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951.
Vadim A. Antonov Faziliddin T. Shamshiev 《Celestial Mechanics and Dynamical Astronomy》1993,56(3):451-469
This paper deals with the plane motion of a star in the gravitational field of a system which is in a steady state and rotates with a constant angular velocity. For these systems a class of potentials permitting a local integral, linear with respect to the velocity components, has been found. The concept of the local integral itself was introduced by one of the authors of the present paper (Antonov, 1981). A detailed model has been constructed. The corresponding domain of the particle motion and the form of the trajectory coils have been determined. The result is compared with the motion in a more realistic potential. 相似文献
952.
J. R. Barnes C. J. Leigh H. R. A. Jones Travis S. Barman D. J. Pinfield A. Collier Cameron J. S. Jenkins 《Monthly notices of the Royal Astronomical Society》2007,379(3):1097-1107
We present a search for the near-infrared spectroscopic signature of the close orbiting extrasolar giant planet HD 75289b. We obtained ∼230 spectra in the wavelength range 2.18–2.19 μm using the Phoenix spectrograph at Gemini South. By considering the direct spectrum, derived from irradiated model atmospheres, we search for the absorption profile signature present in the combined star and planet light. Since the planetary spectrum is separated from the stellar spectrum at most phases, we apply a phase-dependent orbital model and tomographic techniques to search for absorption signatures.
Because the absorption signature lies buried in the noise of a single exposure we apply a multiline deconvolution to the spectral lines available in order to boost the effective signal-to-noise ratio (S/N) of the data. The wavelength coverage of 80 Å is expected to contain ∼100 planetary lines, enabling a mean line with S/N of 800 to be achieved after deconvolution. We are nevertheless unable to detect the presence of the planet in the data and carry out further simulations to show that broader wavelength coverage should enable a planet like HD 75289b to be detected with 99.9 per cent confidence. We investigate the sensitivity of our method and estimate detection tolerances for mismatches between observed and model planetary atmospheres. 相似文献
Because the absorption signature lies buried in the noise of a single exposure we apply a multiline deconvolution to the spectral lines available in order to boost the effective signal-to-noise ratio (S/N) of the data. The wavelength coverage of 80 Å is expected to contain ∼100 planetary lines, enabling a mean line with S/N of 800 to be achieved after deconvolution. We are nevertheless unable to detect the presence of the planet in the data and carry out further simulations to show that broader wavelength coverage should enable a planet like HD 75289b to be detected with 99.9 per cent confidence. We investigate the sensitivity of our method and estimate detection tolerances for mismatches between observed and model planetary atmospheres. 相似文献
953.
954.
955.
Roberto O. Aquilano Juan C. Muzzio Hugo D. Navone Alejandra F. Zorzi 《Celestial Mechanics and Dynamical Astronomy》2007,99(4):307-324
We used a multipolar code to create, through the dissipationless collapses of systems of 1,000,000 particles, three self-consistent
triaxial stellar systems with axial ratios corresponding to those of E4, E5 and E6 galaxies. The E5 and E6 models have small,
but significant, rotational velocities although their total angular momenta are zero, that is, they exhibit figure rotation;
the rotational velocity decreases with decreasing flattening of the models and for the E4 model it is essentially zero. Except
for minor changes, probably caused by unavoidable relaxation effects, the systems are highly stable. The potential of each
system was subsequently approximated with interpolating formulae yielding smooth potentials, stationary for the non-rotating
model and stationary in the rotating frame for the rotating ones. The Lyapunov exponents could then be computed for randomly
selected samples of the bodies that make up the different systems, allowing the recognition of regular and partially and fully
chaotic orbits. Finally, the regular orbits were Fourier analyzed and classified using their locations on the frequency map.
As it could be expected, the percentages of chaotic orbits increase with the flattening of the system. As one goes from E6
through E4, the fraction of partially chaotic orbits relative to that of fully chaotic ones increases, with the former surpassing
the latter in model E4; the likely cause of this behavior is that triaxiality diminishes from E6 through E4, the latter system
being almost axially symmetric. We especulate that some of the partially chaotic orbits may obey a global integral akin to
the long axis component of angular momentum. Our results show that is perfectly possible to have highly stable triaxial models
with large fractions of chaotic orbits, but such systems cannot have constant axial ratios from center to border: a slightly
flattened reservoir of highly chaotic orbits seems to be mandatory for those systems. 相似文献
956.
R. D. Alexander C. J. Clarke J. E. Pringle 《Monthly notices of the Royal Astronomical Society》2005,358(1):283-290
We present the results of an analysis of ultraviolet observations of T Tauri stars (TTs). By analysing emission measures taken from the literature, we derive rates of ionizing photons from the chromospheres of five classical TTs in the range ∼1041 –1044 photon s−1 , although these values are subject to large uncertainties. We propose that the He ii /C iv line ratio can be used as a reddening-independent indicator of the hardness of the ultraviolet spectrum emitted by TTs. By studying this line ratio in a much larger sample of objects, we find evidence for an ionizing flux which does not decrease, and may even increase, as TTs evolve. This implies that a significant fraction of the ionizing flux from TTs is not powered by the accretion of disc material on to the central object, and we discuss the significance of this result and its implications for models of disc evolution. The presence of a significant ionizing flux in the later stages of circumstellar disc evolution provides an important new constraint on disc photoevaporation models. 相似文献
957.
Massimiliano Guzzo 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):303-323
We describe a numerical application of the Nekhoroshev theorem to investigate the long-term stability of quasi-integrable systems. We extend the results of a previous paper to a class of degenerate systems, which are typical in celestial mechanics. 相似文献
958.
A simple approximate model of the asteroid dynamics near the 3:1 mean–motion resonance with Jupiter can be described by a
Hamiltonian system with two degrees of freedom. The phase variables of this system evolve at different rates and can be subdivided
into the ‘fast’ and ‘slow’ ones. Using the averaging technique, wisdom obtained the evolutionary equations which allow to
study the long-term behavior of the slow variables. The dynamic system described by the averaged equations will be called
the ‘Wisdom system’ below. The investigation of the, wisdom system properties allows us to present detailed classification
of the slow variables’ evolution paths. The validity of the averaged equations is closely connected with the conservation
of the approximate integral (adiabatic invariant) possessed by the original system. Qualitative changes in the behavior of
the fast variables cause the violations of the adiabatic invariance. As a result the adiabatic chaos phenomenon takes place.
Our analysis reveals numerous stable periodic trajectories in the region of the adiabatic chaos. 相似文献
959.
960.
Jamie Pearce 《New Zealand geographer》2007,63(2):149-153
Abstract: The restricted influence of geographers in the policy arena has been the source of some angst. This paper reports on a new initiative at the University of Canterbury, which aims to strengthen geography's contribution to health policy debates in New Zealand. The GeoHealth Laboratory is a joint initiative between the Department of Geography and Public Health Intelligence group at the Ministry of Health that seeks to provide a pathway for the integration of health geography research into policy development. This new facility aligns the expertise in health geography, GIS and other spatial analytical methods with policy-relevant research priorities. An overview of the strategic aims of the GeoHealth Laboratory is provided along with some examples of recent research activities that are contributing to understandings of the health landscape in New Zealand. It is argued that such partnerships provide important opportunities for geographers to engage with policy-relevant issues. 相似文献