全文获取类型
收费全文 | 30052篇 |
免费 | 633篇 |
国内免费 | 301篇 |
专业分类
测绘学 | 676篇 |
大气科学 | 2222篇 |
地球物理 | 6286篇 |
地质学 | 10558篇 |
海洋学 | 2468篇 |
天文学 | 6683篇 |
综合类 | 67篇 |
自然地理 | 2026篇 |
出版年
2021年 | 207篇 |
2020年 | 245篇 |
2019年 | 272篇 |
2018年 | 578篇 |
2017年 | 561篇 |
2016年 | 681篇 |
2015年 | 546篇 |
2014年 | 730篇 |
2013年 | 1451篇 |
2012年 | 855篇 |
2011年 | 1243篇 |
2010年 | 1037篇 |
2009年 | 1429篇 |
2008年 | 1282篇 |
2007年 | 1253篇 |
2006年 | 1157篇 |
2005年 | 988篇 |
2004年 | 961篇 |
2003年 | 947篇 |
2002年 | 869篇 |
2001年 | 772篇 |
2000年 | 725篇 |
1999年 | 632篇 |
1998年 | 641篇 |
1997年 | 633篇 |
1996年 | 505篇 |
1995年 | 473篇 |
1994年 | 436篇 |
1993年 | 379篇 |
1992年 | 358篇 |
1991年 | 318篇 |
1990年 | 345篇 |
1989年 | 322篇 |
1988年 | 270篇 |
1987年 | 347篇 |
1986年 | 304篇 |
1985年 | 402篇 |
1984年 | 436篇 |
1983年 | 423篇 |
1982年 | 389篇 |
1981年 | 370篇 |
1980年 | 357篇 |
1979年 | 322篇 |
1978年 | 359篇 |
1977年 | 292篇 |
1976年 | 296篇 |
1975年 | 300篇 |
1974年 | 265篇 |
1973年 | 269篇 |
1972年 | 176篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
The morphological and velocity structures in the gaseous (HI and CO) and stellar components of two interacting systems are
examined. Both Arp 140 and Arp 104 reveal extended tidal tails in the HI. The Hα and FIR fluxes of Arp 140 yield similar SFR
of ∼ 0.8 M⊙ yr-1. In contrast the Hα flux of Arp 104 yields a SFR of ∼ 0.05 M⊙ yr-1, ∼ 20 times smaller than that obtained from the FIR flux. Spectra were used to examine the changing velocity of atomic and
molecular gas in NGC 5218 (Arp 104). The atomic and molecular gas were found to be dynamically similar with comparable velocities
and velocity widths across the galaxy; consistent with the two phases responding similarly to the interaction, or enhanced
HI to CO conversion in the centre of the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
53.
Piero F. Spinnato Michael Fellhauer Simon F. Portegies Zwart 《Monthly notices of the Royal Astronomical Society》2003,344(1):22-32
We study the efficiency at which a black hole or dense star cluster spirals in to the Galactic Centre. This process takes place on a dynamical friction time-scale, which depends on the value of the Coulomb logarithm (ln Λ). We determine the accurate value of this parameter using the direct N -body method, a tree algorithm and a particle-mesh technique with up to two million plus one particles. The three different techniques are in excellent agreement. Our measurement for the Coulomb logarithm appears to be independent of the number of particles. We conclude that ln Λ= 6.6 ± 0.6 for a massive point particle in the inner few parsec of the Galactic bulge. For an extended object, such as a dense star cluster, ln Λ is smaller, with a value of the logarithm argument Λ inversely proportional to the object size. 相似文献
54.
55.
56.
A numerical study of the pre-ejection, magnetically-sheared corona as a free boundary problem 总被引:1,自引:0,他引:1
A class of magnetostatic equilibria with axial symmetry outside a unit sphere in the presence of plasma pressure and an r
–2 gravitational field is constructed. The structure contains a localized current-carrying region confined by a background bipolar potential field, and the shape of the region changes subject to the variation of the electric current. The continuity requirement for the magnetic field and plasma pressures at the outer boundary of the cavity defines a free boundary problem, which is solved numerically using a spectral boundary scheme. The model is then used to study the expansion of the current-carrying region, caused by the buildup of magnetic shear, against the background confining field. The magnetic shear in our model is induced by the loading of an azimuthal field, accompanied by a depletion of plasma density.We show that due to the additional effect of confinement by the dense surrounding plasma, the energy of the magnetic field can exceed the energy of its associated open field, presumably a necessary condition for the onset of coronal mass ejections. (However, the plasma beta of the confining fluid is higher than that in the outer boundary of a realistic helmet-streamer structure.) Furthermore, under the assumption that coronal mass ejections are driven by magnetic buoyancy, the result from our model study lends further support to the notion of a suspended magnetic flux rope in the low-density cavity of a helmet-streamer as a promising pre-ejection configuration.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
57.
58.
Non-Newtonian topographic relaxation on Europa 总被引:1,自引:0,他引:1
Models of topographic support on Europa by lateral shell thickness variations have previously assumed a Newtonian ice viscosity. Here I show that using a more realistic stress-dependent viscosity gives relaxation times which can be significantly different. Topography of wavelength 100 km cannot be supported by lateral shell thickness variations for ∼50 Myr, unless the shell thickness is <10 km or the ice grain size >10 mm. Shorter wavelength topography would require even thinner shells, but may be supported elastically. Global-scale variations in shell thickness, however, can be supported for geological timescales if the shell thickness is O(10 km). 相似文献
59.
60.