全文获取类型
收费全文 | 4995篇 |
免费 | 522篇 |
国内免费 | 804篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 397篇 |
地球物理 | 1246篇 |
地质学 | 1562篇 |
海洋学 | 1331篇 |
天文学 | 732篇 |
综合类 | 159篇 |
自然地理 | 878篇 |
出版年
2024年 | 14篇 |
2023年 | 35篇 |
2022年 | 79篇 |
2021年 | 75篇 |
2020年 | 98篇 |
2019年 | 151篇 |
2018年 | 102篇 |
2017年 | 111篇 |
2016年 | 111篇 |
2015年 | 125篇 |
2014年 | 153篇 |
2013年 | 279篇 |
2012年 | 135篇 |
2011年 | 199篇 |
2010年 | 190篇 |
2009年 | 307篇 |
2008年 | 349篇 |
2007年 | 395篇 |
2006年 | 356篇 |
2005年 | 276篇 |
2004年 | 275篇 |
2003年 | 304篇 |
2002年 | 270篇 |
2001年 | 205篇 |
2000年 | 231篇 |
1999年 | 231篇 |
1998年 | 213篇 |
1997年 | 138篇 |
1996年 | 149篇 |
1995年 | 120篇 |
1994年 | 96篇 |
1993年 | 99篇 |
1992年 | 75篇 |
1991年 | 71篇 |
1990年 | 62篇 |
1989年 | 53篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 19篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1975年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有6321条查询结果,搜索用时 31 毫秒
1.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
2.
3.
4.
5.
6.
7.
In the upper Chesapeake Bay (Maryland, U.S.A.) field surveys were conducted at 18 multiple longshore sand bar sites. The multiple bar systems were found in water depths less than approximately 2 m (mean sea level), and exhibited mild bottom slopes of 0·0052 or less. The number of bars composing each system ranged from four to 17 and the spacing between the crests typically increased in the offshore direction, ranging from 12 to 70 m. Bar height also typically increased with distance offshore and ranged from 0·03 to 0·61 m. A grain size analysis of crest and trough sediment did not reveal any significant differences and the sediment was categorized as ‘fine sand’. A review of the literature data indicated that the Chesapeake Bay multiple bars possessed similar characteristics to those found in Gelding Bay (Baltic Sea); similarities in fetch, wave height and tidal range between the two bays may account for this finding. The surf-scaling parameter indicated that the multiple bar systems were extremely dissipative with regard to wave energy, and wave height appeared to be an important factor in controlling bar spacing and bar height. A multiple wave break point hypothesis was discussed as a possible mechanism for the formation of Chesapeake Bay multiple longshore bars, and limited observational evidence appeared to support such a mechanism. 相似文献
8.
S. A. Lamzin 《Astrophysics and Space Science》1995,224(1-2):211-214
I argue that temperatures of spots, responsible for observed periodical light variations of T Tauri stars (TTS), are not known with reliable accuracy to discriminate between chromospheric and accretion theories of TTS 's phenomenon. The hypothesis is set up that spots on classical TTS (CTTS) are due to heating of stellar surface by radiation from a collisional accretion shock, whereas spots on weak line TTS (WTTS), at least in some cases, are connected with a collisionless accretion shock rather than chromospheric activity. Possible scenarios of WTTS interaction with circumstellar matter are discussed. 相似文献
9.
Joachim Köppen 《Astrophysics and Space Science》2003,284(2):837-840
Representative results from a comparison of the chemical evolution of spherical collapse models without and with a intercloud
medium are presented. The hot metal-rich gas distributes quickly the metals produced in supernovae throughout the galaxy,
thus leading to a more homogeneous chemical evolution and flatter metallicity gradients in the gas and the stars. The stellar
population is somewhat less concentrated towards the centre. The strong outflow results in a substantial loss of metals from
the galaxy to its surroundings, and a lower effective yield in the galaxy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.