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941.
We investigate the background dynamics when dark energy is coupled to dark matter in the universe described by loop quantum
cosmology. We consider dark energy of the form modified Chaplygin gas. The dynamical system of equations is solved numerically
and a stable scaling solution is obtained. It henceforth resolves the famous cosmic coincidence problem in modern cosmology.
The statefinder parameters are also calculated to classify this dark energy model. 相似文献
942.
Einar Tandberg-Hanssen 《Solar physics》2011,269(2):237-251
The article starts with an autobiographical account, where the author relates how his several study-trips abroad gradually
led him to the study of solar physics in general, and prominences particularly. 相似文献
943.
We explore the hard X-ray source distributions of an C1.1 flare occurred on 14 December 2007. Both Hinode/EIS and RHESSI observations are used. One of EIS rasters perfectly covers the double hard X-ray footpoints, where the EUV
emission appears strong from the cool line of He ii (log T=4.7) to the hot line of Fe xvi (log T=6.4). We analyze RHESSI X-ray images at different energies and different times before the hard X-ray maximum. The results
show a similar topology for the time-dependent source distribution (i.e. at 14:14:35 UT) as that for energy-dependent source distribution (i.e. at a given energy band of 6 – 9 keV) overlapped on EUV bright kernels, which seems to be consistent with the evaporation
model. 相似文献
944.
Similarity model of feed support system for FAST 总被引:1,自引:0,他引:1
A new design of feed support system for Five hundred meter Aperture Spherical Telescope (FAST) is proposed in this paper.
According to the similarity theory, a 1:15 scale model of feed support system has been built to make systemic research on
the feasibility of the system. Then the control system and hardware structure of the feed support system are illustrated.
A complete astronomical observation track is run by the scale model and the experiments results demonstrate that the new feed
support system can satisfy the observation accuracy requirement of FAST. 相似文献
945.
József Vanyó Bruno Escribano Julyan H. E. Cartwright Diego L. González Oreste Piro Tamás Tél 《Celestial Mechanics and Dynamical Astronomy》2011,109(2):181-200
We study tidal synchronization and orbit circularization in a minimal model that takes into account only the essential ingredients
of tidal deformation and dissipation in the secondary body. In previous work we introduced the model (Escribano et al. in
Phys. Rev. E, 78:036216, 2008); here we investigate in depth the complex dynamics that can arise from this simplest model of tidal synchronization and
orbit circularization. We model an extended secondary body of mass m by two point masses of mass m/2 connected with a damped spring. This composite body moves in the gravitational field of a primary of mass M ≫ m located at the origin. In this simplest case oscillation and rotation of the secondary are assumed to take place in the plane
of the Keplerian orbit. The gravitational interactions of both point masses with the primary are taken into account, but that
between the point masses is neglected. We perform a Taylor expansion on the exact equations of motion to isolate and identify
the different effects of tidal interactions. We compare both sets of equations and study the applicability of the approximations,
in the presence of chaos. We introduce the resonance function as a resource to identify resonant states. The approximate equations
of motion can account for both synchronization into the 1:1 spin-orbit resonance and the circularization of the orbit as the
only true asymptotic attractors, together with the existence of relatively long-lived metastable orbits with the secondary
in p:q (p and q being co-prime integers) synchronous rotation. 相似文献
946.
Xiaodong Liu Hexi Baoyin Xingrui Ma 《Celestial Mechanics and Dynamical Astronomy》2011,109(3):303-320
Frozen orbits are always important foci of orbit design because of their valuable characteristics that their eccentricity
and argument of pericentre remain constant on average. This study investigates quasi-circular frozen orbits and examines their
basic nature analytically using two different methods. First, an analytical method based on Lagrangian formulations is applied
to obtain constraint conditions for Martian frozen orbits. Second, Lie transforms are employed to locate these orbits accurately,
and draw the contours of the Hamiltonian to show evolutions of the equilibria. Both methods are verified by numerical integrations
in an 80 × 80 Mars gravity field. The simulations demonstrate that these two analytical methods can provide accurate enough
results. By comparison, the two methods are found well consistent with each other, and both discover four families of Martian
frozen orbits: three families with small eccentricities and one family near the critical inclination. The results also show
some valuable conclusions: for the majority of Martian frozen orbits, argument of pericentre is kept at 270° because J
3 has the same sign as J
2; while for a minority of ones with low altitude and low inclination, argument of pericentre can be kept at 90° because of
the effect of the higher degree odd zonals; for the critical inclination cases, argument of pericentre can also be kept at
90°. It is worthwhile to note that there exist some special frozen orbits with extremely small eccentricity, which could provide
much convenience for reconnaissance. Finally, the stability of Martian frozen orbits is estimated based on the trace of the
monodromy matrix. The analytical investigations can provide good initial conditions for numerical correction methods in the
more complex models. 相似文献
947.
