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991.
The morphological content of Markarian galaxies (MG) in groups and in single galaxies is examined. It is found that MG do
not conform to the long established rule that the relative number of elliptical and lenticular galaxies in groups is higher
than in single galaxies. 相似文献
992.
A time-dependent model for the energy of a flaring solar active region is presented based on an existing stochastic jump-transition
model (Wheatland and Glukhov in Astrophys. J.
494, 858, 1998; Wheatland in Astrophys. J.
679, 1621, 2008 and Solar Phys.
255, 211, 2009). The magnetic free energy of an active region is assumed to vary in time due to a prescribed (deterministic) rate of energy
input and prescribed (random) jumps downwards in energy due to flares. The existing model reproduces observed flare statistics,
in particular flare frequency – size and waiting-time distributions, but modeling presented to date has considered only the
time-independent choices of constant energy input and constant flare-transition rates with a power-law distribution in energy.
These choices may be appropriate for a solar active region producing a constant mean rate of flares. However, many solar active
regions exhibit time variation in their flare productivity, as exemplified by NOAA active region (AR) 11029, observed during
October – November 2009 (Wheatland in Astrophys. J.
710, 1324, 2010). Time variation is incorporated into the jump-transition model for two cases: (1) a step change in the rates of flare transitions,
and (2) a step change in the rate of energy supply to the system. Analytic arguments are presented describing the qualitative
behavior of the system in the two cases. In each case the system adjusts by shifting to a new stationary state over a relaxation
time which is estimated analytically. The model exhibits flare-like event statistics. In each case the frequency – energy
distribution is a power law for flare energies less than a time-dependent rollover set by the largest energy the system is
likely to attain at a given time. The rollover is not observed if the mean free energy of the system is sufficiently large.
For Case 1, the model exhibits a double exponential waiting-time distribution, corresponding to flaring at a constant mean
rate during two intervals (before and after the step change), if the average energy of the system is large. For Case 2 the
waiting-time distribution is a simple exponential, again provided the average energy of the system is large. Monte Carlo simulations
of Case 1 are presented which confirm the estimate for the relaxation time and the expected forms of the frequency – energy
and waiting-time distributions. The simulation results provide a qualitative model for observed flare statistics in AR 11029. 相似文献
993.
V. P. Kozhevnikov 《Astronomy Letters》2010,36(8):554-568
Recently, it has been shown that the cataclysmic variable EI UMa should be attributed to intermediate polars on the basis
of its X-ray spectrum. However, no short-period oscillations with a high degree of coherence typical of intermediate polars
could be detected in this star. Therefore, it was suggested to call it a “hidden” intermediate polar. Using a multichannel
photometer and a 70-cm telescope, we performed observations of EI UMa for 60 h. Analysis of the observations has clearly revealed
a brightness oscillation with a period of 769.63±0.10 s and a mean semiamplitude of 0·
m
008 completely coherent during one month of our observations that was detectable during each of the 13 observing nights. On
the basis of this detection, EI UMa should be considered a classical intermediate polar rather than a hidden one. In addition,
we have managed to detect the orbital variability of EI UMa for the first time. The orbital light curve is extremely interesting,
showing evidence of partial eclipses of the accretion flow. 相似文献
994.
The initial principles of a method for analyzing the spatial distribution of visible matter in the universe with structures on size scales of thousands of Mpc are discussed. This method is based on analyzing the distribution N(z) of the photometric redshifts of galaxies in deep fields using large bins Δ z=0.1–0.3. Fluctuations in the numbers of galaxies in these bins in terms of redshifts are caused by Poisson noise, correlated structures, and systematic errors in estimating photo-z. This method involves covering a sufficiently large region of the celestial sphere with a grid of deep multi-band surveys with a cell size on the order of 10º×10º, with deep fields of size ~10'×10' observed with 3-10 meter telescopes at its nodes. The distribution of the photometric redshifts of the galaxies within each deep field will yield information on the radial extent of superlarge structures, while comparing the radial distributions in neighboring fields will yield information on the tangential extent of these structures. A necessary element of this method is an analysis of possible distortions in the radial distributions of the galaxies associated with the technique for evaluating the photometric redshifts. 相似文献
995.
D. Minniti P.W. Lucas J.P. Emerson R.K. Saito M. Hempel P. Pietrukowicz A.V. Ahumada M.V. Alonso J. Alonso-Garcia J.I. Arias R.M. Bandyopadhyay R.H. Barbá B. Barbuy L.R. Bedin E. Bica J. Borissova L. Bronfman G. Carraro M. Catelan J.J. Clariá G. Pietrzynski 《New Astronomy》2010,15(5):433-443
We describe the public ESO near-IR variability survey (VVV) scanning the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high. The survey will take 1929 h of observations with the 4-m VISTA telescope during 5 years (2010–2014), covering ~109 point sources across an area of 520 deg2, including 33 known globular clusters and ~350 open clusters. The final product will be a deep near-IR atlas in five passbands (0.9–2.5 μm) and a catalogue of more than 106 variable point sources. Unlike single-epoch surveys that, in most cases, only produce 2-D maps, the VVV variable star survey will enable the construction of a 3-D map of the surveyed region using well-understood distance indicators such as RR Lyrae stars, and Cepheids. It will yield important information on the ages of the populations. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, INTEGRAL, WISE, Fermi LAT, XMM-Newton, GAIA and ALMA for a complete understanding of the variable sources in the inner Milky Way. This public survey will provide data available to the whole community and therefore will enable further studies of the history of the Milky Way, its globular cluster evolution, and the population census of the Galactic Bulge and center, as well as the investigations of the star forming regions in the disk. The combined variable star catalogues will have important implications for theoretical investigations of pulsation properties of stars. 相似文献
996.
