全文获取类型
收费全文 | 333篇 |
免费 | 8篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 12篇 |
地球物理 | 102篇 |
地质学 | 115篇 |
海洋学 | 22篇 |
天文学 | 57篇 |
综合类 | 3篇 |
自然地理 | 37篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 14篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 12篇 |
2008年 | 12篇 |
2007年 | 20篇 |
2006年 | 11篇 |
2005年 | 20篇 |
2004年 | 7篇 |
2003年 | 12篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1973年 | 5篇 |
1969年 | 1篇 |
1968年 | 3篇 |
排序方式: 共有354条查询结果,搜索用时 46 毫秒
221.
222.
本文是作者另一篇文章的续篇。文中列出隋初至清代的陕西天文人物共94条,110人。对每个人物简要给出人物全貌、与陕西的关系、天文内容以及史料和研究文献线索。 相似文献
223.
Abstract— A structurally ordered cubic metal grain containing ~39 wt% Co, 61 wt% Fe, and <0.6 wt% Ni (~Fe3Co2) was found associated with troilite and pentlandite in the matrix of the Ningqiang carbonaceous chondrite. This mineral is similar to terrestrial wairauite. Experimental data in the Fe-Co system indicate that this CsCl-type Co-rich metal is stable below 700 °C. Phase relations in the Fe-Co-Ni system show that Co cannot fractionate from Ni above 500 °C. The dominant opaque minerals of awaruite, magnetite, and pentlandite in Ningqiang suggest relatively oxidizing conditions. 相似文献
224.
225.
226.
Summary Isotropic earth models are unable to provide uniform fits to the gross Earth normal mode data set or, in many cases, to regional Love-and Rayleigh-wave data. Anisotropic inversion provides a good fit to the data and indicates that the upper 200km of the mantle is anisotropic. The nature and magnitude of the required anisotropy, moreover, is similar to that found in body wave studies and in studies of ultramafic samples from the upper mantle. Pronounced upper mantle low-velocity zones are characteristic of models resulting from isotropic inversion of global or regional data sets. Anisotropic models have more nearly constant velocities in the upper mantle.
Normal mode partial (Frediét) derivatives are calculated for a transversely isotropic earth model with a radial axis of symmetry. For this type of anisotropy there are five elastic constant. The two shear-type moduli can be determined from the toroidal modes. Spheroidal and Rayleigh modes are sensitive to all five elastic constants but are mainly controlled by the two compressional-type moduli, one of the shear-type moduli and the remaining, mixed-mode, modulus. The lack of sensitivity of Rayleigh waves to compressional wave velocities is a characteristic only of the isotropic case. The partial derivatives of the horizontal and vertical components of the compressional velocity are nearly equal and opposite in the region of the mantle where the shear velocity sensitivity is the greatest. The net compressional wave partial derivative, at depth, is therefore very small for isotropic perturbations. Compressional wave anisotropy, however, has a significant effect on Rayleigh-wave dispersion. Once it has been established that transverse anisotropy is important it is necessary to invert for all five elastic constants. If the azimuthal effect has not been averaged out a more general anisotropy may have to be allowed for. 相似文献
Normal mode partial (Frediét) derivatives are calculated for a transversely isotropic earth model with a radial axis of symmetry. For this type of anisotropy there are five elastic constant. The two shear-type moduli can be determined from the toroidal modes. Spheroidal and Rayleigh modes are sensitive to all five elastic constants but are mainly controlled by the two compressional-type moduli, one of the shear-type moduli and the remaining, mixed-mode, modulus. The lack of sensitivity of Rayleigh waves to compressional wave velocities is a characteristic only of the isotropic case. The partial derivatives of the horizontal and vertical components of the compressional velocity are nearly equal and opposite in the region of the mantle where the shear velocity sensitivity is the greatest. The net compressional wave partial derivative, at depth, is therefore very small for isotropic perturbations. Compressional wave anisotropy, however, has a significant effect on Rayleigh-wave dispersion. Once it has been established that transverse anisotropy is important it is necessary to invert for all five elastic constants. If the azimuthal effect has not been averaged out a more general anisotropy may have to be allowed for. 相似文献
227.
The chromophores responsible for coloring the jovian atmosphere are embedded within Jupiter’s vertical aerosol structure. Sunlight propagates through this vertical distribution of aerosol particles, whose colors are defined by ?0(λ), and we remotely observe the culmination of the radiative transfer as I/F(λ). In this study, we employed a radiative transfer code to retrieve ?0(λ) for particles in Jupiter’s tropospheric haze at seven wavelengths in the near-UV and visible regimes. The data consisted of images of the 2008 passage of Oval BA to the south of the Great Red Spot obtained by the Wide Field Planetary Camera 2 on-board the Hubble Space Telescope. We present derived particle colors for locations that were selected from 14 weather regions, which spanned a large range of observed colors. All ?0(λ) curves were absorbing in the blue, and ?0(λ) increased monotonically to approximately unity as wavelength increased. We found accurate fits to all ?0(λ) curves using an empirically derived functional form: ?0(λ) = 1 − A exp(−Bλ). The best-fit parameters for the mean ?0(λ) curve were A = 25.4 and B = 0.0149 for λ in units of nm. We performed a principal component analysis (PCA) on our ?0(λ) results and found that one or two independent chromophores were sufficient to produce the variations in ?0(λ). A PCA of I/F(λ) for the same jovian locations resulted in principal components (PCs) with roughly the same variances as the ?0(λ) PCA, but they did not result in a one-to-one mapping of PC amplitudes between the ?0(λ) PCA and I/F(λ) PCA. We suggest that statistical analyses performed on I/F(λ) image cubes have limited applicability to the characterization of chromophores in the jovian atmosphere due to the sensitivity of I/F(λ) to horizontal variations in the vertical aerosol distribution. 相似文献
228.
229.
Don P. Mitchell 《Solar System Research》2012,46(5):382-384
Some anomalies in the video images from Venera-13 are explained as possible artifacts of the telemetry system. One anomaly may be a shadow caused by a change in the distribution of illumination. 相似文献
230.
Graciela MATRAJT Scott MESSENGER Don BROWNLEE Dave JOSWIAK 《Meteoritics & planetary science》2012,47(4):525-549
Abstract– Coordinated in situ transmission electron microscopy and isotopic measurements of carbonaceous phases in interplanetary dust particles were performed to determine their origins. Five different types of carbonaceous materials were identified based on their morphology and texture, observed by transmission electron microscopy: globular, vesicular, dirty, spongy, and smooth. Flash heating experiments were performed to explore whether some of these morphologies are the result of atmospheric entry processes. Each of these morphologies was found to have isotopically anomalous H and N. Rare C isotopic anomalies were also observed. The isotopic and morphological properties of several of these phases, particularly the organic globules, are remarkably similar to those observed in other extraterrestrial materials including carbonaceous chondrites, comet 81P/Wild 2 particles collected by the Stardust spacecraft, and Antarctic micrometeorites, indicating that they were widespread in the early solar system. The ubiquitous nature and the isotopic anomalies of the nanoglobules and some other morphologies strongly suggest that these are very primitive phases. Given that some of the isotopic anomalies (D and 15N excesses) are indicative of mass fractionation chemical reactions in a very cold environment, and some others (13C and 15N depletions) have other origins, these carbonaceous phases come from different reservoirs. Whatever their origins, these materials probably reflect the first stages of the evolution of solar system organic matter, having originated in the outermost regions of the protosolar disk and/or interstellar cold molecular clouds. 相似文献