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441.
Magnetic susceptibility of 72 cambisol profiles from the vicinity of the Vír dam, NW Moravia was measured. The enhanced susceptibility
of topsoil, particularly of the horizon O, was assessed from the aspect of vegetation setting and magnetic mineralogy. Magnetic
susceptibility variations with field and temperature as well as frequency dependent susceptibility were applied to indicate
magnetic carriers. It was found that the enhanced magnetic susceptibility is caused very likely by the presence of maghemite
and magnetite of various grain sizes. Magnetic minerals are pedogenic in origin in all three horizons, while in the O and
A horizons they are mostly anthropogenic in origin. Magnetic susceptibility was correlated with contents of trace elements
Mo, Cu, Pb, Zn, Ag, As, Cd, Sb, Bi, Hg, Se, furthermore with TOT/C, TOT/S, and 137C. The close association of susceptibility with Pb, Sb and Hg, or also with Mo, As, Se and their similar depth variations
suggest a slight anthropogenic input in soils from a long-distant source. The same is valid for 137C, its strong correlation with magnetic susceptibility has been found. 相似文献
442.
Petr Pruner Nadja Zupan Hajna Andrej Mihevc Pavel Bosák Otakar Man Petr Schnabl Daniela Venhodová 《Studia Geophysica et Geodaetica》2010,54(1):27-48
Clastic and chemogenic cave sediments were sampled and analyzed from Račiška pečina and Pečina v Borštu caves of southwestern
Slovenia. Samples were subjected to both thermal and alternating field demagnetization; specimens belonging to the same sample
of the same layer produce identical results. Unblocking temperatures of 540 to 560°C on average suggests magnetite as the
principal carrier of magnetization. These directions also pass a reversals test indicating the demagnetization results are
free of secondary overprints and have adequately averaged out paleosecular variation. Normally magnetized clays containing
fauna belonging to the MN17 mammal biozone at a depth of ∼ 4 m in Račiška pecina cave indicate these clays were deposited
at the beginning of the Olduvai subchron (1.95 Ma). Correlation with the Geomagnetic Polarity Time Scale (GPTS) indicates
the base of the speleothems in Račiška pečina terminate in the upper part of subchron C2An.3n with numerous breaks in deposition,
lasting up to 250 ka and more. Therefore rates of speleothem growth cannot be calculated. Fold tests on dome-like stalagmites
of differing sizes and ages (Pleistocene, Pliocene) from the two caves indicate the domelike structures are primary. 相似文献
443.
Soejono Igor Janoušek Vojtěch Žáčková Eliška Sláma Jiří Konopásek Jiří Machek Matěj Hanžl Pavel 《International Journal of Earth Sciences》2017,106(6):2109-2129
International Journal of Earth Sciences - Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and... 相似文献
444.
Pavel Florin Vacareanu Radu Calotescu Ileana Sandulescu Ana-Maria Arion Cristian Neagu Cristian 《Natural Hazards》2017,87(2):1167-1187
Natural Hazards - This paper focuses on the investigation of seismic risk for residential buildings situated in Bucharest, the capital city of Romania. With a population of nearly 2 million... 相似文献
445.
A model of thermally driven dynamo in the Boussinesq approximation in the spherical shell with the free rotating inner core is considered. To solve equations we use a new in dynamo modeling control volume technique (for details of this method for hydrodynamics see Patankar, 1980). The main advantage of this method over previous attempts to solve magnetohydrodynamics equations in the spherical grids is that no filtering of high harmonics in the pole regions is needed. We present the results of simulations for the self-consistent dynamo system evolution over the diffusion time and longer periods. Different ways of stabilizations of magnetohydrodynamics equations, when convective terms are of the same order (or larger) as conductive ones, are considered. 相似文献
446.
