全文获取类型
收费全文 | 1717篇 |
免费 | 98篇 |
国内免费 | 38篇 |
专业分类
测绘学 | 65篇 |
大气科学 | 26篇 |
地球物理 | 74篇 |
地质学 | 49篇 |
海洋学 | 15篇 |
天文学 | 1594篇 |
综合类 | 19篇 |
自然地理 | 11篇 |
出版年
2024年 | 9篇 |
2023年 | 21篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 10篇 |
2014年 | 31篇 |
2013年 | 14篇 |
2012年 | 25篇 |
2011年 | 30篇 |
2010年 | 26篇 |
2009年 | 111篇 |
2008年 | 90篇 |
2007年 | 140篇 |
2006年 | 112篇 |
2005年 | 128篇 |
2004年 | 160篇 |
2003年 | 112篇 |
2002年 | 106篇 |
2001年 | 105篇 |
2000年 | 95篇 |
1999年 | 89篇 |
1998年 | 118篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 34篇 |
1994年 | 25篇 |
1993年 | 10篇 |
1992年 | 25篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有1853条查询结果,搜索用时 0 毫秒
251.
252.
W. H. McCutcheon G. Sandell H. E. Matthews T. B. H. Kuiper E. C. Sutton W. C. Danchi T. Sato 《Monthly notices of the Royal Astronomical Society》2000,316(1):152-164
The northern section of the molecular cloud complex NGC 6334 has been mapped in the CO and CS spectral line emission and in continuum emission at a wavelength of 1300 μm. Our observations highlight the two dominant sources, I and I(N), and a host of weaker sources. NGC 6334 I is associated with a cometary ultracompact H ii region and a hot, compact core ≤10 arcsec in size. Mid-infrared and CH3 OH observations indicate that it is also associated with at least two protostellar sources, each of which may drive a molecular outflow. For region I we confirm the extreme high-velocity outflow first discovered by Bachiller & Cernicharo and find that it is very energetic with a mechanical luminosity of 390 L⊙ . A dynamical age for the outflow is ∼3000 yr. We also find a weaker outflow originating from the vicinity of NGC 6334 I. In CO and CS this outflow is quite prominent to the north-west, but much less so on the eastern side of I, where there is very little molecular gas. Spectral survey data show a molecular environment at position I which is rich in methanol, methyl formate and dimethyl ether, with lines ranging in energy up to 900 K above the ground state. NGC 6334 I(N) is more dense than I, but cooler, and has none of the high-excitation lines observed toward I. I(N) also has an associated outflow, but it is less energetic than the outflow from I. The fully sampled continuum map shows a network of filaments, voids and cores, many of which are likely to be sites of star formation. A striking feature is a narrow, linear ridge which defines the western boundary. It is unclear if there is a connection between this filament and the many potential sites of star formation, or if the filament existed prior to the star formation activity. 相似文献
253.
Anita Enmark Thomas Berkefeld Oskar von der Lühe Torben Andersen 《Experimental Astronomy》2006,21(2):87-99
A simulation model of the adaptive optics of the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife, is
presented. The model uses modules from the integrated model of the Euro50 extremely large telescope, and includes submodels
of a Shack-Hartmann wavefront sensor, a de-formable mirror, a tip-tilt mirror, high-voltage amplifier low-pass filters, a
reconstructor and a controller. We investigate the impact on the closed loop bandwidth of changes in controller configuration
and certain system parameters, such as low pass filter bandwidth and camera integration and readout time. Control strategies
were tested on simple models before implementation on the full VTT model. Using the models, different control strategies are
compared. 相似文献
254.
255.
256.
257.
Both, observational and theoretical results support the close connection between bars and box/peanut‐shaped bulges in spiral galaxies. However, for the sub‐class of thick box/peanut‐shaped bulges, an environmental process instead of an internal mechanism is suggested to account for the prominence of the box/peanut component. In this paper a multiwavelength study of the morphology and the kinematics of a sample of thick box/peanut‐shaped bulges is presented. The results suggest a scenario in which interaction events play a significant role in the history of thick box/peanut‐shaped bulge galaxies. Most likely these sources have experienced a mass infall. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
258.
近地天体望远镜是巡天望远镜, 具有短焦距、大视场、低空间分辨率的光学特点. 望远镜只有一个主焦点, 焦距1.8 m, 底片比例9um/'', 像斑几何能量集中度EE80 ≤2''(像斑环绕能量的80%,即80% encircled energy, 记为EE80), 有效视场直径为4.28-°(14.3deg2), 目前配10k times 10k的STA1600LN CCD (charge-coupled device) camera, 观测视场为9deg2. 通过光学系统设计, 在原光学系统上增加副镜及场改正镜, 获得了焦距9m的卡氏焦点和内氏焦点,底片比例43.6 um /",在直径15''的可用视场内,像斑EE80≤0.5",为近地天体望远镜实现多终端观测提供了理论依据. 相似文献
259.
Magnetic fields control the inconstant Sun. The key to understanding solar variability and its direct impact on the Earth rests with understanding all aspects of these magnetic fields. The Advanced Technology Solar Telescope (ATST) has been design specifically for magnetic remote sensing. Its collecting area, spatial resolution, scattered light, polarization properties, and wavelength performance all insure ATST will be able to observe magnetic fields at all heights in the solar atmosphere from photosphere to corona. After several years of design efforts, ATST has been approved by the U.S. National Science Foundation to begin construction with a not to exceed cost cap of approximately $298M. Work packages for major telescope components will be released for bid over the next several months. An application for a building permit has been submitted (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
260.
Hari Om Vats M. R. Deshpande K. N. Iyer Tetsuro Kondo Takeshi Isobe 《Astrophysics and Space Science》1996,243(1):251-254
This article describes the observations of a type III radio burst observed at 103 MHz simultaneously by the two radio telescopes situated at Rajkot (22.3°N, 70.7°E) and Thaltej (23°N, 72.4°E). This event occurred on September 30, 1993 at about 0430 UT and lasted for only half a minute. The event consisted of several sharp spikes in a group. The rise and fall time of these are comparable, however the peaks of individual spikes varied by a factor of four. The comparison of these observations with the data of solar radio spectrograph HiRAS indicates that this was a metric radio burst giving highest emission at about 103 MHz. 相似文献