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91.
Ravi?S.?JakkaEmail author G.?V.?Ramana Manoj?Datta 《Geotechnical and Geological Engineering》2011,29(5):821-835
Utilization of pond ash in large earthworks for geotechnical applications like construction of highway embankments, raising
of ash dykes and filling low lying areas (construction fills), solves the waste disposal problem besides conserving the natural
soils. However, design and construction of such geotechnical structures particularly in earthquake prone areas, requires thorough
understanding of dynamic response of these structures under different seismic loading conditions. Here in this article, dynamic
stability of embankments raised around the perimeter of ash ponds by the upstream and down stream methods of construction
with coarse (ash from inflow point) and fine (ash from outflow point) pond ash materials, has been computed for different
site specific earthquake scenarios appropriate for Delhi region. The performance of the embankments is analyzed using Quake/w
and Slope/w software packages for steady-state seepage condition. The required dynamic properties of the materials are obtained
form the various field and laboratory tests. The geotechnical structures constructed with ash exhibited similar type of response
as that of with the natural soils. The performance of the structures is influenced by number factors such as type of construction
(e.g. upstream or downstream), insitu conditions (e.g. stresses, density, phreatic line), and magnitude of dynamic loads,
besides on the static and dynamic characteristics of the materials. The structures with the fine ash exhibit higher vulnerability
to liquefaction related failures, which emphasizes need for carrying site-specific studies and adoption of proper construction
measures to ensure design parameters. 相似文献
92.
Determining the genetic origin of nitrate contamination in aquifers of Northern Gujarat,India 总被引:2,自引:0,他引:2
Kumari Rina P. S. Datta Chander Kumar Singh Saumitra Mukherjee 《Environmental Earth Sciences》2014,71(4):1711-1719
Over the past decades, the Gujarat state of India experienced intensive agricultural and industrial activities, fertilizer consumption and abstraction of groundwater, which in turn has degraded the ground water quality. Protection of aquifers from nitrate pollution is a matter of prime concern for the planners and decision-makers. The present study assessed the spatial and temporal variation of groundwater nitrate levels in areas with different land use/land cover activities for both pre- and post-monsoon period. The pre-monsoon nitrate level (1.6–630.7 mg/L) in groundwater was observed to be higher as compared to the post-monsoon level (2.7–131.7 mg/L), possibly due to insufficient recharge and evaporation induced enrichment of agrichemical salts in groundwater. High HCO3 ? (200–1,000 mg/L) as well as SO4 2?/Cl? (0.111–0.992) in post-monsoon period provides a favourable environment for denitrification, and lower the NO3 levels during the post-monsoon period. The K vs NO3 scatter plot suggests a common source of these ions when the concentration is <5 mg/L, the relationships between different pollutants and nitrate also suggest that fertilizers and other sources, such as, animal waste, crop residue, septic tanks and effluents from different food processing units present in the area can be attributed to higher nitrate levels in the groundwater. Appropriate agronomic practices such as application of fertilizers based on calibrated soil tests and proper irrigation with respect to crop can minimize the requirement for inorganic fertilizers, which can bring down the cost of cultivation considerably, and also protect groundwater from further degradation. 相似文献
93.
94.
Asim Mahmood Julien E. G. Devriendt Joseph Silk 《Monthly notices of the Royal Astronomical Society》2005,359(4):1363-1378
An empirically motivated model is presented for accretion-dominated growth of supermassive black holes (SMBH) in galaxies, and the implications are studied for the evolution of the quasar population in the Universe. We investigate the core aspects of the quasar population, including space density evolution, evolution of the characteristic luminosity, plausible minimum masses of quasars, the mass function of SMBH and their formation epoch distribution. Our model suggests that the characteristic luminosity in the quasar luminosity function arises primarily as a consequence of a characteristic mass scale above which there is a systematic separation between the black hole and the halo merging rates. At lower mass scales, black hole merging closely tracks the merging of dark haloes. When combined with a declining efficiency of black hole formation with redshift, the model can reproduce the quasar luminosity function over a wide range of redshifts. The observed space density evolution of quasars is well described by formation rates of SMBH above ∼108 M⊙ . The inferred mass density of SMBH agrees with that found independently from estimates of the SMBH mass function derived empirically from the quasar luminosity function. 相似文献
95.
Jai Krishna Pandey Deepa Agarwal Sanjoy Gorain Rajnish Kumar Dubey Manoj Kumar Vishwakarma Kamlesh Kumar Mishra Asim Kumar Pal 《Arabian Journal of Geosciences》2017,10(7):183
This paper presents dust exposure study of 69 workers engaged in 11 categories of jobs over seven coalmines of Jharia Coalfields. Dust samples were analysed for dust concentration, maximum exposure limit (MEL), free silica and other minerals present, and particle size and shape. Study reveals that workers engaged in vicinity of coal/rock cutting operation, are exposed to higher dust concentration (50% samples exceeding MEL), and contain more fine particles (d 50 < 5 μm) with sharp edges. Samples exceeding MEL are classified as high-risk category which needs special attention for taking preventive and protective measure like use of personal protective equipments, job rotation and reduction in dust generation through engineering control using appropriate technology of dust suppression and dust extraction as per their applicability. The study also suggests presence of kaolinite and asbestos along with quartz which make the dust more harmful in nature necessitating further investigation and careful control measures. 相似文献
96.