New stacked central configurations for the planar 5-body problem 总被引:1,自引:0,他引:1
Jaume Llibre Luis Fernando Mello Ernesto Perez-Chavela 《Celestial Mechanics and Dynamical Astronomy》2011,110(1):43-52
A stacked central configuration in the n-body problem is one that has a proper subset of the n-bodies forming a central configuration. In this paper we study the case where three bodies with masses m
1, m
2, m
3 (bodies 1, 2, 3) form an equilateral central configuration, and the other two with masses m
4, m
5 are symmetric with respect to the mediatrix of the segment joining 1 and 2, and they are above the triangle generated by
{1, 2, 3}. We show the existence and non-existence of this kind of stacked central configurations for the planar 5-body problem. 相似文献
948.
We revisit a set of symplectic variables introduced by Andre Deprit (Celest Mech 30, 181–195, 1983), which allows for a complete symplectic reduction in rotation invariant Hamiltonian systems, generalizing to arbitrary dimension
Jacobi’s reduction of the nodes. In particular, we introduce an action-angle version of Deprit’s variables, connected to the
Delaunay variables, and give a new hierarchical proof of the symplectic character of Deprit’s variables. 相似文献
949.
We re-formulate the 3+1 GRMHD equations for the Schwarzschild black hole in a Veselago medium. Linear perturbation in rotating
(non-magnetized and magnetized) plasma is introduced and their Fourier analysis is considered. We discuss wave properties
with the help of wave vector, refractive index and change in refractive index in the form of graphs. It is concluded that
some waves move away from the event horizon in this unusual medium. We conclude that for the rotating non-magnetized plasma,
our results confirm the presence of Veselago medium while the rotating magnetized plasma does not provide any evidence for
this medium. 相似文献
950.
A relative complete set of He I 10830 Å profiles and their coincident slit-jaw Hα images of the large limb flare (2N/X20) of 16 August 1989 were observed by the solar spectrograph at Purple Mountain Observatory. In addition to the unusually broadened spectral profiles observed in the impulsive phase, more than half of the observed He I 10830 Å profiles are characterized by central reversals, which were detected not only in the impulsive phase but also in the late decaying phase. The central-reversed profiles may exist at different heights, ranging from the solar limb to (3–4) × 104 km above. The absorption varies with time and position, with a typical lifetime and size of several minutes and 5–6 arc sec, respectively. Depths of the absorption profiles also change clearly. The absorptions are usually deeper at the loop footpoint near the solar limb and shallower at loop-top. However, the most unusual feature is that all the line-center wavelengths of them show no shift relative to that of the quiet chromosphere near the limb, implying the apparent velocities are zero while the associated emission profiles have different apparent velocities. Theoretical simulations demonstrate that the Doppler widths of the absorptions are in the range of (0.35–0.5)Å and increase with height, and the source functions are (0.11–0.3) times the disk center intensity. However, the absorptions have a relative large range of optical thickness (0.1–1.3) in the I
3 component of the He I 10830 Å triplet. We have not observed such absorption in other limb flares, including the SB/X2.9 flare of 17 August 1989 that occurred in the same active region as the studied one (NOAA 5629). Our studies show that the absorption could not result from he scattering by the telluric atmosphere or from normal chromospheric absorption. This unique phenomenon may be related to extra intense X-ray flux and caused by diffuse and non uniform materials dissociated from the flare instead of self-absorption of the flare. 相似文献