全文获取类型
收费全文 | 858篇 |
免费 | 50篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 40篇 |
地球物理 | 249篇 |
地质学 | 276篇 |
海洋学 | 62篇 |
天文学 | 194篇 |
综合类 | 2篇 |
自然地理 | 78篇 |
出版年
2021年 | 18篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 19篇 |
2017年 | 21篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 35篇 |
2012年 | 18篇 |
2011年 | 43篇 |
2010年 | 27篇 |
2009年 | 31篇 |
2008年 | 34篇 |
2007年 | 25篇 |
2006年 | 31篇 |
2005年 | 32篇 |
2004年 | 20篇 |
2003年 | 27篇 |
2002年 | 13篇 |
2001年 | 30篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 26篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1985年 | 12篇 |
1984年 | 17篇 |
1983年 | 26篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 21篇 |
1977年 | 24篇 |
1976年 | 15篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1968年 | 8篇 |
1967年 | 5篇 |
排序方式: 共有915条查询结果,搜索用时 828 毫秒
81.
82.
83.
Scott MurchieMark Robinson Deborah DomingueHan Li Louise ProckterS.Edward Hawkins III William OwenBeth Clark Noam Izenberg 《Icarus》2002,155(1):229-243
During the Near-Earth Asteroid Rendezvous (NEAR) spacecraft's investigation of asteroid 433 Eros, inflight calibration measurements from the multispectral imager (MSI) have provided refined knowledge of the camera's radiometric performance, pointing, and light-scattering characteristics. Measurements while at Eros corroborate most earlier calibration results, although there appears to be a small, gradual change in instrument dark current and flat field due to effects of aging in the space environment. The most pronounced change in instrument behavior, however, is a dramatic increase in scattered light due to contaminants accumulated on the optics during unscheduled fuel usage in December 1998. Procedures to accurately quantify and to remediate the scattered light are described in a companion paper (Li et al. 2002, Icarus155, 00-00). Acquisition of Eros measurements has clarified the relative, filter-to-filter, radiometric performance of the MSI. Absolute radiometric calibration appears very well constrained from flight measurements, with an accuracy of ∼5%. Pointing relative to the spacecraft coordinate system can be determined from the temperature of the spacecraft deck with an accuracy of ∼1 pixel. 相似文献
84.
Paul G. LuceyJohn Hinrichs Mary KellyDennis Wellnitz Noam IzenbergScott Murchie Mark RobinsonBeth E. Clark James F. Bell III 《Icarus》2002,155(1):181-188
Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros. 相似文献
85.
86.
Min Zhu Wadge G. Holley R.J. James I.N. Clark P.A. Changgui Wang Woodage M.J. 《Geoscience and Remote Sensing Letters, IEEE》2007,4(3):401-405
Propagation delay due to variable tropospheric water vapor (WV) is one of the most intractable problems for radar interferometry, particularly over mountains. The WV field can be simulated by an atmospheric model, and the difference between the two fields is used to correct the radar interferogram. Here, we report our use of the U.K. Met Office Unified Model in a nested mode to produce high-resolution forecast fields for the 3-km-high Mount Etna volcano. The simulated precipitable-water field is validated against that retrieved from the Medium-Resolution Imaging Spectrometer (MERIS) radiometer on the Envisat satellite, which has a resolution of 300 m. Two case studies, one from winter (November 24, 2004) and one from summer (June 25, 2005), show that the mismatch between the model and the MERIS fields ( rms = 1.1 and 1.6 mm, respectively) is small. One of the main potential sources of error in the models is the timing of the WV field simulation. We show that long-wavelength upper tropospheric troughs of low WV could be identified in both the model output and Meteosat WV imagery for the November 24, 2004 case and used to choose the best time of model output. 相似文献
87.
In order to predict wind loading on trees (canopy height h) in partially harvested forests, it is necessary to characterize air flow and momentum transfer in progressively more complex
patterns where groups of trees (or aggregates) are retained. In this study, we used large-eddy simulation to explore the effects
of aggregate size, inter-aggregate spacing, and the ratio between the aggregate size and inter-aggregate spacing on air flow
and momentum transfer. Forty-five grid points across an aggregate were needed to achieve an adequate level of turbulence.
Using grid sizes of h/15 throughout was too viscous for the smaller aggregates. Vertical and horizontal flow deflection by the leading aggregates
sheltered some of the downstream aggregates to varying degrees where turbulence increased for subsequent rows. The number
of rows of protected aggregates decreased as aggregate dimensions and the space between aggregates increased. A theoretical
treatment of time-dependent wind is presented for the lead aggregate and a simulation case is presented for the case of a
gust of reduced wind passing through the aggregate pattern. The leading aggregate responded with decreasing moment for decreasing
ambient wind speed as predicted by theory. However, downwind aggregates experienced substantial increases in bending moment.
The overall results of the disruptive aspects of time dependence agrees with arguments regarding the role of irrotational
(potential) flow to this problem. Our treatment of retention pattern design is only a first step and further research suggestions
are presented. 相似文献
88.
89.
90.