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951.
This paper examines the relaxation of planetary surface features in the size range from one to several hundred kilometers. For this purpose a new type of computational method is used. This involves the assumption of axial symmetry and supposes also that motion takes place in a vertical direction only. Although this later assumption may seem restrictive, comparison with results computed by other techniques show that it produces relatively exact results. Furthermore, the method may be easily applied to a wide variety of situations in which for example the viscosity is a function of position time, shear-gradient, and even previous history, as well as cases in which inertial terms are important.In this paper the results of applying the method to two particular problems are briefly described — relaxation under a highly depth-dependent viscosity condition, and the relaxation of lunar mascons. 相似文献
952.
A.J. Conacher P.L. Combes P.A. Smith R.C. McLellan 《Applied geography (Sevenoaks, England)》1983,3(1):29-44
Increasing soil and water salinity in southwestern Australia is a major social, economic and environmental problem. Hydrological imbalances following extensive clearing of the natural vegetation for agriculture have redistributed soluble salts into soils and streams. Interceptors have been designed by farmers to control the throughflow component of this hydrological imbalance, to reduce waterlogging of low-lying areas, and thus to ameliorate salinity problems.Farmer interviews show that, to date, interceptors have only partly achieved these objectives. Many interceptor systems are insufficiently comprehensive and leakages are common. Further, too short a period of time has elapsed since interceptor construction to have reversed the severe deterioration of soil properties. 相似文献
953.
V. A. Kudryavtsev N. J. C. Spooner P. K. Lightfoot J. W. Roberts M. J. Lehner T. Gamble M. J. Carson T. B. Lawson R. Lüscher J. E. McMillan B. Morgan S. M. Paling M. Robinson D. R. Tovey N. J. T. Smith P. F. Smith G. J. Alner S. P. Hart J. D. Lewin R. M. Preece T. J. Sumner W. G. Jones J. J. Quenby B. Ahmed A. Bewick D. Davidge J. V. Dawson A. S. Howard I. Ivaniouchenkov M. K. Joshi V. Lebedenko I. Liubarsky J. C. Barton G. Gerbier J. Mallet L. Mosca C. Tao 《Astroparticle Physics》2002,17(4):79-408
The status of dark matter searches with inorganic scintillator detectors at Boulby mine is reviewed and the results of tests with a CsI(Tl) crystal are presented. The objectives of the latter experiment were to study anomalous fast events previously observed and to identify ways to remove this background. Clear indications were found that these events were due to surface contamination of crystals by alphas, probably from radon decay. A new array of unencapsulated NaI(Tl) crystals immersed either in liquid paraffin or pure nitrogen atmosphere is under construction at Boulby. Such an approach allows complete control of the surface of the crystals and the ability to remove any surface contamination. First data from the unencapsulated NaI(Tl) do not show the presence of anomalous fast events. 相似文献
954.
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956.
Multiple-expert hazard/risk assessments have considerable precedent, particularly in the Yucca Mountain site characterization
studies. A certain amount of expert knowledge is needed to interpret the geological data used in a probabilistic data analysis.
As may be the situation in science, experts disagree on crucial points. Consequently, lack of consensus in some studies is
a sure outcome. In this paper, we present a Bayesian approach to statistical modeling in volcanic hazard assessment for the
Yucca Mountain site. Specifically, we show that the expert opinion on the site disruption parameterp is incorporated into the prior distribution, π(p), based on geological information that is available. Moreover, π(p) can
combine all available geological information motivated by conflicting but realistic arguments (e.g., simulation, cluster analysis,
structural control, ..., etc.). The incorporated uncertainties about the probability of repository disruptionp
eventually will be averaged out by taking the expectation over π(p). We use the following priors in the analysis: (1) priors
selected for mathematical convenience: Beta (r,s) for (r,s) = (2, 2), (3, 3), (5, 5), (2, 1),(2, 8), (8, 2), and (1, 1);and (2) three priors motivated by expert knowledge. Sensitivity analysis is performed for each prior distribution. Our study
concludes that estimated values of hazard based on the priors selected for mathematical simplicity are uniformly higher than
those obtained based on the priors motivated by expert knowledge. And, the model using the prior, Beta (8, 2), yields the
highest hazard (=2.97 × 10-2
. The minimum hazard is produced by the “three-expert prior” (i.e., values of
p
are equally likely for
p = 10-3, 10-2,and 10-1
. The estimate of the hazard is 1.39 × 10-3, which is only about one order of magnitude smaller than the maximum value. The term, “hazard, ” is defined as the probability
of at least one disruption of a repository at the Yucca Mountain site by basaltic volcanism for the next 10,000 years. 相似文献
957.
958.
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960.
M. A. Bautista H. Hartman T. R. Gull N. Smith K. Lodders 《Monthly notices of the Royal Astronomical Society》2006,370(4):1991-2003
We study the nature of the [Ti ii ] and [Ni ii ] emission from the so-called strontium filament found in the ejecta of η Carinae. To this purpose, we employ multilevel models of the Ti ii and Ni ii systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Ti ii ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 107 cm−3 and a temperature around 6000 K. In analysing three observations with different slit orientations recorded between 2000 March and 2001 November, we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust–gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of η Carinae. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of Ti is likely the result of selective photoevaporation of Ti-bearing grains. Some mechanisms for such a scenario are proposed. 相似文献