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31.
We propose a model of the evolution of the tachyonic scalar field over two phases in the universe. The field components do not interact in phase I, while in the subsequent phase II, they change flavours due to relative suppression of the radiation contribution. In phase II, we allow them to interact mutually with time-independent perturbation in their equations of state, as Shifted Cosmological Parameter (SCP) and Shifted Dust Matter (SDM). We determine the solutions of their scaling with the cosmic redshift in both phases. We further suggest the normalised Hubble function diagnostic, which, together with the low- and high-redshift H(z) data and the concordance values of the present density parameters from the CMBR, BAO statistics etc., constrain the strength of interaction by imposing the viable conditions to break degeneracy in 3-parameter $(\gamma, \varepsilon, \dot{\phi}^{2})$ space. The range of redshifts (z=0.1 to z=1.75) is chosen to highlight the role of interaction during structure formation, and it may lead to a future analysis of power spectrum in this model vis a vis Warm Dark Matter (WDM) or ΛCDM models. We further calculate the influence of interaction in determining the age of the universe at the present epoch, within the degeneracy space of model parameters. 相似文献
32.
Alexander Henderson Edison Liang Pablo Yepes Hui Chen Scott Wilks 《Astrophysics and Space Science》2011,336(1):273-277
Irradiating high-Z targets such as gold with ultra-intense lasers creates electron-positron pairs. In particular, the positron
density in the plasma created by this procedure is higher than that obtained via other laboratory-based methods, with theoretical
maximum densities exceeding 1018 cm−3. All of the significantly contributing processes are well-known and hence we can study this phenomenon using Monte Carlo
simulation. We focus on the latter part of this procedure, the passage of high-energy electrons through the target creating
pairs. In particular, we discuss the usefulness of CERN’s GEANT4 Monte Carlo code in simulating this process. Once this code
is successfully calibrated, we will use it to perform parameter studies, and design future targets to optimize the positron
yield. 相似文献
33.
Applications of laser-created dense e<Superscript>+</Superscript>e<Superscript>−</Superscript> pairs
We review the recent developments of laser pair creation in the laboratory and their potential applications to astrophysics
and other frontiers. Many astrophysical phenomena involving e+e− plasmas may be systematically investigated in the laboratory setting. We also discuss potential applications of dense positronium
gas. 相似文献
34.
Jianke Li & Dayal T. Wickramasinghe 《Monthly notices of the Royal Astronomical Society》1998,300(4):1015-1022
The recent BATSE observations of the spin-up and spin-down of accreting pulsars have shown that the standard formulation for the accretion torque as proposed by Ghosh &38; Lamb may need to be revised. The observations indicate alternate spin-up and spin-down phases driven by torques of similar magnitude and typically larger than the mean torque. The variations of the torque in systems such as Cen X-3 are difficult to explain in terms of changes of the mass accretion rate. The implication is that the torque does not depend on the accretion rate as in the GL model. In this paper we argue that the observed changes in the spin rate can result from stochastic transitions between two magnetospheric states. In particular, we show that intermediate magnetospheric systems are not admissible, because of a disc-induced magnetospheric instability which exists in a star–disc magnetic interaction system. This explains why torque reversal occurs in disc accreting pulsars with similar magnitudes. 相似文献
35.
Jianke Li & Dayal T. Wickramasinghe 《Monthly notices of the Royal Astronomical Society》1998,300(3):718-732
The role of an external magnetic field in the magnetic braking of a star with a dipolar field is investigated. In a magnetic cataclysmic variable system (i.e. the primary compact star has a strong magnetic field), the field external to the braking star (a late-type main-sequence star with a dynamo-generated field) originates from the compact star. A closed field region — the system dead zone — is formed within the binary system, and it does not take part in magnetic braking. The overall braking rate depends on the extent of this region and of the open flux, and is dependent on centrifugal effects. In the case of two interacting dipoles, the dipole orientations relative to the spin axes and to each other are found to be important, leading to different amounts of open flux and therefore of magnetic braking, owing to different centrifugal effects on closed field regions. However, in circumstances consistent with observations and dynamo theory, the white dwarf's field reduces the magnetic braking of the secondary significantly, a finding qualitatively similar to the results previously obtained for two anti-aligned dipoles perpendicular to the orbital plane. In the cases where the two dipole axes are not perpendicular to the orbital plane, but are inclined in the plane that links them, the 'cut-off' in magnetic braking is less abrupt, and this effect is more obvious as the inclinations increase. Only in the extreme cases when the two dipole axes are aligned in the orbital plane does the braking increase with white dwarf field strength. We conclude that detailed evolutionary modelling of AM Herculis systems needs to take account of the inclination effect. 相似文献
36.
E. Dayal 《The Professional geographer》1978,30(3):289-296
The measurement of agricultural intensity is fundamental to an understanding of spatial organization of agriculture. This paper develops a new index of cropping intensity from land use data. The length of time for which a crop stays in the field, a factor ignored in other indirect measures of cropping intensity, has been incorporated in the new index. To illustrate the method, cropping intensity in India is measured, mapped and discussed. Differences between the patterns derived from the new index and the traditional index are noted and explained. 相似文献
37.
