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61.
Diagnostic infrared spectra of individual nanogram-sized interplanetary dust particles (IDPs) collected in the Earth's stratosphere have been obtained. A mount containing three crushed “chondritic” IDPs shows features near 1000 and 500 cm?1, suggestive of crystalline pyroxene, and different from those of crystalline olivine, amorphous olivine, or meteoritic clay minerals. The structural diversity of chondritic IDPs and possible effects of atmospheric heating must be considered when comparing this spectrum with astrophysical spectra of interplanetary and cometary dust. Transmission electron microscope (TEM) and infrared observations are also reported on one member of the rare subset of IDPs which resemble hydrated carbonaceous chondrite matrix material. The infrared spectrum of this particle between 4000 and 400 cm?1 closely matches that of the C2 meteorite Murchison. TEM observations suggest that this class of particles might serve as a thermometer for the process of heating on atmospheric entry. 相似文献
62.
The interplanetary magnetic field has been shown to influence the ring current field represented by Dst. Explorer 28 hourly magnetic field observations have been used with the hourly Dst values. The moderate geomagnetic storms of 60 and quiet-time fluctuations of 10–30 are correlated with the North to South change of the interplanetary field component perpendicular to the ecliptic. This change in the interplanetary field occurs one to three hours earlier than the corresponding change in the Dst field. 相似文献
63.
José F. Gómez Joaquín Trapero Sergio Pascual Nimesh Patel Carmen Morales José M. Torrelles 《Monthly notices of the Royal Astronomical Society》2000,314(4):743-746
We present NH3 (1,1) and (2,2) observations of MBM 12, the closest known molecular cloud (65-pc distance), aimed at finding evidence for on-going star formation processes. No local temperature (with a T rot upper limit of 12 K) or linewidth enhancement is found, which suggests that the area of the cloud that we have mapped (15-arcmin size) is not currently forming stars. Therefore this nearby 'starless' molecular gas region is an ideal laboratory to study the physical conditions preceding new star formation.
A radio continuum source has been found in Very Large Array archive data, close to but outside the NH3 emission. This source is likely to be a background object. 相似文献
A radio continuum source has been found in Very Large Array archive data, close to but outside the NH
64.
65.
Rounding of pumice clasts during transport: field measurements and laboratory studies 总被引:1,自引:0,他引:1
Volcanic clasts in many pyroclastic density current deposits are notably more round than their counterparts in corresponding
fall deposits. This increase in roundness and sphericity reflects different degrees of comminution, abrasion and breakup during
transport. We performed experimental measurements to determine an empirical relationship between particle shape and mass loss caused by particle–particle interactions. We consider, as examples, pumice
from four volcanoes: Medicine Lake, California; Lassen, California; Taupo, New Zealand; Mount St Helens, Washington. We find
that average sample roundness reaches a maximum value once particles lose between 15% and 60% of their mass. The most texturally
homogeneous clasts (Taupo) become the most round. Crystal-rich pumice abrades more slowly than crystal-free pumice of similar
density. Abrasion rates also decrease with time as particles become less angular. We compare our experimental measurements
with the shapes of clasts in one of the May 18, 1980 pyroclastic density current units at Mount St Helens, deposited 4–8 km
from the vent. The measured roundness of these clasts is close to the experimentally determined maximum value. For a much
smaller deposit from the 1915 Lassen eruption, clast roundness is closer to the value for pumice in fall deposits and suggests
that only a few volume percent of material was removed from large clasts. In neither field deposit do we see a significant
change in roundness with increasing distance from the vent. We suggest that this trend is recorded because much of the rounding
and ash production occur in proximal regions where the density currents are the most energetic. As a result, all clasts that
are deposited have experienced similar amounts of comminution in the proximal region, and similar amounts of abrasion as they
settle through the dense, near-bed region prior to final deposition. 相似文献
66.
Satish J. Patel Apurva D. Shitole Jaquilin K. Joseph 《Journal of the Geological Society of India》2018,91(1):41-46
Plug-shaped ichnofossils Conichnus conicus, Conostichus broadheadi and C. stouti are found in the intercalated micritic sandstone and sandy allochemic limestone shale sequence of Bagh Group, Narmada district, Gujarat. These ichnospecies occur at two stratigraphic levels and shows distinct morphological features interpreted as resting/dwelling structures of sea anemone. The occurrence of these ichnospecies along with oyster fossils genera like Bosostrea and Indostrea indicate shallow marine environment. 相似文献
67.
