全文获取类型
收费全文 | 851篇 |
免费 | 20篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 58篇 |
地球物理 | 159篇 |
地质学 | 361篇 |
海洋学 | 62篇 |
天文学 | 164篇 |
综合类 | 3篇 |
自然地理 | 67篇 |
出版年
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 20篇 |
2014年 | 26篇 |
2013年 | 43篇 |
2012年 | 27篇 |
2011年 | 27篇 |
2010年 | 36篇 |
2009年 | 29篇 |
2008年 | 37篇 |
2007年 | 29篇 |
2006年 | 35篇 |
2005年 | 29篇 |
2004年 | 32篇 |
2003年 | 25篇 |
2002年 | 33篇 |
2001年 | 25篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 24篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 24篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 18篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1971年 | 6篇 |
排序方式: 共有883条查询结果,搜索用时 0 毫秒
881.
Mark Paul Speeg Krekeler C. Scott Allen Lance E. Kearns J. Barry Maynard 《Environmental Earth Sciences》2010,61(1):93-106
Kyanite Mining Corporation, located in Dillwyn, Virginia has been in operation for over 50 years and their local operation
is the largest kyanite mine in the world. As part of the processing at this location, a magnetic separate is generated and
a minimum estimation of 3.57 million tons of waste has accumulated. Currently no use for the magnetic separate has been identified.
We investigated eight representative samples of the magnetic mine waste which varied in color from a dark tan to black, to
determine if the waste could be recycled as an ore or could be used as an environmental media. Mineralogical investigations
indicate the composition of the magnetic mine waste is dominated by magnetite, kyanite, lesser amounts of hematite and charcoal.
Magnetite occurs as fine grained crystals and as inclusions in kyanite. Hematite occurs largely as botryoidal textures, as
discrete grains, and as coatings on kyanite grains. Fe-oxide spheres ranging in diameter from approximately 5–100 μm are common
and may compose up to 10% in some samples. Titanium dioxide was rarely observed as coatings on silicate mineral grains. Energy
dispersive spectroscopy analysis on magnetite crystals indicates they have end-member compositions. Bulk property investigations
indicate that grain size distributions of samples are primarily unimodal with 20–40% of material being between 0.600 and 0.250 mm.
Hydraulic conductivity values of samples investigated vary between 0.0036 and 0.0077 cm/s and are broadly consistent with
those expected of sands with similar grain size distributions. In addition to the magnetic waste stream a light blue, water
soluble, amorphous Cu sulfate occurs as a coating on surfaces of boulders. The coating is composed of rounded interlocking
particles 5–60 μm in diameter. This material is of some environmental concern for freshwater invertebrates, but can be managed
using sorption media. Hyperspectral data were gathered of the magnetic separate, kyanite ore samples, and the light blue Cu
sulfate. The signatures of the kyanite ore, the blue mineral coating, and a mixture of the two provide spectral fingerprints
that an imaging spectrometer could exploit for rapid detection and subsequent environmental monitoring. 相似文献
882.
J. R. L. Allen 《Geological Journal》1974,9(1):1-16
The lateral lithological variability of 18 stratigraphically close fluviatile cyclothems is analysed in three ways: (1) qualitatively, (2) by means of the upwards facies transition probability matrix, and (3) using the non-parametric Mann-Whitney U statistic. Some cyclothems are relatively very uniform over lateral distances comparable with 100 cyclothem thicknesses, whereas others have a lateral variability similar to the variability characteristic of the set of cyclothems. Hence some amongst stratigraphically close cyclothems are considered to show real differences, which may be attributed to allocyclic environmental factors operating on a relatively large time scale. The variation within cyclothems can be explained by shorter term autocyclic factors. 相似文献
883.
J. R. L. Allen 《Geoarchaeology》1989,4(2):143-155
The shape property of transposed pottery sherds that changes most rapidly due to wear during water transport in natural sedimentary environments is roundness, the degree of curvature of edges and corners. of the many methods for the measurement of particle roundness, which are briefly reviewed, that proposed by Wadell (1932, 1933) is considered to specify roundness best. A simple and rapid procedure for the measurement of the Wadell projection roundness is described, which yields roundness values having a precision of the order of a few percent, the precision improving with the degree of roundness. the technique is therefore suitable for the analysis of large samples of transposed and transported sherds. 相似文献