全文获取类型
收费全文 | 294篇 |
免费 | 14篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 10篇 |
地球物理 | 65篇 |
地质学 | 121篇 |
海洋学 | 43篇 |
天文学 | 32篇 |
综合类 | 2篇 |
自然地理 | 33篇 |
出版年
2021年 | 1篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 15篇 |
2012年 | 8篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 14篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
排序方式: 共有320条查询结果,搜索用时 281 毫秒
241.
RbSr ( and U-Pb () measurements were undertaken in the Sudbury area, Sudbury, Ontario to determine the ages of the Sudbury Nickel Irruptive, Superior Province granites north of Sudbury, Sudbury Breccia and subsequent metamorphism. The Sudbury Nickel Irruptive norite whole rock Rb-Sr data yield an age of (; all results quoted at 2π level) while the Nickel Irruptive micropegmatite Rb-Sr system has been disturbed and does not yield an isochron. A plagioclase-whole rock pair from the norite near the norite-micropegmatite transition yields an age of 1866 Myr, which when taken in conjunction with field (Stevenson and Colgrove, 1968) and geochemical (Naldrettet al., 1970, 1972) data does not support the conclusion of gibbins and McNurr (1972) that the micropegmatite is a later intrusion rather than a differentiate of the magma which produced the norite. Rb-Sr studies of the Superior Province granites north of Sudbury yield an age of (). U-Pb zircon studies of these granites and granitic clasts within the Sudbury Breccia yield an age of Byr and suggest the breccia granitic clasts were derived from the Superior Province granites. The granitic rocks ~150 km north of Sudbury have been undisturbed for ~ 2.6 Byr based on Rb-Sr mineral studies, whereas the granites and Sudbury Breccia within ~ 15 km of the Nickel Irruptive, as well as the Sudbury norite at the perimeter of the Irruptive have been disturbed by the Penokean Orogeny 1.7–1.75 Byr ago. The Penokean event appears to have overprinted isotopic evidence of the Sudbury impact event at least in the area studied. 相似文献
242.
243.
244.
245.
The equations determining cosmic nucleosynthesis up to4He are modified to take account of black-hole evaporation during nucleosynthesis. Numerical calculation shows that deuterium is enhanced by the presence of these micro-mini black holes (mBH); but very high-density universes are difficult to reconcile with observations, even with a very large abundance of mBH. 相似文献
246.
247.
Dale F. Hurst David W. T. Griffith John N. Carras David J. Williams Paul J. Fraser 《Journal of Atmospheric Chemistry》1994,18(1):33-56
During 18–23 July 1990, 31 smoke samples were collected from an aircraft flying at low altitudes through the plumes of tropical savanna fires in the Northern Territory, Australia. The excess (above background) mixing ratios of 17 different trace gases including CO2, CO, CH4, several non-methane hydrocarbons (NMHC), CH3CHO, NO
x
(– NO + NO2), NH3, N2O, HCN and total unspeciated NMHC and sulphur were measured. Emissionratios relative to excess CO2 and CO, and emissionfactors relative to the fuel carbon, nitrogen or sulphur content are determined for each measured species. The emission ratios and factors determined here for carbon-based gases, NO
x
, and N2O are in good agreement with those reported from other biomass burning studies. The ammonia data represent the first such measurements from savanna fires, and indicate that NH3 emissions are more than half the strength of NO
x
emissions. The emissions of NO
x
, NH3, N2O and HCN together represent only 27% of the volatilised fuel N, and are primarily NO
x
(16%) and NH3 (9%). Similarly, only 56% of the volatilised fuel S is accounted for by our measurements of total unspeciated sulphur. 相似文献
248.
Hydrophone measurements of acoustic noise levels in the Crater Lake of Mount Ruapehu, New Zealand were made on 18 January 1991 from an inflatable rubber boat on the lake. The greatest sound pressures were recorded in the 1–10 Hz band, with sound levels generally decreasing about 20 dB per decade from 10 Hz to 80 kHz. The low frequency noise did not have an obvious relationship to the tremor observed at a seismic station within 1 km of the lake. The comparatively low levels of middle and high frequency sound meant that at the time of measurement, direct steam input did not make a significant contribution to the heating of Crater Lake. This is consistent with the earlier conclusion that during the last decade a major part of the heat input of Crater Lake has come from lake water that was heated below the lake and recycled back into the lake. 相似文献
249.
250.
Alan T. Murray Timothy C. Matisziw Tony H. Grubesic 《Journal of Geographical Systems》2007,9(2):103-117
Effective management of critical network infrastructure requires the assessment of potential interdiction scenarios. Optimization
approaches have been essential for identifying and evaluating such scenarios in networked systems. Although a primary function
of any network is the distribution of flow between origins and destinations, the complexity and difficulty of mathematically
abstracting interdiction impacts on connectivity or flow has been a challenge for researchers. This paper presents an optimization
approach for identifying interdiction bounds with respect to connectivity and/or flow associated with a system of origins
and destinations. Application results for telecommunications flow are presented, illustrating the capabilities of this approach.
相似文献
Alan T. Murray (Corresponding author)Email: |
Timothy C. MatisziwEmail: |
Tony H. GrubesicEmail: |