Umesh Dayal 《Applied Ocean Research》1980,2(1):39-43
The application of a free fall penetrometer for determining the in situ shear strength properties of marine sediments is discussed. The penetrometer is instrumented with three sensors for measuring the acceleration/deceleration, cone thrust and local side friction simultaneously and continuously. The instrument is simple and fast in operation (the entire operation of deploying, testing and retrieving the instrument takes only 20 minutes) and may prove to be a useful ground truth equipment for deep toe acoustic surveys. Recent trials offshore Newfoundland are discussed. Preliminary field test results indicate that with this system the dynamic strength profile, the soil type and the location and depth of different stratigraphic layers can be directly evaluated up to penetrated depths. A procedure is outlined for estimating the static strength profile from the dynamic strength profile by applying the correction for penetration rate effects.The penetrometer developed to date is capable of penetrating to a maximum depth of about 4 m but, in the future, it may be possible to obtain soil profiles to a depth of approximately 15 m (50 ft) with some modifications in the instrument design. 相似文献
38.
Edison P. Liang 《Astrophysics and Space Science》1995,231(1-2):69-76
We review emission models of soft gamma-ray repeaters (SGRs) within the context of magnetized neutron star origins. Motivations for moderate field (1010–12G) versus ultrastrong field ( 5 × 1014G) neutron stars are considered. Implications for the astrophyiscal models are discussed. 相似文献
39.
B. Anu Radha P. L. Srinivasa Rao M. A. Rasheed D. J. Patil A. M. Dayal 《Journal of the Geological Society of India》2012,80(6):802-812
Seepage of hydrocarbons, either as macroseepage or microseepage, can set up near-surface oxidation-reduction zones that favour the development of a diverse array of chemical and mineralogic changes. In this study trace metal alterations were mapped that appear to be associated with hydrocarbon microseepages in the oil/gas fields. A total of 210 soil samples were collected from near surface sediments of Kutch and Saurashtra Basins, India. The soil samples were collected from a depth of 2–2.5 m. The paper reports the chemical alterations associated with trace metals in soils that are related to hydrocarbon microseepages above the Kutch and Saurashtra Basins, India. The soil samples for trace metals; Scandium (Sc), Vanadium (V), Chromium (Cr), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Barium (Ba) and Strontium (Sr) were analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The concentrations of the trace elements ranged between for Sc (12.69 to 21.91 ppm), V (109.20 to 436.05 ppm), Cr (87.15 to 481.57 ppm), Co (18.25 to 64.31 ppm), Ni (57.55 to 263.15 ppm), Cu (44.88 to 143.96 ppm), Zn (137.60 to 502.31 ppm), Ba (149.27 to 921.46 ppm) and Sr (143.93 to 425.63 ppm) were obtained. It was observed that trace elements concentrations were tremendously increased when compared with normal concentration in the soils. The adsorbed soil gas analysis showed the presence of high concentrations of ΣC2+ (C2H6, C3H8 and n-C4H10) ranged between 1 to 121 ppb respectively. Integrated studies of trace elements over adsorbed light gaseous hydrocarbon (ΣC2+) anomalies showed good correlation. The carbon isotopic composition of δ13C1 of the samples ranges between — 36.6 ‰ to ?22.7‰ (Pee Dee Belemnite) suggest thermogenic source for hydrocarbon gases. The increase in trace metal concentrations near oil/gas producing areas, suggests that soil chemical change to a reducing environment, presumably due to the influence of hydrocarbon microseepage, which could be applied with other geo-scientific data to identify areas of future hydrocarbon exploration in the frontier areas. 相似文献
40.
The Deccan Syneclise is considered to have significant hydrocarbon potential.However,significant hydrocarbon discoveries,particularly for Mesozoic sequences,have not been established through conventional exploration due to the thick basalt cover over Mesozoic sedimentary rocks.In this study,near-surface geochemical data are used to understand the petroleum system and also investigate type of source for hydrocarbons generation of the study area.Soil samples were collected from favorable areas identified by integrated geophysical studies.The compositional and isotopic signatures of adsorbed gaseous hydrocarbons(methane through butane) were used as surface indicators of petroleum micro-seepages.An analysis of 75 near-surface soil-gas samples was carried out for light hydrocarbons(C1-C4) and their carbon isotopes from the western part of Tapti graben,Deccan Syneclise,India.The geochemical results reveal sites or clusters of sites containing anomalously high concentrations of light hydrocarbon gases.High concentrations of adsorbed thermogenic methane(C_1 = 518 ppb) and ethane plus higher hydrocarbons(ΣC_(2+) = 977 ppb) were observed.Statistical analysis shows that samples from 13% of the samples contain anomalously high concentrations of light hydrocarbons in the soil-gas constituents.This seepage suggests largest magnitude of soil gas anomalies might be generated/source from Mesozoic sedimentary rocks,beneath Deccan Traps.The carbon isotopic composition of methane,ethane and propane ranges are from-22.5‰ to-30.2‰ PDB,-18.0‰to 27.1‰ PDB and 16.9‰-32.1‰ PDB respectively,which are in thermogenic source.Surface soil sample represents the intersection of a migration conduit from the deep subsurface to the surface connected to sub-trappean Mesozoic sedimentary rocks.Prominent hydrocarbon concentrations were associated with dykes,lineaments and presented on thinner basaltic cover in the study area,which probably acts as channel for the micro-seepage of hydrocarbons. 相似文献