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131.
Sampa Hazra Pritam Saha Jyotisankar Ray Avijit Podder 《Journal of the Geological Society of India》2010,75(5):760-768
The porphyritic granite body (∼ 600 Ma) around Mylliem (25°32′N: 91°52′E), east Khasi hills district, Meghalaya occurs as
a distinct intrusive body into the host rock of low- grade meta-sediments belonging to Proterozoic Shillong Group. The porphyritic
granite body manifests prominent lath- shaped feldspar phenocrysts giving rise to dominant porphyritic texture. Further, this
porphyritic granite body is characterized by primary foliation (defined by parallely arranged feldspar laths), tongues and
appophyses and xenoliths of older metamorphics. Petrographically, the Mylliem porphyritic granite is grey leucocratic, coarse
grained, phanerocrystalline with modal variants ranging from granite to granodiorite tending to tonalite. Simple statistical
studies based on correlation coefficient values involving modal variables of the Mylliem porphyritic granite bodies appear
significant in majority of the cases indicating magmatic crystallization. Use of relevant thermometric method indicates temperature
of equilibration of the body in the range of 369°C to 507°C. The crystallization of the Mylliem porphyritic granite pluton
initiated at an average lithostatic pressure in the tune of ∼11 Kb followed by dominant PH2O controlled milieu. Spatially projected mineralogical parameters suggest a general trend of the magmatic cooling of the body
from margin inward with sudden influx of volatile matters that occasionally offsets mineralogical trends. 相似文献
132.
Dilip Saha S. Chakraborti V. Tripathy 《Journal of the Geological Society of India》2010,75(1):323-337
Recent works suggest Proterozoic plate convergence along the southeastern margin of India which led to amalgamation of the
high grade Eastern Ghats belt (EGB) and adjoining fold-and-thrust belts to the East Dhrawar craton. Two major thrusts namely
the Vellikonda thrust at the western margin of the Nellore Schist belt (NSB) and the Maidukuru thrust at the western margin
of the Nallamalai fold belt (NFB) accommodate significant upper crustal shortening, which is indicated by juxtaposition of
geological terranes with distinct tectonostratigraphy, varying deformation intensity, structural styles and metamorphic grade.
Kinematic analysis of structures and fabric of the fault zone rocks in these intracontinental thrust zones and the hanging
wall and footwall rocks suggest spatially heterogeneous partitioning of strain into various combinations of E-W shortening,
top-to-west shear on stratum parallel subhorizontal detachments or on easterly dipping thrusts, and a strike slip component.
Although relatively less prominent than the other two components of the strain triangle, non-orthogonal slickenfibres associated with flexural slip folds and mylonitic foliation-stretching lineation orientation
geometry within the arcuate NSB and NFB indicate left lateral strike slip subparallel to the overall N-S trend. On the whole
an inclined transpression is inferred to have controlled the spatially heterogeneous development of thrust related fabric
in the terrane between the Eastern Ghats belt south of the Godavari graben and the East Dharwar craton. 相似文献
133.
134.
Tarun Souradeep Sanjit Mitra Anand Sengupta Subharthi Ray Rajib Saha 《New Astronomy Reviews》2006,50(11-12):1030
In the era of high precision CMB measurements, systematic effects are beginning to limit the ability to extract subtler cosmological information. The non-circularity of the experimental beam has become progressively important as CMB experiments strive to attain higher angular resolution and sensitivity. The effect of non-circular beam on the power spectrum is important at multipoles larger than the beam-width. For recent experiments with high angular resolution, optimal methods of power spectrum estimation are computationally prohibitive and sub-optimal approaches, such as the Pseudo-Cl method are used. We provide an analytic framework for correcting the power spectrum for the effect of beam non-circularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. We advocate that when the non-circular beams are important, it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transforms die down fast with m. 相似文献
135.