M. Collados F. Bettonvil L. Cavaller I. Ermolli B. Gelly A. Prez H. Socas‐Navarro D. Soltau R. Volkmer the EST team 《Astronomische Nachrichten》2010,331(6):615-619
In this paper, the present status of the development of the design of the European Solar Telescope is described. The telescope is devised to have the best possible angular resolution and polarimetric performance, maximizing the throughput of the whole system. To that aim, adaptive optics and multi‐conjugate adaptive optics are integrated in the optical path. The system will have the possibility to correct for the diurnal variation of the distance to the turbulence layers, by using several deformable mirrors, conjugated at different heights. The present optical design of the telescope distributes the optical elements along the optical path in such a way that the instrumental polarization induced by the telescope is minimized and independent of the solar elevation and azimuth. This property represents a large advantage for polarimetric measurements. The ensemble of instruments that are planned is also presented (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
997.
The Dark Spot in the atmosphere of Uranus in 2006: Discovery, description, and dynamical simulations
We report the first definitive detection of a discrete dark atmospheric feature on Uranus in 2006 using visible and near-infrared images from the Hubble Space Telescope and the Keck II 10-m telescope. Like Neptune's Great Dark Spots, this Uranus Dark Spot had bright companion features that exhibited considerable variability in brightness and location relative to the Dark Spot. We detected the feature or its bright companions on 16 June (Hubble), 30 July and 1 August (Keck), 23-24 August (Hubble), and 15 October (Keck). The dark feature—detected at latitude ∼28±1° N with an average physical extent of roughly 2° (1300 km) in latitude and 5° (2700 km) in longitude—moved with a nearly constant zonal velocity of , which is roughly 20 m s−1 greater than the average observed speed of bright features at this latitude. The dark feature's contrast and extent varied as a function of wavelength, with largest negative contrast occurring at a surprisingly long wavelength when compared with Neptune's dark features: the Uranus feature was detected out to 1.6 μm with a contrast of −0.07, but it was undetectable at 0.467 μm; the Neptune GDS seen by Voyager exhibited its most prominent contrast of −0.12 at 0.48 μm, and was undetectable longward of 0.7 μm. Computational fluid dynamic simulations of the dark feature on Uranus suggest that structure in the zonal wind profile may be a critical factor in the emergence of large sustained vortices. 相似文献
998.
Thomas G. Müller Emmanuel Lellouch Hermann Böhnhardt John Stansberry Antonella Barucci Jacques Crovisier Audrey Delsanti Alain Doressoundiram Elisabetta Dotto René Duffard Sonia Fornasier Olivier Groussin Pedro J. Gutiérrez Olivier Hainaut Alan W. Harris Paul Hartogh Daniel Hestroffer Jonathan Horner Dave Jewitt Mark Kidger Csaba Kiss Pedro Lacerda Luisa Lara Tanya Lim Michael Mueller Raphael Moreno Jose-Luis Ortiz Miriam Rengel Pablo Santos-Sanz Bruce Swinyard Nicolas Thomas Audrey Thirouin David Trilling 《Earth, Moon, and Planets》2009,105(2-4):209-219
Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well. 相似文献
999.
P. Louarn C. Diéval V. Génot B. Lavraud A. Opitz A. Fedorov J. A. Sauvaud D. Larson A. Galvin M. H. Acuňa J. Luhmann 《Solar physics》2009,259(1-2):311-321
The “strahl” is a specific population of the solar wind, constituted by strongly field aligned electrons flowing away from the Sun, with energies >60 eV. Using the Solar Wind Electron Analyzer (SWEA) onboard STEREO, we investigate the short time scale fluctuations of this population. It is shown that its phase space density (PSD) at times presents fluctuations larger than 50% at scales of the order of minutes and less. The fluctuations are particularly strong for periods of a few tens of hours in high-speed streams, following the crossing of the corotating interaction region, when the strahl is also the most collimated in pitch angle. The amplitude of the fluctuations tends to decrease in conjunction with a broadening in pitch angle. Generally, the strongly fluctuating strahl is observed when the magnetic field is also highly perturbed. That SWEA is able to perform a very rapid 3D analysis at a given energy is essential since it can be demonstrated that the observed magnetic turbulence can only marginally perturb the PSD measurements. 相似文献
1000.
Motivated by the recent interest in phantom fields as candidates for the dark energy component, we investigate the consequences
of the phantom field when is minimally coupled to gravity. In particular, the necessary (but insufficient) conditions for
the acceleration and superacceleration of the universe are obtained when the non-minimal coupling term is taken into account.
Furthermore, the necessary condition for the cosmic acceleration is derived when the phantom field is non-minimally coupled
to gravity and baryonic matter is included. 相似文献