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71.
K. R. Muraleedharan P. K. Dinesh Kumar S. Prasanna Kumar Sebin John B. Srijith K. Anil Kumar K. Naveen Kumar S. Gautham V. Samiksha 《Estuaries and Coasts》2018,41(4):1021-1035
Mud bank formation during the southwest monsoon along the southwest coast of India remains an enigma to the researchers and coastal community in spite of several earlier studies. The present study attempts to unravel the mystery through a high-frequency, season-long time-series observation at Alappuzha, located at the southern part of the west coast of India, a region of frequent occurrence of mud bank. Using 7-month-long weekly time-series observation, we identified strong winds and high waves associated with onset of the southwest monsoon and subsequent three episodic atmospheric low-pressure events (LPEs).With the help of in situ time-series data, we show that the strong winds and high waves associated with southwest monsoon pre-conditions the near shore bottom sediment to bring it into suspension. The high amplitude waves associated with the southwest monsoon, while propagating from the deep water to shallow water region, interact with the bottom initiating bottom-sediment movement and its suspension due to wave refraction and shoaling. The sporadic occurrence of the atmospheric LPEs enhances the process of suspension of bottom sediment in the near shore region leading to the formation of fluid mud. Simulations with a cohesive sediment transport model yielded realistic estimates of sediment transport, in the presence of an onshore current, a pre-requisite for transporting the fluid mud toward the coast. The prevailing onshore upwelling current during the southwest monsoon provides the favorable pre-requisite conditions for transporting the fluid mud through depression channel network towards the coast. Once sufficient quantity and thickness of fluid mud is accumulated in the near shore region, it acts as a wave damper for subsequent high monsoon waves, as indicated by the time-series wave data, leading to the formation of tranquil mud bank region. Depression channel networks extending from the shelf to the coast off Alappuzha, Kochi, Ponnani, Beypore, and Ullal were found in the bathymetric charts, thus explaining why mud banks occur only at few locations in spite of the prevalence of similar monsoon conditions. 相似文献
72.
Rao G. Srinivasa Kumar Manish Radhakrishna M. 《International Journal of Earth Sciences》2018,107(6):2191-2207
International Journal of Earth Sciences - The continental breakup history at the northwest continental margin of India remained conjectural due to lack of clearly discernable magnetic anomaly... 相似文献
73.
Surendra Kumar Jha J. P. Shrivastava C. L. Bhairam 《Journal of the Geological Society of India》2012,79(2):117-134
Clays associated with the Precambrian unconformity-related (sensu lato) uranium mineralization that occur along fractures of Rohini carbonate, Bandai sandstone and clay-organic rich black carbonaceous
Gorakalan shale of the Sonrai Formation from Bijawar Group is significant. Nature and structural complexity of these clays
have been studied to understand depositional mechanism and palaeoenvironmental conditions responsible for the restricted enrichment
of uranium in the Sonrai basin. Clays (<2 μm fraction) separated from indurate sedimentary rocks by disaggregation, chemical
treatment and centrifugation were examined using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Presence
of tv-1M type illite is inferred from the Rohini and Bandai Members of the Sonrai Formation, indicative of high fluid/rock
interaction and super-saturation state of the fluids available in proximity with the uranium mineralization. It is observed
that the Sonrai Formation is characterized by kaolinite > chlorite > illite > smectite mineral assemblages, whereas, Solda
Formation contains kaolinite > illite > chlorite clays. It has been found that the former mineral assemblage resulted from
the alteration process is associated with the uranium mineralization and follow progressive reaction series, indicating palaeoenvironmental
(cycles of tropical humid to semi-arid/arid) changes prevailed during maturation of the Sonrai basin. The hydrothermal activity
possibly associated with Kurrat volcanics is accountable for the clay mineral alterations. 相似文献
74.
Static deformation of two monoclinic elastic half-spaces in welded contact due to a long inclined strike-slip fault situated
in one of the half-spaces is studied analytically and numerically. Closed-form algebraic expressions for the displacement
at any point of the medium are obtained. The variation of the displacement at the interface with the horizontal distance from
the fault is studied. The effect of anisotropy on the displacement field is examined. It is found that while the anisotropy
of the source half-space has a significant effect on the displacement at the interface, the anisotropy of the other half-space
has only a marginal effect. 相似文献
75.