C. Manikyamba Sohini Ganguly M. Santosh M. Rajanikanta Singh Abhishek Saha 《Geological Journal》2015,50(5):651-669
The Neoarchaean Jonnagiri greenstone terrane (JGT) is located at the centre of the arcuate Hutti–Jonnagiri–Kadiri–Kolar composite greenstone belt in the eastern Dharwar Craton. High MgO (MgO = ~14 wt.%; Nb = 0.2 ppm), low Nb (LNB) (MgO = 7.8–12 wt.%; Nb = 0.1–5.1 ppm) and high Nb basalts (HNB) (MgO = 5.6–10.1 wt.%; Nb = 9.0–10.6 ppm) metamorphosed to lower amphibolite facies are identified based on their geochemical compositions. These metabasalts exhibit depleted HFSE (Nb–Ta, Zr–Hf), pronounced LREE and LILE enrichments suggesting contribution from subduction‐related components during their genesis. Th and U enrichment over Nb–Ta indicates influx of fluids dehydrated from subducted oceanic lithosphere. The high MgO basalts with higher Mg# (51) than that of the associated LNB and HNB (Mg# = 34–47) represent early fractionated melts of subduction‐modified mantle peridotite. The LNB were produced by partial melting of mantle wedge metasomatized by slab‐dehydrated fluids, whereas the HNB represents melts of subducted oceanic crust and hybridized mantle wedge. Lower Dy/Yb and variable La/Yb ratios suggest their generation at shallower depth within spinel peridotite stability field. The low Ce–Yb trend of these metabasalts reflects intraoceanic type subduction which straddles the fields of arc and back‐arc basin basalts, resembling the Mariana‐type arc basalts. The Jonnagiri metabasalts were derived in a paired arc‐back‐arc setting marked by nascent back‐arc rift system that developed in the proximity of an intraoceanic arc. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
136.
Dr. Bijan Saha PhD 《Astrophysics and Space Science》2006,302(1-4):83-91
We consider a self-consistent system of Bianchi type-I (BI) gravitational field and a binary mixture of perfect fluid and
dark energy given by a cosmological constant. The perfect fluid is chosen to be the one obeying either the usual equation
of state, i.e., p = ζ, with ζ ∊ [0, 1] or a van der Waals equation of state. Role of the Λ term in the evolution of the BI Universe has been
studied. 相似文献
137.
N. R. Patel V. K. Dadhwal S. K. Saha 《Journal of the Indian Society of Remote Sensing》2011,39(3):383-391
The present study investigates the characteristics of CO2 exchange (photosynthesis and respiration) over agricultural site dominated by wheat crop and their relationship with ecosystem
parameters derived from MODIS. Eddy covariance measurement of CO2 and H2O exchanges was carried out at 10 Hz interval and fluxes of CO2 were computed at half-hourly time steps. The net ecosystem exchange (NEE) was partitioned into gross primary productivity
(GPP) and ecosystem respiration (R
e) by taking difference between day-time NEE and respiration. Time-series of daily reflectance and surface temperature products
at varying resolution (250–1000 m) were used to derive ecosystem variables (EVI, NDVI, LST). Diurnal pattern in Net ecosystem
exchange reveals negative NEE during day-time representing CO2 uptake and positive during night as release of CO2. The amplitude of the diurnal variation in NEE increased as LAI crop growth advances and reached its peak around the anthesis
stage. The mid-day uptake during this stage was around 1.15 mg CO2 m−2 s−1 and night-time release was around 0.15 mg CO2 m−2 s−1. Linear and non-linear least square regression procedures were employed to develop phenomenological models and empirical
fits between flux tower based GPP and NEE with satellite derived variables and environmental parameters. Enhanced vegetation
index was found significantly related to both GPP and NEE. However, NDVI showed little less significant relationship with
both GPP and NEE. Furthemore, temperature-greenness (TG) model combining scaled EVI and LST was parameterized to estimate
daily GPP over dominantly wheat crop site. (R
2 = 0.77). Multi-variate analysis shows that inclusion of LST or air temperature with EVI marginally improves variance explained
in daily NEE and GPP. 相似文献
138.
