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151.
Holger Class Anozie Ebigbo Rainer Helmig Helge K. Dahle Jan M. Nordbotten Michael A. Celia Pascal Audigane Melanie Darcis Jonathan Ennis-King Yaqing Fan Bernd Flemisch Sarah E. Gasda Min Jin Stefanie Krug Diane Labregere Ali Naderi Beni Rajesh J. Pawar Adil Sbai Sunil G. Thomas Laurent Trenty Lingli Wei 《Computational Geosciences》2009,13(4):409-434
152.
R. Rajesh Kumar B. Prasad Kumar A. N. V. Satyanarayana D. Bala Subrahamanyam A. D. Rao S. K. Dube 《Natural Hazards》2009,49(2):213-224
This work reports an efficient bulk formulation of sea surface drag that incorporates effect of dynamic stability under varied
atmospheric forcing. The proposed formulation exhibits a polynomial dependence of wind speed on air–sea temperature difference
based on statistical analysis. Quality checked meteorological and oceanographic data from four shallow water buoys located
off Korean seas having measurements at an interval of every 1 h were used for this study. The analyses of in situ records
for this region suggest stability ranging from highly stable to very unstable conditions. Importance of this proposed formulation
is better reflected during unstable condition where other popular bulk formulations fail. In addition, importance and impact
of such a study on wind-wave growth using the state-of-art wave model was also investigated. Finally, we advocate a new drag
formulation, which accounts for varied atmospheric stability and suggest that this should be considered as an essential pre-requisite
for ocean modeling studies. 相似文献
153.
The Bastar craton has experienced many episodes of mafic magmatism during the Precambrian. This is evidenced from a variety
of Precambrian mafic rocks exposed in all parts of the Bastar craton in the form of volcanics and dykes. They include (i)
three distinct mafic dyke swarms and a variety of mafic volcanic rocks of Precambrian age in the southern Bastar region; two
sets of mafic dyke swarms are sub-alkaline tholeiitic in nature, whereas the third dyke swarm is high-Si, low-Ti and high-Mg
in nature and documented as boninite-norite mafic rocks, (ii) mafic dykes of varying composition exposed in Bhanupratappur-Keskal
area having dominantly high-Mg and high-Fe quartz tholeiitic compositions and rarely olivine and nepheline normative nature,
(iii) four suites of Paleoproterozoic mafic dykes are recognized in and around the Chattisgarh basin comprising metadolerite,
metagabbro, and metapyroxenite, Neoarchaean amphibolite dykes, Neoproterozoic younger fine-grained dolerite dykes, and Early
Precambrian boninite dykes, and (iv) Dongargarh mafic volcanics, which are classified into three groups, viz. early Pitepani
mafic volcanic rocks, later Sitagota and Mangikhuta mafic volcanics, and Pitepani siliceous high-magnesium basalts (SHMB).
Available petrological and geochemical data on these distinct mafic rocks of the Bastar craton are summarized in this paper.
Recently high precision U-Pb dates of 1891.1±0.9 Ma and 1883.0±1.4 Ma for two SE-trending mafic dykes from the BD2 (subalkaline)
dyke swarm, from the southern Bastar craton have been reported. But more precise radiometric age determinations for a number
of litho-units are required to establish discrete mafic magmatic episodes experienced by the craton. It is also important
to note that very close geochemical similarity exist between boninite-norite suite exposed in the Bastar craton and many parts
of the world. Spatial and temporal correlation suggests that such magmatism occurred globally during the Neoarchaean-Paleoproterozoic
boundary. Many Archaean terrains were united as a supercontinent as Expanded Ur and Arctica at that time, and its rifting
gave rise to numerous mafic dyke swarms, including boninitenorite, world-wide. 相似文献
154.
155.
N. V. Chalapathi Rao Rajesh K. Srivastava 《Contributions to Mineralogy and Petrology》2009,157(2):245-265
The petrology and geochemistry of some new occurrences of Mesoproterozoic diamondiferous hypabyssal-facies kimberlites from
the Chigicherla, Wajrakarur-Lattavaram and Kalyandurg clusters of the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton
(EDC), southern India, are reported. The kimberlites contain two generations of olivine, and multiple groundmass phases including
phlogopite, spinel, calcite, dolomite, apatite, perovskite, apatite and rare titanite, and xenocrysts of eclogitic garnet
and picro-ilmenite. Since many of the silicate minerals in these kimberlites have been subjected to carbonisation and alteration,
the compositions of the groundmass oxide minerals play a crucial role in their characterisation and in understanding melt
compositions. While there is no evidence for significant crustal contamination in these kimberlites, some limited effects
of ilmenite entrainment are evident in samples from the Kalyandurg cluster. Geochemical studies reveal that the WKF kimberlites
are less differentiated and more primitive than those from the Narayanpet kimberlite field (NKF), Eastern Dharwar craton.
