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101.
J. Delgado P. Alfaro J. Galindo-Zaldivar A. Jabaloy A. C. López Garrido C. Sanz de Galdeano 《Pure and Applied Geophysics》2002,159(11-12):2733-2749
—?This paper presents the results of the application of a technique of geophysical surveying based on resonance frequency of materials, in a small basin within the Internal Zones of the Betic Cordillera (southern Spain). The frequencies determined have enabled the main features of the basin's structure to be delineated, clearly identifying its asymmetry due to variations in the position of the rigid basement in different sectors. The results show that this method does not guarantee a perfect identification of coarse sediments, unless these overlie substantial more rigid materials. On the other hand, the same method was very effective for studying very soft sediments (peat), and it was possible to establish a quantitative relationship for determining the thickness of these sediments based on their resonance frequency. This relationship was then used to map peat thickness in the basin. The results have been compared with gravity studies and mechanical drillings undertaken in the region. 相似文献
102.
103.
This study analyses and discusses well preserved examples of Late Jurassic structures in the Northern Calcareous Alps, located at the Loferer Alm, about 35 km southwest of Salzburg. A detailed sedimentary and structural study of the area was carried out for a better understanding of the local Late Jurassic evolution. The Grubhörndl and Schwarzenbergklamm breccias are chaotic, coarse-grained and locally sourced breccias with mountain-sized and hotel-sized clasts, respectively. Both breccias belong to one single body of breccias, the Grubhörndl breccia representing its more proximal and the Schwarzenbergklamm breccia its more distal part, respectively. Breccia deposition occurred during the time of deposition of the Ruhpolding Radiolarite since the Schwarzenbergklamm breccia is underlain and overlain by these radiolarites. Formation of the breccias was related to a major, presumably north-south trending normal fault scarp. It was accompanied and post-dated by west-directed gravitational sliding of the Upper Triassic limestone (“Oberrhätkalk”), which was extended by about 6% on top of a glide plane in underlying marls. The breccia and slide-related structures are sealed and blanketed by Upper Jurassic and Lower Cretaceous sediments. The normal fault scarp, along which the breccia formed, was probably part of a pull-apart basin associated with strike slip movements. On a regional scale, however, we consider this Late Jurassic strike-slip activity in the western part of the Northern Calcareous Alps to be synchronous with gravitational emplacement of “exotic” slides and breccias (Hallstatt mélange), triggered by Late Jurassic shortening in the eastern part of the Northern Calcareous Alps. Hence, two competing processes affected one and the same continental margin. 相似文献
104.
Ground temperature changes in eastern Canada: borehole temperature evidence compared with proxy data
Borehole temperature logs have been inverted to infer ground temperature histories (GTH) in eastern and central Canada. Regional ground temperature histories were obtained by simultaneous inversion of several temperature profiles from the same areas. Simultaneous inversion of 21 temperature logs sampled across all of eastern and central Canada yielded an average solution for this region. All but three of the studied sites show signs of warming in the last 150 years. This period of warming, which started after 1800 AD, was found throughout this part of Canada. The warming followed a cooler period corresponding to the little Ice Age. The inferred ground temperature histories exhibit long-term trends similar to those obtained from treering growth indices in nearby regions and stable isotope data in the southern hemisphere. The modern warming appears correlated with the atmospheric concentration of CO2 as measured in ice cores. 相似文献
105.
Roberto O. Aquilano Juan C. Muzzio Hugo D. Navone Alejandra F. Zorzi 《Celestial Mechanics and Dynamical Astronomy》2007,99(4):307-324
We used a multipolar code to create, through the dissipationless collapses of systems of 1,000,000 particles, three self-consistent
triaxial stellar systems with axial ratios corresponding to those of E4, E5 and E6 galaxies. The E5 and E6 models have small,
but significant, rotational velocities although their total angular momenta are zero, that is, they exhibit figure rotation;
the rotational velocity decreases with decreasing flattening of the models and for the E4 model it is essentially zero. Except
for minor changes, probably caused by unavoidable relaxation effects, the systems are highly stable. The potential of each
system was subsequently approximated with interpolating formulae yielding smooth potentials, stationary for the non-rotating
model and stationary in the rotating frame for the rotating ones. The Lyapunov exponents could then be computed for randomly
selected samples of the bodies that make up the different systems, allowing the recognition of regular and partially and fully
chaotic orbits. Finally, the regular orbits were Fourier analyzed and classified using their locations on the frequency map.
As it could be expected, the percentages of chaotic orbits increase with the flattening of the system. As one goes from E6
through E4, the fraction of partially chaotic orbits relative to that of fully chaotic ones increases, with the former surpassing
the latter in model E4; the likely cause of this behavior is that triaxiality diminishes from E6 through E4, the latter system
being almost axially symmetric. We especulate that some of the partially chaotic orbits may obey a global integral akin to
the long axis component of angular momentum. Our results show that is perfectly possible to have highly stable triaxial models
with large fractions of chaotic orbits, but such systems cannot have constant axial ratios from center to border: a slightly
flattened reservoir of highly chaotic orbits seems to be mandatory for those systems. 相似文献
106.
Ammonoid diversity patterns show that the spreading of oceanic anoxia is not the initial and major kill mechanism for the
Cenomanian/Turonian mass extinction as usually suggested. In the Anglo-Paris Basin and the Vocontian Basin, the drop of ammonoid
species richness starts around the middle/late Cenomanian boundary, i.e. 0.75 myr before the occurrence of anoxic deepwater
sediments. The stepwise extinction of first heteromorphs and then acanthoceratids is incompatible with the rise of the oxygen
minimum zone. Moreover, shelf environments of these basins remained well oxygenated during the Cenomanian/Turonian boundary
interval. Thus, we stress that other causative mechanisms initiated the ammonoid extinction even if anoxia subsequently participated
in the demise of marine ecosystems.
Editorial handling: M.J. Benton & J.-P. Billon-Bruyat 相似文献
107.
108.
Adriana?V.?R.?SilvaEmail author Tatiana?F.?Laganá C.?Guillermo?Gimenez?De?Castro Pierre?Kaufmann Joaquim?E.?R.?Costa Hugo?Levato Marta?Rovira 《Solar physics》2005,227(2):265-281
Solar maps at 212 and 405 GHz obtained by the Solar Submillimetric Telescope (SST) show regions of enhanced brightness temperature, which coincide with the location of active regions. A statistical study of the radio emission from these active regions was performed for the first time at such high frequencies during 23 days on June and July 2002, when the atmospheric opacity was low. The brightest regions on the maps were chosen for this study, where the brightness excess observed varies from 3 to 20% above quiet Sun levels (i.e., 200–1000 K) at both wavelengths. Sizes of the regions of enhanced emission calculated at half the maximum value were estimated to be between 2′ and 7′. These sizes agree with observed sizes of active regions at other wavelengths such as Hα and ultraviolet. An important result is that the flux density spectra of all sources increase toward submillimeter frequencies, yielding flux density spectral index with an average value of 2.0. The flux density of the active region sources were complemented with that from maps at 17 and 34 GHz from the Nobeyama Radio Heliograph. The resulting spectra at all four frequencies were fit considering the flux density to be due to thermal bremsstrahlung from the active region. In the calculations, the source radius was assumed to be the mean of the measured values at 212 and 405 K. The effective temperatures of the radio emitting source, assumed homogeneous, obtained from this fit were 0.6–2.9 × 104 K, for source diameters of 2′–7′. 相似文献
109.
J. Delgado C. López Casado J. Giner A. Estévez A. Cuenca S. Molina 《Pure and Applied Geophysics》2000,157(9):1445-1462
110.