全文获取类型
收费全文 | 700篇 |
免费 | 41篇 |
国内免费 | 43篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 55篇 |
地球物理 | 51篇 |
地质学 | 52篇 |
海洋学 | 13篇 |
天文学 | 599篇 |
综合类 | 2篇 |
自然地理 | 1篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 10篇 |
2012年 | 12篇 |
2011年 | 19篇 |
2010年 | 16篇 |
2009年 | 45篇 |
2008年 | 46篇 |
2007年 | 54篇 |
2006年 | 58篇 |
2005年 | 46篇 |
2004年 | 50篇 |
2003年 | 75篇 |
2002年 | 51篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 34篇 |
1998年 | 40篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有784条查询结果,搜索用时 15 毫秒
101.
Christian Wolf Alfonso Aragón-Salamanca Michael Balogh Marco Barden Eric F. Bell Meghan E. Gray Chien Y. Peng David Bacon Fabio D. Barazza Asmus Böhm John A. R. Caldwell Anna Gallazzi Boris Häußler Catherine Heymans Knud Jahnke Shardha Jogee Eelco van Kampen Kyle Lane Daniel H. McIntosh Klaus Meisenheimer Casey Papovich Sebastian F. Sánchez y Taylor Lutz Wisotzki Xianzhong Zheng 《Monthly notices of the Royal Astronomical Society》2009,393(4):1302-1323
We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of σ cz ≈ 2000 km s−1 . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of log M * /M⊙ =[10, 11] where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At log M * /M⊙ < 10 , such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on spirals play a minor role; despite being dust reddened they form only a small fraction of spirals independent of environment. 相似文献
102.
103.
104.
本文重点阐述高等级公路非标准缓和曲线的施工放样测量.缓和曲线是设置在直线和圆曲线之间的一种线型,起缓和过渡作用,其目的在于保证车辆由直线进入圆曲线(或由圆曲线进入直线)时的横向稳定,缓和曲线的曲率半径随曲线长度的增加而均匀连续地变小,本文综合了各种情况下的曲线计算,给出了直接计算和间接计算两种计算方法,并用C编写了计算... 相似文献
105.
106.
We describe simulations of the response of a gaseous disc to an active spiral potential. The potential is derived from an N -body calculation and leads to a multi-armed time-evolving pattern. The gas forms long spiral arms typical of grand-design galaxies, although the spiral pattern is asymmetric. The primary difference from a grand-design spiral galaxy, which has a consistent two-/four-armed pattern, is that instead of passing through the spiral arms, gas generally falls into a developing potential minimum and is released only when the local minimum dissolves. In this case, the densest gas is coincident with the spiral potential, rather than offset as in the grand-design spirals. We would therefore expect no offset between the spiral shock and star formation, and no obvious corotation radius. Spurs which occur in grand-design spirals when large clumps are sheared off leaving the spiral arms, are rare in the active, time-evolving spiral reported here. Instead, large branches are formed from spiral arms when the underlying spiral potential is dissolving due to the N -body dynamics. We find that the molecular cloud mass spectrum for the active potential is similar to that for clouds in grand-design calculations, depending primarily on the ambient pressure rather than the nature of the potential. The largest molecular clouds occur when spiral arms collide, rather than by agglomeration within a spiral arm. 相似文献
107.
108.
109.
A. Pizzella E. M. Corsini M. Sarzi J. Magorrian J. Méndez-Abreu L. Coccato L. Morelli F. Bertola 《Monthly notices of the Royal Astronomical Society》2008,387(3):1099-1116
Photometry and long-slit spectroscopy are presented for a sample of six galaxies with a low surface-brightness stellar disc and a bulge. The characterizing parameters of the bulge and disc components were derived by means of a two-dimensional photometric decomposition of the images of the sample galaxies. Their surface-brightness distribution was assumed to be the sum of the contribution of a Sérsic bulge and an exponential disc, with each component being described by elliptical and concentric isophotes of constant ellipticity and position angle. The stellar and ionized-gas kinematics were measured along the major and minor axes in half of the sample galaxies, whereas the other half was observed only along two diagonal axes. Spectra along two diagonal axes were obtained also for one of the objects with major and minor axis spectra. The kinematic measurements extend in the disc region out to a surface-brightness level μ R ≈ 24 mag arcsec−2 , reaching in all cases the flat part of the rotation curve. The stellar kinematics turns out to be more regular and symmetric than the ionized-gas kinematics, which often shows the presence of non-circular, off-plane and non-ordered motions. This raises the question about the reliability of the use of the ionized gas as the tracer of the circular velocity in the modelling of the mass distribution, in particular in the central regions of low surface-brightness galaxies. 相似文献
110.
P. Tsoutsis C. Efthymiopoulos N. Voglis † 《Monthly notices of the Royal Astronomical Society》2008,387(3):1264-1280
In a previous paper (Voglis et al., Paper I), we demonstrated that, in a rotating galaxy with a strong bar, the unstable asymptotic manifolds of the short-period family of unstable periodic orbits around the Lagrangian points L 1 or L 2 create correlations among the apocentric positions of many chaotic orbits, thus supporting a spiral structure beyond the bar. In this paper, we present evidence that the unstable manifolds of all the families of unstable periodic orbits near and beyond corotation contribute to the same phenomenon. Our results refer to a N -body simulation, a number of drawbacks of which, as well as the reasons why these do not significantly affect the main results, are discussed. We explain the dynamical importance of the invariant manifolds as due to the fact that they produce a phenomenon of 'stickiness' slowing down the rate of chaotic escape in an otherwise non-compact region of the phase space. We find a stickiness time of the order of 100 dynamical periods, which is sufficient to support a long-living spiral structure. Manifolds of different families become important at different ranges of values of the Jacobi constant. The projections of the manifolds of all the different families in the configuration space produce a pattern due to the 'coalescence' of the invariant manifolds. This follows closely the maxima of the observed m = 2 component near and beyond corotation. Thus, the manifolds support both the outer edge of the bar and the spiral arms. 相似文献