This paper includes a discussion of the validity of theobjections which are usuallyraised against the physical plausibility of the correlationsbetween extraterrestrialphenomena and changes in circulation in the lower atmosphere.The behaviour of the winterlower troposphere in the Northern Hemisphere was analysed bothon a month-to-month timescale and on a day-to-day time scale. The mechanisms which cansatisfactorily explainthe behaviour of the winter lower troposphere on these timescales have been described.The basic features of the results presented were explained bymeans of a mechanism basedon the propagation of planetary waves. Attention was focussedon studying the connectionsamong the changes in the pressure and temperature fields, thechanges in solar/geomagnetic activity and QBO phases by the method of composites. It hasbeen found that the compositeswithout considering QBO phases are similar to the QBO-eastpatterns under the highestactivities. Pressure deviations during QBO-west high solaractivity or low geomagneticactivity and temperature deviations during QBO-east/west lowgeomagnetic activity provedto be of negligible statistical significance. 相似文献
447.
Pavel Voráček 《Astrophysics and Space Science》1989,159(2):181-188
The hyperbolic motion of an idealized globular particle with the Planck length radius is described by means of special relativity in order to derive an upper quantum limit of acceleration. Furthermore, it is shown that the existence of a relative acceleration can be excluded by principle. Finally, by assuming validity of Mach's principle, it is deduced that the acceleration of the rate of increase of the radius of the (closed) Universe in the Planck era, is equal, in its absolute value, to one-half of the maximum quantum limit of acceleration; the result is then shortly discussed. 相似文献
448.
Under assumption of the closed FRW-universe, the idea is presented that the cosmological expansion/contraction on its own, has an entropy balancing effectively the changing entropy of the cosmic fluid in such a way that at every epoch the total entropy of the Universe remains constant. 相似文献
449.
Pavel Kroupa Sverre Aarseth Jarrod Hurley 《Monthly notices of the Royal Astronomical Society》2001,321(4):699-712
Direct N -body calculations are presented of the formation of Galactic clusters using GasEx , which is a variant of the code Nbody6 . The calculations focus on the possible evolution of the Orion nebula cluster (ONC) by assuming that the embedded OB stars explosively drove out 2/3 of its mass in the form of gas about 0.4 Myr ago. A bound cluster forms readily and survives for 150 Myr despite additional mass loss from the large number of massive stars, and the Galactic tidal field. This is the very first time that cluster formation is obtained under such realistic conditions. The cluster contains about 1/3 of the initial 104 stars, and resembles the Pleiades cluster to a remarkable degree, implying that an ONC-like cluster may have been a precursor of the Pleiades. This scenario predicts the present expansion velocity of the ONC, which will be measurable by upcoming astrometric space missions. These missions should also detect the original Pleiades members as an associated expanding young Galactic-field subpopulation. The results arrived at here suggest that Galactic clusters form as the nuclei of expanding OB associations.
The results have wide implications, also for the formation of globular clusters and the Galactic-field and halo stellar populations. In view of this, the distribution of binary orbital periods and the mass function within and outside the model ONC and Pleiades is quantified, finding consistency with observational constraints. Advanced mass segregation is evident in one of the ONC models. The calculations show that the primordial binary population of both clusters could have been much the same as is observed in the Taurus–Auriga star-forming region. The computations also demonstrate that the binary proportion of brown dwarfs is depleted significantly for all periods, whereas massive stars attain a high binary fraction. 相似文献
The results have wide implications, also for the formation of globular clusters and the Galactic-field and halo stellar populations. In view of this, the distribution of binary orbital periods and the mass function within and outside the model ONC and Pleiades is quantified, finding consistency with observational constraints. Advanced mass segregation is evident in one of the ONC models. The calculations show that the primordial binary population of both clusters could have been much the same as is observed in the Taurus–Auriga star-forming region. The computations also demonstrate that the binary proportion of brown dwarfs is depleted significantly for all periods, whereas massive stars attain a high binary fraction. 相似文献
450.
Pavel Voráček 《Astrophysics and Space Science》1985,116(1):197-206
Mach's principle is formulated in two different ways, heuristic and mathematical. Known problems of the principle are listed and two of them, the problem of its validity in the case the Universe is open and the boundary condition problem, are analyzed separately. Moreover, the history of the cosmic potential is outlined and a short modification of Horák's deduction of the potential is presented together with a discussion on the conditions of the solution. The conclusions are drawn that the Universe is closed and that Mach's principle is compatible with the general theory of relativity, provided that the Big Bang did not start from a singularity but from finite volume and density. In the last section it is shown that Rosen's bimetric theory is compatible with our picture of the Universe. 相似文献