全文获取类型
收费全文 | 1168篇 |
免费 | 129篇 |
国内免费 | 210篇 |
专业分类
测绘学 | 53篇 |
大气科学 | 194篇 |
地球物理 | 324篇 |
地质学 | 473篇 |
海洋学 | 141篇 |
天文学 | 146篇 |
综合类 | 48篇 |
自然地理 | 128篇 |
出版年
2023年 | 9篇 |
2022年 | 32篇 |
2021年 | 39篇 |
2020年 | 33篇 |
2019年 | 41篇 |
2018年 | 50篇 |
2017年 | 61篇 |
2016年 | 62篇 |
2015年 | 54篇 |
2014年 | 75篇 |
2013年 | 76篇 |
2012年 | 83篇 |
2011年 | 75篇 |
2010年 | 56篇 |
2009年 | 66篇 |
2008年 | 63篇 |
2007年 | 58篇 |
2006年 | 56篇 |
2005年 | 43篇 |
2004年 | 36篇 |
2003年 | 33篇 |
2002年 | 30篇 |
2001年 | 28篇 |
2000年 | 46篇 |
1999年 | 35篇 |
1998年 | 31篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1970年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有1507条查询结果,搜索用时 343 毫秒
151.
José I. Muñoz 《Climate Policy》2013,13(2):87-105
How does financial performance risk affect investments in low-carbon electricity-generating technologies to achieve climate policy targets? A detailed risk simulation of price formation in the Great Britain wholesale power market is used to show that the increasing replacement of fossil facilities with wind, ceteris paribus, may cause a deterioration of the financial risk–return performance metrics for incremental investments. Low-carbon investments appear to be high risk, low return, and as such may require a progressively higher level of support over time than envisaged by the conventional degression trajectories. The increasing riskiness of the wholesale market will to some extent offset the benefits of lower capital costs and operational efficiencies if investors need to satisfy cautious debt coverage ratios alongside positive expected returns. This increased risk is additional to the well-known ‘merit order effect’ of low-carbon investments progressively depressing wholesale prices and hence their expected investment returns. Policy relevance Policy support for renewable technologies such as wind is usually based upon levelized costs and is expected to reduce over time as capital costs and operational efficiencies improve. However, levelized costs do not take full account of the risk aversion that investors may have in practice. Expected policy support reductions may be moderated to some extent by the increased financial performance risk that intermittent technologies bring to the power market. The annual risk-return profiles for incremental investments deteriorate for all technologies as wind replaces fossil fuels. This extra risk premium will need to be incorporated into evaluating policy incentives for new investments in a decarbonizing power market. 相似文献
152.
153.
Fen-Fei Wang Jian-Jun Liu Chun-Lai Li Xin Ren Ling-Li Mu Wei Yan Wen-Rui Wang Jing-Tao Xiao Xu Tan Xiao-Xia Zhang Xiao-Duan Zou Xing-Ye Gao 《中国天文和天体物理学报》2014,(12)
The establishment of a lunar control network is one of the core tasks in selenodesy, in which defining an absolute control point on the Moon is the most important step. However, up to now, the number of absolute control points has been very sparse. These absolute control points have mainly been lunar laser ranging retroreflectors, whose geographical location can be observed by observations on Earth and also identified in high resolution lunar satellite images. The Chang'e-3(CE-3) probe successfully landed on the Moon, and its geographical location has been monitored by an observing station on Earth. Since its positional accuracy is expected to reach the meter level, the CE-3 landing site can become a new high precision absolute control point. We use a sequence of images taken from the landing camera, as well as satellite images taken by CE-1 and CE-2, to identify the location of the CE-3 lander. With its geographical location known, the CE-3 landing site can be established as a new absolute control point, which will effectively expand the current area of the lunar absolute control network by 22%, and can greatly facilitate future research in the field of lunar surveying and mapping, as well as selenodesy. 相似文献
154.
