全文获取类型
收费全文 | 62809篇 |
免费 | 726篇 |
国内免费 | 381篇 |
专业分类
测绘学 | 1583篇 |
大气科学 | 4444篇 |
地球物理 | 11462篇 |
地质学 | 24812篇 |
海洋学 | 5201篇 |
天文学 | 13074篇 |
综合类 | 213篇 |
自然地理 | 3127篇 |
出版年
2021年 | 403篇 |
2020年 | 402篇 |
2019年 | 454篇 |
2018年 | 3759篇 |
2017年 | 3487篇 |
2016年 | 2592篇 |
2015年 | 724篇 |
2014年 | 1030篇 |
2013年 | 2075篇 |
2012年 | 2153篇 |
2011年 | 4168篇 |
2010年 | 3885篇 |
2009年 | 4421篇 |
2008年 | 3564篇 |
2007年 | 4247篇 |
2006年 | 1629篇 |
2005年 | 1777篇 |
2004年 | 1614篇 |
2003年 | 1666篇 |
2002年 | 1435篇 |
2001年 | 1080篇 |
2000年 | 1017篇 |
1999年 | 811篇 |
1998年 | 813篇 |
1997年 | 829篇 |
1996年 | 668篇 |
1995年 | 656篇 |
1994年 | 616篇 |
1993年 | 570篇 |
1992年 | 526篇 |
1991年 | 495篇 |
1990年 | 506篇 |
1989年 | 496篇 |
1988年 | 474篇 |
1987年 | 553篇 |
1986年 | 489篇 |
1985年 | 604篇 |
1984年 | 650篇 |
1983年 | 592篇 |
1982年 | 527篇 |
1981年 | 589篇 |
1980年 | 488篇 |
1979年 | 458篇 |
1978年 | 433篇 |
1977年 | 433篇 |
1976年 | 386篇 |
1975年 | 378篇 |
1974年 | 376篇 |
1973年 | 384篇 |
1971年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
22.
We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during
1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal
that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles.
The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease
of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles
of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed. 相似文献
23.
We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem. 相似文献
24.
W. H. Jefferys G. F. Benedict P. D. Hemenway P. J. Shelus R. L. Duncombe 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):299-305
The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed. 相似文献
25.
26.
27.
M.S. Hanner E. Tedesco A.T. Tokunaga G.J. Veeder D.F. Lester F.C. Witteborn J.D. Bregman J. Gradie L. Lebofsky 《Icarus》1985,64(1):11-19
The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ~2 × 105 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ~0.04 at 1.25 μm and ~0.05 at 2.2 μm. 相似文献
28.
29.
30.
D. Montes M. C. Gálvez M. J. Fernández-Figueroa I. Crespo-Chacón 《Astrophysics and Space Science》2006,304(1-4):367-369
High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D1&D2, He i D3, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics. 相似文献