全文获取类型
收费全文 | 309篇 |
免费 | 13篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 9篇 |
地球物理 | 83篇 |
地质学 | 142篇 |
海洋学 | 21篇 |
天文学 | 49篇 |
综合类 | 3篇 |
自然地理 | 19篇 |
出版年
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 9篇 |
2014年 | 17篇 |
2013年 | 16篇 |
2012年 | 21篇 |
2011年 | 17篇 |
2010年 | 15篇 |
2009年 | 21篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1967年 | 1篇 |
1965年 | 3篇 |
1964年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有335条查询结果,搜索用时 171 毫秒
81.
82.
A. V. Boldycheva A. A. Lipovka N. M. Lipovka K. L. Maslennikov J. Sausedo 《Astronomy Reports》2010,54(8):730-734
We present a catalog of galaxies in and around the cluster A1367, together with the results of a spectroscopic study of eight faint galaxies projected onto the central part of the cluster. The observations were carried out with the Boller and Chivens spectrograph of the 2m telescope of the Guillermo Haro Observatory (Cananea, Mexico). Redshifts of eight galaxies were derived from both emission and absorption lines; the redshift for one of these, derived from Hα, SII, OIII, and Hβ emission lines, is z = 0.015. The spectrum of this galaxy displays no absorption lines at z = 0.026, testifying that it is located between the observer and A1367. 相似文献
83.
Anton J. J. Van Rompaey Gert Verstraeten Kristof Van Oost Gerard Govers Jean Poesen 《地球表面变化过程与地形》2001,26(11):1221-1236
In this paper a spatially distributed model for the calculation of sediment delivery to river channels is presented (SEDEM: SEdiment DElivery Model). The model consists of two components: (1) the calculation of a spatial pattern of mean annual soil erosion rates in the catchment using a RUSLE (Revised Soil Erosion Equation) approach; and (2) the routing of the eroded sediment to the river channel network taking into account the transport capacity of each spatial unit. If the amount of routed sediment exceeds the local transport capacity, sediment deposition occurs. An existing dataset on sediment yield for 24 catchments in central Belgium was used to calibrate the transport capacity parameters of the model. A validation of the model results shows that the sediment yield for small and medium sized catchments (10–5000 ha) can be predicted with an average accuracy of 41 per cent. The predicted sediment yield values with SEDEM are significantly more accurate than the predictions using a lumped regression model. Moreover a spatially distributed approach allows simulation of the effect of different land use scenarios and soil conservation techniques. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
84.
Polarized FTIR spectra of near endmember forsterite single crystals from Pamir, Tadzikistan show the existence of sharp strongly pleochroic absorption bands in the region of the OH stretching fundamental. Bands centered at 3674/3624, 3647/3598 and 3640/ 3592 cm-1 are attributed to OH dipoles oriented parallel to [100]. An OH band doublet at 3570/3535 cm-1 shows both, a strong absorption parallel to [100] and a strong component parallel to [001]. On the basis of the pleochroic scheme and under the assumption of vacancies on Si- and M-sites it is proposed that O1 is partially replaced by OH defects pointing to the vacant Si-site. O3 is donator oxygen of OH dipoles lying near the O3-O1 tetrahedral edge or roughly pointing to a vacant M2-site. Also O2 can act as donator oxygen of an OH group oriented along the O2-O3 edge of a vacant M1 octahedron. The splitting of the bands is explained by the presence of Fe2+ in cation sites surrounding the OH defects. 相似文献
85.
86.
Eleven rare earth elements (REE) have been determined in ten USGS and two CCRMP igneous rock standards using high performance ion chromatography. Duplicate analyses of two or more separately prepared aliquots of each sample were undertaken; reproducibility was better than 5% for each of the REE. In most cases, the results compare closely with published REE values for those samples for which the REE are well characterised. Where the results for individual elements are in disagreement with published data, the more erratic patterns yielded by the earlier data when plotted on chondrite-normalised REE diagrams suggest that values determined in this study are of greater accuracy. 相似文献
87.
The phenomenon of the seismic coda, which is composed of seismic energy delayed by scattering, is seen on both the Earth and the Moon. On the Moon the scattered coda is very large relative to body wave arrivals with a delay of the time of maximum energy, whereas on Earth scattered codas are relatively small and show no delay of the energy maximum. In both cases the form of the coda is controlled by three distance scales, the mean free path L, which is the average distance seismic energy travels before it is scattered, the attenuation distance , which is the average distance seismic energy travels before it is attenuated, and the source-receiver distance R. Two coda models are discussed based on these parameters; a strong scattering (diffusion) model, and a weak scattering (single scattering) model. A discussion of the diffusion scattering model indicates that if , diffusion scattering is an appropriate model, but if , single scattering is the appropriate model, within the appropriate range of R. A survey of the literature indicates that for the frequency range 0.5–10 Hz, diffusion scattering is important in lunar codas, but for the frequency range 1–25 Hz single scattering is important in terrestrial codas. Another important effect of attenuation is the elimination of scattering paths much longer than . On the Moon, this means that seismic energy in the coda can only propagate directly in the near-surface strong scattering zone between surface sources and the seismometer for source-seismometer separations of the order of ; otherwise, scattering is limited to regions near the source and the receiver. On Earth, this effect probably prevents multiple scattering. 相似文献
88.
Effects on sandy beach microfauna of soluble pollutants, such as might be associated with an oil spill, were investigated in terms of nitrate generation. Nitrate generation by the microfauna in small sand columns in the laboratory was severely inhibited by water-soluble fractions of crude oil, dispersant and oil/dispersant mixtures in order of increasing effects. Short-term effects of such pollutants on nutrient regeneration by exposed sandy beaches are discussed. 相似文献
89.
Long-term impacts of increased metal loading (Hg, Cu, Cd, Zn and Pb) on phytoplankton communities of large limno-corrals (diameter
12 m, depth 10 m) were studied. Increased metal concentrations initially lowered phytoplankton biomass, as well as species
number and photosynthetic activity of phytoplankton. They caused changes in metal speciation and shifts in phytoplankton community
structure, favoring less susceptible species. Although adaptation was not sufficient to completely prevent the metal-induced
depression of photosynthesis, due to depressed zooplankton grazing, at the end of the experiment even higher phytoplankton
densities were observed in the metal-loaded corrals than in the control. 相似文献
90.
Two Karroo dolerite sills display chemical and mineralogical variation compatible with cumulus enrichment. The Blaauwkrans sill is an olivine tholeiite and contains a central zone slightly enriched in olivine, plagioclase and clinopyroxene. The thicker Hangnest sill is a quartz tholeiite and shows evidence of crystal settling and has a lower zone enriched in cumulus orthopyroxene and plagioclase.The two sills differ quite markedly in their trace element compositions, with the Hangnest magma enriched by a factor of two in LIL elements (Rb, Ba, Nb, Zr, Y) relative to the Blaauwkrans magma. The Hangnest magma contained extremely low Ni contents (3–5 ppm), whereas the Blaauwkrans magma contained higher but more normal Ni (100–110ppm). Such contrasting trace element compositions preclude any simple genetic relationship between the two Karroo magmas but they may be related either through a common parent or are derivatives from separate parental magmas.South African Contribution No. 24 to the International Geodynamics Project 相似文献