全文获取类型
收费全文 | 2413篇 |
免费 | 95篇 |
国内免费 | 52篇 |
专业分类
测绘学 | 81篇 |
大气科学 | 176篇 |
地球物理 | 507篇 |
地质学 | 808篇 |
海洋学 | 149篇 |
天文学 | 636篇 |
综合类 | 13篇 |
自然地理 | 190篇 |
出版年
2023年 | 15篇 |
2022年 | 12篇 |
2021年 | 40篇 |
2020年 | 51篇 |
2019年 | 46篇 |
2018年 | 95篇 |
2017年 | 86篇 |
2016年 | 90篇 |
2015年 | 82篇 |
2014年 | 99篇 |
2013年 | 141篇 |
2012年 | 93篇 |
2011年 | 136篇 |
2010年 | 108篇 |
2009年 | 132篇 |
2008年 | 112篇 |
2007年 | 118篇 |
2006年 | 103篇 |
2005年 | 81篇 |
2004年 | 82篇 |
2003年 | 69篇 |
2002年 | 71篇 |
2001年 | 48篇 |
2000年 | 50篇 |
1999年 | 46篇 |
1998年 | 32篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 21篇 |
1992年 | 28篇 |
1991年 | 12篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 20篇 |
1975年 | 11篇 |
1974年 | 13篇 |
排序方式: 共有2560条查询结果,搜索用时 93 毫秒
1.
2.
3.
4.
R. J. Beswick A. Pedlar M. S. Clemens P. Alexander 《Monthly notices of the Royal Astronomical Society》2003,346(2):424-432
We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (H i ) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H i absorption ( N H ∼ 1022 atoms cm−2 ) traces a velocity gradient of 0.5 km s−1 pc−1 across the central kpc of NGC 520. The H i absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here. 相似文献
5.
Flavio Scappini Cesare Cecchi-Pestellini Harvey Smith William Klemperer Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661
We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H2 SO4 · n H2 O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects. 相似文献
6.
7.
8.
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
9.
Using photoclinometry, topographic profiles across europan ridges have been produced. These profiles allow the identification of bulges in the terrain adjacent to the ridges. The bulges are assumed to have been produced by flexure of the elastic lithosphere due to the load of the ridges, which lie along cracks in the crust. The distance from the crack to these “fore-bulges” depends on the thickness of the elastic plate being flexed. Based on a survey of ridges in Galileo images with resolution <300 m/pixel, the thickness of the elastic lithosphere has been determined by this method at a wide variety of sites along the leading and trailing hemispheres of Europa. The average thickness is about 200 m. The elastic lithosphere underneath smooth dilational bands tends to be thicker than plains morphology, an effect that is pronounced at Thynia Linea and Astypalaea Linea. Among the ridges investigated here, more recent loading correlates with a thicker elastic lithosphere, which may either reflect an intrinsically thicker layer, or less viscous relaxation over the shorter time period. 相似文献
10.
S. W. Allen R. W. Schmidt A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2002,334(2):L11-L15
We present precise measurements of the X-ray gas mass fraction for a sample of luminous, relatively relaxed clusters of galaxies observed with the Chandra observatory, for which independent confirmation of the mass results is available from gravitational lensing studies. Parametrizing the total (luminous plus dark matter) mass profiles using the model of Navarro, Frenk & White, we show that the X-ray gas mass fractions in the clusters asymptote towards an approximately constant value at a radius r 2500 , where the mean interior density is 2500 times the critical density of the Universe at the redshifts of the clusters. Combining the Chandra results on the X-ray gas mass fraction and its apparent redshift dependence with recent measurements of the mean baryonic matter density in the Universe and the Hubble constant determined from the Hubble Key Project, we obtain a tight constraint on the mean total matter density of the Universe, , and measure a positive cosmological constant, . Our results are in good agreement with recent, independent findings based on analyses of anisotropies in the cosmic microwave background radiation, the properties of distant supernovae, and the large-scale distribution of galaxies. 相似文献