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1.
2.
We find errors in theory and application in the paper by van der Kolk et al. (Geophysical Prospecting 49 , 179–197 (2001)) that invalidate their arguments for the cause of the reduction in the velocity of the vertically propagating slower split shear-wave in the gas cap over the Natih field in Oman. We suggest that existing theories are adequate and can explain the anomaly. 相似文献
3.
A two‐dimensional, discrete‐element modelling technique is used to investigate the initiation and growth of detachment folds in sedimentary rocks above a weak décollement level. The model depicts the sedimentary rocks as an assemblage of spheres that obey Newton's equations of motion and that interact with elastic forces under the influence of gravity. Faulting or fracturing between neighbouring elements is represented by a transition from repulsive–attractive forces to solely repulsive forces. The sedimentary sequence is mechanically heterogeneous, consisting of intercalated layers of markedly different strengths and thicknesses. The interlayering of weak and strong layers within the sedimentary rocks promotes the localization of flexural flow deformation within the weak layers. Even with simple displacement boundary conditions, and straightforward interlayering of weak and strong layers, the structural geometries that develop are complex, with a combination of box, lift‐off and disharmonic detachment fold styles forming above the décollement. In detail, it is found that the modelled folds grow by both limb rotation and limb lengthening. The combination of these two mechanisms results in uplift patterns above the folds that are difficult, or misleading, to interpret in terms of simple kinematic models. Comparison of modelling results with natural examples and with kinematic models highlights the complexities of structural interpretation in such settings. 相似文献
4.
Partitioning of volatile chemicals among the gas, liquid, and solid phases during freezing of liquid water in clouds can impact
trace chemical distributions in the troposphere and in precipitation. We describe here a numerical model of this partitioning
during the freezing of a supercooled liquid drop. Our model includes the time-dependent calculation of the coupled processes
of crystallization kinetics, heat transport, and solute mass transport, for a freezing hydrometeor particle. We demonstrate
the model for tracer partitioning during the freezing of a 1000 μm radius drop on a 100 μm ice substrate, under a few ambient
condition scenarios. The model effectively simulates particle freezing and solute transport, yielding results that are qualitatively
and quantitatively consistent with previous experimental and theoretical work. Results suggest that the ice shell formation
time is governed by heat loss to air and not by dendrite propagation, and that the location of ice nucleation is not important
to freezing times or the effective partitioning of chemical solutes. Even for the case of nucleation at the center of the
drop, we found that dendrites propagated rapidly to form surface ice. Freezing then proceeded from the outside in. Results
also indicate that the solid-liquid interfacial surface area is not important to freezing times or the effective partitioning
of chemical solutes, and that the rate aspects of trapping are more important than equilibrium solid-liquid partitioning to
the effective partitioning resulting from freezing. 相似文献
5.
Jörg Giese Diane Seward Finlay M. Stuart Eliane Wüthrich Edwin Gnos Daniel Kurz Urs Eggenberger Guido Schreurs 《Geostandards and Geoanalytical Research》2010,34(1):39-48
Apatite fission-track and (U-Th)/He analyses require the liberation of intact idiomorphic apatite grains from rock samples. While routinely being carried out by mechanical methods, electrodynamic disaggregation (ED) offers an alternative approach. The high-voltage discharges produced during the ED process create localised temperature peaks (10000 K) along a narrow plasma channel. In apatite, such high temperatures could potentially reduce the length of fission tracks, which start to anneal at temperatures > 60 °C, and could also enhance He diffusion, which becomes significant at 30–40 °C over geological time scales. A comparison of fission-track analyses and (U-Th)/He ages of apatites prepared both by mechanical (jaw crusher, disk mill) and ED processing provides a way of determining whether heating during the latter method has any significant effect. Apatites from three samples of different geological settings (an orthogneiss from Madagascar, the Fish Canyon Tuff, and a muscovite-gneiss from Greece) yielded statistically identical track length distributions compared to samples prepared mechanically. Additionally, (U-Th)/He ages of apatites from a leucogranite from Morocco prepared by both methods were indistinguishable. These first results indicated that during electrodynamic disaggregation apatite crystals were not heated enough to partially anneal the fission tracks or induce significant diffusive loss of He. 相似文献
6.
