全文获取类型
收费全文 | 834篇 |
免费 | 47篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 46篇 |
地球物理 | 241篇 |
地质学 | 185篇 |
海洋学 | 62篇 |
天文学 | 164篇 |
自然地理 | 182篇 |
出版年
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 28篇 |
2015年 | 19篇 |
2014年 | 19篇 |
2013年 | 45篇 |
2012年 | 24篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 47篇 |
2008年 | 41篇 |
2007年 | 36篇 |
2006年 | 33篇 |
2005年 | 33篇 |
2004年 | 48篇 |
2003年 | 26篇 |
2002年 | 41篇 |
2001年 | 30篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 23篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 23篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 11篇 |
1975年 | 9篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1970年 | 3篇 |
1924年 | 2篇 |
排序方式: 共有894条查询结果,搜索用时 765 毫秒
221.
Observations of stress relaxation before earthquakes 总被引:20,自引:0,他引:20
222.
223.
Stuart Ross Taylor 《Journal of Earth System Science》2005,114(6):587-591
Before spacecraft exploration, facts about the Moon were restricted to information about the lunar orbit, angular momentum
and density. Speculations about composition and origin were unconstrained. Naked eye and telescope observations revealed two
major terrains, the old heavily cratered highlands and the younger mostly circular, lightly cratered maria. The lunar highlands
were thought to be composed of granite or covered with volcanic ash-flows. The maria were thought to be sediments, or were
full of dust, and possibly only a few million years old. A few perceptive observers such as Ralph Baldwin (Baldwin 1949) concluded
that the maria were filled with volcanic lavas, but the absence of terrestrial-type central volcanoes like Hawaii was a puzzle.
The large circular craters were particularly difficult to interpret. Some thought, even after the Apollo flights, that they
were some analogue to terrestrial caldera (e.g., Green 1971), formed by explosive volcanic activity and that the central peaks
were volcanoes. The fact that the craters were mostly circular was difficult to accommodate if they were due to meteorite
impact, as meteorites would hit the Moon at all angles. The rilles were taken by many as definitive evidence that there was
or had been, running water on the lunar surface. Others such as Carl Sagan thought that organic compounds were likely present
(see Taylor 1975, p. 111, note 139). 相似文献
224.
Smaller source earthquakes and improved measuring techniques allow the largest earthquakes in Iceland to be stress forecast (with hindsight) 总被引:3,自引:0,他引:3
Jing Wu Stuart Crampin Yuan Gao Ping Hao Theodora Volti Yun-Tai Chen 《Geophysical Journal International》2006,166(3):1293-1298
A group of three earthquakes in 2000 June in SW Iceland included the two largest earthquakes in Iceland in the past 30 yr. Previously, temporal changes in shear-wave splitting had not been recognized before these earthquakes as there were too few small earthquakes to provide adequate shear-wave data, and they were not stress forecast, even with hindsight. These large earthquakes were subject to a special investigation by the European Community funded PREPARED Project during which the seismic catalogue was extended to include smaller magnitude earthquakes. This more detailed data set, together with a semi-automatic programme for measuring the parameters of shear-wave splitting greatly increased the number of time-delay measurements.
The new measurements displayed the typical temporal variations before larger earthquakes as seen elsewhere: a long-term increase in time delays, interpreted as stress accumulation before the earthquake; and a decrease, interpreted as crack coalescence, immediately prior to the earthquake. The logarithms of the durations of both the implied accumulation of stress and the crack coalescence have the same self-similar relationships to earthquake magnitude as found elsewhere in Iceland. This means that, in principle, the time and magnitude of the larger earthquakes could have been stress forecast in real time had the smaller source earthquakes of the extended catalogue and the improved measuring procedures been available at the time. 相似文献
The new measurements displayed the typical temporal variations before larger earthquakes as seen elsewhere: a long-term increase in time delays, interpreted as stress accumulation before the earthquake; and a decrease, interpreted as crack coalescence, immediately prior to the earthquake. The logarithms of the durations of both the implied accumulation of stress and the crack coalescence have the same self-similar relationships to earthquake magnitude as found elsewhere in Iceland. This means that, in principle, the time and magnitude of the larger earthquakes could have been stress forecast in real time had the smaller source earthquakes of the extended catalogue and the improved measuring procedures been available at the time. 相似文献
225.
