全文获取类型
收费全文 | 47276篇 |
免费 | 982篇 |
国内免费 | 374篇 |
专业分类
测绘学 | 1463篇 |
大气科学 | 3453篇 |
地球物理 | 10802篇 |
地质学 | 15578篇 |
海洋学 | 3787篇 |
天文学 | 11072篇 |
综合类 | 140篇 |
自然地理 | 2337篇 |
出版年
2021年 | 425篇 |
2020年 | 477篇 |
2019年 | 525篇 |
2018年 | 1208篇 |
2017年 | 1127篇 |
2016年 | 1511篇 |
2015年 | 905篇 |
2014年 | 1375篇 |
2013年 | 2353篇 |
2012年 | 1487篇 |
2011年 | 1825篇 |
2010年 | 1702篇 |
2009年 | 2255篇 |
2008年 | 1947篇 |
2007年 | 1934篇 |
2006年 | 1823篇 |
2005年 | 1382篇 |
2004年 | 1403篇 |
2003年 | 1298篇 |
2002年 | 1316篇 |
2001年 | 1174篇 |
2000年 | 1104篇 |
1999年 | 951篇 |
1998年 | 968篇 |
1997年 | 956篇 |
1996年 | 767篇 |
1995年 | 734篇 |
1994年 | 712篇 |
1993年 | 603篇 |
1992年 | 538篇 |
1991年 | 536篇 |
1990年 | 528篇 |
1989年 | 530篇 |
1988年 | 482篇 |
1987年 | 544篇 |
1986年 | 514篇 |
1985年 | 577篇 |
1984年 | 704篇 |
1983年 | 623篇 |
1982年 | 617篇 |
1981年 | 557篇 |
1980年 | 486篇 |
1979年 | 484篇 |
1978年 | 506篇 |
1977年 | 418篇 |
1976年 | 376篇 |
1975年 | 394篇 |
1974年 | 362篇 |
1973年 | 411篇 |
1972年 | 298篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Carlos J.A.P. Martins 《Astrophysics and Space Science》2003,283(4):439-444
I briefly present the Organizing Committee's and my own motivation for organizing this workshop, and I suggest a few key questions
for which we will try to find possible answers in the coming days.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
42.
43.
44.
In the first paper of this series, we presented EBAS – Eclipsing Binary Automated Solver, a new fully automated algorithm to analyse the light curves of eclipsing binaries, based on the ebop code. Here, we apply the new algorithm to the whole sample of 2580 binaries found in the Optical Gravitational Lensing Experiment (OGLE) Large Magellanic Cloud (LMC) photometric survey and derive the orbital elements for 1931 systems. To obtain the statistical properties of the short-period binaries of the LMC, we construct a well-defined subsample of 938 eclipsing binaries with main-sequence B-type primaries. Correcting for observational selection effects, we derive the distributions of the fractional radii of the two components and their sum, the brightness ratios and the periods of the short-period binaries. Somewhat surprisingly, the results are consistent with a flat distribution in log P between 2 and 10 d. We also estimate the total number of binaries in the LMC with the same characteristics, and not only the eclipsing binaries, to be about 5000. This figure leads us to suggest that (0.7 ± 0.4) per cent of the main-sequence B-type stars in the LMC are found in binaries with periods shorter than 10 d. This frequency is substantially smaller than the fraction of binaries found by small Galactic radial-velocity surveys of B stars. On the other hand, the binary frequency found by Hubble Space Telescope ( HST ) photometric searches within the late main-sequence stars of 47 Tuc is only slightly higher and still consistent with the frequency we deduced for the B stars in the LMC. 相似文献
45.
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
46.
47.
48.
An analysis of the UV spectra of 28 asteroids obtained with the Internal Ultraviolet Explorer (IUE) satellite is presented. The spectra lie within the range 2100–3200 Å. Our results are examined in terms of both asteroid classification and of current ideas concerning the surface mineralogy of asteroids. For all the asteroids examined, UV reflectivity declines approximately linearly toward shorter wavelengths. In general, the same taxonomic groups are seen in the UV as in the visible and IR, although there is some evidence for asteroids with anomalous UV properties and for UV subclasses within the S class. No mineral absorption features are reported of strength similar to the strongest features in the visible and IR regions, but a number of shallow absorptions do occur and may provide valuable information on the surface composition of many asteroids. 相似文献
49.
Laser-induced plasmas in various gas mixtures were used to simulate lightning in other planetary atmospheres. This method of simulation has the advantage of producing short-duration, high-temperature plasmas free from electrode contamination. The laser-induced plasma discharges in air are shown to accurately simulate terrestrial lightning and can be expected to simulate lightning spectra in other planetary atmospheres. Spectra from 240 to 880 nm are presented for simulated lightning in the atmospheres of Venus, Earth, Jupiter, and Titan. The spectra of lightning on the other giant planets are expected to be similar to that of Jupiter because the atmospheres of these planets are composed mainly of hydrogen and helium. The spectra of Venus and Titan show substantial amounts of radiation due to the presence of carbon atoms and ions and show CN Violet radiation. Although small amounts of CH4 and NH3 are present in the Jovian atmosphere, only emission from hydrogen and helium is observed. Most differences in the spectra can be understood in terms of the elemental ratios of the gas mixtures. Consequently, observations of the spectra of lightning on other planets should provide in situ estimates of the atmospheric and aerosol composition in the cloud layers in which lightning is occuring. In particular, the detection of inert gases such as helium should be possible and the relative abundance of these gases compared to major constituents might be determined. 相似文献
50.
Observations of the brightness, color, and polarization of the fuor V1057 Cyg over more than 30 years are presented and briefly discussed. Variability of the linear polarization was found. 相似文献