全文获取类型
收费全文 | 240篇 |
免费 | 50篇 |
国内免费 | 17篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 43篇 |
地球物理 | 86篇 |
地质学 | 60篇 |
海洋学 | 42篇 |
天文学 | 8篇 |
综合类 | 3篇 |
自然地理 | 22篇 |
出版年
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 16篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 18篇 |
2013年 | 11篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 19篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有307条查询结果,搜索用时 31 毫秒
51.
本文系统地介绍了所建立的一个数字近景摄影测量系统PV—1的检校方法,并得出了该系统的点定位精度。初步实验表明。运用直接线性变换法进行点定位精度评定,物方坐标的中误差为:M_x=0.247mm,M_y=0.158mm,M_z=0.272mm,象方坐标的中误差为0.2像元,相对精度为1/6000。 相似文献
52.
A numerical model describing the propagation and run-up process of nearshore tsunamis in the vicinity of shorelines is developed based on an approximate Riemann solver. The governing equations of the model are the nonlinear shallow-water equations. The governing equations are discretized explicitly by using a finite volume method. The nonlinear terms in the momentum equations are solved with the Harten-Lax-van Leer-Contact (HLLC) approximate Riemann solver. The developed model is first applied to prediction of water motions in a parabolic basin, and propagation and subsequent run-up process of nearshore tsunamis around a circular island. Computed results are then compared with available analytical solutions and laboratory measurements. Very reasonable agreements are observed. 相似文献
53.
There has been a long-standing debate concerning how dangerous seismic surveys are with respect to marine life. Marine seismic
work today is dominated by airgun technology, where high energy is generated by a release of compressed air into the water.
The objective of the “Time coded impulse seismic technique” project is to examine whether a new low energy acoustic source
can be used for seismic purposes. If the method turns out to be successful, the low output energy and continuous operation
will make the source suitable in environmental sensitive areas. The Low level Acoustic Combustion Source (LACS) is a petrol
driven pulsed underwater acoustic source. It operates at a few meters depth, and each shot can be digitally controlled from
the surface by a computer located in the mother vessel. A presentation of the recorded LACS signal characteristics, the modulation,
the Pseudo Noise coding/decoding principles and field test results, is given. The importance of using an optimized code with
fine resolution and of using the near field recording as a correlator sequence is demonstrated. Clear correlation peaks could
then be seen from the bottom and sub bottom reflectors. 相似文献
54.
55.
The goal of this study is to understand the movement of unexploded ordnance that may become unburied and forced by currents. Symmetrical, smooth, finite-length, unrestrained cylinders were studied in steady, uniform flows over a range of Reynolds numbers in a smooth-bottomed, horizontal flume. The study uses PIV tracking methods in the laboratory to identify the movement of ordnance simulated by unrestrained cylinders. The PIV is supported with a numerical analysis using a RANS flow solver. The simulations showed that at low Reynolds numbers the cylinders should roll at speeds near 70% of the free-stream flow. 相似文献
56.
Carbon dioxide flux techniques performed during GasEx-98 总被引:2,自引:0,他引:2
Wade R. McGillis James B. Edson Jonathan D. Ware John W. H. Dacey Jeffrey E. Hare Christopher W. Fairall Rik Wanninkhof 《Marine Chemistry》2001,75(4):851
A comprehensive study of air–sea interactions focused on improving the quantification of CO2 fluxes and gas transfer velocities was performed within a large open ocean CO2 sink region in the North Atlantic. This study, GasEx-98, included shipboard measurements of direct covariance CO2 fluxes, atmospheric CO2 profiles, atmospheric DMS profiles, water column mass balances of CO2, and measurements of deliberate SF6–3He tracers, along with air–sea momentum, heat, and water vapor fluxes. The large air–sea differences in partial pressure of CO2 caused by a springtime algal bloom provided high signals for accurate CO2 flux measurements. Measurements were performed over a wind speed range of 1–16 m s−1 during the three-week process study. This first comparison between the novel air-side and more conventional water column measurements of air–sea gas transfer show a general agreement between independent air–sea gas flux techniques. These new advances in open ocean air–sea gas flux measurements demonstrate the progress in the ability to quantify air–sea CO2 fluxes on short time scales. This capability will help improve the understanding of processes controlling the air–sea fluxes, which in turn will improve our ability to make regional and global CO2 flux estimates. 相似文献
57.
本文详细讨论了利用井下和地面观测直达波到时资料联合确定震源位置,发震时刻及区域平均波速的最优化方法,该方法对震源深度及波速的确定给予特别的重视与处理。理论检验和实际算例表明,用该方法编制的程序定位精度高,计算速度快,可以在地层差异小的地区推广应用。 相似文献
58.
59.
Turbulence statistics obtained by direct numerical simulations are analysed to investigate spatial heterogeneity within regular
arrays of building-like cubical obstacles. Two different array layouts are studied, staggered and square, both at a packing
density of . The flow statistics analysed are mean streamwise velocity (), shear stress (), turbulent kinetic energy (k) and dispersive stress fraction (). The spatial flow patterns and spatial distribution of these statistics in the two arrays are found to be very different.
Local regions of high spatial variability are identified. The overall spatial variances of the statistics are shown to be
generally very significant in comparison with their spatial averages within the arrays. Above the arrays the spatial variances
as well as dispersive stresses decay rapidly to zero. The heterogeneity is explored further by separately considering six
different flow regimes identified within the arrays, described here as: channelling region, constricted region, intersection
region, building wake region, canyon region and front-recirculation region. It is found that the flow in the first three regions
is relatively homogeneous, but that spatial variances in the latter three regions are large, especially in the building wake
and canyon regions. The implication is that, in general, the flow immediately behind (and, to a lesser extent, in front of)
a building is much more heterogeneous than elsewhere, even in the relatively dense arrays considered here. Most of the dispersive
stress is concentrated in these regions. Considering the experimental difficulties of obtaining enough point measurements
to form a representative spatial average, the error incurred by degrading the sampling resolution is investigated. It is found
that a good estimate for both area and line averages can be obtained using a relatively small number of strategically located
sampling points. 相似文献
60.