全文获取类型
收费全文 | 17049篇 |
免费 | 1946篇 |
国内免费 | 3069篇 |
专业分类
测绘学 | 922篇 |
大气科学 | 2492篇 |
地球物理 | 3397篇 |
地质学 | 8471篇 |
海洋学 | 2351篇 |
天文学 | 1871篇 |
综合类 | 1000篇 |
自然地理 | 1560篇 |
出版年
2024年 | 115篇 |
2023年 | 322篇 |
2022年 | 740篇 |
2021年 | 966篇 |
2020年 | 856篇 |
2019年 | 891篇 |
2018年 | 1102篇 |
2017年 | 1032篇 |
2016年 | 1029篇 |
2015年 | 767篇 |
2014年 | 989篇 |
2013年 | 1039篇 |
2012年 | 1011篇 |
2011年 | 1102篇 |
2010年 | 994篇 |
2009年 | 944篇 |
2008年 | 893篇 |
2007年 | 922篇 |
2006年 | 827篇 |
2005年 | 434篇 |
2004年 | 377篇 |
2003年 | 433篇 |
2002年 | 499篇 |
2001年 | 455篇 |
2000年 | 341篇 |
1999年 | 364篇 |
1998年 | 285篇 |
1997年 | 308篇 |
1996年 | 258篇 |
1995年 | 256篇 |
1994年 | 232篇 |
1993年 | 182篇 |
1992年 | 164篇 |
1991年 | 110篇 |
1990年 | 95篇 |
1989年 | 111篇 |
1988年 | 79篇 |
1987年 | 63篇 |
1986年 | 57篇 |
1985年 | 46篇 |
1984年 | 42篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 29篇 |
1978年 | 17篇 |
1977年 | 17篇 |
1975年 | 22篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
912.
913.
本文对1949年以来出现的10次ENSO事件进行了分析,得出如下结果:开始於东太平洋增暖和中大平洋增暖的两类ENSO现象分别对应四川地区粮食产量的减产和增产。此结果对四川地区粮食生产政策的制定及产量的预测研究均有较重要的参考价值。 相似文献
914.
Within the framework of a pair two-body problem (Sun–Jupiter, Sun–comet), the kinematics of the encounter of a minor body with a planet is investigated. The notion of points of low-velocity tangency of the orbits of the comet and Jupiter, as well as the point of Jovicentric velocity and the low-velocity tangent section of a cometary orbit, is introduced. The conditions and definitions of low-velocity and high-velocity encounters are proposed. The systems of inequalities relating the aand eparameters, which make it possible to single out those comets that are likely to be objects with low-velocity encounters, are presented. The regions of orbits that have low-velocity tangent sections, i.e., regions of low-velocity tangency of orbits, are singled out on the (a, e) plane. These regions agree well with the corresponding parameters of the orbits of real comets whose evolution contains low-velocity encounters with Jupiter. 相似文献
915.
L. S. Gurin N. P. Belyaeva G. S. Bisnovatyi-Kogan E. Yu. Boudnick S. V. Boudnick 《Astrophysics and Space Science》1988,147(2):307-320
The problem of discovery and estimation of the period, slowly changing in time is considered, when the pulses are rare. Several criteria are proposed on the base of which a multilevel algorithm of the period detection is constructed. The reliability and precision of the period determination are investigated with taking into account of the correlated errors of corresponding values of criteria. 相似文献
916.
917.
I. G. Kovalenko Yu. A. Shchekinov Al. A. Suchkov 《Astrophysics and Space Science》1989,152(2):223-238
The available data speak in favour of space and time inhomogeneity of gaseous corona of our Galaxy. The observedCIV and SiIV ions are formed mainly by fast photons and localized inHII-clouds of the galactic halo. On the other hand, theNV ions are thermally ionized and localized in the gas corresponding to a transformation of hot intercloud coronal gas in theHII-clouds. TheHII-clouds exhibit downward the gas flow. The galactic fountain can eject the interstellar matter up to height of 1 kpc. Such ejections may be also displayed inCIV, SiIV, and partiallyNV, and partiallyNV absorptions. But large gaseous corona extending up to 3–5 kpc proves to be mass-unbalanced. It is possible that the existence of corona is evidence for violent star formation in the galactic disc in the recent past. 相似文献
918.
Kiev Polytechnic Institute. Translated from Astrofizika, Vol. 30, No. 1, pp. 208–219, January–February, 1989. 相似文献
919.
Erevan State University. Translated from Astrofizika, Vol. 31, No. 1, pp. 111–123, July–August, 1989. 相似文献
920.
One of the main problems of selenodesy consists of the construction of a net of basic reference points on the surface of the Moon. At present there exist many catalogues containing the coordinates of selected objects on the Moon. These catalogues differ by the presence of both systematic and accidental errors.The investigations concerning the comparison of catalogues and the elucidation of their systematic differences are of very recent date. Various methods of interpretation of the systematic differences between catalogues have been proposed. Without an attempt to encompass the whole problem in what follows, we shall describe one method for comparative study of catalogues based on the theory of the deformation of continuous media. 相似文献