全文获取类型
收费全文 | 292篇 |
免费 | 27篇 |
国内免费 | 22篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 12篇 |
地球物理 | 49篇 |
地质学 | 38篇 |
海洋学 | 28篇 |
天文学 | 140篇 |
综合类 | 19篇 |
自然地理 | 16篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 11篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2010年 | 24篇 |
2009年 | 19篇 |
2008年 | 17篇 |
2007年 | 28篇 |
2006年 | 38篇 |
2005年 | 25篇 |
2004年 | 15篇 |
2003年 | 16篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 13篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有341条查询结果,搜索用时 46 毫秒
41.
正1 Introduction Annually laminated(varve)sedimentary deposits are considered as one of the most important archives,since they offer precise temporal information(years)in combination with high time resolutions.Bottom sediments of the lakes contain detailed geochemical information on 相似文献
42.
A. Tokovinin T. Travouillon 《Monthly notices of the Royal Astronomical Society》2006,365(4):1235-1242
New measurements of optical turbulence profile at the Cerro Pachón observatory in Chile are analysed jointly with previously published data to model the variations of the intensity and thickness of the ground layer and free atmosphere under a variety of observing conditions. This work is motivated by the need to predict statistically the performance of ground-layer adaptice optics. We find that the ground-layer profile can be represented by a decaying exponent with a scale height of 20–40 m, increasing to 100 m under bad conditions. The zone from 6 to 500 m contributes typically about 61 per cent to the total integral, the latter causing a median seeing of 0.77 arcsec. Turbulence integrals in the ground layer and in free atmosphere vary independently of each other, in 50 per cent of cases they deviate by less than 1.8 times from their respective median values. The existence of periods with low turbulence in the free atmosphere and their importance for adaptive optics is stressed. 相似文献
43.
Ren Rutten Maarten Blanken Richard McDermid Thomas Gregory Paul Jolley Tim Morris Richard Myers Johan Pragt Ton Schoenmaker Remko Stuik Gordon Talbot 《New Astronomy Reviews》2006,49(10-12):632
The scientific exploitation of adaptive optics (AO) with natural guide stars is severely constrained by the limited presence of bright guide stars for wavefront sensing. Use of a laser beam as an alternative means to provide a source for wavefront sensing has the potential of drastically improving the sky coverage for AO. For this reason at the 4.2-m William Herschel Telescope a project was started to develop a Rayleigh laser beacon to work together with the existing NAOMI adaptive optics instrumentation and the OASIS integral field spectrograph. This paper presents the rationale for this development, highlights some of the technical aspects, and gives some expected performance measures. 相似文献
44.
Plans for future optical telescopes of diameter more than 10 m are based on segmented mirrors, made up of hundreds or even thousands of segments. A challenge for these telescopes is the alignment in piston (cophasing) where phase differences between individual segments have to be reduced to a small fraction of the observing wavelength in order to avoid degradation of image quality.
Based on the phase discontinuity sensing method used at the Keck telescopes to measure small piston errors using infrared wavelengths, we develop a new method that allows fast high-precision measurements of large piston errors even at visible wavelengths. 相似文献
Based on the phase discontinuity sensing method used at the Keck telescopes to measure small piston errors using infrared wavelengths, we develop a new method that allows fast high-precision measurements of large piston errors even at visible wavelengths. 相似文献
45.
在充分考虑道路频谱在不同频带、不同方向上能量分布的基础上,提出一种基于Gabor纹理与几何特征相结合的高分辨率遥感影像城区道路提取方法。首先通过Gabor滤波器组得到遥感影像不同频带、不同方向上的Gabor纹理特征,并利用K-means方法对遥感影像进行分割;然后利用形态学方法分割与道路相连的地物,并选取适当的几何特征剔除非道路地物;最后利用形态学方法对道路网进行修整。实验结果表明,该方法可以有效、便捷地从高分辨率遥感影像中提取城区主干道路网。 相似文献
46.
