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991.
992.
Makoto Kishimoto Robert Antonucci Omer Blaes 《Monthly notices of the Royal Astronomical Society》2003,345(1):253-260
We have found for the first time a Balmer-edge feature in the polarized flux spectrum of a quasar (Ton 202). The edge feature is seen as a discontinuity in the slope, rather than as a discontinuity in the absolute flux. As the polarized flux contains essentially no broad emission lines, it is considered to arise interior to the broad emission line region, showing the spectrum with all the emissions outside the nucleus scraped off and removed. Therefore, the polarized flux spectrum is likely to reveal features intrinsic to the big blue bump emission. In this case, the existence of the Balmer-edge feature, seen in absorption in the shorter wavelength side, indicates that the big blue bump is indeed thermal and optically thick. 相似文献
993.
We model the reflected spectrum expected from localized magnetic flares above an ionized accretion disc. We concentrate on the case of very luminous magnetic flares above a standard accretion disc extending down to the last stable orbit, and use a simple parametrization to allow for an X-ray-driven wind. Full disc spectra including relativistic smearing are calculated. When fitted with the constant-density reflection models, these spectra give both a low reflected fraction and a small linewidth as seen in the hard spectra from galactic black hole binaries and active galactic nuclei. We fit our calculated spectra to real data from the low/hard state of Nova Muscae and Cyg X-1 and show that these models give comparable χ 2 to those obtained from the constant-density reflection models, which implied a truncated disc. This explicitly demonstrates that the data are consistent either with magnetic flares above an ionized disc extending down to the last stable orbit around a black hole, or with non-ionized, truncated discs. 相似文献
994.
995.
996.
Klaus Wilhelm Ingolf E. Dammasch Donald M. Hassler 《Astrophysics and Space Science》2002,282(1):189-207
The plasma conditions in the solar atmosphere and, in particular, in coronal holes are summarized, before space-borne instrumentation
for observing these regions in vacuum-ultraviolet light is briefly introduced with the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) as example. Spectroscopic measurements of
small plasma jets are then analyzed in detail. Magnetic reconnection is thought to be responsible for heating the corona of
the Sun as well as accelerating the solar wind by converting magnetic energy into thermal and kinetic energies. The continuous
outflow of the fast solar wind from coronal holes on ‘open’ field lines, which reach out into interplanetary space, then requires
many reconnection events of very small scale sizes – most of them probably below the resolution capabilities of present-day
instruments. Our observations of such an event have been obtained with the Solar and Heliospheric Observatory (SOHO) providing
both high-resolution imaging and spectral information for structural and dynamical studies. We find whirling or rotating motions
as well as jets with acceleration along their propagation paths in close spatial and temporal vicinity to the coronal jet.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
998.
Taishi Nakamoto Masayuki Umemura Hajime Susa 《Monthly notices of the Royal Astronomical Society》2001,321(4):593-604
Assuming simple dynamics for the growth of density fluctuations, we implement six-dimensional (6D) radiative transfer calculations to elucidate the effects of photon propagation during the reionization of an inhomogeneous universe. The ionizing sources are postulated to be AGN-like in this paper. The present simulations reveal that radiative transfer effects are still prominent considerably after the percolation epoch, in which patchy ionized regions connect with each other. In other words, owing to the collective opacity, the Universe does not become perfectly transparent against ionizing radiation even though strongly self-shielded regions disappear. It turns out that the inhomogeneity of the medium enhances the opacity effects and delays the end of reionization. Owing to such radiative transfer effects, the reionization in an inhomogeneous universe proceeds fairly slowly, in contrast to the prompt reionization in a homogeneous universe, and as a result the surface of reionization is not so sharply edged, but highly uneven. As a signature of the uneven surface of reionization, the cosmic IR background (CIB) radiation, which is produced by Ly photons resulting from radiative recombination, could exhibit strong anisotropies, reflecting the amplitude of density fluctuations at the reionization era. The predicted CIB intensity lies on a level of possible detection by forthcoming IR space telescope facilities. 相似文献
999.
连续谱辐射是研究活动星系核结构主要手段之一,谱型,光变,偏振是表征连续谱性质的最主要内容,活动星系是的最主要特征是几乎覆盖了整个电磁波波段,且有着大幅度和快速时标的光变,主要评述了活动星系核从射电到γ射线的全波段性质,观测对活动星系结构核的物理限制及现存的物理模型和解释,并指出了将来的课题。 相似文献
1000.
俞志尧 《中国天文和天体物理学报》1994,(3)
我们用ⅢZw35的流量密度函数,来拟合观测得到的OHmegamaser辐射谱。OHmegamaser斑点处在窄线区薄盘上,作旋转运动和径向膨胀运动。窄线区薄盘是侧向的。从理论上我们得到OHmegamaser辐射流量密度.发现与其辐射谱中主峰和伴峰相对应的OHmegamaser斑点处在窄线区薄盘的不同位置。 相似文献