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排序方式: 共有345条查询结果,搜索用时 390 毫秒
21.
A method for rapid evaluation of magnetic anomalies over thin sheets is presented. This method is based on characteristic distancesX 3/4,X 1/2,X 1/4 at which the anomaly falls off to 3/4, 1/2, and 1/4 of the total (peak to peak) amplitude, respectively. Simple mathematical relations using these characteristic distances are presented to estimate the death and dip of the sheet. This method is fast and does not require prior knowledge of the base level and the origin. A few field examples are included to show the applicability and efficacy of the method. 相似文献
22.
Impact of tsunami on texture and mineralogy of a major placer deposit in southwest coast of India 总被引:1,自引:0,他引:1
The great Indonesian earth quake (26 December 2004) triggered a tsunami wave across the Bay of Bengal and Indian Ocean basins
and has brought a major havoc in several countries including India. The coastal segment between Thotapalli and Valiazhikal
in Kerala state of southwest India, where considerably rich beach placer deposit with ilmenite percentage of more than 70%
is concentrated, has been investigated to understand the impact of tsunami on coastal sediments. The grain size analysis flashes
out the significant differences between the pre- and post-tsunami littoral environments. While the mineral grains collected
during pre-tsunami period show well-sorted nature, the post-tsunami samples represent moderately to poorly sorted nature.
Similarly, unimodal and bimodal distributions of the sediments have been recorded for pre- and post-tsunami sediments, respectively.
Further, mineral assemblages corresponding to before and after this major wave activity clearly indicate the large-scale redistribution
of sediments. The post-tsunami sediments register increasing trends of garnet, sillimanite and rutile. The total heavy mineral
percentage of the post-tsunami sediment also shows an improved concentration, perhaps due to the large-scale transport of
lighter fraction. Magnetite percentage of post-tsunami samples reflects higher concentration compared to the pre-tsunami samples,
indicating the intensity of reworking process. X-ray diffraction patterns of ilmenite grains have confirmed the increased
presence of pseduorutile, and pseudobrookite in post-tsunami samples, which could be due to the mixing of more altered grains.
SEM examination of grains also confirms the significant alteration patterns on the ubiquitous mineral of placer body, the
ilmenite. The reason for these textural, mineralogical and micromorphological changes in heavy minerals particularly in ilmenite,
could be due to the churning action on the deeper sediments of onshore region or on the sediments entrapped in the near shelf
region of the area, by the ∼ 6 m high tsunami waves. 相似文献
23.
V. S. N. Murty Y. V. B. Sarma M. T. Babu D. P. Rao 《Journal of Earth System Science》1992,101(1):67-75
The distribution of temperature and salinity in the upper 500 m of the northwestern Bay of Bengal, adjoining the east coast
of India, during the retreat of southwest monsoon (September) of 1983 is presented. This study reveals coastal upwelling (limited
to the upper 40 m) induced by the local winds. Waters of higher surface salinity near the coast characterize the upwelling.
The freshwater influx near the head of the Bay diluted the surface salinity to as low as 26.0 × 10−3. The surface circulation was weak and led to a net transport of 2.0 × 106m3.s−1 directed towards northeast. 相似文献
24.
P. V. L. P. Babu 《Journal of the Indian Society of Remote Sensing》1973,1(1-2):65-67
Morphostructure is a form of the earth’s relief, developed due to tectonic movements. Structures which have undergone movement in the Quaternary time are commonly recognised in areas of low relief and recent deposition. A number of morphpstructures are delineated through geomorphologlcal studies in the Krishna and the Godavari delta region of the coastal Andhra Pradesh which are likely to entrap oil and gas. The morphostructural trends are in confirmation with the known regional trends. 相似文献
25.
A. V. Suresh Babu V. Venkateshwar Rao I. V. Muralikrishna 《Journal of the Indian Society of Remote Sensing》2007,35(1):81-91
Water Utilisation Index (WUI) defined as area irrigated per unit volume is a measure of water delivery performance and constitutes
one of the important spatial performance indicators of an irrigation system. WUI also forms basis for evaluating the adequacy
of seasonal irrigation supplies in an irrigation system (inverse of WUI is delta, i.e. depth of water supplied to a given
irrigation unit). In the present study WUI and adequacy indicators were used in benchmarking the performance of Nagarjunasagar
Left Canal Command (NSLC) in Andhra Pradesh. Optimised temporal satellite data of rabi season during the years 1990–91 and
1998–99 was used in deriving irrigated crop areas adopting hierarchical classification approach. Paddy is the predominant
crop grown and cotton, chillies, sugarcane etc. are the other crops grown in the study area. Equivalent wet area (paddy crop
area) was estimated using the operationally used project specific conversion factors. WUI was estimated at disaggregated level
viz., distributary, irrigation block, irrigation zone level using the canal discharge data. At project level, WUI estimated
to be 65 ha/MCM and 92 ha/MCM during rabi season of 1990–91 and 1998–99 years respectively. A comparison of total irrigated
area and discharges corresponding to both the years indicate that irrigation service is extensive and sub optimal during 1998–99
and it is intensive and optimal in 1990–91. It was also observed that WUI is lesser in blocks of with higher Culturable Command
Area (CCA) compared to the blocks of lower CCA. All the disaggregated units were ranked into various groups of different levels
of water distribution performance. The study demonstrates the utility of WUI as spatial performance indicator and thus useful
for benchmarking studies of irrigation command areas. The WUI together with satellite data derived spatial irrigation intensity,
crop productivity constitutes important benchmarking indices in irrigation command areas. 相似文献
26.
