全文获取类型
收费全文 | 47919篇 |
免费 | 6423篇 |
国内免费 | 9115篇 |
专业分类
测绘学 | 10965篇 |
大气科学 | 7209篇 |
地球物理 | 7689篇 |
地质学 | 15917篇 |
海洋学 | 5674篇 |
天文学 | 2928篇 |
综合类 | 4588篇 |
自然地理 | 8487篇 |
出版年
2024年 | 173篇 |
2023年 | 466篇 |
2022年 | 1455篇 |
2021年 | 1736篇 |
2020年 | 1957篇 |
2019年 | 2272篇 |
2018年 | 1659篇 |
2017年 | 2256篇 |
2016年 | 2150篇 |
2015年 | 2406篇 |
2014年 | 2712篇 |
2013年 | 3121篇 |
2012年 | 3078篇 |
2011年 | 3107篇 |
2010年 | 2508篇 |
2009年 | 2757篇 |
2008年 | 2937篇 |
2007年 | 3398篇 |
2006年 | 3228篇 |
2005年 | 2887篇 |
2004年 | 2594篇 |
2003年 | 2131篇 |
2002年 | 1968篇 |
2001年 | 1570篇 |
2000年 | 1561篇 |
1999年 | 1377篇 |
1998年 | 1170篇 |
1997年 | 910篇 |
1996年 | 749篇 |
1995年 | 645篇 |
1994年 | 582篇 |
1993年 | 478篇 |
1992年 | 358篇 |
1991年 | 258篇 |
1990年 | 179篇 |
1989年 | 192篇 |
1988年 | 114篇 |
1987年 | 95篇 |
1986年 | 78篇 |
1985年 | 43篇 |
1984年 | 33篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1977年 | 13篇 |
1973年 | 5篇 |
1971年 | 6篇 |
1954年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
31.
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
32.
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
33.
A. Habib J. Vernin Z. Benkhaldoun H. Lanteri 《Monthly notices of the Royal Astronomical Society》2006,368(3):1456-1462
In this paper, we present a new method to estimate, for each turbulent layer labelled i , the horizontal wind speed v ( h i ) , the standard deviation of the horizontal wind speed fluctuations σ v ( hi ) and the integrated value of C 2 n over the thickness Δ hi of the turbulent layer C 2 n ( hi )Δ hi , where hi is the altitude of the turbulent layer. These parameters are extracted from single star scintillation spatiotemporal cross-correlation functions of atmospheric speckles obtained within the generalized mode. This method is based on the simulated annealing algorithm to find the optimal solution required to solve the problem. Astrophysics parameters for adaptive optics are also calculated using C 2 n ( hi ) and v ( hi ) values. The results of other techniques support this new method. 相似文献
34.
35.
36.
V. J. Mclntyre A. C. Gilmore J. B. Hearnshaw 《Journal of Astrophysics and Astronomy》1990,11(1):81-123
Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings
of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper
presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements
of selected lines in the spectra 相似文献
37.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
38.
空间数据仓库的认知过程 总被引:3,自引:3,他引:0
从理论上探讨了空间数据仓库的认知过程.主要是十一个层次的世界模型通过十个算子转换的过程,对十一个层次世界及十个算子概念进行了较详细地讨论,并用代数系统对其进行了定义。 相似文献
39.
罗卫敏 《成都信息工程学院学报》2004,19(2):209-213
针对信息系统安全的考虑,介绍在PowerBuilder环境中对用户权限的具体控制. 相似文献
40.
针对多通道滤光器太阳磁场望远镜的磁场观测定标及掌握(所采用的)谱线特征之需要,取VAL宁静太阳大气模型计算了7条Fel光球线的Stokes轮廓、形成深度、贡献函数分布,从而较为系统地对多条反常及正常Zeeman线的特征及性质作出了分析与总结,解释了在磁光效应影响下Stokes Q,U参量的形成深度曲线在近线心区域处出现陡峭峰值的原因。 相似文献