Satish J. Patel Jehova L. Darngawn Jaquilin K. Joseph Apurva D. Shitole 《Journal of the Geological Society of India》2018,92(4):419-426
Chorar Island exposes ~109 m thick middle Jurassic (Bathonian-Callovian) succession in the eastern most part of the Kachchh Basin, Patan District, Gujarat and is divided into two, Khadir and Gadhada formations. It mainly comprises of mixed siliciclastic-carbonate sediments and limestones; the shales dominate the lower part of the succession while the top of the succession is marked by ferruginous sandstone which also forms the vast, prominent peripheral zone of the Chorar dome. The field and laboratory analysis of the succession reveals nine lithofacies which includes ferruginous sandstone, cross bedded white sandstone, micritic sandstone, allochemic sandstone, sandy micrite, mudstone, sandy allochemic limestone, coralline limestone and shale. The mix siliciclastic-carbonate sediments and ferruginous facies are fossiliferous in nature and display sedimentary structures, like ripple marks, cross- and planar- lamination with biogenic sedimentary structures. Coralline limestone facies comprise of large size (>1m diameter) corals, which are diagenetically modified severely and have lost its original internal structures. The sediment characteristics and associated bioclasts indicates low to moderate wave and current energy in shoreface-offshore subsequently changing to wave dominated shoreface during the deposition of the middle Jurassic sediments of the Chorar Island. 相似文献
68.
Net Primary Productivity (NPP) is a significant biophysical vegetation variable to understand the spatio-temporal distribution of carbon and source-sink nature of the ecosystem. This study was carried out in a forest plantation area and aimed to (i) estimate the spatio-temporal patterns of NPP during 2009 and 2010 using Carnegie-Ames-Stanford Approach [CASA] model and (ii) study the effects of climate variables on the NPP using generalized linear modelling (GLM) approach. The total annual NPP varied from 157.21 to 1030.89 gC m?2 yr?1 for the year 2009 and from 154.36 to 1124.85 g C m?2 yr?1 for the year 2010. The annual NPP was assessed across four major plantation types, where maximum NPP gain (106 and 139 g C m?2 yr?1 ) in October was noticed in teak (Tectona grandis) and minimum (77 and 109 g C m?2 yr?1 ) in eucalyptus (Eucalyptus hybrid) during 2009 and 2010.The validation, using field-estimated NPP, showed under-estimation of modelled NPP, with maximum MAPE of 34% for eucalyptus and minimum of 13% for teak. The dominant influence of precipitation on the NPP was revealed by GLM explaining more than 20% of variation. CASA model efficiently estimated the annual NPP of plantations. The accuracy could be improved further with inclusion of higher resolution data. 相似文献
69.
Exhumation has been recognised as a key factor in understanding the dynamics of a mountain belt. Normal faulting, erosion and ductile thinning are the three basic mechanisms to exhume the deeper high grade metamorphic rocks to the surface. Convergent orogenic belts are characterised by over-thickening of the crust due to thrusting and folding. The interplay of uplift due to over-thickening of crust and climatic-erosion is the most plausible mechanism of exhumation as suggested by the numerical models and analogue experiments. The analysis of 534 thermo-chronological dates through 1D-thermal numerical model in the Himalaya suggest that the exhumation is dominantly due to erosion but the pattern of erosion is controlled by local tectonic activities in different sector of the Himalaya since Miocene, indicating that tectonic force as the prime mechanism of exhumation in Himalaya. 相似文献
70.
T. M. Patel K. Nath 《International Journal of Environmental Science and Technology》2014,11(5):1237-1248
Nanofiltration of ternary mixtures of sodium chloride and aqueous solutions of Reactive Black-5 was studied in two different modules, namely, flat sheet and spiral wound over a wide range of operating conditions. Hydrophilized polyamide membrane with molecular weight cutoff of 150 was used for the experiments. Combined effect of dye and salt concentration, trans-membrane pressure drop, initial pH of feed solution on the permeate flux, and observed retention were investigated. Extent of color removal, chemical oxygen demand (COD), total dissolved solid (TDS), and conductivity were determined to assess performance of the membrane. The experimental results showed that both the permeate flux and observed retention decreased with increase in dye as well as salt concentration in the feed. Permeate fluxes were lower at higher pH values. Substantial removal of color was achieved in the nanofiltration experiments with a marked reduction in COD and TDS. The process allowed the production of permeate stream with great reutilization possibilities. 相似文献