N. S. Krishnamurthy V. Ananda Rao Dewashish Kumar K. K. K. Singh Shakeel Ahmed 《Journal of the Geological Society of India》2009,73(5):639-650
Exploration and exploitation of coal seams is one of the major resources for the energy sector in any country but at the same
time water filled voids/water logged areas in the old workings of these seams are very critical problems for the coal mining
industry. In such situations, disasters like inundation, landslides, collapsing of the old seams may occur. In this regard,
it is necessary to find out the water saturated/water filled voids and zones in the mining areas. Since no established technique
is available to find such zones, an experimental study using Electrical Resistivity Imaging (ERI) has been carried out in
one of the coal mining areas near Dhanbad, to find out the feasibility of finding the barrier thickness and the water logged
area in underground coal mines. The area under study forms part of Jharia coalfield in Dhanbad district, Jharkhand state.
The coal bearing rocks of Barakar Formation of Lower Permian age (Gondwana period) occur in the area under a thin cover (10
m to15 m) of soil and or alluvium. Coal bearing Barakar Formations consist mainly of sandstone of varying grain size, intercalation
of shale and sandstone, grey and carbonaceous-shale and coal seams.
Since the water saturation reduces the resistivity of a formation to a large extent, water filled voids and old coal workings
are expected to have significant resistivity contrast with the surrounding host rock. Hence, ERI technique was applied in
such an environment as this technique uses high-density data acquisition both laterally and vertically by using multiple number
of electrodes. Along with ERI, mise-à-la-masse (also called charged body) technique was also employed at one of the promising
sites to find out the connectivity of water logged areas and also detection of these old workings from the surface measurements
was analyzed. The interpreted 2D resistivity sections have clearly indicated the water bearing zone(s) along the profile which
was well confirmed with the existing water level in the nearby borewells. On the other hand, this technique did not identify
the size of the coal pillar and gallery (air filled voids), which might be due to the small size of the voids (i.e. about
2 m × 2 m) below a depth of 15m and more but have indicated altogether as a high resistive zone ranging from 600–1000 Ohm-m. 相似文献
76.
T. Madhavi T. Satish Kumar M. A. Rasheed G. Kalpana D. J. Patil A. M. Dayal 《Journal of the Geological Society of India》2009,74(1):7-15
A study was carried out to test the usefulness of surface geochemical methods as regional evaluation tools in petroliferous
region of the Mehsana block, North Cambay Basin. A suite of 135 soil samples collected from the depth of 2.5 m, were analyzed
for adsorbed light gaseous hydrocarbons and carbon isotopes (δ13Cmethane and δ13Cethane). The light gaseous hydrocarbon analysis show that the concentration ranges 402 ppb, 135 ppb, 70 ppb, 9 ppb and 18 ppb of
C1, C2, C3, iC4 and nC4, respectively. The value of carbon isotopic ranges of methane −29.5 to −43.0‰ (PDB) and ethane −19.1 to −20.9‰ (PDB). This
data, when mapped, indicates patterns coinciding with major known oil and/or gas field of Sobhasan/Linch in this study area.
The existence of un-altered petroliferous microseeps of catagenetic origin is observed in the study area. A regional study,
such as the one described here, can provide important exploration facts concerning the regional hydrocarbon potential in a
block. This method has been confirmed and can be applied successfully in frontier basins. 相似文献
77.
Arsenic is present in groundwater at Siliguri–Jalpaiguri area, West Bengal, India. This is the place where Tista river descending
from the Himalayas meets the alluvial plain. The area represents alluvial fan and floodplains of Tista, Mahananda-Balasan,
Jaladhaka and its tributaries. In the river sediment samples, para- and ferro-magnetic minerals within 0.3–0.05 mm fraction
contain 9–80 ppm of arsenic. The study indicates that iron bearing minerals viz. biotite, hornblende as well as iron coated
grains of the sediment are major contributors towards arsenic budget. Though magnetite as a mineral shows maximum arsenic
content (22 ppm), it is volumetrically not of much significance. Measurement of groundwater collected from tube wells shows
up to 0.05 ppm of arsenic. These arsenic contaminated tube wells occur in a linear fashion along the course of the rivers.
