全文获取类型
收费全文 | 5461篇 |
免费 | 591篇 |
国内免费 | 401篇 |
专业分类
测绘学 | 175篇 |
大气科学 | 169篇 |
地球物理 | 911篇 |
地质学 | 1350篇 |
海洋学 | 253篇 |
天文学 | 2788篇 |
综合类 | 122篇 |
自然地理 | 685篇 |
出版年
2024年 | 26篇 |
2023年 | 45篇 |
2022年 | 95篇 |
2021年 | 107篇 |
2020年 | 97篇 |
2019年 | 176篇 |
2018年 | 91篇 |
2017年 | 98篇 |
2016年 | 109篇 |
2015年 | 126篇 |
2014年 | 188篇 |
2013年 | 194篇 |
2012年 | 198篇 |
2011年 | 236篇 |
2010年 | 165篇 |
2009年 | 477篇 |
2008年 | 401篇 |
2007年 | 495篇 |
2006年 | 480篇 |
2005年 | 394篇 |
2004年 | 345篇 |
2003年 | 342篇 |
2002年 | 254篇 |
2001年 | 223篇 |
2000年 | 184篇 |
1999年 | 190篇 |
1998年 | 216篇 |
1997年 | 90篇 |
1996年 | 84篇 |
1995年 | 62篇 |
1994年 | 49篇 |
1993年 | 55篇 |
1992年 | 30篇 |
1991年 | 18篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有6453条查询结果,搜索用时 15 毫秒
1.
2.
3.
对于隧道和煤矿井巷的安全掘进 ,超前预报显得特别重要。但由于掌子面前的特殊环境限制及多种干扰的严重影响 ,给隧道及井巷超前预报技术的研究带来许多困难。在瞬变电磁理论的基础上 ,引入新的电磁传播理论———电磁导弹技术 ,作为对该技术的初步探索 ,文章论证了该技术在隧道超前预报中应用的可能性 ,并提出了研究的主要内容和发展方向以及可能取得的新的技术突破和技术支撑 相似文献
4.
5.
6.
A highly automated moving object detection package 总被引:1,自引:0,他引:1
7.
8.
George Saklatvala Michael P. Hobson Stafford Withington 《Monthly notices of the Royal Astronomical Society》2006,367(3):1194-1200
We describe a procedure for the numerical modelling of astronomical interferometers, with particular relevance to far-infrared and submillimetre wavelengths. The scheme is based on identifying a set of modes that carry power from the sky to the detector. The procedure is extremely general, and can be used to model scalar or vector fields, in any state of coherence and polarization, the only limitation being that the propagation of a coherent field through the system be described by an integral transform, a constraint that is in practise always met.
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
We present simulations of ideal, multimode two-dimensional interferometers, and show that the modal theory reproduces the correct behaviour of both Michelson and Fizeau interferometers. We calculate simulated visibility data for a multimode bolometric Michelson interferometer, with a synthesized source, and produce a dirty map, recovering the original source with the usual artefacts associated with interferometers. 相似文献
9.
10.
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