全文获取类型
收费全文 | 5446篇 |
免费 | 220篇 |
国内免费 | 49篇 |
专业分类
测绘学 | 128篇 |
大气科学 | 459篇 |
地球物理 | 1402篇 |
地质学 | 1767篇 |
海洋学 | 509篇 |
天文学 | 866篇 |
综合类 | 20篇 |
自然地理 | 564篇 |
出版年
2021年 | 70篇 |
2020年 | 75篇 |
2019年 | 80篇 |
2018年 | 101篇 |
2017年 | 96篇 |
2016年 | 144篇 |
2015年 | 141篇 |
2014年 | 146篇 |
2013年 | 291篇 |
2012年 | 166篇 |
2011年 | 266篇 |
2010年 | 199篇 |
2009年 | 273篇 |
2008年 | 228篇 |
2007年 | 212篇 |
2006年 | 222篇 |
2005年 | 188篇 |
2004年 | 192篇 |
2003年 | 158篇 |
2002年 | 160篇 |
2001年 | 83篇 |
2000年 | 103篇 |
1999年 | 93篇 |
1998年 | 95篇 |
1997年 | 74篇 |
1996年 | 70篇 |
1995年 | 94篇 |
1994年 | 86篇 |
1993年 | 66篇 |
1992年 | 72篇 |
1991年 | 56篇 |
1990年 | 74篇 |
1989年 | 65篇 |
1988年 | 65篇 |
1987年 | 70篇 |
1986年 | 70篇 |
1985年 | 77篇 |
1984年 | 101篇 |
1983年 | 78篇 |
1982年 | 78篇 |
1981年 | 66篇 |
1980年 | 79篇 |
1979年 | 61篇 |
1978年 | 61篇 |
1977年 | 47篇 |
1976年 | 56篇 |
1975年 | 58篇 |
1974年 | 51篇 |
1973年 | 59篇 |
1972年 | 28篇 |
排序方式: 共有5715条查询结果,搜索用时 15 毫秒
71.
Preston E. James 《The Professional geographer》1976,28(1):1-7
Every active scientific discipline has arrived at its own peculiar definition of acceptable problems and acceptable ways of attacking them through a social process of mutual consent. 相似文献
72.
73.
We have used Pollack et al.'s 1976 calculations of the quasi-equilibrium contraction of Saturn to study the influence of the planet's early high luminosity on the formation of its satellites and rings. Assuming that the condensation of ices ceased at the same time within Jupiter's and Saturn's primordial nebulae, and using limits for the time of cessation derived for Jupiter's system by Pollack and Reynolds (1974) and Cameron and Pollack (1975), we arrive at the following tentative conclusions. Titan is the innermost satellite at whose position a methane-containing ice could condense, a result consistent with the presence of methane in this satellite's atmosphere. Water ice may have been able to condense at the position of all the satellites, a result consistent with the occurrence of low-density satellites close to Saturn. The systematic decrease in the mass of Saturn's regular satellites with decreasing distance from Saturn may have been caused partially by the larger time intervals for the closer satellites between the start of contraction and the first condensation of ices at their positions and between the start of contraction and the time at which Saturn's radius became less than a satellite's orbital radius. Ammonia ices, principally NH4SH, were able to condense at the positions of all but the innermost satellites.Water ice may bave been able to condense in the region of the rings close to the end of the condensation period. We speculate that the rings are unique to Saturn because on the one hand, temperatures within Jupiter's Roche limit never became cool enough for ice particles to form before the end of the condensation period and on the other hand, ice particles formed only very early within Uranus' and Neptune's Roche limits, and were eliminated by gas drag effects that caused them to spiral into the planet before the gas of these planets' nebula was eliminated. Gas drag would also have eliminated any rocky particles initially present inside the Roche limit.We also derive an independent estimate of several million years for the time between the start of the quasi-equilibrium contraction of Saturn and the cessation of condensation. This estimate is based on the density and mass characteristics of Saturn's satellites. Using this value rather than the one found for Jupiter's satellites, we find that the above conclusions about the rings and the condensation of methane-and ammonia-containing ices remain valid. 相似文献
74.
The July 12, 1973, occultation of Europa by Io was observed in 30 wavelength channels in the spectral region λλ3200-11, 000 Å with the 200-inch Hale telescope and a multichannel spectrometer. The data are presented in absolute units above the Earth's atmosphere. The data are analyzed to obtain the spectral reflectivity of seven localized areas on the disk of Europa centered on 324°W longitude. The equatorial material is confirmed to be darker than the eastward-skewed bright north polar cap and a hint is evident that the darker material as well may be somewhat redder than the cap material. 相似文献
75.
