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941.
K. R. Hari N. V. Chalapathi Rao Vikas Swarnkar 《Journal of the Geological Society of India》2011,78(6):501-509
We report the occurrence of orthopyroxene gabbro from the Phenai Mata Igneous Complex (containing thoeliitic and alkaline
rocks) that occur within Deccan Traps. The P-T calculations based on two pyroxene thermometry vary from 8.5±1.0 kbar and 963±39
°C. These gabbroic rocks exhibit high Mg# (0.67 to 0.71). But their primary magma signature can be negated due to their high
SiO2 (> 50 wt %), low Ni (32–35 ppm) and Cr (105–182 ppm) contents. Further, simple fractional crystallization was not responsible
for the modification of the magma. Modeling carried out using trace element concentrations revealed that concurrent assimilation
and fractional crystallization (AFC) was responsible for the genesis of these rocks. Small pods of magma could have accumulated
in the crustal portions and concurrent assimilation and fractional crystallization have taken place in the generation of gabbro
and orthopyroxene gabbro in the present study area. 相似文献
942.
943.
N. V. Chalapathi Rao B. Lehmann D. Mainkar B. Belyatsky 《Contributions to Mineralogy and Petrology》2011,161(5):721-742
We present mineral chemistry, geochemistry and Sr and Nd isotope data of drillcore samples from the Late Cretaceous (65 Ma),
diamondiferous Behradih ultramafic pipe, Bastar craton, Central India, which is emplaced synchronous with the Deccan flood
basalt eruption. The rock is affected by pervasive serpentine–talc–carbonate alteration and consists of pelletal lapilli and
variously sized olivine and phlogopite macrocrysts, set in a groundmass of abundant clinopyroxene, chrome spinel, apatite,
Fe-rich perovskite (<50 μm), zircon, titanite, rutile and calcite. Mineralogical studies identify the Behradih pipe as orangeite
(formerly termed as Group II kimberlite) and establish the occurrence of such rocks outside the Kaapvaal craton, southern
Africa. As the age of the Behradih orangeite overlaps with that of the main phase of the Deccan flood basalt magmatism, we
infer a common tectonomagmatic control vis-a-vis the Deccan-related mantle plume. Trace element ratios and the Nd isotope
signatures of the Behradih pipe imply that the Deccan plume has only contributed heat, but not substantial melt, to the Behradih
magma with a cause-and-consequence relationship between them. Our study highlights (a) a striking similarity in the genesis
of Late Cretaceous orangeites associated with the continental flood basalts in the Kaapvaal and Bastar cratons but related
to different mantle plumes and (b) the role of plume–lithosphere interaction in the generation of orangeites. 相似文献
944.
The surface layers of the Bay of Bengal along the east coast of India exhibit intricate stratification owing to the differential
distribution of freshwaters. The winter (January–February) cooling of the salinity-induced stable layers results in the development
of thermal inversions that deteriorate toward the end of the season. The study focuses on the behavior of the thermal inversions
in the light of the variable stratification and the monsoon imposed reversing coastal current. To address the associated processes,
a three-dimensional Princeton Ocean Model is applied for the east coast of India, and numerical experiments carried out to
study the means by which the thermal inversions tend to perish with the passage of winter. The model domain with variable
curvilinear grid uses input fields that comprise realistic bathymetry and initial temperature/salinity conforming to winter/specified
stratification. The surface forcing comprises wind stress and diurnal pattern air–sea heat fluxes. The body forcing is derived
from the periodic tidal elevations at the open boundaries. It has been found that the thermal inversions tend to sustain as
the equator-ward flowing East India Coastal Current (EICC) traps the cool low saline waters between Paradip and Kakinada.
The current off Paradip is weak and variable and is not a part of EICC. Consequently, in the absence of replenishment of cool
and freshsurface waters, the temperature/salinity gradients get eroded steadily. No thermal inversions are noticed south of
Kakinada because of relatively weak current with diminished vertical salinity gradient. As the nature of stratification encountered
in the bay is highly variable due to diverse reasons, the behavior of internal waves under different stratification scenarios
is also addressed. Numerical experiments indicate that the energy/amplitude of the internal waves are comparable in the surface
layers for any stratification, where as it is certain orders exalted in the deeper waters of the strong stratification scenario.
Further, it is found that the energies and pattern of the temperature oscillations conform to the nature of mixed tide at
the corresponding latitude. The underneath stratification is found to be more responsible for the generation of internal waves compared to the local stratification. This implies that the body forcing emanating from below is the cardinal contributor for the generation of internal waves.
The numerical experiment with a flat and uniform bottom showing weak manifestation of internal waves endorses the same. This
connotes that the continental slopes are an effective generator of the internal waves and the energy flux conversion of the
barotropic tide to internal waves seems to be heavily dependent on the shoaling bottom. 相似文献
945.
946.