97.
A. Datta S. K. Sharma R. C. Harit V. Kumar T. K. Mandal H. Pathak 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(3):275-281
Ammonia (NH3) emission from wheat (November to April) and rice (July to October) crops was measured using the chemiluminescence method at a subtropical agricultural area of India during 2009?C2010. Samples were collected from the canopy height during different growth stages of wheat crop to study the variations of NH3 emission during different growth stages of the crop. Background atmospheric concentration of NH3 was measured at 5 m height at the study site. Background NH3 concentration was subtracted from the NH3 concentration at crop canopy height to estimate the emission of NH3 from crop canopy. The NH3 emission from the wheat crop were recorded as 33.3 to 57.0; 15.3 to 29.2; 10.3 to 28.0; 8.7 to 23.9 and 13.9 to 28.9 ??g m?2 d?1 during sowing, crown root initiation (CRI), panicle initiation, grain filling and maturity stages of the crop respectively. The NH3 emission followed a diurnal pattern with significant correlation with ambient temperature at different crop growth stages. Cumulative seasonal NH3 emission to the atmosphere was accounted for the loss of ??10% of applied N-fertilizer during the wheat crop growing period. Immediate increase in NH3 emission was recorded from rice crop, grown under temperature gradient tunnel (TGT). However, the NH3 emission inside the TGT decreases within 3?C4 h after the N-fertilizer application. Continuous estimation of NH3 concentration at the crop canopy inside the TGT, suggests that the NH3 emission to the atmosphere reaches its peak within ??20 h of N-fertilizer application and continues up to 5 d following a diurnal pattern. 相似文献
98.
Ingestion of As – contaminated soil by children is a growing concern in former agricultural lands converted to residential or recreational land use areas. The mobility and bioavailability of As is controlled by its reactions with soil particles. The degree and strength of As retention by soil constituents may vary greatly with time. The present authors hypothesize that aging results in reduced mobility of As thereby decreasing As release and its bioavailability. The present study is aimed at evaluating the effect of aging on soil As fractionation and bioaccessibility in a temperature and humidity-controlled greenhouse setting. The design allowed the evaluation of dynamic interactions between soils, pesticides, water, and plants. Therefore, 4 soil types (Immokalee, Millhopper, Pahokee Muck, and Orelia) were selected based on their potential differences in As reactivity. The soils were amended with the pesticide Na arsenate at two rates. Rice was used as the test crop. Soil samples collected after different time periods (0, 6 months, 1 a and 3 a) were extracted for soil-As forms via a sequential extraction technique. Bioaccessible As was extracted via an in vitro gastrointestinal method. At time 0, most of the extractable As in soil was in the soluble form, resulting in high bioaccessibility. As expected, soluble and exchangeable fractions decreased with time for up to 6 months, but remained constant thereafter. After 3 a of soil–pesticide equilibration, As bioaccessibility was still high in all the soils except for the Pahokee Muck. No significant difference in As bioaccessibility was observed between the soils. Arsenic was present predominantly as As(V) with 5–10% of the total dissolved As being present as As(III). Data obtained suggest that although aging had an impact on the geochemical forms, gastric pH was the sole important factor effecting As bioaccessibility. 相似文献
99.
100.
Basudeb Datta 《Journal of Earth System Science》2005,114(3):227-245
Sandstones of early Neoproterozoic Chandarpur Group, Chattisgarh Supergroup, central India display progressive change towards
greater textural and mineralogical maturity from base to top of the succession. The clay-silt matrix decreases, sorting of
sand grains improves, frequency of rounded grains increases, monocrystalline quartz content increases with concomitant decrease
in polycrystalline quartz, feldspar and rock fragments. The trend of variations in different mineralogical and textural attributes,
however, exhibits inflections at different stratigraphic levels. The sandstones of the basal Lohardih Formation are alluvial
fan deposits, characterized by high matrix and feldspar content, iron-oxide impregnated highly angular grains and poor sorting.
Petrographic properties collectively indicate that the sandstones were derived from a weathered granitic crust under a humid
climatic condition. Abundance of well rounded grains within the alluvial fan and overlying braided fluvial deposit indicates
prolonged wind action during episodes of high aridity. The shallow marine deposit overlying the fluvial deposits in the upper
part of the Lohardih Formation exhibits bed-to-bed variation in the frequency of angular grains, feldspar content and overall
maturity suggesting environmentally controlled segregation of sediments. The abrupt appearance of coarse-grained immature
sandstones with concomitant reappearance of iron-oxide impregnated/altered feldspar grains in the upper part of the shelf
deposits of the Chaporadih Formation point to a phase of tectonic uplift that possibly triggered a regression. Continued regression
and peneplanation heralded the deposition of supermature medium-grained purple quartzarenite of the upper shoreface Kansapathar
Formation in the uppermost part of the Chandarpur succession under a hot desertic climatic condition. The provenance analysis
revealed that the Chandarpur clastics were derived from granites and granite-gneisses of a continental block tectonic provenance.
Petrographic studies further indicate that high grade metamorphic rocks did not make any perceptible contribution to the Chandarpur
system. The Eastern Ghats Granulite Belt apparently did not emerge till the early Neoproterozoic. 相似文献