全文获取类型
收费全文 | 1354篇 |
免费 | 43篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 114篇 |
地球物理 | 274篇 |
地质学 | 496篇 |
海洋学 | 119篇 |
天文学 | 214篇 |
综合类 | 16篇 |
自然地理 | 165篇 |
出版年
2023年 | 7篇 |
2021年 | 16篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 34篇 |
2017年 | 20篇 |
2016年 | 23篇 |
2015年 | 39篇 |
2014年 | 40篇 |
2013年 | 82篇 |
2012年 | 49篇 |
2011年 | 83篇 |
2010年 | 54篇 |
2009年 | 68篇 |
2008年 | 58篇 |
2007年 | 76篇 |
2006年 | 58篇 |
2005年 | 46篇 |
2004年 | 37篇 |
2003年 | 33篇 |
2002年 | 40篇 |
2001年 | 22篇 |
2000年 | 32篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 11篇 |
排序方式: 共有1422条查询结果,搜索用时 15 毫秒
1.
The paper employs statistical hypothesis tests to explore the question of whether natural hazards (hail and tornadoes being considered here) are or are not intertemporally random. The answer to this question, at least for these two hazards, is surprising and has important policy implications: hazards appear to be more likely in year t if an event was experienced in year t?1: hence, apparent ‘Gambler's Fallacy’ behaviour on the part of farmers and others may indeed be rational. Should this result hold for a full range of climate-related hazard types. as we suspect, hundreds of millions of dollars of crop loss and other damages may be preventable (e.g., rotating to frost-resistant crops if past events suggest greater than usual likelihood of early or late frost). The degree of positive serial correlation is also seen to vary a great deal regionally, with individuals in some states being unable to benefit from knowledge of prior hazard occurrence. 相似文献
2.
Glenn M. Frye Jr. Philip P. Dunphy Edward L. Chupp Paul Evenson 《Solar physics》1988,118(1-2):321-346
3.
4.
5.
The impact of wave loads and pore-water pressure generation on initiation of sediment transport 总被引:3,自引:0,他引:3
Edward C. Clukey Fred H. Kulhawy Philip L. -F. Liu George B. Tate 《Geo-Marine Letters》1985,5(3):177-183
The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported. 相似文献
6.
7.
8.
G. Philip 《Journal of the Indian Society of Remote Sensing》1994,22(4):237-244
An insight into the geomorphic evolution of any area can be obtained by detailed landform mapping. In the present study, an area in the Middle Ganga Plain has been selected for the study using mainly remote sensing data. Various fluvial landforms have been mapped and the changes in planform of rivers over approximately 50 years have been evaluated. Both fluvial processes and tectonic activities are considered to have collectively influenced the migration of the rivers in this region. Digital enhancements of Landsat MSS and TM data are found to be quite useful in identification and mapping of subtle fluvial palaeofeatures. The present study demonstrates the utility of remote sensing in examining the geomorphic evolution of the area. 相似文献
9.
The strength of the Sun's polar fields 总被引:3,自引:0,他引:3
The magnetic field strength within the polar caps of the Sun is an important parameter for both the solar activity cycle and for our understanding of the interplanetary magnetic field. Measurements of the line-of-sight component of the magnetic field generally yield 0.1 to 0.2 mT near times of sunspot minimum. In this paper we report measurements of the polar fields made at the Stanford Solar Observatory using the Fe i line 525.02 nm. We find that the average flux density poleward of 55° latitude is about 0.6 mT peaking to more than 1 mT at the pole and decreasing to 0.2 mT at the polar cap boundary. The total open flux through either polar cap thus becomes about 3 × 1014 Wb. We also show that observed magnetic field strengths vary as the line-of-sight component of nearly radial fields. 相似文献
10.
The mid-Holocene (ca. 8000-4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000-7000 yr ago) and out of (ca. 5000-2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼ 5-36 yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7-4.0 vs. 0.6-1.7 mm2 cm− 2 yr− 1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming. 相似文献