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81.
The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting. 相似文献
82.
Hasan Raja Naqvi Javed Mallick Laishram Mirana Devi Masood Ahsan Siddiqui 《Arabian Journal of Geosciences》2013,6(10):4045-4056
The present comparative study is multi-temporal in nature. The Revised Universal Soil Loss Equation (RUSLE), remote sensing, and GIS were used to model the soil loss estimation for soil conservation and vegetation rehabilitation in Nun Nadi watershed for the years 2000 and 2009. The estimated mean soil loss for the year 2000 and 2009 is 3,283.11 and 1,419.39 Mg?ha?1 year?1, respectively. The study finds that about 80 % area has low or least risk of erosion and about 7 % is exposed to high or very high risk which indicates the improvement in terms of soil loss if we compare the data of both the time periods. The findings show that the rainfall, LULC change, and elevation are the main responsible factors for the soil loss in Nun Nadi watershed. Conservation measures have been adopted; however, the problem still remains serious and demands urgent attention. 相似文献
83.
Manish Mehta Nilton O. Renno John Marshall Anita Sengupta Jasper F. Kok Raymond E. Arvidson Mark T. Lemmon 《Icarus》2011,211(1):172-194
While steady thruster jets caused only modest surface erosion during previous spacecraft landings on the Moon and Mars, the pulsed jets from the Phoenix spacecraft led to extensive alteration of its landing site on the martian arctic, exposed a large fraction of the subsurface water ice under the lander, and led to the discovery of evidence for liquid saline water on Mars. Here we report the discovery of the ‘explosive erosion’ process that led to this extensive erosion. We show that the impingement of supersonic pulsed jets fluidizes porous soils and forms cyclic shock waves which propagate through the soil and produce erosion rates more than an order of magnitude larger than that of other jet-induced processes. The understanding of ‘explosive erosion’ allows the calculation of bulk physical properties of the soils altered by it, provides insight into a new behavior of granular flow at extreme conditions and explains the rapid alteration of the Phoenix landing site’s ground morphology at the northern arctic plains of Mars. 相似文献
84.
Manzoor?A.?MalikEmail author Raja?Nisar?Ali Farooq?Ahmad 《Astrophysics and Space Science》2011,336(2):447-454
We derive the distribution function and the allied thermodynamic quantities for a system of galaxies with three mass species.
A new clustering parameter b
3 that inherently takes into account the masses and the number of galaxies of each kind, emerges directly from the calculations.
Our general conclusion is that the inclusion of the third component does not significantly effect the overall features of
the distribution function. 相似文献
85.
A. Raja Bayanna Shibu K. Mathew K. Sankarasubramanian P. Venkatakrishnan J. Singh B. R. Prasad 《Experimental Astronomy》2011,29(3):145-153
This paper addresses some of the issues related to externally occulted solar coronagraph; vignetting and achievable resolution
due to an external occulter. The analytical expression by Evans (J Opt Soc Am 38:1083–1085, 1948) is used to perform the initial calculations. An expression for the vignetting for a given external occulter and field angle
is derived. The values obtained with the derived expression are verified with those obtained by ZEMAX an Optical design software.
The degradation in angular resolution of the system due to vignetting is also presented and an empirical relation to calculate
the normalized resolution for a given amount of vignetting is obtained. 相似文献
86.
K. S. Banerjee R. Guin J. L. Gutierrez-Villanueva M. E. Charro D. Sengupta 《Environmental Earth Sciences》2012,65(7):2103-2110
The determination of the natural radioactivity has been carried out, by means of gamma-ray spectrometry, in exposed rock samples
collected from various geological formations across the Singhbhum Shear Zone of India. The spatial variation in the concentration
of primordial radionuclides reflects, in general, the geochemical variance among the analyzed rocks and affirms the earlier
views on genesis of uranium mineralization. This study further speculates new possibilities of thorium depletion during shearing
and metamorphism. All the obtained U-values were more than the worldwide average U-concentration (which is about 40 Bq/kg).