采用太湖地区水面光谱数据以及MODIS遥感影像数据,利用辐射传输模式6S,选择自定义气溶胶类型,反演得到太湖地区气溶胶光学厚度(aerosol optical depth,AOD)分布,将其与太阳光度计CE318实测气溶胶光学厚度分别应用于太湖区域的大气校正中,得到不同的水面反射率,并参考实测水面反射率进行对比分析。结果表明:反演的太湖地区气溶胶光学厚度分布较为合理,造成此分布的原因可能是太湖北岸工业较发达,污染较严重。太湖颗粒物的吸收特性和卫星接收到的表观反射率导致反演数据的差异,是反演气溶胶光学厚度分布不均匀的主要原因。使用MODIS数据反演得到的太湖地区AOD进行大气校正,更加精确。该研究方法和结果可为气溶胶光学厚度反演、精确卫星数据大气校正提供参考。 相似文献
47.
Adaptive optics (AO), which provides diffraction limited imaging over a field-of-view (FOV), is a powerful technique for solar observation. In the tomographic approach, each wavefront sensor (WFS) is looking at a single reference that acts as a guide star. This allows a 3D reconstruction of the distorted wavefront to be made. The correction is applied by one or more deformable mirrors (DMs). This technique benefits from information about atmospheric turbulence at different layers, which can be used to reconstruct the wavefront extremely well. With the assistance of the MAOS software package, we consider the tomography errors and WFS aliasing errors, and focus on how the performance of a solar telescope (pointing toward zenith) is related to atmospheric anisoplanatism. We theoretically quantify the performance of the to- mographic solar AO system. The results indicate that the tomographic AO system can improve the average Strehl ratio of a solar telescope in a 10" - 80" diameter FOV by only employing one DM conjugated to the telescope pupil. Furthermore, we discuss the effects of DM conjugate altitude on the correction achievable by the AO system by selecting two atmospheric models that differ mainly in terms of atmospheric prop- erties at ground level, and present the optimum DM conjugate altitudes for different observation sites. 相似文献
48.
Paul D. Allen Simon P. Driver Alister W. Graham Ewan Cameron Jochen Liske Roberto De Propris 《Monthly notices of the Royal Astronomical Society》2006,371(1):2-18
We present near-infrared (NIR) adaptive optics-assisted spectroscopic observations of the CO (Δμ= 2) absorption bands towards the centre of the giant elliptical galaxy NGC 1399. The observations were made with NAOS-CONICA (on the European Southern Observatory's Very Large Telescope) and have a full width at half-maximum resolution of 0.15 arcsec (14 pc). Kinematic analysis of the observations reveals a decoupled core and strongly non-Gaussian line-of-sight velocity profiles in the central 0.2 arcsec (19 pc). NIR imaging also indicates an asymmetric elongation of the central isophotes in the same region.
We use spherical orbit-superposition models to interpret the kinematics, using a set of orthogonal 'eigen-velocity profiles' that allow us to fit models directly to spectra. The models require a central black hole of mass 1.2+0.5 −0.6 × 109 M⊙ , with a strongly tangentially biased orbit distribution in the inner 40 pc. 相似文献
We use spherical orbit-superposition models to interpret the kinematics, using a set of orthogonal 'eigen-velocity profiles' that allow us to fit models directly to spectra. The models require a central black hole of mass 1.2
49.
50.
Christopher Packham Keith L. Thompson Almudena Zurita Johan H. Knapen Ian Smail Robert Greimel Daniel F. M. Folha Chris Benn rew Humphrey Rene Rutten David Ciardi Matthieu Bec Richard Bingham Simon Craig Kevin Dee Derek Ives Paul Jolley Peter Moore Marti Pi i Puig Simon Rees Gordon Talbot Sue Worswick 《Monthly notices of the Royal Astronomical Society》2003,345(2):395-405