全文获取类型
收费全文 | 4986篇 |
免费 | 154篇 |
国内免费 | 228篇 |
专业分类
测绘学 | 230篇 |
大气科学 | 321篇 |
地球物理 | 123篇 |
地质学 | 231篇 |
海洋学 | 71篇 |
天文学 | 3886篇 |
综合类 | 105篇 |
自然地理 | 401篇 |
出版年
2024年 | 10篇 |
2023年 | 10篇 |
2022年 | 34篇 |
2021年 | 38篇 |
2020年 | 39篇 |
2019年 | 43篇 |
2018年 | 44篇 |
2017年 | 61篇 |
2016年 | 42篇 |
2015年 | 72篇 |
2014年 | 73篇 |
2013年 | 101篇 |
2012年 | 187篇 |
2011年 | 89篇 |
2010年 | 95篇 |
2009年 | 394篇 |
2008年 | 343篇 |
2007年 | 398篇 |
2006年 | 412篇 |
2005年 | 416篇 |
2004年 | 439篇 |
2003年 | 402篇 |
2002年 | 291篇 |
2001年 | 301篇 |
2000年 | 276篇 |
1999年 | 257篇 |
1998年 | 329篇 |
1997年 | 34篇 |
1996年 | 17篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1977年 | 2篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有5368条查询结果,搜索用时 31 毫秒
1.
The formal opportunity to learn geography in the United States is unevenly distributed across space, creating possible geography deserts. Data on the number of exams taken in Advanced Placement Human Geography (APHG) and bachelor’s degrees earned in geography are mapped at the state and regional scales. Normalized rates are ranked and grouped into quintiles. For APHG exams, states in the southeastern region of the United States are in the uppermost quintiles while states in the northeastern region are in the lowermost quintiles. The pattern for bachelor’s degrees in geography is somewhat the spatial inverse of that for APHG. 相似文献
2.
3.
4.
5.
6.
7.
A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems, one EA type and two EB type eclipsing binaries (one of them could be a W UMa system), and seven pulsating stars including three candidates of δScuti stars. 相似文献
8.
9.
10.
Sergei A. Klioner 《Celestial Mechanics and Dynamical Astronomy》1996,66(4):345-363
Intermediate orbit for general planetary theory is constructed in the form of multivariate Fourier series with numerical coefficients. The structure and efficiency of the derived series are illustrated by giving various statistical properties of the coefficients.The ability of the recently proposed elliptic function approach to compress the Fourier series representing the intermediate orbit is investigated. Our results confirm that when mutual perturbations of a pair of planets are considered the elliptic function approach is quite efficient and allows one to compress the series substantially. However, when perturbations of three or more planets are under study the elliptic function approach does not give any advantages. 相似文献