Elastic properties of eclogite rocks from the Bohemian massif 总被引:1,自引:0,他引:1
Vladislav Babuška Jiří Fiala D. J. Mayson R. C. Liebermann Reviewer J. Buben 《Studia Geophysica et Geodaetica》1978,22(4):348-361
Summary Compressional velocity anistropy has been studied in detail at atmospheric pressure for 78 specimens of 23 types of eclogite rocks from the Bohemian massif. For nine of these rock types, compressional and shear velocities were measured as a function of pressure to750 MPa at room temperature. The velocity anisotropy for both compressional and shear waves is less than4% at high pressure. The velocities increase with increasing garnet content and decrease with increasing symplectitization. The Moldanubian eclogites have significantly higher velocities, on the average, than the eclogites from the Kruné hory crystalline complex, although the densities of both groups are comparable. 相似文献
27.
Age-dependent Large-scale Fabric of the Mantle Lithosphere as Derived from Surface-wave Velocity Anisotropy 总被引:3,自引:0,他引:3
V. Babuška J.-P. Montagner J. Plomerová N. Girardin 《Pure and Applied Geophysics》1998,151(2-4):257-280
—Systematic variations of the seismic radial anisotropy ξ to depths of 200–250 km in North America and Eurasia and their surroundings are related to the age of continental provinces, and typical depth dependences of ξ R are determined. The relative radial anisotropy ξ R in the mantle lithosphere of Phanerozoic orogenic belts is characterized by ν SH > ν SV , with its maximum depth of about 70 km, on the average, while beneath old shields and platforms, it exhibits a maximum deviation from ACY400 model (Montagner and Anderson, 1989) at depths of about 100 km with ν SV ≥ν SH signature. An interpretation of the observed seismic anisotropy by the preferred orientation of olivine crystals results in a model of the mantle lithosphere characterized by anisotropic structures plunging steeply beneath old shields and platforms, compared to less inclined anisotropies beneath Phanerozoic regions. This observation supports the idea derived from petrological and geochemical observations that a mode of continental lithosphere generation may have changed throughout earth's history. 相似文献
28.
D. S. Suresh Babu V. Nandakumar B. John B. K. Jayaprasad S. V. Pramod 《Environmental Geology》2000,39(3-4):390-397
Impact of catchment erosion and the resultant reservoir siltation from a tropical environment is reported here to discuss
the effect of a reservoir in the natural degradation of an evergreen-forested segment. While an area of 8.01 km2 has been affected by direct inundation at the full reservoir level, another 2.6 km2 area once under thick forest cover, had also lost its identity over the last 38 years by indirect degradation. This zone
mainly falls in the confluence of tributaries, namely Neyyar and Mullayar, with the reservoir. The capacity of the reservoir
was found to be reduced by 28.8 Mm3 during this period and the annual average loss is calculated as 0.75 Mm3 (0.71%), indicating the intensity of erosion from the catchment zone. In case the proposed upper dam in the reservoir comes
into existence, an additional area of 2.4 km2 from the virgin forest would be submerged and more area would face degradation around the inundated zone.
Received: 29 July 1998 · Accepted: 16 November 1998 相似文献
29.
We present a detailed thermal and structural analysis of a 2 m class solar telescope mirror which is subjected to a varying heat load at an observatory site. A 3-dimensional heat transfer model of the mirror takes into account the heating caused by a smooth and gradual increase of the solar flux during the day-time observations and cooling resulting from the exponentially decaying ambient temperature at night. The thermal and structural response of two competing materials for optical telescopes, namely Silicon Carbide – best known for excellent heat conductivity and Zerodur – preferred for its extremely low coefficient of thermal expansion, is investigated in detail. The insight gained from these simulations will provide a valuable input for devising an efficient and stable thermal control system for the primary mirror. 相似文献
30.
In recent years, spatial variability modeling of soil parameters using random field theory has gained distinct importance in geotechnical analysis. In the present study, commercially available finite difference numerical code FLAC 5.0 is used for modeling the permeability parameter as spatially correlated log-normally distributed random variable and its influence on the steady state seepage flow and on the slope stability analysis are studied. Considering the case of a 5.0 m high cohesive–frictional soil slope of 30°, a range of coefficients of variation (CoV%) from 60 to 90% in the permeability values, and taking different values of correlation distance in the range of 0.5–15 m, parametric studies, using Monte Carlo simulations, are performed to study the following three aspects, i.e., (i) effect of stochastic soil permeability on the statistics of seepage flow in comparison to the analytic (Dupuit′s) solution available for the uniformly constant permeability property; (ii) strain and deformation pattern, and (iii) stability of the given slope assessed in terms of factor of safety (FS). The results obtained in this study are useful to understand the role of permeability variations in slope stability analysis under different slope conditions and material properties. 相似文献