Tapan K. Saha Nikhil C. Bhoumik Subarna Karmaker Mahmooda G. Ahmed Hideki Ichikawa Yoshinobu Fukumori 《洁净——土壤、空气、水》2011,39(10):984-993
Adsorption of reactive black 5 (RB5) from aqueous solution onto chitosan was investigated in a batch system. The effects of solution pH, initial dye concentration, and temperature were studied. Adsorption data obtained from different batch experiments were modeled using both pseudo first‐ and second‐order kinetic equations. The equilibrium adsorption data were fitted to the Freundlich, Tempkin, and Langmuir isotherms over a dye concentration range of 45–100 µmol/L. The best results were achieved with the pseudo second‐order kinetic and Langmuir isotherm equilibrium models, respectively. The equilibrium adsorption capacity (qe) was increased with increasing the initial dye concentration and solution temperature, and decreasing solution pH. The chitosan flakes for the adsorption of the dye was regenerated efficiently through the alkaline solution and was then reused for dye removal. The activation energy (Ea) of sorption kinetics was estimated to be 13.88 kJ/mol. Thermodynamic parameters such as changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) were evaluated by applying the van't Hoff equation. The thermodynamics of reactive dye adsorption by chitosan indicates its spontaneous and endothermic nature. 相似文献
139.
Sourav Saha Anupam Ghosh Santanu Banerjee Pratul K. Saraswati Stuart D. Burley 《Journal of the Geological Society of India》2011,77(5):409-418
This study highlights lithofacies and biofacies characteristics of the open coast tidal flat near Daman on the eastern flank
of Gulf of Khambhat. Sedimentological and biological observation record six facies within the tidal flat area including older
beach, beach face, sand flat, mud flat/mixed flat, sand bar and beach rock. Distinct sedimentary structures, foraminiferal
assemblage and bioturbation intensity characterize each facies. A wide variety of wave and current generated sedimentary features
characterize the sand flat facies. Semiconsolidated sands of older beach running parallel the coastline at a level higher
than the present beach face possibly records the latest sea level highstand. The beach rock reflects early cementation of
sands in tropical environments. Foraminifera are widely distributed in sand flats, mixed flats and mud flats and grouped into
two biofacies — Ammonia-Elphidium-Quinqueloculina biofacies (sand flat and mixed flat) and Trochammina-Miliammina biofacies (mud flats). The beach face and sand bar facies contain forminifera reworked from sand flat and mud/mixed flat.
Seasonal variation in depositional style is marked by deposition of fresh mud deposited over large areas of the intertidal
flat during monsoon time, most of which is washed away by waves and current actions well before the onset of the next monsoon. 相似文献
140.
O. P. Mishra D. Zhao Chandan Ghosh Z. Wang O. P. Singh Biman Ghosh K. K. Mukherjee D. K. Saha G. K. Chakrabortty S. G. Gaonkar 《Natural Hazards》2011,57(1):51-64
The Andaman–Nicobar (A–N) Islands region has attracted many geo-scientists because of its unique location and complex geotectonic
settings. The recent occurrence of tsunamis due to the megathrust tsunamigenic north Sumatra earthquake (Mw 9.3) with a series
of aftershocks in the A–N region caused severe damage to the coastal regions of India and Indonesia. Several pieces of evidence
suggest that the occurrence of earthquakes in the A–N region is related to its complex geodynamical processes. In this study,
it has been inferred that deep-seated structural heterogeneities related to dehydration of the subducting Indian plate beneath
the Island could have induced the process of brittle failure through crustal weakening to contribute immensely to the coastal
hazard in the region. The present study based on 3-D P-wave tomography of the entire rupture zone of the A–N region using
the aftershocks of the 2004 Sumatra–Andaman earthquake (Mw 9.3) clearly demonstrates the role of crustal heterogeneity in
seismogenesis and in causing the strong shakings and tsunamis. The nature and extent of the imaged crustal heterogeneity beneath
the A–N region may have facilitated the degree of damage and extent of coastal hazards in the region. The 3-D velocity heterogeneities
reflect asperities that manifest what type of seismogenic layers exist beneath the region to dictate the size of earthquakes
and thereby they help to assess the extent of earthquake vulnerability in the coastal regions. The inference of this study
may be used as one of the potential inputs for assessment of seismic vulnerability to the region, which may be considered
for evolving earthquake hazard mitigation model for the coastal areas of the Andaman–Nicobar Islands region. 相似文献