Highly fractionated (La/Yb = 108–145) chondrite-normalised distribution patterns with La abundances of 500–1,000 × chondrite
and low heavy rare earth elements (HREE) abundances of 5–10 × chondrite are characteristic of these rocks. Metasomatism by
percolating melts from the convecting mantle, rather than by subduction-related processes, is inferred to have occurred in
their source regions based on incompatible element signatures. While the majority of the Eastern Dharwar craton kimberlites
are similar to the Group I kimberlites of southern Africa in terms of petrology, geochemistry and Sr–Nd isotope systematics,
others show the geochemical traits of Group II kimberlites or an overlap between Group I and II kimberlites. Rare earth element
(REE)-based semi-quantitative forward modelling of batch melting of southern African Group I and II kimberlite source compositions
involving a metasomatised garnet lherzolite and very low degrees of partial melting demonstrate that (1) WKF and NKF kimberlites
display a relatively far greater range in the degree of melting than those from the on-craton occurrences from southern Africa
and are similar to that of world-wide melilitites, (2) different degrees of partial melting of a common source cannot account
for the genesis of all the EDC kimberlites, (3) multiple and highly heterogeneous kimberlite sources involve in the sub-continental
lithospheric mantle (SCLM) in the Eastern Dharwar craton and (4) WKF and NKF kimberlites generation is a resultant of complex
interplay between the heterogeneous sources and their different degrees of partial melting. These observations are consistent
with the recent results obtained from inversion modelling of REE concentrations from EDC kimberlites in that both the forward
as wells as inverse melting models necessitate a dominantly lithospheric, and not asthenospheric, mantle source regions. The
invading metasomatic (enriching) melts percolating from the convecting (asthenosphere) mantle impart an OIB-like isotopic
signature to the final melt products. 相似文献
156.
Identification and mapping of chromium (VI) plume in groundwater for remediation: A case study at Kanpur,Uttar Pradesh 总被引:1,自引:0,他引:1
R. K. Singh B. Sengupta Rameshwar Bali B. P. Shukla V. V. S. Gurunadharao Rajesh Srivatstava 《Journal of the Geological Society of India》2009,74(1):49-57
With only twenty five percent population living in urban areas, India has cities amongst the biggest in the world. Urban growth
in most of Indian cities is concomitant with rise in water demand for community, as well as, for industrial purposes. The
complex situation resulting from indiscriminate disposal of waste and its severe impact on groundwater quality is set for
continuous worsening mainly for want of sustained effort aimed at site-specific remediation.
The study, a prerequisite for actual remediation in an industrial city of Kanpur, India, envisages detailed investigation
about pollutant transport, evaluation of concept of Bio-remediation and a range of other options and finally full scale implementation
of the best suited. Drilling of piezometers and resistivity survey indicates that the area is constituted of alluvial sands,
gravels and their various admixtures. Chemical analysis of water samples collected from piezometers and hand pumps shows the
presence of hexavalent chromium rich horizons at various depths. The alarming concentration of this carcinogenic heavy metal
of the order of 16.3 mg/l against the permissible concentration (of 0.05 mg/l) for drinking water and high concentration within
sediments of the area poses a major threat to the entire ecosystem. The projection of migration contaminant plume of hexavalent
chromium as depicted in the paper is indicative of a concentrated extent of core zone existing in shallow alluvial aquifer,
which may be targeted for interception by remedial measures.
The present work, elaborating on the source, potential and monitoring the migration of the pollutant plume is the first field
scale study of its kind in the country. The findings of these studies are of strong relevance in addressing the ground water
pollution due to indiscriminate disposal practices of hazardous waste in areas located within the alluvial zones. 相似文献
157.
Granularity and textural analysis as a proxy for extreme wave events in southeast coast of India 总被引:1,自引:0,他引:1
C. S. Vijaya Lakshmi P. Srinivasan S. G. N. Murthy Deshraj Trivedi Rajesh R. Nair 《Journal of Earth System Science》2010,119(3):297-305
Extreme wave events of 1000 and 1500 years (radiocarbon ages) have been recently reported in Mahabalipuram region, southeast
coast of India. Subsequently, we carried out extensive sedimenttological analysis in regions covering a total lateral coverage
of 12 km with a new archeological site as the central portion of the study area. Twelve trenches in shore normal profiles
exhibit landward thinning sequences as well as upward fining sequences confirming with the global signatures of extreme wave
events. The sediment size ranges from fine-to-medium and moderately well sorted-to-well sorted, and exhibit positive skewness
with platykurtic-to-leptokurtic nature. We now propose the abrupt winnowing or back and forth motion including unidirectional
transport of these deposited sediments, which results in positive skewness. Textural analyses derived from scanning electron
microscope studies (SEM) demonstrate the alteration produced, in the ilmenite mineral with vivid presence of pits and crescents
with deformation observed on the surface due to extreme wave activities. This is further confirmed with the predominance of
high-density mineral such as magnetite (5.2) and other heavy minerals in these deposits inferred the high-intensity of the
reworking process of the beach shelf sediments. 相似文献
158.