Interestingly, U-concentration in mica schists from Singhbhum group of rocks and in slates and argillaceous quartzites from
Iron Ore group of rocks was five to seven times higher than the global values. In contrast, the granites in study area showed
comparatively lower U-concentration. The overall results suggest the control of complex metamorphism and shearing on U-distribution
in the terrane. The contribution of 238U, 232Th and 40K to the total radiation dose in the study area was found to be significant ranging from 110 to 310 nGy/h in comparison with
the lower global, as well as Indian average values. 相似文献
87.
Isolation and characterization of phosphate-solubilizing bacteria from seagrass rhizosphere soil 总被引:1,自引:0,他引:1
Upasana Ghosh Ponnambalam Subhashini Elangovan Dilipan Subramanian Raja Thirunavukarassu Thangaradjou Lakshmanan Kannan 《中国海洋大学学报(英文版)》2012,11(1):86-92
Phosphate-solubilizing bacterial strains(6 Nos.) were isolated from the rhizosphere soils of two seagrasses(Halophila ovalis(R.Br.) Hook and Halodule pinifolia(Miki) Hartog) in the Vellar estuary.Experimental studies found that the strain PSSG6 was effective in phosphate solubilization with Phosphate Solubilization efficiency index E = 375 ± 8.54,followed by the strain PSSG5 with Phosphate Solubilization efficiency index E = 275 ± 27.3.Of the 6 strains isolated,the strains PSSG4 and PSSG5 be-longed to the genus Bacillus,and PSSG1,PSSG2 and PSSG3 were identified as Citrobacter sp.,Shigella sp.,and Klebsiella sp.,respectively,by conventional method,and PSSG6 was identified as Bacillus circulans using conventional and molecular methods. 相似文献
88.
Indian coastal waters are subjected to considerable pressure from sewage and industrial wastes, which are responsible for
the contamination of the coastal sediments with consequent loss in biosphere. The present investigation attempts to study
the significance of coarse material (Sand fraction) in the distribution of metals in polluted marine sediments. The study
revealed that coarse Sand component contains a relatively significant proportion of the anthropogenic metals (Cd, Cu, Pb and
Zn) and therefore it cannot be neglected in metal pollution studies of coastal sediments. Further, the distribution of anthropogenic
metals in both Silt + Clay and Sand fraction follow the same suit indicating similar pollution sources. From the total sediment
type (Silt + Clay and Sand fraction) all anthropogenic metals had a noticeable amount (>50%) in the acid extractable (and
potentially bio-available) fraction. This article stresses the importance of coarse fraction in metal pollution studies in
Indian coastal system. 相似文献
89.
S. Sengupta 《Journal of the Geological Society of India》2009,74(5):597-600
Megalospheric form of a striate Nummulites, provisionally identified here as Nummulites sp. aff. chavannesi de la Harpe, is documented from the Early Oligocene rocks of SW Kutch, Gujarat. This striate Nummulites occurs in association with N. fichteli-clipeus Group, N. cf. fichteli, Heterostegina, Operculina and Gypsina. High abundance of microspheric tests of reticulate Nummulites and virtual absence of microspheric tests of striate Nummulites reflect contrasting success of growth and sexual reproduction of the two groups of sympatric Nummulites. 相似文献
90.
Jyothirmayi Palaparthi Ramananda Chakrabarti Santanu Banerjee Rasmohan Guin Shayantani Ghosal Sudha Agrahari Debashish Sengupta 《Arabian Journal of Geosciences》2017,10(9):201
A comprehensive study was carried out in order to determine the radioelement and rare earth element (REE) concentrations in beach placer deposits at selected locations along the eastern coast of Andhra Pradesh in India. This was done to evaluate the economic value of these deposits. The findings of this study suggest that high Th and low K concentrations delineate the prospective regions having REE deposits. The beach placers, in general, can be characterized by high thorium and moderate uranium concentrations. The concentrations of REEs vary in the following order: Ce > La> Nd > Pr > Sm > Gd > Dy. Rapid in situ thorium prospectivity coupled with laboratory-based techniques like ICP-MS, as proposed in this study, would help in the identification of prospective REE sources along the coastal placers. The development of indigenous resources of light rare earth elements (LREEs), medium rare earth elements (MREEs), and heavy rare earth elements (HREEs) would decrease the dependence on imports, which have a strategic hold on the production and supply of the REEs, globally. 相似文献