全文获取类型
收费全文 | 16353篇 |
免费 | 3463篇 |
国内免费 | 4129篇 |
专业分类
测绘学 | 613篇 |
大气科学 | 1033篇 |
地球物理 | 4419篇 |
地质学 | 10649篇 |
海洋学 | 1924篇 |
天文学 | 2098篇 |
综合类 | 857篇 |
自然地理 | 2352篇 |
出版年
2024年 | 48篇 |
2023年 | 213篇 |
2022年 | 523篇 |
2021年 | 554篇 |
2020年 | 630篇 |
2019年 | 708篇 |
2018年 | 648篇 |
2017年 | 670篇 |
2016年 | 705篇 |
2015年 | 780篇 |
2014年 | 866篇 |
2013年 | 808篇 |
2012年 | 978篇 |
2011年 | 1015篇 |
2010年 | 843篇 |
2009年 | 1206篇 |
2008年 | 1040篇 |
2007年 | 1171篇 |
2006年 | 1170篇 |
2005年 | 1007篇 |
2004年 | 1018篇 |
2003年 | 987篇 |
2002年 | 792篇 |
2001年 | 744篇 |
2000年 | 728篇 |
1999年 | 665篇 |
1998年 | 700篇 |
1997年 | 440篇 |
1996年 | 395篇 |
1995年 | 384篇 |
1994年 | 340篇 |
1993年 | 301篇 |
1992年 | 241篇 |
1991年 | 139篇 |
1990年 | 105篇 |
1989年 | 93篇 |
1988年 | 71篇 |
1987年 | 72篇 |
1986年 | 44篇 |
1985年 | 24篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1954年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
72.
Wing-Huen Ip 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):197-202
In the context of the survival of periodic comets of different origins, rotational breakup and tidal disruption could be important, especially of the short period comets injected from the Kuiper belt. This is because long-period comets from the distant Oort cloud tend to be subject to thermal stress and volatile 'explosion' far more severely. A simple calculation using the Öpik method of random planetary close encounters was performed to estimate the probability of tidal disruption of comets and scattered Kuiper belt objects (SKBOs) during their orbital migration. It was found that a large fraction of the short period comets and SKBOs might have been internally fragmented by single or multiple close encounters with the outer planets. 相似文献
73.
74.
75.
76.
77.
Natalia Orlova Vladimir Korchagin Nobuhiro Kikuchi Shoken. M. Miyama Aleksei Moiseev 《Astrophysics and Space Science》2003,284(2):739-742
We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample
of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four
galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions
and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented
two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach
is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic
disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support
the global modal approach as a theoretical explanation of spiral structure in galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
78.
Genetic diversity and differentiation of the oyster Crassostreaplicatula populations from China's coast were studied basedon seven microsatellite loci.All loci showed high polymorphism for all five C.plicatula populations,with an average number of alleleper locus of 19.3-27.9 and an average expected heterozygosity of 0.889-0.952.Significant departures from Hardy-Weinberg equilib-rium and deficits of heterozygotes were observed over most populations at each locus,which were fully explained by null alleles.Microsatellite analysis revealed significant subdivision in the C.plicatula populations.According to the neighbor-joining tree con-structed on the basis of the D,A distance,the five populations fell into three regional groups,showing a relatively homogeneous geneticstructure in geographically close populations.Assignation tests correctly assigned high percentages of individuals to their originalpopulations and groups,and also confirmed the existence of genetic differentiation among C.plicatula populations.The results ob-tained in this study will facilitate the formulation of appropriate fisheries management programs,stock identification and conservationof biodiversity for the species. 相似文献
79.
80.