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601.
This paper presents a study of the envelope of the young stellar object (YSO) GGD30IR. What distinguishes this from most other YSOs is the elongated absorption feature seen in silhouette against the background emission in the Spitzer Galactic Legacy Infrared Midplane Survey Extraordinaire 8 μm Infrared Array Camera image of the region. The size and the symmetrical placement of GGD30IR in the centre of this feature suggest that it is an extended envelope, perhaps the remnant of the collapse of the GGD30 core. We have used the extinction in the envelope measured from (i) the reduction in the 8 μm background intensity and (ii) field star colour excesses, to estimate the envelope mass, obtaining values of 0.6 ± 0.2 and 0.5 ± 0.3 M⊙ , respectively. To investigate the envelope further, we have obtained Australia Telescope Compact Array 3 mm continuum and HCO+ line observations of the region. The continuum emission at 3 mm arises from both a compact (unresolved; ≤730 au) core embedded in an extended envelope ∼18 000 au × 38 000 au in extent. We estimate the core mass to be 0.11 ± 0.02 M⊙ . The HCO+ emission is extended in a direction perpendicular to the long axis of the envelope, suggesting it comes from an outflow. The spectral energy distribution (SED) provides a 2–24 μm spectral index, α= 1.0, which places GGD30IR in the Class I YSO category. Integrating the SED provides a luminosity of L * ≃ 25 ± 5 L⊙ . 相似文献
602.
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604.
为了研究尘埃消光对伽玛射线暴余辉的影响,基于严格的Mie理论和最新的星际尘埃光学性质,进行了高精度的数值计算,并分析具有不同物理参数的尘埃所产生的消光曲线.结果表明,介质密度和金属丰度是决定消光总量的主要物理参数,而尘埃颗粒大小的分布则是产生不同消光曲线轮廓的重要物理参数.如果尘埃颗粒相互聚集形成导致尺度增大,将产生较平或者较灰的消光曲线,同时绝对总量将减少;相反,如果尘埃颗粒由于某种原因发生离解导致尺度变小,将产生较陡的消光曲线,同时消光总量将增加.这些结果将对理解光学暗暴的形成机制提供重要的启示. 相似文献
605.
P. Jakobsson D. Malesani J. Hjorth J.P.U. Fynbo B. Milvang‐Jensen 《Astronomische Nachrichten》2011,332(3):276-280
We describe the current status and recent results from our Swift/VLT legacy survey, a VLT Large Programme aimed at characterizing the host galaxies of a homogeneously selected sub‐sample of Swift gamma‐ray bursts (GRBs). The immediate goals are to determine the host luminosity function, study the effects of reddening, determine the fraction of Lyα emitters in the hosts, and obtain redshifts for targets without a reported one. We have defined a very carefully selected sample, obeying strict and well‐defined criteria: 68 targets in total. Among the preliminary results is a large optical detection rate, the lack of extremely red objects (only one possible case in the sample), and 10 new GRB redshifts with the mean redshift of the host sample assessed to be 〈z 〉 ≳ 2 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
606.
上海地区大气气溶胶光学特性的初步研究 总被引:4,自引:1,他引:3
上海是东亚重要的沿海城市之一,其上空大气气溶胶光学特性的研究对了解上海及我国东部沿海地区的环境和气候影响等方面都具有重要性,至今尚无这方面的实际观测分析。本工作利用2000年6月到2002年12月之间测得的上海地区太阳直接辐照度数据,分析之后得出大气气溶胶光学厚度值,并统计分析了大气气溶胶光学厚度的季节变化及其与地面能见度的关系,最后给出了气溶胶消光谱。通过上述工作,发现上海地区大气气溶胶光学厚度具有夏季最大,春季次之,冬季最小的相对稳定的特点。此外,地面能见度及其倒数作为一个相对容易获得的参数,与大气气溶胶的光学厚度具有较好的相关性,可以考虑将其倒数作为一个约束气溶胶光学厚度分布的物理参数,这对今后的观测和研究都具有一定的实际意义。 相似文献
607.
Robert J. Papoular Renaud Papoular 《Monthly notices of the Royal Astronomical Society》2009,394(4):2175-2181
A random, hydrogen-free, assembly of microscopic sp2 carbon chips, forming a macroscopically homogeneous and isotropic solid, is proposed as a model carrier for the ultraviolet (UV) interstellar extinction band. The validity of this model is based on the calculation of the Bruggeman average dielectric function of a mixture of the known parallel and perpendicular dielectric functions of graphite. The π absorption feature of Rayleigh-sized spheres of this mixture falls near 4.6 μm−1 (2175 Å), but its width is 1.5 μm−1 , somewhat larger than the astronomically observed average, 1 μm−1 . This is confirmed by measurements of the reflectance of an industrial material, polycrystalline graphite. A better fit to the interstellar feature position and width is obtained with a hypothetical material, having the same dielectric functions as natural graphite, except for less extended wings of the π resonance. Physically, this could result from changes in the electronic band structure due to previous thermal histories. In this model, the Frölich feature central wavelength depends only on the π resonance frequency, while its width depends only on the damping constant of the same resonance. This explains the range of observed feature widths at constant feature wavelength. 相似文献
608.
L. Dunne S. J. Maddox R. J. Ivison L. Rudnick T. A. DeLaney B. C. Matthews C. M. Crowe H. L. Gomez S. A. Eales S. Dye 《Monthly notices of the Royal Astronomical Society》2009,394(3):1307-1316
If Type II supernovae – the evolutionary end points of short-lived, massive stars – produce a significant quantity of dust (>0.1 M⊙ ) then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe. Submillimetre (submm) observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for the formation of significant quantities of dust in Type II supernovae. In this paper, we present new data which show that the submm emission from Cas A is polarized at a level significantly higher than that of its synchrotron emission. The orientation is consistent with that of the magnetic field in Cas A, implying that the polarized submm emission is associated with the remnant. No known mechanism would vary the synchrotron polarization in this way and so we attribute the excess polarized submm flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the presence of both polarized and unpolarized dust emission in the north of the remnant where there is no contamination from foreground molecular clouds. The inferred dust polarization fraction is unprecedented ( f pol ∼ 30 per cent) which, coupled with the brief time-scale available for grain alignment (<300 yr), suggests that supernova dust differs from that seen in other Galactic sources (where f pol = 2−7 per cent) or that a highly efficient grain alignment process must operate in the environment of a supernova remnant. 相似文献
609.
Research on two-dimensional (2-D) properties of galaxies is a significant component of the study of galaxy formation and evolution.
Through the spatial distribution of physical properties (derived from integrated luminosity and spectroscopy) of galaxies,
we are allowed to realize the inner environment and evolution history of each individual galaxy and finally answer how galaxies
were assembled. In this paper, with reviewing previous work, we present a proposal for study on 2-D properties of nearby galaxies.
In our prospective work, we will make use of multi-wavelength data covering a range from ultraviolet to far-infrared to determine
the distributions of properties such as age, metallicity and dust-reddening in nearby galaxies, and try to remove the degeneracy
among them. Combining with surface photometry and spectroscopy, we will also analyze the distribution of HII regions and star
formation properties in galaxies. In our future plan, the World Space Observatory for Ultraviolet (WSO/UV) will be applied to our research and allow detail diagnosis of nearby galaxies at ultraviolet band. 相似文献
610.