Josep M. TRIGO‐RODRÍGUEZ Jií BOROVIKA Pavel SPURNÝ Jos L. ORTIZ Jos A. DOCOBO Alberto J. CASTRO‐TIRADO Jordi LLORCA 《Meteoritics & planetary science》2006,41(4):505-517
Abstract— The L6 ordinary chondrite Villalbeto de la Peña fall occurred on January 4, 2004, at 16: 46: 45 ± 2 s UTC. The related daylight fireball was witnessed by thousands of people from Spain, Portugal, and southern France, and was also photographed and videotaped from different locations of León and Palencia provinces in Spain. From accurate astrometric calibrations of these records, we have determined the atmospheric trajectory of the meteoroid. The initial fireball velocity, calculated from measurements of 86 video frames, was 16.9 ± 0.4 km/s. The slope of the trajectory was 29.0 ± 0.6° to the horizontal, the recorded velocity during the main fragmentation at a height of 27.9 ± 0.4 km was 14.2 ± 0.2 km/s, and the fireball terminal height was 22.2 ± 0.2 km. The heliocentric orbit of the meteoroid resided in the ecliptic plane (i = 0.0 ± 0.2°), having a perihelion distance of 0.860 ± 0.007 AU and a semimajor axis of 2.3 ± 0.2 AU. Therefore, the meteorite progenitor body came from the Main Belt, like all previous determined meteorite orbits. The Villalbeto de la Peña fireball analysis has provided the ninth known orbit of a meteorite in the solar system. 相似文献
155.
Josep Maria Trigo-Rodriguez Jeremie Vaubaillon José Luís Ortiz Alberto Castro-Tirado Jordi Llorca Esko Lyytinen Martin Jelínek Antonio de Ugarte Postigo Pablo Santos Sanz Francisco J. Aceituno Castro Albert Sánchez Caso Antonio Bernal González Juan Pastor Erades Francisco Ocaña 《Earth, Moon, and Planets》2005,97(3-4):269-278
Jupiter and Saturn produce important gravitational impulses on meteoroids released by comet 109P/Swift-Tuttle. The meteoroids from this comet once released follow retrograde orbits that during their periodic approaches to these planets (within 1.6 and 0.9 A.U., respectively) are impulsed gaining orbital energy. This perturbation effect is translated into a net inward shift in the node of the perturbed meteoroids. Such geometry with Jupiter occurred in 2004 over a meteoroid trail ejected by this comet during the 1862 A.D. return of the comet to perihelion. In order to study the predicted outburst produced by one-revolution meteoroids, the Spanish Photographic Meteor Network (SPMN) performed an extensive campaign. As a part of this observational effort here are presented 10 accurate meteoroid orbits. We discuss their origin by comparing them with the theoretical orbital elements of the dust trails intercepting the Earth during the 2004 Perseid return. 相似文献
156.
157.
158.
Anton M. Dainty M. Nafi Toksöz Kenneth R. Anderson P. Jacques Pines Y. Nakamura G. Latham 《Earth, Moon, and Planets》1974,9(1-2):11-29
Long, reverberating trains of seismic waves produced by impacts and moonquakes may be interpreted in terms of scattering in a surface layer overlying a non-scattering elastic medium. Model seismic experiments are used to qualitatively demonstrate the correctness of the interpretation. Three types of seismograms are found, near impact, far impact and moonquake. Only near impact and moonquake seismograms contain independent information. Details are given in the paper of the modelling of the scattering processes by the theory of diffusion.Interpretation of moonquake and artificial impact seismograms in two frequency bands from the Apollo 12 site indicates that the scattering layer is 25 km thick, with a Q of 5000. The mean distance between scatterers is approximately 5 km at 25 km depth and approximately 2 km at 14 km depth; the density of scatterers appears to be high near the surface, decreasing with depth. This may indicate that the scatterers are associated with cratering, or are cracks that anneal with depth. Most of the scattered energy is in the form of scattered surface waves.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973. 相似文献
159.
160.