全文获取类型
收费全文 | 189篇 |
免费 | 2篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 14篇 |
地球物理 | 38篇 |
地质学 | 53篇 |
海洋学 | 18篇 |
天文学 | 23篇 |
综合类 | 1篇 |
自然地理 | 42篇 |
出版年
2022年 | 1篇 |
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有191条查询结果,搜索用时 15 毫秒
21.
22.
Observations of active galactic nuclei imply that shocks must be an essential and important part of their structure. We outline the basic observations, and discuss those features which must be addressed by any physical model of active nuclei. These features, in particular the observed spectrum of strong emission and absorption lines, lead naturally to the conclusion that shocks are present. The velocity widths of these lines, which range from hundreds to many thousands of kilometres per second, are most readily explained by models in which shocks play an important role in the generation of cool gas. The extreme parameters of the shocks in and around active nuclei provide a unique application for the physics discussed in this meeting. 相似文献
23.
24.
25.
The Hydrogeology of an Induced Streambed Infiltration Area 总被引:1,自引:0,他引:1
Perry H. Rahn 《Ground water》1968,6(3):21-32
26.
Nancy Perry 《Urban geography》2016,37(1):141-161
This study examines the eminent domain action in 1942 where the federal government took 411 acres of land, including an African American neighborhood, to construct the Pentagon building in Arlington County, Virginia. The Fifth Amendment of the U.S. Constitution acknowledges the right of the federal government to exercise eminent domain where needed for the common good, but requires that property owners be given just compensation. This study explores the issue of compensation: what the residents lost when they were forced to move, how that loss was compensated, and whether the compensation was “just.” The study data include interviews with former residents of the neighborhood, oral histories, land records, census data, photographs, and newspaper articles. The study concludes that the federal government compensated the residents for land and buildings, but was unable to compensate for a lost community. For many residents, that community is mourned even 72 years later. 相似文献
27.
This paper examines the recent economic turmoil in East Asia which has been linked to the convulsive nature of global capital movements. East Asia, once the site of rapid capital accumulation, lost its economic momentum beginning in July 1997 with a series of currency devaluations, culminating in a net outflow of private capital within a year. International capital's ability to disembed the region, however, has been highly uneven over space. That China, Hong Kong, Singapore, and Taiwan are far more territorially resilient while others like Indonesia, Thailand, and South Korea initiated major political changes suggests that the geography of crisis is far more complex than is currently presented. 相似文献
28.
Mark E. Perry Daniel S. Kahan Olivier S. Barnouin Carolyn M. Ernst Sean C. Solomon Maria T. Zuber David E. Smith Roger J. Phillips Dipak K. Srinivasan Jürgen Oberst Sami W. Asmar 《Planetary and Space Science》2011,59(15):1925-1931
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft completed three flybys of Mercury in 2008–2009. During the first and third of those flybys, MESSENGER passed behind the planet from the perspective of Earth, occulting the radio-frequency (RF) transmissions. The occultation start and end times, recovered with 0.1 s accuracy or better by fitting edge-diffraction patterns to the RF power history, are used to estimate Mercury's radius at the tangent point of the RF path. To relate the measured radius to the planet shape, we evaluate local topography using images to identify the high-elevation feature that defines the RF path or using altimeter data to quantify surface roughness. Radius measurements are accurate to 150 m, and uncertainty in the average radius of the surrounding terrain, after adjustments are made from the local high at the tangent point of the RF path, is 350 m. The results are consistent with Mercury's equatorial shape as inferred from observations by the Mercury Laser Altimeter and ground-based radar. The three independent estimates of radius from occultation events collectively yield a mean radius for Mercury of 2439.2±0.5 km. 相似文献
29.
30.
We present measurements of hillslope debris flow impact pressures on small obstacles. Two impact sensors have been installed in a real-scale experimental site where 50?m3 of water-saturated soil material are released from rest. Impact velocities vary between 2 and 13?m/s; flow heights between 0.3 and 1.0?m. The maximum impact pressures measured over 15 events represent between 2 and 50 times the equivalent static pressures. The measurements reveal that quadratic velocity-dependent formulas can be used to estimate impact pressures. Impact coefficients C are constant from front to tail and range between 0.4?<?C?<?0.8 according to the individual events. The pressure fluctuations to depend on the sensor size and are between 20% and 60% of the mean pressure values. Our results suggest that hazard guidelines for hillslope debris flows should be based on quadratic velocity-dependent formulas. 相似文献