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91.
92.
Abstract— Crater‐ejecta correlation is an important element in the analysis of crater formation and its influence on the geological evolution. In this study, both the ejecta distribution and the internal crater development of the Jurassic/Cretaceous Mjølnir crater (40 km in diameter; located in the Barents Sea) are investigated through numerical simulations. The simulations show a highly asymmetrical ejecta distribution, and underscore the importance of a layer of surface water in ejecta distribution. As expected, the ejecta asymmetry increases as the angle of impact decreases. The simulation also displays an uneven aerial distribution of ejecta. The generation of the central high is a crucial part of crater formation. In this study, peak generation is shown to have a skewed development, from approximately 50–90 sec after impact, when the peak reaches its maximum height of 1‐1.5 km. During this stage, the peak crest is moved about 5 km from an uprange to a downrange position, ending with a final central position which has a symmetrical appearance that contrasts with its asymmetrical development. 相似文献
93.
One of the major limitations of the classical ensemble Kalman filter (EnKF) is the assumption of a linear relationship between
the state vector and the observed data. Thus, the classical EnKF algorithm can suffer from poor performance when considering
highly non-linear and non-Gaussian likelihood models. In this paper, we have formulated the EnKF based on kernel-shrinkage
regression techniques. This approach makes it possible to handle highly non-linear likelihood models efficiently. Moreover,
a solution to the pre-image problem, essential in previously suggested EnKF schemes based on kernel methods, is not required.
Testing the suggested procedure on a simple, illustrative problem with a non-linear likelihood model, we were able to obtain
good results when the classical EnKF failed. 相似文献
94.
N. Tolich Y. -D. Chan C. A. Currat B. K. Fujikawa R. Henning K. T. Lesko A. W. P. Poon M. P. Decowski J. Wang K. Tolich 《Earth, Moon, and Planets》2006,99(1-4):229-240
A significant fraction of the 44TW of heat dissipation from the Earth’s interior is believed to originate from the decays
of terrestrial uranium and thorium. The only estimates of this radiogenic heat, which is the driving force for mantle convection,
come from Earth models based on meteorites, and have large systematic errors. The detection of electron antineutrinos produced
by these uranium and thorium decays would allow a more direct measure of the total uranium and thorium content, and hence
radiogenic heat production in the Earth. We discuss the prospect of building an electron antineutrino detector approximately
700 m3 in size in the Homestake mine at the 4850’ level. This would allow us to make a measurement of the total uranium and thorium
content with a statistical error less than the systematic error from our current knowledge of neutrino oscillation parameters.
It would also allow us to test the hypothesis of a naturally occurring nuclear reactor at the center of the Earth. 相似文献
95.
96.
We simulate the impact of a dipolar stellar magnetic field rooted in a classical T Tauri star on the accretion disk and the halo above using a 2.5D finite difference code. The gas is assumed resistive, and inside the disk accretion is driven by a Shakura-Sunyaev-type eddy viscosity. The rotational shear between the star and the Keplerian disk causes the magnetic field to be wound up and stretched outwards, away from the star. Part of the field lines open and an outflow is launched. Direct disk disruption by the Lorentz force only occurs for sufficient field strength. For our model system with a solar-mass central star, an accretion rate of 10-7M⊙/a, and a viscosity parameter αSS=0.01, a field strength of 1 kG, measured at the poles on the surface of the star, was found insufficient for disk disruption. 相似文献
97.
98.
Henning DYPVIK Ray E. FERRELL Pl T. SANDBAKKEN 《Meteoritics & planetary science》2003,38(10):1437-1450
Abstract— The 40 km diameter Mjølnir Crater is located on the central Barents Sea shelf, north of Norway. It was formed about 142 ± 2.6 Myr ago by the impact of a 1–2 km asteroid into the shallow shelf clays of the Hekkingen Formation and the underlying Triassic to Jurassic sedimentary strata. A core recovered from the central high within the crater contains slump and avalanche deposits from the collapse of the transient crater and central high. These beds are overlain by gravity flow conglomerates, with laminated shales and marls on top. Here, impact and post‐impact deposits in this core are studied with focus on clay mineralogy obtained from XRD decomposition and simulation analysis methods. The clay‐sized fractions are dominated by kaolinite, illite, mixed‐layered clay minerals and quartz. Detailed analyses showed rather similar composition throughout the core, but some noticeable differences were detected, including varying crystal size of kaolinite and different types of illites and illite/smectite. These minerals may have been formed by diagenetic changes in the more porous/fractured beds in the crater compared to time‐equivalent beds outside the crater rim. Long‐term post‐impact changes in clay mineralogy are assumed to have been minor, due to the shallow burial depth and minor thermal influence from impact‐heated target rocks. Instead, the clay mineral assemblages, especially the abundance of chlorite, reflect the impact and post‐impact reworking of older material. Previously, an ejecta layer (the Sindre Bed) was recognized in a nearby well outside the crater, represented by an increase in smectite‐rich clay minerals, genetically equivalent to the smectite occurring in proximal ejecta deposits of the Chicxulub crater. Such alteration products from impact glasses were not detected in this study, indicating that little, if any, impact glass was deposited within the upper part of the crater fill. Crater‐fill deposits inherited their mineral composition from Triassic and Jurassic sediments underlying the impact site. 相似文献
99.
This paper analyses factors that contributed to the evolution of SO2, NOx and CO2 emissions in Europe from 1960 to 2010. Historical energy balances, along with population and economic growth data, are used to quantify the impacts of major determinants of changing emission levels, including energy intensity, conversion efficiency, fuel mix, and pollution control. Time series of emission levels are compared for countries in Western and Eastern Europe, throwing light on differences in the importance of particular emission-driving forces. Three quarters of the decline in SO2 emissions in Western Europe resulted from a combination of reduced energy intensity and improved fuel mix, while dedicated end-of-pipe abatement measures played a dominant role in the reduction of NOx emissions. The increase in atmospheric emissions in Eastern Europe through the mid-1990s was associated with the growth of energy-intensive industries, which off-setted the positive impact of better fuel quality and changes in fuel mix. A continuous decrease in energy intensity and higher conversion efficiencies have been the main factors responsible for the moderate rate of growth of European CO2 emissions. 相似文献
100.
Henning Mørch M.Sc. 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):21-35
Mørch, H., 1975: Population and resources on the minor Danish islands. Geografisk Tidsskrift 74: 21–35. København, juni 1, 1975. An investigation made on the basis of a simple, linear regression of the relationship between resources—defined as areas after different criteria—and size of population on the minor Danish islands 1860, 1900, and 1960. 相似文献