全文获取类型
收费全文 | 236篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 13篇 |
地球物理 | 39篇 |
地质学 | 93篇 |
海洋学 | 23篇 |
天文学 | 47篇 |
综合类 | 1篇 |
自然地理 | 29篇 |
出版年
2024年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 8篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 16篇 |
2007年 | 7篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 2篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 0 毫秒
1.
Ari Lehto 《Astrophysics and Space Science》1996,244(1-2):321-328
Several invariant properties of matter seem to fit remarkably well to quantized values obtained from Planck domain units by period doubling in three dimensions. The units are defined using natural constants only. Such properties include the elementary electric charge, electron and proton rest energies and others. It has been shown by W. G. Tifft that the quantized redshifts of galaxies fit the pattern, too. Magnetic moments of the electron, proton, neutron, muon and lambda particles also seem to obey the doubling rule. The same number of doublings seems to yield the electron and proton rest masses and magnetic moments correspondingly. The proton rest mass is E0×2–64 and the magnetic moment µ
o
× 264, where E0 and µ
o
are the Planck domain units. The corresponding exponent of 2 for the electron is 75.66. The units for the proton and the electron differ by a factor of
. The magnetic moment of the muon suggests a close relationship between the magnetic structures of the muon and the proton, whereas the lambda particle seems to be related to the neutron. Reasons for the supposed existence of quantized 3-d time are represented. 相似文献
2.
3.
4.
5.
6.
Temperature response to future urbanization and climate change 总被引:2,自引:0,他引:2
Daniel Argüeso Jason P. Evans Lluís Fita Kathryn J. Bormann 《Climate Dynamics》2014,42(7-8):2183-2199
This study examines the impact of future urban expansion on local near-surface temperature for Sydney (Australia) using a future climate scenario (A2). The Weather Research and Forecasting model was used to simulate the present (1990–2009) and future (2040–2059) climates of the region at 2-km spatial resolution. The standard land use of the model was replaced with a more accurate dataset that covers the Sydney area. The future simulation incorporates the projected changes in the urban area of Sydney to account for the expected urban expansion. A comparison between areas with projected land use changes and their surroundings was conducted to evaluate how urbanization and global warming will act together and to ascertain their combined effect on the local climate. The analysis of the temperature changes revealed that future urbanization will strongly affect minimum temperature, whereas little impact was detected for maximum temperature. The minimum temperature changes will be noticeable throughout the year. However, during winter and spring these differences will be particularly large and the increases could be double the increase due to global warming alone at 2050. Results indicated that the changes were mostly due to increased heat capacity of urban structures and reduced evaporation in the city environment. 相似文献
7.
Elemental and mineralogical changes in soils due to bioturbation along an earthworm invasion chronosequence in Northern Minnesota 总被引:1,自引:0,他引:1
Kathryn Resner Kyungsoo Yoo Cindy Hale Anthony Aufdenkampe Alex Blum Stephen Sebestyen 《Applied Geochemistry》2011
Minnesota forested soils have evolved without the presence of earthworms since the last glacial retreat. When exotic earthworms arrive, enhanced soil bioturbation often results in dramatic morphological and chemical changes in soils with negative implications for the forests’ sustainability. However, the impacts of earthworm invasion on geochemical processes in soils are not well understood. This study attempts to quantify the role of earthworm invasion in mineral chemical weathering and nutrient dynamics along an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota. Depth and rates of soil mixing can be tracked with atmospherically derived short lived radioisotopes 210Pb and 137Cs. Their radioactivities increase in the lower A horizon at the expense of the peak activities near the soil surface, which indicate that soil mixing rate and its depth reach have been enhanced by earthworms. Enhanced soil mixing by earthworms is consistent with the ways that the vertical profiles of elemental and mineralogical compositions were affected by earthworm invasion. Biologically cycled Ca and P have peak concentrations near the soil surface prior to earthworm invasion. However, these peak abundances significantly declined in the earthworm invaded soils presumably due to enhanced soil mixing. It is clear that enhanced soil mixing due to earthworms also profoundly altered the vertical distribution of most mineral species within A horizons. Though the mechanisms are not clear yet, earthworm invasion appears to have contributed to net losses of clay mineral species and opal from the A horizons. As much as earthworms vertically relocated minerals and elements, they also intensify the contacts between organic matter and cations as shown in the increased amount of Ca and Fe in organically complexed and in exchangeable pools. With future studies on soil mixing rates and elemental leaching, this study will quantitatively and mechanically address the role of earthworms in geochemical evolution of soils and forests’ nutrient dynamics. 相似文献
8.
Asymmetric-Flow Field-Flow Fractionation (AsFlFFF) coupled to an inductively coupled plasma-mass spectrometer (ICP-MS) was used to determine whether colloidal As exists in mine tailings from abandoned Au mine sites in Nova Scotia. Using this technique, the chemical composition and the size of the colloidal material was determined. Tailings samples were collected from the sites and leachates were analyzed. The resulting fractograms showed the presence of colloidal As. Arsenic co-elutes with Fe and Al suggesting that the As is associated with colloids containing these elements. The colloidal material present in the samples has a calculated median size of 7 nm. The leachates were also analyzed for totalAs, Fe and Al using ICP-MS. The colloidal fraction was determined to account for approximately 20% of the total dissolved As present in these samples. Dissolved As concentrations at the selected mine sites are very high and the arbitrary cutoff for dissolved still incorporates colloidal material. Therefore. it is important to distinguish between truly dissolved and colloidal As as the speciation will affect the toxicity and mobility of As at these locations. 相似文献
9.
10.
In order to investigate the formation of martian gullies and the stability of fluids on Mars, we examined about 120 gully images. Twelve HiRISE images contained a sufficient number of Transverse Aeolian Ridges (TARs) associated with the gullies to make the following measurements: overall gully length, length of the alcove, channel and apron, and we also measured the frequency of nearby TARs. Six of the 12 images examined showed a statistically significant negative correlation between overall gully length (alcove, channel and apron length) and TAR frequency. Previous experimental work from our group has shown that at temperatures below ∼200 K, evaporation rate increases by about an order of magnitude as wind speed increases from 0 to ∼15 m/s. Thus the negative correlations we observe between gully length and dune frequency can be explained by formation at temperatures below ∼200 K where wind speed/evaporation is a factor governing gully length. In these cases evaporation of the fluid carving the gully was a constraint on their dimensions. Cases where there is no correlation between gully length and TAR frequency, can be explained by formation at temperatures >200 K. The temperatures are consistent with Global Circulation Model and Thermal Emission Spectrometer (TES) data for these latitudes. The temperatures suggested by these trends are consistent with the fluid responsible for gully formation being a strong brine, such as Fe2(SO4)3 which has a eutectic temperature of ∼200 K. We also find that formation timescales for gullies are 105-106 years. 相似文献