D. Purushotham Mehnaz Rashid Mahjoor Ahmad Lone A. Narsing Rao Shakeel Ahmed E. Nagaiah Farooq A. Dar 《Journal of the Geological Society of India》2013,81(3):385-396
Anthropogenic activities in Maheshwaram watershed have deteriorated water, air and soil quality during the last ten years due to rapid urbanisation and industrial development. Maheshwaram watershed experienced drastic changes in land use pattern, being very close to the Hyderabad city. Base-line data was collected during post monsoon season (October-November) of 2010 in Maheshwaram watershed to assess the impacts of change in land use, urbanisation and industrialisation on air, water and soil quality for Environmental Impact Assessment (EIA). Air samples were analysed for Suspended Particulate Matter (SPM) and Respirable Suspended Particulate Matter (RSPM). Groundwater samples were analysed for pH; EC; TDS; TH; cations, anions and heavy metals viz., Fe, Mn, Al, Si, V, Cr, As, Sr, Rb, Se, Ba, Li, B, Be, Co, Ni, Zn, Cd, and Pb using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Analysed data were compared with the National and International Standards and subjected to Factor Analysis (FA) for six chemical variables to assess and characterise hydro-chemical processes. A comparison of the results of groundwater samples with WHO and BIS guidelines show that most of the groundwater samples are heavily contaminated with heavy metals like lead, chromium, nickel, barium, aluminium, boron and selenium, which was quantified and presented in the form of spatial variation diagrams prepared using ArcGIS. 9.3.1. Similarly the results of air samples compared with the Central Pollution Control Board, Ministry of Environment and Forests, Government of India guidelines show that most of the air samples for residential, rural and industrial areas are contaminated by SPM and RSPM. 相似文献
947.
N. V. Chalapathi Rao Anup K. Sinha Suresh Kumar Rajesh K. Srivastava 《Journal of the Geological Society of India》2013,81(6):733-736
We report a rare accessory groundmass mineral of K-rich titanate, having a composition close to that of potassium triskaidecatitanate (K2Ti13O27), from an underground drill-core sample of ultrapotassic rock from southwestern part of the Jharia coal field in the Damodar valley, at the northern margin of the Singhbhum craton, Eastern India. Potassium triskaidecatitanate is regarded as a typomorphic mineral of orangeites (Group II kimberlites) of Kaapvaal craton, southern Africa, and its occurrence in the Jharia ultrapotassic rock is significant since ultrapotassic suite of rocks elsewhere from the Damodar valley have been recently suggested to be peralkaline lamproites based on mineral-genetic classification. The important role played by a unique geodynamic setting (involving a thinned metasomatised lithospheric mantle and inheritance of an Archaean subduction component) at the northern margin of the Singhbhum craton in deciding the petrological diversity of the early Cretaceous ultrapotassic intrusives from the Damodar valley is highlighted in this study. 相似文献
948.
Occurrence of native gold in ultramafic rocks is rather rare. Such occurrences serve as snapshots of the underlying processes leading to their formation and modifications thereafter. Presence of native gold as flakes were earlier reported from the chromites of rock massifs of Kraka, southern Urals, Russia (Kovalev et al. 2007). Gold spherules also occur as tiny inclusions (5–30 μm) in olivine, pyrrohotite and magnetite grains from the ultrabasic rocks of Loveld deposit, South Africa (Rozhkov, 1967). Here we report, probably for the first time, occurrence of native gold from the chromitites of the Mesoarchaean Tagadur Mines of the Nuggihalli Schist Belt (NSB), Dharwar Craton, south India. Geological Survey of India (2006) has already reported significant gold content from the bulk ultramafic rocks of Kempinakote area far south of the current study area. A short discussion on the preliminary petrographic features of the gold grains and its significance is presented. 相似文献
949.
N. V. Chalapathi Rao Bernd Lehmann B. K. Panwar Alok Kumar Datta Mainkar 《Journal of the Geological Society of India》2013,82(6):595-600
We report the occurrence of garnierite (a general term referring to Ni-Mg bearing hydrous silicates in laterites) from the crater-facies Tokapal kimberlite of the Bastar craton, Central India. Garnierite occurs as discrete ovoid or amoeboid segregations (up to 200 mm) or as veinlets with up to 18.1 wt% NiO and high iron contents (up to 36.2 wt% FeOT). Chemical composition of the garnierite implies its derivation from a magnesium-rich protolith. Extensive lateritisation of the large crater-facies (~2.5 km diameter) saucer-shaped kimberlite under tropical weathering conditions, aided by suitable topography, drainage and favourable structural set-up, are the factors inferred to be responsible for the formation of garnierite in the Tokapal system. As lateritic nickel ores constitute significant resources for nickel exploration, the perspective of the Tokapal kimberlite as a nickel prospect needs to be investigated. 相似文献
950.
S. Viswanathan K. Surya Prakash Rao B. Mahabaleswar 《Journal of the Geological Society of India》2013,82(6):621-627
Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours. 相似文献