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571.
A certain class of non-thermal electron distributions can exhibit more mono-energetic shape and a higher peak than the Maxwellian
distribution. This type of electron distribution can be observed mainly in flaring plasmas. We have studied the influence
of this kind of electron energy distribution on the excitation equilibrium of Fe VIII – Fe XVI in the solar corona. The changes
in synthetic spectra of the emission lines belonging to these ions due to this non-thermal distribution are shown. The possibilities
of finding the shape of the energy distribution function of electrons from the Fe line ratios are also discussed. The results
can be used for diagnostics of coronal plasmas where the deviations of particle energy distributions from the Maxwellian one
can be significant. 相似文献
572.
Luis Jiménez-Benito Angeles Díaz Roberto Terlevich Elena Terlevich 《Astrophysics and Space Science》1998,263(1-4):111-114
We have analyzed high signal-to-noise spectra of 10 active galaxies in order to investigate the stellar populations of these
objects and the kinematics of the gas and stars in their nuclei.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
573.
The modern analogue technique (MAT) was applied to six pollen sequences from the Belledonne Massif (northwestern French Alps) to estimate the effect of altitude and local parameters on pollen‐based climate reconstruction during the Lateglacial and the early Holocene. The six sites (Le Vivier (345 m a.s.l.), Les Etelles (700 m a.s.l.), La Coche (980 m a.s.l.), Montendry (1330 m a.s.l.), Le Grand Leyat (1660 m a.s.l.), La Gouille (1800 m a.s.l.)) are located in different vegetation belts (mixed deciduous woods, conifer woods, alpine pastures with maple). The main vegetation changes in the past are recorded at each site. The evolution of four climate parameters (coldest month temperature, warmest month temperature, mean annual temperature, annual precipitation) was quantitatively inferred from pollen data using MAT. The curves obtained were compared to the Les Etelles site, which was the least affected by non‐local pollen transport. The results show consistent trends for the climate parameters reconstructed at the different sites. However, the reconstruction does not indicate a decrease in temperature values related to the increasing elevation. Difficulties in reconstructing the altitudinal variations of climate parameters from pollen data during the periods studied are discussed and perspectives for improvement are considered. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
574.
575.
Mitchell C. Begelman Elena M. Rossi † Philip J. Armitage 《Monthly notices of the Royal Astronomical Society》2008,387(4):1649-1659
We study the structure and evolution of 'quasi-stars', accreting black holes embedded within massive hydrostatic gaseous envelopes. These configurations may model the early growth of supermassive black hole seeds. The accretion rate on to the black hole adjusts so that the luminosity carried by the convective envelope equals the Eddington limit for the total mass, M * + M BH ≈ M * . This greatly exceeds the Eddington limit for the black hole mass alone, leading to rapid growth of the black hole. We use analytic models and numerical stellar structure calculations to study the structure and evolution of quasi-stars. We show that the photospheric temperature of the envelope scales as T ph ∝ M −2/5 BH M 7/20 * , and decreases with time while the black hole mass increases. Once T ph < 104 K , the photospheric opacity drops precipitously and T ph hits a limiting value, analogous to the Hayashi track for red giants and protostars, below which no hydrostatic solution for the convective envelope exists. For metal-free (Population III) opacities, this limiting temperature is approximately 4000 K. After a quasi-star reaches this limiting temperature, it is rapidly dispersed by radiation pressure. We find that black hole seeds with masses between 103 and 104 M⊙ could form via this mechanism in less than a few Myr. 相似文献
576.
Elena Dzifčáková 《Solar physics》2000,196(1):113-127
The influence of electron non-Maxwellian distributions (power and -distribution) on the electron excitation rate in the solar corona is demonstrated. It is shown that the deviations in electron excitation rate are sufficient to affect intensities of spectral lines. As an example the diagnostics of a power-law distribution are demonstrated for a simplified calculation of the resonance lines of Fexxiv, Fexxv and Fexxvi. The results can be used in diagnosing solar flare plasmas, where the deviations of the electron distribution from a Maxwellian distribution can be large. 相似文献
577.
578.
Elena Pavlenko Kirill Antoniuk Sergei Yu. Shugarov Nataly A. Katysheva Lenie Muzhdabaeva Vyacheslav Mikhajlov 《Astrophysics and Space Science》2005,296(1-4):461-464
We present results of multicolour photometry of the nova-like binary MV Lyr in the years 2002–2003, corresponding to the transition
of the star from its low (V = 17.8) to high (V = 12.3) brightness state. The transition lasted at most 200 days. During the first ∼50 days MV Lyr brightened at the rate
0.06 mag/day, and during the next ∼150 days at the rate 0.01 mag/day. The brightening was accompanied by a blue shift from
0.45 to 0.05 in V−R, interpreted as an increase of the accretion disk contribution to the total light. During the transition MV Lyr displayed
well-known ‘quasi-orbital’ light variations and fast quasi-periodic oscillations with a typical time scale of tens of minutes. 相似文献
579.
580.
An early Norian flora from the Partizansk River Basin of Primorye, Far-East of Russia, is described in detail for the first time, in which over 25 taxa are reported. The flora is dominated by cycadoalean, bennettitalean and coniferous plants, associated with a lot of ferns and czekanowskialean plants, and with a few ginkgoalean. In floristic characteristics, the flora can be well comparable with Late Triassic Mongugai flora of southwestern Primorye and its neighboring Tianqiaoling flora of eastern Jilin, China, as well with the Yamanoi and Nariwa floras from southwestern Japan. As the plant-bearing strata are sandwiched in the lower Norian marine beds yielding marine fauna, the age of the Partizansk flora is well evidenced as the early Norian. Paleophytogeographically, the flora appears to be in the ecotone of the Medio-Triassic and Arcto-Triassic floristic regions in Eurasia, and indicates probably warm temperate or subtropic vegetation in nature. Four new species are reported in this paper, including Ctenis elegantus sp. nov, Ixostrobus pacificus sp. nov., Elatocladus elegantus sp. nov. and E. prynadae sp. nov. 相似文献