Jiemin Lu Mark Wilkinson R. Stuart Haszeldine Adrian J. Boyce 《Environmental Earth Sciences》2011,62(3):507-517
Miller field of the North Sea has had high concentrations of natural CO2 for ~70 Ma. It is an ideal analog for the long-term fate of CO2 during engineered storage, particularly for formation of carbonate minerals that permanently lock up CO2 in solid form. The Brae Formation reservoir sandstone contains an unusually high quantity of calcite concretions; however,
C and O stable isotopic signatures suggest that these are not related to the present-day CO2 charge. Margins of the concretions are corroded, probably because of reduced pH due to CO2 influx. Dispersed calcite cements are also present, some of which postdate the CO2 charge and, therefore, are the products of mineral trapping. It is calculated that only a minority of the reservoired CO2 in Miller (6–24%) has been sequestrated in carbonates, even after 70 Ma of CO2 emplacement. Most of the CO2 accumulation is dissolved in pore fluids. Therefore, in a reservoir similar to the Brae Formation, engineered CO2 storage must rely on physical retention mechanisms because mineral trapping is both incomplete and slow. 相似文献
7.
Peder Norberg Carlton M. Baugh Ed Hawkins Steve Maddox John A. Peacock Shaun Cole Carlos S. Frenk Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Darren Madgwick Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,328(1):64-70
We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range . The clustering of galaxies in real space is well-fitted by a correlation length and power-law slope . The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M *, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al. 相似文献
8.
Parasitic programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. We describe a microprocessor-based automated SETI acquisition system which searches for and records spectra of narrowband signals in the IF band of an observatory receiver. Data taken with this system over 35 days at the Hat Creek Radio Observatory at 1612 MHz are discussed. Out of approximately 105 spectra processed during this period, 4000 were identified by the system as containing narrowband signals and were recorded. Subsequent analysis indicates that over 3900 of these are due to local RF contamination. The remainder are undergoing further investigation. 相似文献
9.
Stuart J. Robbins Jamie D. Riggs Brian P. Weaver Edward B. Bierhaus Clark R. Chapman Michelle R. Kirchoff Kelsi N. Singer Lisa R. Gaddis 《Meteoritics & planetary science》2018,53(4):891-931
Impact crater populations help us to understand solar system dynamics, planetary surface histories, and surface modification processes. A single previous effort to standardize how crater data are displayed in graphs, tables, and archives was in a 1978 NASA report by the Crater Analysis Techniques Working Group, published in 1979 in Icarus. The report had a significant lasting effect, but later decades brought major advances in statistical and computer sciences while the crater field has remained fairly stagnant. In this new work, we revisit the fundamental techniques for displaying and analyzing crater population data and demonstrate better statistical methods that can be used. Specifically, we address (1) how crater size-frequency distributions (SFDs) are constructed, (2) how error bars are assigned to SFDs, and (3) how SFDs are fit to power-laws and other models. We show how the new methods yield results similar to those of previous techniques in that the SFDs have familiar shapes but better account for multiple sources of uncertainty. We also recommend graphic, display, and archiving methods that reflect computers’ capabilities and fulfill NASA's current requirements for Data Management Plans. 相似文献
10.
Kirsty J. Rhook Paul M. Geil J. Stuart B. Wyithe 《Monthly notices of the Royal Astronomical Society》2009,392(4):1388-1396
It has recently been suggested that the power spectrum of redshifted 21 cm fluctuations could be used to measure the scale of baryonic acoustic oscillations (BAOs) during the reionization era. The resulting measurements are potentially as precise as those offered by the next generation of galaxy redshift surveys at lower redshift. However, unlike galaxy redshift surveys, which in the linear regime are subject to a scale-independent galaxy bias, the growth of ionized regions during reionization is thought to introduce a strongly scale-dependent relationship between the 21 cm and mass power spectra. We use a seminumerical model for reionization to assess the impact of ionized regions on the precision and accuracy with which the BAO scale could be measured using redshifted 21 cm observations. For a model in which reionization is completed at z ∼ 6 , we find that the constraints on the BAO scale are not systematically biased at z ≳ 6.5 . In this scenario, and assuming the sensitivity attainable with a low-frequency array comprising 10 times the collecting area of the Murchison Widefield Array, the BAO scale could be measured to within 1.5 per cent in the range 6.5 ≲ z ≲ 7.5 . 相似文献