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991.
S. P. S. Eyres R. J. Cohen R. J. Davis H. T. Kenny H. M. Lloyd M. F. Bode S. M. Dougherty 《Astrophysics and Space Science》1995,224(1-2):457-458
We observed HM Sagittae with theMulti-Element Radio Linked Interferometer Network (MERLIN) at 6 cm and 18cm. We find non-thermal bipolar outflow in the eastwest direction, associated with optical emission lines, and thermal ridges to the north and south associated with the UV nebulosity detected by the HST. 相似文献
992.
M. Bro D. Vokrouhlický F. Roig D. Nesvorný W. F. Bottke A. Morbidelli 《Monthly notices of the Royal Astronomical Society》2005,359(4):1437-1455
The 2/1 mean motion resonance with Jupiter, intersecting the main asteroid belt at ≈3.27 au, contains a small population of objects. Numerical investigations have classified three groups within this population: asteroids residing on stable orbits (i.e. Zhongguos), those on marginally stable orbits with dynamical lifetimes of the order of 100 Myr (i.e. Griquas), and those on unstable orbits. In this paper, we reexamine the origin, evolution and survivability of objects in the 2/1 population. Using recent asteroid survey data, we have identified 100 new members since the last search, which increases the resonant population to 153. The most interesting new asteroids are those located in the theoretically predicted stable island A, which until now had been thought to be empty. We also investigate whether the population of objects residing on the unstable orbits could be resupplied by material from the edges of the 2/1 resonance by the thermal drag force known as the Yarkovsky effect (and by the YORP effect, which is related to the rotational dynamics). Using N -body simulations, we show that test particles pushed into the 2/1 resonance by the Yarkovsky effect visit the regions occupied by the unstable asteroids. We also find that our test bodies have dynamical lifetimes consistent with the integrated orbits of the unstable population. Using a semi-analytical Monte Carlo model, we compute the steady-state size distribution of magnitude H < 14 asteroids on unstable orbits within the resonance. Our results provide a good match with the available observational data. Finally, we discuss whether some 2/1 objects may be temporarily captured Jupiter-family comets or near-Earth asteroids. 相似文献
993.
994.
A. P. Markeev 《Astronomy Letters》2005,31(9):627-633
We investigate the stability of the periodic motion of a satellite, a rigid body, relative to the center of mass in a central Newtonian gravitational field in an elliptical orbit. The orbital eccentricity is assumed to be low. In a circular orbit, this periodic motion transforms into the well-known motion called hyperboloidal precession (the symmetry axis of the satellite occupies a fixed position in the plane perpendicular to the radius vector of the center of mass relative to the attractive center and describes a hyperboloidal surface in absolute space, with the satellite rotating around the symmetry axis at a constant angular velocity). We consider the case where the parameters of the problem are close to their values at which a multiple parametric resonance takes place (the frequencies of the small oscillations of the satellite’s symmetry axis are related by several second-order resonance relations). We have found the instability and stability regions in the first (linear) approximation at low eccentricities. 相似文献
995.
Stéphane Corbel 《Astrophysics and Space Science》2005,300(1-3):275-281
Relativistic jets are now believed to be a fairly ubiquitous property of accreting compact objects, and are intimately coupled
with the accretion history. Associated with rapid changes in the accretion states of the binary systems, ejections of relativistic
plasma can be observed at radio frequencies on timescale of weeks before becoming undetectable. However, recent observations
point to long-term effects of these ejecta on the interstellar medium with the formation of large-scale relativistic jets
around binary systems. In this paper, we review the observations of these large-scale structures in microquasars, highlighting
their contributions at high energies. 相似文献
996.
997.
998.
999.
A. P. Markeev 《Astronomy Letters》2005,31(5):350-356
We consider a periodic (in time) linear Hamiltonian system that depends on a small parameter. At a zero value of this parameter, the matrix of the system is constant, has two identical pairs of purely imaginary roots, and is not reducible to diagonal form. Therefore, the unperturbed system is unstable. We propose an algorithm for determining the boundaries of the instability regions for the system at nonzero values of the small parameter. This algorithm was used to analyze the stability of triangular libration points in the elliptical restricted three-body problem and in the stability problem in one special case of stationary rotation of a satellite relative to the center of mass. 相似文献
1000.
E. Rovilos P. J. Diamond C. J. Lonsdale H. E. Smith C. J. Lonsdale 《Monthly notices of the Royal Astronomical Society》2005,359(3):827-834
We present multi-epoch observations of Arp 220 with the VLBA and focus on the continuum emission from the luminous radio supernovae (RSNe) whose 1.6-GHz light curves are shown. The supernovae seem to be generally stable or only slowly decaying in flux with time, a result which deviates from the model of Type IIn RSNe. Hints of new eruptions confirm that they are indeed new sources and not supernova remnants, which could be several hundred years old. The slow decay of the sources for which monitoring data were available forces us to reconsider the starburst model for Arp 220 and adopt a more modest value of 0.7 yr−1 for the supernova rate based on these new eruptions. The starburst efficiency should also be modified accordingly which gives rise to the issue of an active nucleus once more. The question is raised whether it is the starburst which creates this active nucleus, something which could affect the evolution of starburst galaxies as a group. 相似文献