76.
Cosmogenic nuclide methods for measuring long-term rates of physical erosion and chemical weathering
James W. Kirchner Clifford S. Riebe Kenneth L. Ferrier Robert C. Finkel 《Journal of Geochemical Exploration》2006,88(1-3):296
Understanding the evolution of geochemical and geomorphic systems requires measurements of long-term rates of physical erosion and chemical weathering. Erosion and weathering rates have traditionally been estimated from measurements of sediment and solute fluxes in streams. However, modern sediment and solute fluxes are often decoupled from long-term rates of erosion and weathering, due to storage or re-mobilization of sediment and solutes upstream from the sampling point. Recently, cosmogenic nuclides such as 10Be and 26Al have become important new tools for measuring long-term rates of physical erosion and chemical weathering. Cosmogenic nuclides can be used to infer the total denudation flux (the sum of the rates of physical erosion and chemical weathering) in actively eroding terrain. Here we review recent work showing how this total denudation flux can be partitioned into its physical and chemical components, using the enrichment of insoluble tracers (such as Zr) in regolith relative to parent rock. By combining cosmogenic nuclide measurements with the bulk elemental composition of rock and soil, geochemists can measure rates of physical erosion and chemical weathering over 1000- to 10,000-year time scales. 相似文献
77.
Thomas A. Vogel Timothy P. Flood Lina C. Patino Melissa S. Wilmot Raymond Patrick R. Maximo Carmencita B. Arpa Carlo A. Arcilla James A. Stimac 《Contributions to Mineralogy and Petrology》2006,151(3):267-281
Silicic volcanic deposits (>65 wt% SiO2), which occur as domes, lavas and pyroclastic deposits, are relatively abundant in the Macolod Corridor, SW Luzon, Philippines.
At Makiling stratovolcano, silicic domes occur along the margins of the volcano and are chemically similar to the silicic
lavas that comprise part of the volcano. Pyroclastic flows are associated with the Laguna de Bay Caldera and these are chemically
distinct from the domes and lavas at Makiling stratovolcano. As a whole, samples from the Laguna de Bay Caldera contain lower
concentrations of MgO and higher concentrations of Fe2O3(t) than the samples from domes and lavas. The Laguna de Bay samples are more enriched in incompatible trace elements. The silicic
rocks from the domes, Makiling Volcano and Laguna de Bay Caldera all contain high alkalis and high K2O/Na2O ratios. Melting experiments of primitive basalts and andesites demonstrate that it is difficult to produce high K2O/Na2O silicic magmas by fractional crystallization or partial melting of a low K2O/Na2O source. However, recent melting experiments (Sisson et al., Contrib Mineral Petrol 148:635–661, 2005) demonstrate that extreme
fractional crystallization or partial melting of K-rich basalts can produce these silicic magmas. Our model for the generation
of the silicic magmas in the Macolod Corridor requires partial melting of mantle-derived, evolved, moderate to K-rich, crystallized
calc-alkaline magmas that ponded and crystallized in the mid-crust. Major and trace element variations, along with oxygen
isotopes and ages of the deposits, are consistent with this model.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
78.
Racism has become a fact of life in Australia over the past decade or so, yet there are relatively few studies of its nature or extent, and still fewer on its geography. Using a social constructivist approach, this study draws on a survey of 5056 respondents to investigate attitudes to racism and cultural diversity in New South Wales and Queensland, and of perceptions of out-groups as instances of ‘strangers in our midst’. On racism, results show the presence of a continuum of attitudes ranging from generally tolerant to generally intolerant, a presence which cuts across compositional (social or aspatial) characteristics to emphasise the existence of a distinctive geography, an everywhere different nature to racist and non-racist attitudes which transcends urban–rural and traditional social layers. On the other hand, perceptions of out-groups are not uniformly correlated with presence or absence of cultural diversity. In many cases, the ability to make judgements about significant ‘others’ or out-groups has been shown to relate more to abstract notions of self and national identity, reproduced in public by mainstream news media and political leaders. In particular, it may reflect an Anglo (or Anglo-Celtic) view on nationalism, which is a hallmark of the ‘new racism’: an assimilationist or ethnocultural view of Australian society which is different from the ‘civic nation’ ideal envisaged by multiculturalism. That the geography of attitudes and perceptions people have towards and about different cultural groups is so ‘everywhere different’ has important implications for attempts to address and redress issues of intolerance in Australia. 相似文献
79.
80.