Moreover, localization of contaminated tube wells coincides with the change of channel gradient as observed in longitudinal
section. The study enumerates a cause–effect relationship of arsenic occurrence with river gradient and fluvial sedimentation. 相似文献
78.
Study of subsurface geology in locating arsenic-free groundwater in Bengal delta,West Bengal,India 总被引:1,自引:0,他引:1
Over a large area of the Bengal delta in West Bengal, India, arsenic distribution patterns in groundwater were studied. One
hundred and ten boreholes at different target locations were made, subsurface sediments were logged and analysed, and arsenic
values in sediments vis-à-vis groundwater were compared. The study elucidates the subsurface geology of the western part of
Bengal delta and characterises the sediments that were intersected in different boreholes with contrasting values of arsenic
in groundwater. It reveals an existence of multiple aquifers stacked over each other. Depending on the color and nature of
aquifer-sands and their overlying clay beds six aquifer types (Type-1 to Type-6) are classified and described. Sediment-arsenic
for all the varieties of aquifer sands are near similar but the groundwater-arsenic of these six aquifers varies widely. Type-2
and Type-5 aquifers host arsenic-contaminated groundwater whereas the other four aquifers are arsenic-free. Type-2 and Type-5
aquifers are capped by a grey to dark grey soft organic matter-rich clay unit which makes these aquifers semi-confined to
leaky-confined. These contribute in releasing arsenic from the sediments. The results of this study are employed in a proposed
georemedial measure against this hazardous toxic element. 相似文献
79.
Manish Kumar Bhawna Sharma AL. Ramanathan M. Someshwar Rao Bhishm Kumar 《Environmental Geology》2009,56(6):1171-1181
Present study is an effort to distinguish between the contributions of natural weathering and anthropogenic inputs towards
high salinity and nutrient concentrations in the groundwater of National Capital Territory (NCT) Delhi, India. Apart from
the source identification, the aquifer of entire territory has been characterized and mapped on the basis of salinity in space
and water suitability with its depth. Major element chemistry, conventional graphical plots and specific ionic ratio of Na+/Cl−, SO4
2−/Cl−, Mg2+/Ca2+ and Ca2+/(HCO3
− + SO4
2−) are conjointly used to distinguish different salinization sources. Results suggest that leaching from the various unlined
landfill sites and drains is the prime cause of NO3
− contamination while study area is highly affected with inland salinity which is geogenic in origin. The seasonal water level
fluctuation and rising water level increases nutrients concentration in groundwater. Mixing with old saline sub-surface groundwater
and dissolution of surface salts in the salt affected soil areas were identified as the principle processes controlling groundwater
salinity through comparison of ionic ratio. Only minor increase of salinity is the result of evaporation effect and pollution
inflows. The entire territory has characterized into four groups as fresh, freshening, near freshening and saline with respect
to salinity in groundwater. The salinity mapping suggests that in general, for drinking needs, groundwater in the fresh, freshening
and near freshening zone is suitable up to a depth of 45, 20 and 12 m, respectively, while the saline zones are unsuitable
for any domestic use. In the consideration of increasing demand of drinking water in the area; present study is vital and
recommends further isotopic investigations and highlights the need of immediate management action for landfill sites and unlined
drains. 相似文献
80.
K. K. Singh R. P. Patel J. Singh B. Kumar A. K. Singh R. P. Singh B. L. Koul Lalmani 《Journal of Earth System Science》2008,117(3):219-225
In this paper, we report observations of unusual whistlers recorded at Jammu (geomag. lat. = 22°26′N; L = 1.17), India on March 8, 1999 during the daytime. They are interpreted as one-hop ducted whistlers having propagated along
higher L-values in closely spaced narrow ducts from the opposite hemispheres. After leakage from the duct, the waves might have propagated
in the earth-ionosphere waveguide towards the equator in surface mode. Tentative explanation of the dynamic spectra of these
events is briefly presented. 相似文献