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131.
Climate change poses formidable challenge to the development of livestock sector in India. The anticipated rise in temperature
between 2.3 and 4.8°C over the entire country together with increased precipitation resulting from climate change is likely
to aggravate the heat stress in dairy animals, adversely affecting their productive and reproductive performance, and hence
reducing the total area where high yielding dairy cattle can be economically reared. Given the vulnerability of India to rise
in sea level, the impact of increased intensity of extreme events on the livestock sector would be large and devastating for
the low-income rural areas. The predicted negative impact of climate change on Indian agriculture would also adversely affect
livestock production by aggravating the feed and fodder shortages. The livestock sector which will be a sufferer of climate
change is itself a large source of methane emissions, an important greenhouse gas. In India, although the emission rate per
animal is much lower than the developed countries, due to vast livestock population the total annual methane emissions are
about 9–10 Tg from enteric fermentation and animal wastes. 相似文献
132.
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134.
Ulf Torkelsson Gordon I. Ogilvie Axel Brandenburg James E. Pringle Åke Nordlund Robert F. Stein 《Monthly notices of the Royal Astronomical Society》2000,318(1):47-57
We excite an epicyclic motion, the amplitude of which depends on the vertical position, z , in a simulation of a turbulent accretion disc. An epicyclic motion of this kind may be caused by a warping of the disc. By studying how the epicyclic motion decays, we can obtain information about the interaction between the warp and the disc turbulence. A high-amplitude epicyclic motion decays first by exciting inertial waves through a parametric instability, but its subsequent exponential damping may be reproduced by a turbulent viscosity. We estimate the effective viscosity parameter, α v , pertaining to such a vertical shear. We also gain new information on the properties of the disc turbulence in general, and measure the usual viscosity parameter, α h , pertaining to a horizontal (Keplerian) shear. We find that, as is often assumed in theoretical studies, α v is approximately equal to α h and both are much less than unity, for the field strengths achieved in our local box calculations of turbulence. In view of the smallness (∼0.01) of α v and α h we conclude that for β p gas p mag ∼10 the time-scale for diffusion or damping of a warp is much shorter than the usual viscous time-scale. Finally, we review the astrophysical implications. 相似文献
135.
136.
A multi‐system geochronology in the Ad‐3 borehole,Pannonian Basin (Hungary) with implications for dating volcanic rocks by low‐temperature thermochronology and for interpretation of (U–Th)/He data
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Martin Danišík László Fodor István Dunkl Axel Gerdes János Csizmeg Mária Hámor‐Vidó Noreen J. Evans 《地学学报》2015,27(4):258-269
Independent geochronological and thermal modelling approaches are applied to a biostratigraphically exceptionally well‐controlled borehole, Alcsútdoboz‐3 (Ad‐3), in order to constrain the age of Cenozoic geodynamic events in the western Pannonian Basin and to test the efficacy of the methods for dating volcanic rocks. Apatite fission track and zircon U–Pb data show two volcanic phases of Middle Eocene (43.4–39.0 Ma) and Early Oligocene (32.72 ± 0.15 Ma) age respectively. Apatite (U–Th)/He ages (23.8–14.8 Ma) and independent thermal and subsidence history models reveal a brief period of heating to 55–70 °C at ~17 Ma caused by an increased heat‐flow related to crustal thinning and mantle upwelling. Our results demonstrate that, contrary to common perception, the apatite (U–Th)/He method is likely to record ‘apparent’ or ‘mixed’ ages resulting from subsequent thermal events rather than ‘cooling’ or ‘eruption’ ages directly related to distinct geological events. It follows that a direct conversion of ‘apparent’ or ‘mixed’ (U‐Th)/He ages into cooling, exhumation or erosion rates is incorrect. 相似文献
137.