226.
Open system alkaline magmatism in northern Kenya: evidence from U-series disequilibria and radiogenic isotopes 总被引:4,自引:0,他引:4
Stuart Black Ray Macdonald Barbara A. Barreiro Peter N. Dunkley Martin Smith 《Contributions to Mineralogy and Petrology》1998,131(4):364-378
U-series activity ratios, Sr-Nd-Pb isotopic ratios and major and trace element compositions have been determined on young
basalts (<10 ka) and trachytes from the volcano Emuruangogolak in the Kenya Rift Valley. The basalts are mildly alkaline and
are associated with small volumes of hawaiite. The mafic rocks are characterised by high (230Th/232Th) (≥1.06) with low (238U/230Th) ratios (≤0.72). They have variable incompatible trace element ratios (e.g. Zr/Nb, Ba/Zr), indicating that they represent
a number of magmatic lineages. The trachytes, which comprise both comenditic and pantelleritic varieties, have significantly
lower (230Th/232Th) ratios than the basalts, with clear differences between pantelleritic and comenditic types. The (238U/230Th) ratios in the pantellerites range from less, to greater, than 1. The variations in composition and isotopic diversity
must represent different sources for the trachytes. Internal isochrons for the trachytes give U-Th ages of 14 to 40 ka, similar
to single crystal laser fusion 40Ar/39Ar ages from sanidine phenocrysts (16–38 ka) for the same rocks. Post-crystallisation residence times of the trachytes were
very short, implying relatively rapid movement of trachyte from magma chamber to the surface. Variations in the initial (230Th/232Th)0 ratios (0.69–1.14) of both basalts and trachytes indicate that Emuruangogolak has erupted a large range of isotopically diverse
magmas over a very short period of time (38 ka), from conduits closely spaced around the summit of the volcano.
Received: 29 May 1996 / Accepted: 24 November 1997 相似文献
227.
Stuart R. Boyd Ian P. Wright Conel M.O'D. Alexander C.T. Pillinger 《Geostandards and Geoanalytical Research》1998,22(1):71-83
An analytical system and operating protocol are described for high resolution, stepped-combustion mass spectrometry, designed for the extraction, purification, quantification and isotopic analysis of light elements (e.g. C and N) in fine-grained reduced components (e.g. diamond) which have been chemically extracted from natural samples (e.g. meteorites). Specifically, a simple model has been developed for the extraction of diamond from meteorite and its analysis by high resolution stepped heating under an atmosphere of oxygen. Changes in the pressure of oxygen within the range 1.3 to 12kPa (10 to 90 torr) were not found to have any detectable effect on the combustion. Results obtained by this procedure were compared with those predicted by a model and excellent agreement was found, taking into account the limitations of this approach. Results of a preliminary attempt to find fine-grained diamond in a lamproite are outlined. 相似文献
228.
229.
230.
Water vapor flux at the sea surface 总被引:1,自引:0,他引:1
Stuart D. Smith 《Boundary-Layer Meteorology》1989,47(1-4):277-293
Methods and instrumentation for determining the rate of evaporation at the sea surface are reviewed. At experimental sites free of local influences, there is a consensus that the evaporation coefficient in neutral conditions C
EN = 1.2 × 10–3 at low and moderate wind speeds. Combining this with Businger-Dyer flux-gradient formulas, a parameterization scheme is proposed. Evaporation of spray droplets from breaking waves is expected to cause C
EN to increase at high wind speeds, but no direct observations of this are found. Recently it has become possible to estimate water vapor flux in tropical regions from satellite data, opening the possiblity of studying large-scale evaporative events as a function of both time and space.Visiting scholar, Department of Atmospheric Sciences AK-40, University of Washington, Seattle, Washington, 98195, U.S.A. (until June, 1989). 相似文献