全文获取类型
收费全文 | 185篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
大气科学 | 14篇 |
地球物理 | 24篇 |
地质学 | 57篇 |
海洋学 | 13篇 |
天文学 | 78篇 |
自然地理 | 8篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 10篇 |
2012年 | 7篇 |
2011年 | 4篇 |
2010年 | 9篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 9篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有194条查询结果,搜索用时 160 毫秒
11.
Gavin Ramsay & Peter J. Wheatley 《Monthly notices of the Royal Astronomical Society》1998,301(1):95-100
We present low–medium resolution optical spectroscopy of the eclipsing AM Her system MN Hya (RX J0929–24). We determine the magnetic field strength at the primary accretion region of the white dwarf to be 42 MG from the spacing of cyclotron features visible during π ∼ 0.4–0.7. From spectra taken during the eclipse we find that the secondary has an M3–4 spectral type. Combined with the eclipse photometry of Sekiguchi, Nakada &38; Bassett and an estimate of the interstellar extinction we find a distance of ∼300–700 pc. We find unusual line variations at π ∼ 0.9: Hα is seen in absorption and emission. This is at the same point in the orbital phase at which a prominent absorption dip is seen in soft X-rays. 相似文献
12.
Age profiling of fossil faunal samples relies on the correlation of animal tooth-wear patterns with life history stages, but the criteria used to infer these stages are not necessarily valid. Here we redefine some commonly used prey age classes, such as “juvenile,” “prime-age adult,” and “old adult,” based on the variable characteristics of tooth wear that we have observed in different ungulate size classes, and argue that prey vulnerability to predation is not so clearly predicted by the simplified age classes in widespread use by zooarchaeologists. We recommend instead classifying the youngest animal remains as either young juvenile or subadult juvenile, and adult remains as early prime, late prime or old, and provide specific criteria of dental eruption and occlusal wear for making these determinations. We argue this refined age profiling system, when used in combination with other types of zooarchaeological and taphonomic data, can provide accurate inferences of faunal accumulation processes. 相似文献
13.
The world’s first archaeological traces from 2.6 million years ago (Ma) at Gona, in Ethiopia, include sharp-edged cutting tools and cut-marked animal bones, which indicate consumption of skeletal muscle by early hominin butchers. From that point, evidence of hominin meat-eating becomes increasingly more common throughout the Pleistocene archaeological record. Thus, the substantive debate about hominin meat-eating now centers on mode(s) of carcass resource acquisition. Two prominent hypotheses suggest, alternatively, (1) that early Homo hunted ungulate prey by running them to physiological failure and then dispatching them, or (2) that early Homo was relegated to passively scavenging carcass residues abandoned by carnivore predators. Various paleontologically testable predictions can be formulated for both hypotheses. Here we test four predictions concerning age-frequency distributions for bovids that contributed carcass remains to the 1.8 Ma. old FLK 22 Zinjanthropus (FLK Zinj, Olduvai Gorge, Tanzania) fauna, which zooarchaeological and taphonomic data indicate was formed predominantly by early Homo. In all but one case, the bovid mortality data from FLK Zinj violate test predictions of the endurance running-hunting and passive scavenging hypotheses. When combined with other taphonomic data, these results falsify both hypotheses, and lead to the hypothesis that early Homo operated successfully as an ambush predator. 相似文献
14.
Ivan Güttler Čedo Branković Travis A. O’Brien Erika Coppola Branko Grisogono Filippo Giorgi 《Climate Dynamics》2014,43(7-8):1753-1772
This study investigates the performance of two planetary boundary layer (PBL) parameterisations in the regional climate model RegCM4.2 with specific focus on the recently implemented prognostic turbulent kinetic energy parameterisation scheme: the University of Washington (UW) scheme. When compared with the default Holtslag scheme, the UW scheme, in the 10-year experiments over the European domain, shows a substantial cooling. It reduces winter warm bias over the north-eastern Europe by 2 °C and reduces summer warm bias over central Europe by 3 °C. A part of the detected cooling is ascribed to a general reduction in lower tropospheric eddy heat diffusivity with the UW scheme. While differences in temperature tendency due to PBL schemes are mostly localized to the lower troposphere, the schemes show a much higher diversity in how vertical turbulent mixing of the water vapour mixing ratio is governed. Differences in the water vapour mixing ratio tendency due to the PBL scheme are present almost throughout the troposphere. However, they alone cannot explain the overall water vapour mixing ratio profiles, suggesting strong interaction between the PBL and other model parameterisations. An additional 18-member ensemble with the UW scheme is made, where two formulations of the master turbulent length scale in unstable conditions are tested and unconstrained parameters associated with (a) the evaporative enhancement of the cloud-top entrainment and (b) the formulation of the master turbulent length scale in stable conditions are systematically perturbed. These experiments suggest that the master turbulent length scale in the UW scheme could be further refined in the current implementation in the RegCM model. It was also found that the UW scheme is less sensitive to the variations of the other two selected unconstrained parameters, supporting the choice of these parameters in the default formulation of the UW scheme. 相似文献
15.
16.
B. J. Travis C. Anderson J. Baumgardner C. W. Gable B. H. Hager R. J. O'Connell 《地球物理与天体物理流体动力学》2013,107(3-4):137-160
Abstract A comparison is made between seven different numerical methods for calculating two-dimensional thermal convection in an infinite Prandtl number fluid. Among the seven methods are finite difference and finite element techniques that have been used to model thermal convection in the Earth's mantle. We evaluate the performance of each method using a suite of four benchmark problems, ranging from steady-state convection to intrinsically time-dependent convection with recurring thermal boundary layer instabilities. These results can be used to determine the accuracy of other computational methods, and to assist in the development of new ones. 相似文献
17.
18.
19.
20.