Additional aspects regarding the optimum fixed and roving sampling techniques, to those already explored in a previous authors’ throughfall study, are further investigated here. The roving technique consists in the random repositioning, with a frequency fr, of N throughfall gauges among M positions (M > N), oppositely to the fixed or stationary arrangement where N = M. Both fixed and roving optimum sampling techniques of 100 monitored throughfall events sampled with 200 fixed gauges under a semideciduous tropical rain forest in Panama were investigated by means of Monte‐Carlo numerical experiments. Mean dispersion was shown to be always smaller in the roving versus the fixed gauge arrangement, independently of the relocation frequency studied (fr = 0.1, 0.2, 0.5, 1), such that all roving schemes with N ≥ 50 gauges lay within ±5% of the mean cumulative throughfall. Results indicated that a low variability, high precision, and accuracy are obtained with a modest relocation frequency fr = 0.2 (i.e. a relocation every five episodes of the original 100 measured events) and N = 30 roving gauges, with no significant improvement worth the extra field work beyond fr > 0.2 and N >30. Only by increasing the number of roving positions from M < < 200 to M = 200, the precision and accuracy of the mean estimate were improved without comprising additional labour. Hence, a roving sampling scheme which relocates gauges over completely new fresh sites each roving cycle is recommended for future throughfall studies. Finally, we designed an a priori sampling strategy which permitted us to conclude that using only the first 20 out of the total 100 measuring events, for the remaining 80 throughfall field measurements, N = 40 roving gauges (i.e. five time less than the originally 200 gauges displayed) would have been sufficient for ensuring ≤5% error, expressed as percentage of the mean cumulative throughfall. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
138.
Andreas Dehnert Oliver Kracht Frank Preusser Naki Akçar Hans Axel Kemna Peter W. Kubik Christian Schlüchter 《Quaternary Geochronology》2011,6(3-4):313-325
Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to Plio–Pleistocene fluvial successions from the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1) measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrations based on a first-order conceptualisation of the geological context and the principal succession of depositions and subsequent erosional and burial phases, and (3) using parameter estimation to identify values for the a priori unknown model parameters (burial age, initial nuclide concentrations, terrace erosion rates) that result in minimal disagreement between hypothetical and measured nuclide concentrations.The Late Pliocene Kieseloolite Formation was dated to 3650 ± 1490 ka and the Early Pleistocene Waalre Formation to 900 ± 280 ka. The unconformably overlying Upper Terrace Formation revealed ages of 740 ± 210 ka and 750 ± 250 ka for the two different sites. These findings are in good agreement with independent age control derived by bio-, magneto-, and litho-stratigraphy. Furthermore, identifiability and uncertainty analysis reveal a relationship between burial depth and sensitivity of isotope concentrations to burial age and erosion rate. Our results indicate that using shallower buried samples would enable a considerably more robust estimation of the burial age and the terrace erosion rate. Uncertainties arose mainly from nuclide measurements, and not from the uncertainties derived from modelling or insufficient knowledge of nuclide production and decay properties. 相似文献
139.
Mary R. Reid Jorge A. Vazquez Axel K. Schmitt 《Contributions to Mineralogy and Petrology》2011,161(2):293-311
Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history
of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe
approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly
similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720°C for zircon
rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon
solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures
are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different
melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal
conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage
in its evolution. There is also no compelling evidence for punctuated heat ± chemical influxes during the intermediate stages
of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but
the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir
by—or zircon entrainment in—a less evolved melt from the one in which the zircons had previously resided. 相似文献
140.
Kerstin Drost Axel Gerdes Teresa Jeffries Ulf Linnemann Craig Storey 《Gondwana Research》2011,19(1):213-231
New LA-ICP-MS U–Pb detrital zircon ages from Ediacaran and Paleozoic siliciclastic rocks are used to constrain provenance and paleogeographic affinities of the Teplá-Barrandian unit (TBU) in the centre of the Bohemian Massif (Central Europe, Czech Republic). The samples taken span the period from ≤ 635 Ma to ~ 385 Ma and permit recognition of provenance changes that reflect changes in geotectonic regime. Detrital zircon age spectra of two Ediacaran, one Lower Cambrian and three Upper Ordovician samples resemble the ages known from the NW African proportion of Gondwana, particularly the Trans-Saharan belt, while three rocks from higher Lower Cambrian to Lowermost Ordovician strata contain detritus that may have been derived exclusively from local sources. The age spectrum of the Devonian rock is a combination of the NW Gondwanan and local features. These new findings in combination with a wide range of published data are in agreement with a Neoproterozoic subduction-related setting at the margin of Gondwana followed by a Cambrian/Early Ordovician rifting stage and an Ordovician passive margin setting. Furthermore the data are in favour of a position of the TBU at the Gondwanan margin throughout pre-Variscan times. 相似文献