全文获取类型
收费全文 | 139339篇 |
免费 | 2144篇 |
国内免费 | 1888篇 |
专业分类
测绘学 | 4079篇 |
大气科学 | 9823篇 |
地球物理 | 26969篇 |
地质学 | 52062篇 |
海洋学 | 11688篇 |
天文学 | 28675篇 |
综合类 | 2458篇 |
自然地理 | 7617篇 |
出版年
2022年 | 770篇 |
2021年 | 1311篇 |
2020年 | 1403篇 |
2019年 | 1571篇 |
2018年 | 7542篇 |
2017年 | 6631篇 |
2016年 | 6042篇 |
2015年 | 2172篇 |
2014年 | 3685篇 |
2013年 | 6224篇 |
2012年 | 4667篇 |
2011年 | 7320篇 |
2010年 | 6282篇 |
2009年 | 7762篇 |
2008年 | 6722篇 |
2007年 | 7186篇 |
2006年 | 4800篇 |
2005年 | 3670篇 |
2004年 | 3846篇 |
2003年 | 3660篇 |
2002年 | 3430篇 |
2001年 | 2831篇 |
2000年 | 2737篇 |
1999年 | 2187篇 |
1998年 | 2277篇 |
1997年 | 2061篇 |
1996年 | 1823篇 |
1995年 | 1785篇 |
1994年 | 1533篇 |
1993年 | 1423篇 |
1992年 | 1369篇 |
1991年 | 1395篇 |
1990年 | 1388篇 |
1989年 | 1174篇 |
1988年 | 1124篇 |
1987年 | 1273篇 |
1986年 | 1152篇 |
1985年 | 1412篇 |
1984年 | 1586篇 |
1983年 | 1470篇 |
1982年 | 1377篇 |
1981年 | 1288篇 |
1980年 | 1181篇 |
1979年 | 1133篇 |
1978年 | 1081篇 |
1977年 | 915篇 |
1976年 | 898篇 |
1975年 | 882篇 |
1974年 | 845篇 |
1973年 | 915篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
23.
24.
25.
The surface digital photometry for NGC 5253 and NGC 2915 is given. The luminosity profiles and colour gradients are discussed and compared. It is concluded that NGC 2915 differs from NGC 5253, both in the extension and intensity of the star burst event because of the kinematical behaviour of the captured gas.CONICET, Buenos Aires, Visiting Astronomer, Cerro Tololo Inter-American Observatory, La Serena, Chile, operated by NSF 相似文献
26.
文中所作的主要工作是为云南天文台十米抛物面设计、制造一付好的对数周期偶极子天线(LPDA)作馈源。工作有:(1)设计一对交叉的LP-DA;(2)分析LPDA特性;(3)估算抛物面的电特性;(4)讨论线极化向园极化转换的问题;(5)天线测量。LPDA的测量结果比较满意。该天线的方向图、平均输入阻抗、三分贝和十分贝波瓣宽度都在从0.5-1.5GHz的频率范围内比较一致和稳定,变化很小。天线理论上的许多成就都是与数子计算机有关的。在文中,我们充分利用了计算机的功能来设计天线,分析天线特性,并从测量所得的所有数据文件中计算天线的参数。所编FORTRAN程序使这一切工作变得容易。最后,我们还讨论了用功率合成器实现线极化向园极化转换的各种情况 相似文献
27.
Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years. 相似文献
28.
H. A. Harutyunian 《Astrophysics》1996,39(4):370-374
The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996. 相似文献
29.
AN ILLUSTRATIVE STUDY ON LOCAL LANDSCAPEAND ITS LONG-TERM CHANGES BASED ON IKONOS AND HISTORICAL AERIAL PHOTO 总被引:2,自引:0,他引:2
RUANRen-zong ErieCELLISt 《中国地理科学(英文版)》2004,14(2):162-169
Nowadays, the research works on landscape at fine scales using high-resolution images are uncommon.This research is based on the analysis of the combination of remote sensing data (1KONOS imagery acquired in 2002 and historical aerial photo taken in 1942). In the paper, the ecotopes in Qiujiadou and Xishao villages in Yixing City of Jiangsu Province in 1942 and 2002 were compared and landscape changes as well as the causes of the considerable changes were analyzed. It was found that the ecotope changes were at greater level in some aspects such as water surface and perennial vegetation coverage etc. This study at fine scale is globally significant for the rural areas, especially for the subsistence agricultural land, which occupies larger percentage in the earth. And it analyzes the structure of landscape based on a new landscape classification system--stratifications method. 相似文献
30.