has been drawn to find out the influence of the rooftop telecommunication tower on the setback-step back building resting on ground at 20° and 30° slopes. A dynamic analysis has been performed and compared on the 4 legged angled section telecommunication tower which is located on the roof top of set back-step back building by varying positions of tower with the existing host structure built up on ground slope of 20° and 30° in both directions(X and Y). 相似文献
39.
Anil Sood B. U. Choudhury S. S. Ray S. K. Jalota P. K. Sharma Shushma Panigrahy 《Journal of the Indian Society of Remote Sensing》2009,37(3):483-491
A remote sensing-based approach was applied to study the impact of changes in cropping system on the exploitation of water
resources in two districts namely Ludhiana in central Punjab and Muktsar in South-Western Punjab. Rice-wheat remained dominant
rotation in Ludhiana while cottonwheat rotation was replaced partially by rice-wheat in Muktsar within a span of over five
years (1998–99 to 2003–04). The solo rice-wheat system in Ludhiana district has resulted in large-scale ground water exploitation
as is evident from the faster decline in water table (up to 0.9m year−1) and higher tube-wells density (440 per 1000 ha). As a result, nearly 60 per cent of the total area of Ludhiana district
has the water table depth greater than 10m and in some blocks, it has reached to a depth of 22 m. In Muktsar district, corresponding
rise in water table is 0.2m per year and tube well density is 114 per 1000 ha. Irrigation water associated with paddy cultivation
in Ludhiana and adjoining areas moves laterally through the buried paleo-channels of Sutlaj in the deeper soil profile and
gets accumulated in the basin lands of Muktsar and adjoining areas and causes an extra water flux and subsequent rise in water
table, recorded at 3 to 7m depth. To minimize the hydrological imbalance of the state, it is suggested to diversify some of
the area in the central districts from irrigation water intensive rice-wheat system to less water intensive cropping system. 相似文献
40.