全文获取类型
| 收费全文 | 117845篇 |
| 免费 | 1978篇 |
| 国内免费 | 971篇 |
专业分类
| 测绘学 | 2851篇 |
| 大气科学 | 8080篇 |
| 地球物理 | 22829篇 |
| 地质学 | 42207篇 |
| 海洋学 | 10745篇 |
| 天文学 | 27216篇 |
| 综合类 | 349篇 |
| 自然地理 | 6517篇 |
出版年
| 2022年 | 770篇 |
| 2021年 | 1288篇 |
| 2020年 | 1402篇 |
| 2019年 | 1570篇 |
| 2018年 | 3333篇 |
| 2017年 | 3107篇 |
| 2016年 | 3741篇 |
| 2015年 | 1975篇 |
| 2014年 | 3622篇 |
| 2013年 | 6208篇 |
| 2012年 | 3848篇 |
| 2011年 | 5035篇 |
| 2010年 | 4521篇 |
| 2009年 | 5775篇 |
| 2008年 | 5062篇 |
| 2007年 | 5130篇 |
| 2006年 | 4750篇 |
| 2005年 | 3494篇 |
| 2004年 | 3478篇 |
| 2003年 | 3299篇 |
| 2002年 | 3209篇 |
| 2001年 | 2793篇 |
| 2000年 | 2688篇 |
| 1999年 | 2174篇 |
| 1998年 | 2254篇 |
| 1997年 | 2060篇 |
| 1996年 | 1819篇 |
| 1995年 | 1782篇 |
| 1994年 | 1533篇 |
| 1993年 | 1421篇 |
| 1992年 | 1365篇 |
| 1991年 | 1397篇 |
| 1990年 | 1386篇 |
| 1989年 | 1173篇 |
| 1988年 | 1092篇 |
| 1987年 | 1240篇 |
| 1986年 | 1117篇 |
| 1985年 | 1391篇 |
| 1984年 | 1568篇 |
| 1983年 | 1452篇 |
| 1982年 | 1361篇 |
| 1981年 | 1260篇 |
| 1980年 | 1158篇 |
| 1979年 | 1113篇 |
| 1978年 | 1071篇 |
| 1977年 | 908篇 |
| 1976年 | 877篇 |
| 1975年 | 877篇 |
| 1974年 | 832篇 |
| 1973年 | 910篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
11.
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
12.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
13.
14.
15.
16.
17.
18.
Mars Global Surveyor accelerometer observations of the martian upper atmosphere revealed large variations in density with longitude during northern hemisphere spring at altitudes of 130-160 km, all latitudes, and mid-afternoon local solar times (LSTs). This zonal structure is due to tides from the surface. The zonal structure is stable on timescales of weeks, decays with increasing altitude above 130 km, and is dominated by wave-3 (average amplitude 22% of mean density) and wave-2 (18%) harmonics. The phases of these harmonics are constant with both altitude and latitude, though their amplitudes change significantly with latitude. Near the South Pole, the phase of the wave-2 harmonic changes by 90° with a change of half a martian solar day while the wave-3 phase stays constant, suggesting diurnal and semidiurnal behaviour, respectively. We use a simple application of classical tidal theory to identify the dominant tidal modes and obtain results consistent with those of General Circulation Models. Our method is less rigorous, but simpler, than the General Circulation Models and hence complements them. Topography has a strong influence on the zonal structure. 相似文献
19.
20.
Zsolt Sándor Bálint Érdi Carl D. Murray 《Celestial Mechanics and Dynamical Astronomy》2002,84(4):355-368
The dynamics of co-orbital motion in the restricted three-body problem are investigated by symplectic mappings. Analytical and semi-numerical mappings have been developed and studied in detail. The mappings have been tested by numerical integration of the equations of motion. These mappings have been proved to be useful for a quick determination of the phase space structure reflecting the main characteristics of the dynamics of the co-orbital problem. 相似文献