全文获取类型
收费全文 | 1219篇 |
免费 | 39篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 81篇 |
地球物理 | 297篇 |
地质学 | 389篇 |
海洋学 | 113篇 |
天文学 | 178篇 |
综合类 | 4篇 |
自然地理 | 170篇 |
出版年
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 57篇 |
2012年 | 45篇 |
2011年 | 51篇 |
2010年 | 38篇 |
2009年 | 45篇 |
2008年 | 53篇 |
2007年 | 40篇 |
2006年 | 47篇 |
2005年 | 41篇 |
2004年 | 30篇 |
2003年 | 31篇 |
2002年 | 40篇 |
2001年 | 28篇 |
2000年 | 24篇 |
1999年 | 16篇 |
1998年 | 25篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 18篇 |
1994年 | 17篇 |
1993年 | 24篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 20篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 15篇 |
1972年 | 7篇 |
1971年 | 6篇 |
排序方式: 共有1265条查询结果,搜索用时 15 毫秒
111.
112.
John B. Anderson Richard Wheeler Charles P. Dunning Sue Shepley Marion Fowke 《Environmental Geology》1978,2(2):67-78
A historical record of the effects of human development upon Lake Macatawa is established using geologic criteria. Significant
cultural events are recognized using the pollen record, particularly ambrosia/vesiculate pollen ratios, and occurrences of
detrital and chemical contaminants within the more recent sedimentary column. Detrital contaminants include such things as
cinder and ash from coal burning power plants and animal hair from early tanning operations. Trace metal contaminants, frequently
associated with specific industrial events, are particularly useful in establishing a modern sedimentary chronology.
The impact of human activity upon Lake Macatawa is measured using fossil diatoms. The advantage of this method of environmental
impact assessment is that it provides a historical perspective in which changes within an environment are related to its natural
conditions. 相似文献
113.
Self-diffusion of oxygen in a natural phlogopite mica (annite 4%) has been measured under hydrothermal conditions at 2000 bars pressure and from 500 to 800°C using water enriched in18O. Diffusional transport is dominantly parallel to the c crystallographic axis. A linear Arrhenius plot was obtained with a pre-exponential term = (1.03 ± 0.38) × 10?9cm2sec?1 a and an activation energy of 29 ± 2kcal/g-atom O. The difference in transport rate between oxygens in the OH groups and those in tetrahedral sites is small to non-existent unless the OH oxygens diffuse much more slowly than the other oxygens, which we consider unlikely. A typical phlogopite crystal, 0.2 mm thick by 1 mm across will lose radiogenic argon faster than it will exchange oxygen at temperatures above 435°C, but the reverse holds at lower temperatures if the diffusion mechanism can be extrapolated to temperatures below 500°C. Such a crystal will lose only 5% of its argon if held at 380°C for 1 m.y., but could exchange 27% of its oxygen in that time. The rate at which phlogopite will undergo deformation by diffusional creep does not appear to be controlled by oxygen diffusion. 相似文献
114.
115.
Though over four-fifths of Indian population is Hindu, there are sizeable numbers of other religious groups: Muslim, Christian, Sikh, Buddhist, Jain and other religion (mainly aboriginal animists). Hindus are spread out all over the country with declining or negligible concentration at the southern, northeastern and northwestern parts of the country. Sikhs are concentrated in Punjab; Muslims have majority in the northwestern Kashmir and Lakhadweep; Buddhists compose over 50% population in Western Kashmir, immediately south of it and Sikkim; Mixed religious areas are in the northeastern and southwestern tip of the country. By applying factor analysis technique it is possible to delineate religious regions of India with five major classes: Mainly Hindu, Muslim, Sikh, Buddhist and Mixed. There are several pockets where Hindus form the main religious group, but Muslims, Christians and others are secondary. 相似文献
116.
By the method of electron reflection, we have identified seven well-defined magnetized regions in the equatorial belt of the lunar far side sampled by the Apollo 16 Particles and Fields subsatellite. Most of these surface magnetic fields lie within one basin radius from the rim of a ringed impact basin, where thick deposits of basin ejecta are observed or inferred. The strongest of the seven magnetic features is linear, at least 250 km long, and radial to the Freundlich-Sharonov basin. The apparent correlation with basin ejecta suggests some form of impact origin for the observed permanently magnetized regions. 相似文献
117.
118.
119.
120.
Richard B. Wheeler John B. Anderson Rudy R. Schwarzer Claudia L. Hokanson 《Environmental Geology》1980,3(3):163-175
Sediments are the ultimate sink for contaminants in the marine environment, and physical processes of sedimentation influence
the distribution and accumulation of these contaminants. Evaluation of contaminant levels in sediments is one approach to
assessing environmental impact; data interpretation depends on consideration of sediment texture and mineralogy, however,
which profoundly influence chemical composition. In this study, comparison of potentially contaminated sediments from the
production field with control populations was done only within the context of similar (as to texture and organic carbon and
carbonate content) sample groups as determined by cluster analysis. Ba, Cd, and Sr are identified as contaminants. Supported
by the identification of a well-crystallized expandable clay—possibly bentonite—drilling fluids are a potential source of
Ba. Ba and Sr may be unnaturally high because of their abundance in discharged produced formation waters, but may also be
naturally controlled by the unique faunal assemblage associated with the structures. Cd is probably derived from corrosion
of the structures and assorted debris on the seafloor. In general, contamination is limited to an area within 100 m of the
platforms. Furthermore, substantial erosion around platforms has probably effectively removed and dispersed the bulk of the
contaminants introduced into the marine environment by the offshore exploration/production operations. 相似文献