全文获取类型
收费全文 | 232篇 |
免费 | 34篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 47篇 |
大气科学 | 76篇 |
地球物理 | 58篇 |
地质学 | 29篇 |
海洋学 | 55篇 |
天文学 | 5篇 |
综合类 | 8篇 |
自然地理 | 19篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 33篇 |
2012年 | 8篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 19篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 6篇 |
2004年 | 8篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有297条查询结果,搜索用时 343 毫秒
91.
In this paper, new expressions of radiation stress and volume flux for long waves have been analytically derived by inclusion of higher-order surface elevations up to the sixth-order. To quantify these expressions, surface elevations along a beach are first simulated using the fully nonlinear Boussinesq-type model COULWAVE. Then, based on the large amount of numerical data, new equations for radiation stress and volume flux are statistically formulated. The research unveils the essential roles of the Ursell parameter, Irribarren number and wave steepness described by the local wave height, wave length and bottom slope. The study shows the importance of nonlinear wave properties in wave-induced currents and mean water levels (set-up/down). The higher-order formulations produce lower values for radiation stress and volume flux than calculated from the lower-order and linear waves. Case studies suggest that the new formulations produce an accurate estimation for mean water level. However, improvement on the computed current profiles is marginal for some cases. This implies that the accurate prediction of the current profile would require more than just the proposed improvement of the radiation stress and volume flux. 相似文献
92.
Existing methods for gross error detection, based on the mean shift model or the variance inflation model, have hardly considered
or taken advantage of the potential prior information on the unknown parameters. This paper puts forward a Bayesian approach
for gross error detection when prior information on the unknown parameters is available. Firstly, based on the basic principle
of Bayesian statistical inference, the Bayesian method—posterior probability method—for the detection of gross errors is established.
Secondly, considering either non-informative priors or normal-gamma priors on the unknown parameters, the computational formula
of the posterior probability is given for both the mean shift model and the variance inflation model, respectively, under
the condition of unequal weight and independent observations. Finally, as an example, a triangulation network is computed
and analyzed, which shows that the method given here is feasible. 相似文献
93.
94.
95.
96.
We present an improved crossover adjustment procedure to determine mean sea surface height using TOPEX, 35-day repeat phase ERS-1, Geosat, and 168-day repeat phase ERS-1 satellite altimeter data. The mean sea surface frame defined by the TOPEX data is imposed as certain constraints in our crossover adjustment procedure rather than held fixed as in some other procedures. The new procedure is discussed in detail. Equations are developed to incorporate the a priori information of Topex data as well as other satellite altimeter data. The numerical computation result shows that the rms crossover discrepancies are reduced by an order of 1 cm when the Topex data is not fixed. Furthermore, the computed mean sea surface is less noisy and more realistic than that computed by the traditional procedure. 相似文献
97.
98.
Traditionally, forest-stand delineation has been assessed based on orthophotography. The application of LiDAR has improved forest management by providing high-spatial-resolution data on the vertical structure of the forest. The aim of this study was to develop and test a semi-automated algorithm for stands delineation in a plantation of Pinus sylvestris L. using LiDAR data. Three specific objectives were evaluated, i) to assess two complementary LiDAR metrics, Assmann dominant height and basal area, for the characterization of the structure of P. sylvestris Mediterranean forests based on object-oriented segmentation, ii) to evaluate the influence of the LiDAR pulse density on forest-stand delineation accuracy, and iii) to investigate the algorithmś effectiveness in the delineation of P. sylvestris stands for map prediction of Assmann dominant height and basal area. Our results show that it is possible to generate accurate P. sylvestris forest-stand segmentations using multiresolution or mean shift segmentation methods, even with low-pulse-density LiDAR − which is an important economic advantage for forest management. However, eCognition multiresolution methods provided better results than the OTB (Orfeo Tool Box) for stand delineation based on dominant height and basal area estimations. Furthermore, the influence of pulse density on the results was not statistically significant in the basal area calculations. However, there was a significant effect of pulse density on Assmann dominant height [F2,9595 = 5.69, p = 0.003].for low pulse density. We propose that the approach shown here should be considered for stand delineation in other large Pinus plantations in Mediterranean regions with similar characteristics. 相似文献
99.
100.