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91.
使用了目前最大的棒旋星系样本之一,着重于研究旋涡星系中央的比恒星形成率(sSFR)和棒结构的关系。我们用1g sSFR=-11 a~(-1)作为星系宁静态和活跃态的分界,统计对比了棒旋星系和非棒旋星系中央的sSFR,发现相对于非棒旋星系,棒旋星系处于中央宁静态的比重更大,而在中央活跃态其恒星形成活动更剧烈。为消除星系样本恒星质量差异对星系中央sSFR统计结果的影响,获得控制样本,使棒旋星系和非棒旋星系具有相同的恒星质量分布。随后发现这两类星系在中央宁静态中的统计差异消失,而在中央活跃态棒旋星系的恒星形成活动依旧相对剧烈,尤其体现在长棒星系中。这说明棒结构对旋涡星系中央的恒星形成起到促进作用,且作用效果与棒的长短相关。 相似文献
92.
In the last few years, galaxies at redshifts up to z ∼ 1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic
and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation
(TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests
of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially
resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at
redshifts 0.1 < z < 1.0. We find evidence for a B-band luminosity increase of up to 2 mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity
as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of
previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical
simulations based on the hierarchical merging scenario.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
93.
We review selected measurements of the galaxy luminosity function including the field, the local group, the local sphere,
nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that, excluding the super-luminous cD and D
galaxies, the overall cluster luminosity function is fully consistent with the field luminosity function over the magnitude
range in common (–22 ≤ M
B
–5log
h
0.68
≤ –17). We find that only in the core regions of clusters (r ≤ 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function
is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall,
efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
94.
A new empirical procedure is introduced to determine the confirmed galaxy members of a cluster. The method depends on both
the projected distances of galaxies in the cluster field from the cluster centre and their radial velocities. Galaxies of
the main body of the cluster are selected first, then the method works iteratively by increasing the standard values of the
relative radial distance and velocity until all galaxies belong to the cluster are included. The general apparent shape of
the cluster will result from the distribution of the celestial coordinates of the cluster members.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
95.
Joseph Silk 《Astrophysics and Space Science》2003,284(2):663-674
I review several of the current issues in the theory of disk galaxy formation. There is still much to be done, observationally
and theoretically, before we can expect to approach an understanding of disk galaxies that is reliable enough to make robust
predictions about the high redshift universe.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
96.
Jia-Yu Tang Zu-Hui FanDepartment of Astronomy Peking University Beijing tangjy@vega.bac.pku.edu.cnChinese Academy of Sciences-Peking University Joint Beijing Astrophysics Center Beijing 《中国天文和天体物理学报》2003,3(3):191-202
We study the counts of resolved SZE(Sunyaev-Zel‘dovich effect)clusters expected from an interferometric survey in different cosmological models under different conditions.The self-similar universal gas model and Press-Schechter mass function are used.We take the observing frequency to be 90GHz,and consider two dish diameters,1.2m and 2.5m.We calculate the number density of the galaxy clusters dN/(dΩdz)at a high flux limit Sv^lim=100mJy and at a relative low Sv^lim=10mJy.The total numbers of SZE clusters N in two low-Ω0 models are compared.The results show that the inθuence of the resolved effect depends not only on D,but also on Sv^lim;at a given D,the effect is more significant for a high than for a low Sv^lim.Also,the resolved effect for a flat universe is more impressive than tnat for an open universe.ForD=1.2m and Sv^lim=10mJy,the resolved effect is very weak.Considering the designed interferometers which will be used to survey SZE clusters,we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys. 相似文献
97.
Empirical and analytical procedures are developed to determine the morphological properties of galaxy clusters. The apparent
orientations and shapes are obtainted in two dimensional space while the direction towards the cluster pole is found in three
dimensional space. These properties were determined for three Abell clusters and found to be strongly related.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
98.
We report the discovery of five Narrow-Line Seyfert 1 galaxies (NLSls) identified from the ROSAT All-Sky Survey bright sources. One of them has a quasarlike luminosity and two, including the quasar-like one, have close companions and/or show interacting features. We calculate the central black hole masses and Eddington ratios for the five NLSls. In combination with the objects of Kaspi et al., we find that NLSls have smaller central black hole masses and higher accretion rate than normal Seyfert ls. 相似文献
99.
Pierre Ocvirk Ariane Lançon Christophe Pichon Philippe Prugniel Damien Le Borgne Brigitte Rocca-Volmerange Michel Fioc Caroline Soubiran Eric Thiébaut 《Astrophysics and Space Science》2003,284(2):933-936
We present inversion techniques which aim at recovering the composite nature and the kinematics of a stellar population from
its high resolution absorption line spectrum. The originality of the combined inversion is its potential to recover both the
stellar content and the kinematics simultaneously. These techniques use new synthetic high resolution spectra produced by
PéGASE and minimization algorithms. We apply them to mock data representing the bulge and disk population of the inner region
of spiral galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
100.
We have started a survey of galaxies at intermediate redshifts using the HST-STIS parallel fields. Our main goal is to analyse
the morphology of faint galaxies in order to estimate the epoch of formation of the Hubble classification sequence. The high
resolution of STIS images (0.05″) is ideal for this work and enables us to perform a morphological classification and to analyse
the internal structures of galaxies. We find that 40% of the 290 galaxies are early types and that there are more irregulars
and ellipticals at the fainter magnitudes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献