Nicolas F. Spycher Montarat Issarangkun S. Sevinç ?engör Tim R. Ginn Rajesh K. Sani 《Geochimica et cosmochimica acta》2011,75(16):4426-4440
One option for immobilizing uranium present in subsurface contaminated groundwater is in situ bioremediation, whereby dissimilatory metal-reducing bacteria and/or sulfate-reducing bacteria are stimulated to catalyze the reduction of soluble U(VI) and precipitate it as uraninite (UO2). This is typically accomplished by amending groundwater with an organic electron donor. It has been shown, however, that once the electron donor is entirely consumed, Fe(III) (hydr)oxides can reoxidize biogenically produced UO2, thus potentially impeding cleanup efforts. On the basis of published experiments showing that such reoxidation takes place even under highly reducing conditions (e.g., sulfate-reducing conditions), thermodynamic and kinetic constraints affecting this reoxidation are examined using multicomponent biogeochemical simulations, with particular focus on the role of sulfide and Fe(II) in solution. The solubility of UO2 and Fe(III) (hydr)oxides are presented, and the effect of nanoscale particle size on stability is discussed. Thermodynamically, sulfide is preferentially oxidized by Fe(III) (hydr)oxides, compared to biogenic UO2, and for this reason the relative rates of sulfide and UO2 oxidation play a key role on whether or not UO2 reoxidizes. The amount of Fe(II) in solution is another important factor, with the precipitation of Fe(II) minerals lowering the Fe+2 activity in solution and increasing the potential for both sulfide and UO2 reoxidation. The greater (and unintuitive) UO2 reoxidation by hematite compared to ferrihydrite previously reported in some experiments can be explained by the exhaustion of this mineral from reaction with sulfide. Simulations also confirm previous studies suggesting that carbonate produced by the degradation of organic electron donors used for bioreduction may significantly increase the potential for UO2 reoxidation through formation of uranyl carbonate aqueous complexes. 相似文献
159.
Rajesh Kumar Ranjan AL. Ramanathan Rita Chauhan Gurmeet Singh 《Environmental Earth Sciences》2011,62(8):1779-1787
Present study examined phosphorus dynamics through delineation of source as well as availability of phosphorus and its fractionation
within the intertidal sediments of Pichavaram mangrove ecosystem. Twelve sediment samples and two cores were collected from
the mangrove forest along with estuarine area (Vellar-Coleroon) during January 2005. Sediments were analyzed for total phosphorus
and its fractionation using operationally defined chemical sequential extraction scheme (SEDEX). Dissolved phosphorus (in
water) and total phosphorus (in sediments) concentrations were high in the Vellar region of Pichavaram mangrove area due to
pollution load from nearby villages and agricultural fields. However, the spatial variation in dissolved phosphorus were insignificant
(at significance level = 0.05). The results for the phosphorus fractionation (post-tsunami) were compared with earlier studies
(pre-tsunami). It was observed that all phosphorus fractions (except adsorbed-phosphorus) showed a highly significant (at
significance level = 0.05) increase in concentration after the tsunami event. There was significant decrease in the adsorbed
phosphorus concentration as a result of tsunami. The changes were more pronounced for organic phosphorus which increased by
almost twofold following the event. These variations were attributed to change in salinity, increase in dissolved oxygen as
well as the retreat of tsunami water carrying the waste load. The vertical distribution of phosphorus through core sediments
showed that mixing after tsunami had altered the different phosphorus fraction and its availability. Overall, the study indicated
that the fluvial weathering along with litter degradation and anthropogenic sources controlled the biogeochemistry of phosphorus
in this mangrove ecosystem. Observed changes in the concentrations are a result of altered physico-chemical characteristics
caused by tsunami. 相似文献
160.
J. Rajesh Banu M.Sc. M.Phil. Ph.D. D. K. Uan Ph.D. S. Kaliappan BE M. Tech. Ph.D. I. T. Yeom Ph.D. 《International Journal of Environmental Science and Technology》2011,8(2):281-290
In the present study, two bench-scale anaerobic/ anoxic/ oxic submerged membrane bioreactors were used to study the effect of thermochemical sludge disintegration system on the excess sludge production. Among the two membrane bioreactors, one was named experimental membrane bioreactor and another one was named as control membrane bioreactor, where a part of the mixed liquor was treated with thermo chemical and was returned back to membrane bioreactor. Thermo chemical digestion of sludge was carried out at fixed pH (11) and temperature (75 °C) for 24 % chemical oxygen demand solution. The other one was named control membrane bioreactor and was used as control. The reactors were operated at three different mixed liquor suspended solids range starting from 7500 mg/L to 15000 mg/L. Both of membrane bioreactors were operated at a flux of 17 LMH over a period of 240 days. The designed flux was increased stepwise over a period of one week. During the 240 days of reactor operation, both of membrane bioreactors maintained relatively constant transmembrane pressure. The sludge digestion had no impact on chemical oxygen demand removal efficiency of the reactor. The results based on the study indicated that the proposed process configuration has potential to reduce the excess sludge production as well as it didn’t deteriorate the treated water quality. 相似文献