全文获取类型
收费全文 | 2185篇 |
免费 | 428篇 |
国内免费 | 515篇 |
专业分类
测绘学 | 163篇 |
大气科学 | 290篇 |
地球物理 | 516篇 |
地质学 | 1365篇 |
海洋学 | 300篇 |
天文学 | 149篇 |
综合类 | 134篇 |
自然地理 | 211篇 |
出版年
2024年 | 21篇 |
2023年 | 62篇 |
2022年 | 114篇 |
2021年 | 154篇 |
2020年 | 124篇 |
2019年 | 151篇 |
2018年 | 135篇 |
2017年 | 143篇 |
2016年 | 142篇 |
2015年 | 144篇 |
2014年 | 149篇 |
2013年 | 157篇 |
2012年 | 128篇 |
2011年 | 153篇 |
2010年 | 125篇 |
2009年 | 130篇 |
2008年 | 111篇 |
2007年 | 105篇 |
2006年 | 69篇 |
2005年 | 71篇 |
2004年 | 54篇 |
2003年 | 73篇 |
2002年 | 69篇 |
2001年 | 56篇 |
2000年 | 50篇 |
1999年 | 36篇 |
1998年 | 34篇 |
1997年 | 43篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 10篇 |
排序方式: 共有3128条查询结果,搜索用时 15 毫秒
31.
32.
Combined Digital Photogrammetry and Time-of-Flight Laser Scanning for Monitoring Cliff Evolution 总被引:4,自引:0,他引:4
Michael Lim David N. Petley Nicholas J. Rosser Robert J. Allison Antony J. Long David Pybus 《The Photogrammetric Record》2005,20(110):109-129
Although cliffs form approximately 75% of the world's coastline, the understanding of the processes through which they evolve remains limited because of a lack of quantitative data on the morphological changes they undergo. In this paper the combination of terrestrial time-of-flight laser scanning with high-resolution digital photogrammetry is examined to generate high-quality data-sets pertaining to the geomorphic processes governing cliff development. The study was undertaken on a section of hard rock cliffs in North Yorkshire, UK, which has been monitored over a 12-month period. High-density, laser-scanned point clouds have been used to produce an accurate representation of these complex surfaces, free from the optical variations that degrade photographic data. These data-sets have been combined with high-resolution photographic monitoring, resampled with the fixed accuracies of the terrestrial laser survey, to generate a new approach to recording the volumetric changes in complex coastal cliffs. This has led to significant improvements in the understanding of the activity patterns of coastal cliffs. 相似文献
33.
The formation of cold air drainage flows in a shallow gully is studied during CASES-99 (Cooperative Atmosphere-Surface Exchange Study). Fast and slow response wind and temperature measurements were obtained on an instrumented 10-m tower located in the gully and from a network of thermistors and two-dimensional sonic anemometers, situated across the gully. Gully flow formed on clear nights even with significant synoptic flow. Large variations in surface temperature developed within an hour after sunset and in situ cooling was the dominant factor in wind sheltered locations. The depth of the drainage flow and the height of the down-gully wind speed maximum were found to be largest when the external wind speed above the gully flow is less than 2 m s-1. The shallow drainage current is restricted to a depth of a few metres, and is deepest when the stratification is stronger and the external flow is weaker. During the night the drainage flow breaks down, sometimes on several occasions, due to intermittent turbulence and downward fluxes of heat and momentum. The near surface temperature may increase by 6 ° C in less than 30 min due to the vertical convergence of downward heat flux. The mixing events are related to acceleration of the flow above the gully flow and decreased Richardson number. These warming events also lead to warming of the near surface soil and reduction of the upward soil heat flux. To examine the relative importance of different physical mechanisms that could contribute to the rapid warming, and to characterize the turbulence generated during the intermittent turbulent periods, the sensible heat budget is analyzed and the behaviour of different turbulent parameters is discussed. 相似文献
34.
35.
一种新的储层孔隙成因类型--石英溶解型次生孔隙 总被引:26,自引:2,他引:26
石英作为碎屑岩储层中的一种难溶组分,普遍认为它和次生孔隙的形成关系不十分密切。研究认为泌阳凹陷核桃园组储层中的碎屑石英颗粒存在明显的溶解现象,并形成以石英直接溶解型孔隙为主的储集空间特征。石英颗粒被溶解的部分在薄片中所占的范围为 2 %~ 7%者常见,高者达 8%以上,在总孔隙中所占的相对含量也多数在10 %~ 35 %之间,早成岩B期是其最主要形成期。石英溶解型次生孔隙的大量存在为碎屑岩储层中SiO2 胶结物及次生孔隙成因等问题的解释以及储层预测和评价提供了新的可能性。 相似文献
36.
应用等效纬度-海拔模型进行地温及多年冻土制图 总被引:2,自引:2,他引:2
KenjiYoshikawa PrasadGogineni 《冰川冻土》2002,24(5):526-531
This research presents a method for permafrost mapping in discontinuous permafrost regions based on equivalent latitude/elevation concept in interior Alaska. In winter months, study site has a strong temperature inversion in air up to 700 m elevation. Air temperature data and the effects of slope, aspect and elevation were used to create an equivalent latitude/elevation model. This model was well correlated with mean annual surface temperature (0.79). In this watershed, the thawing index (It≈1 400 ℃*days) at the ground surface and snow depth do not vary greatly from south facing to north facing slopes. The primary controlled factor that determines the mean annual surface temperature was the winter surface temperature. The permafrost stability is effectively controlled by the freezing index. We determined 37.5% of Caribou-Poker Creeks Research Watershed has unstable or thawing permafrost. At least 2.1% of the permafrost in this watershed may have disappeared in the last 90 years due to climate warming. This method makes it possible to evaluate the permafrost stability in the present, past and future. 相似文献
37.
38.
39.
Through the accurate determination of hypocenter location,the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with Ms=5.0 occurred along the middle segment of Longmenshan fault zone on November 30,1999,the distribution of focal depth section,the stress relase and seismicity features are given to reveal the earthquake-geneating structure of the earthquake sequence.The obtained results show the activity features for this sequence as follows:(1) There is no obvious foreshock,the accumulated strain energy releases in nearly pulse way,fluctuation of the seismic activity level is not quite evident during the duration of the sequence,and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation;(2) The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground,but near the hidden Longmenshan piedmont faults.The direction of epicenter distribution is not very coincident with the fault strikes.The microscopic epicenters are relatively far from the macroscopic epicenters,The focal depths range from 5km to 16km;(3) The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction.From these,we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk. 相似文献
40.
以大平山铜矿、天台山黄铁矿矿为例,阐述了该区的矿区、矿床地质及火山机构特征,并从成矿时间、空间及成因三个方面论述了矿床成矿与古火山机构的关系。 相似文献