全文获取类型
收费全文 | 350篇 |
免费 | 13篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 46篇 |
地球物理 | 52篇 |
地质学 | 115篇 |
海洋学 | 39篇 |
天文学 | 57篇 |
综合类 | 1篇 |
自然地理 | 32篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 13篇 |
2012年 | 17篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 18篇 |
2008年 | 10篇 |
2007年 | 18篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 6篇 |
1947年 | 1篇 |
排序方式: 共有365条查询结果,搜索用时 343 毫秒
31.
32.
A new parameterisation is described that predicts the temperature perturbations due to sub-grid scale orographic gravity waves
in the atmosphere of the 19 level HadAM3 version of the United Kingdom Met Office Unified Model. The explicit calculation
of the wave phase allows the sign of the temperature perturbation to be predicted. The scheme is used to create orographic
clouds, including cirrus, that were previously absent in model simulations. A novel approach to the validation of this parameterisation
makes use of both satellite observations of a case study, and a simulation in which the Unified Model is nudged towards ERA-40
assimilated winds, temperatures and humidities. It is demonstrated that this approach offers a feasible way of introducing
large scale orographic cirrus clouds into GCMs. 相似文献
33.
V -band polarimetric observations of HD 108 were obtained during 1994 August and September. This is the first time that the temporal polarimetric variability of this star has been investigated. Its percentage polarization and position angle vary randomly, and no evidence of its proposed binary nature is detected. The random variability is consistent with that seen for previously observed Wolf–Rayet stars and OB supergiants. Nightly variations do show some systematic behaviour consistent with the blob ejection model of Underhill & Fehey (1984). From the data it is estimated that the mass-loss rate resulting from blobs is ∼1-10−7 M⊙ yr−1 . The total mass-loss rate of the star is estimated to be ∼1-10−5 M⊙ yr−1 . The stellar rotation rate is estimated to be V rot ∼400 km s−1 with an inclination of i <20c. The data are also interpreted in terms of perturbations occurring in an equatorial disc plus bipolar jets viewed equatorially (Underhill 1994). It is found that the perturbation mass-loss rate is about ∼3-10−7 M⊙ yr−1 , giving a total mass-loss rate for the star of 13-10−5 M⊙ yr−1 . Both models are consistent with HD 108 being an OB supergiant or of the class Ofpe/WR9. 相似文献
34.
Dean S. Oliver 《Mathematical Geology》1998,30(7):911-933
In reservoir characterization, the covariance is often used to describe the spatial correlation and variation in rock properties or the uncertainty in rock properties. The inverse of the covariance, on the other hand, is seldom discussed in geostatistics. In this paper, I show that the inverse is required for simulation and estimation of Gaussian random fields, and that it can be identified with the differential operator in regularized inverse theory. Unfortunately, because the covariance matrix for parameters in reservoir models can be extremely large, calculation of the inverse can be a problem. In this paper, I discuss four methods of calculating the inverse of the covariance, two of which are analytical, and two of which are purely numerical. By taking advantage of the assumed stationarity of the covariance, none of the methods require inversion of the full covariance matrix. 相似文献
35.
Willard S. Moore Walter E. Dean S. Krishnaswami D.V. Borole 《Earth and Planetary Science Letters》1980,46(2):191-200
226Ra is used to document the growth histories of six manganese nodules from Oneida Lake, New York. Detailed sectioning and analysis reveal that there are discontinuous gradients in226Ra content in these samples. These gradients result from periods of rapid growth (>1 mm/100 years) separated by periods of no growth of erosion. Although the226Ra “age” of the nodules approximates the age of Oneida Lake, the nodules are not sediment-covered because they occur only in areas of the lake where fine-grained sediments are not accumulating. 相似文献
36.
37.
In studies of iron silicate liquids under reducing conditions at 1 atm pressure, iron losses from the melt can be minimized by suspending the liquid as a drop from a short segment of fine Pt wire. For a basaltic composition at 1275°C and oxygen fugacities appropriate to terrestrial magmas, iron losses from the melt are less than 0.5 wt.% of the amount present for run times less than about 20 hr. 相似文献
38.
39.
We have developed a finite-difference (FD) method to model the response of a multiple-spacing triaxial array induction tool with a multiple-electrode type sleeve. The FD software was verified versus two other independent modeling methods. The model response was checked for the FD grid refinement, while attempting to minimize run time. Many details of the electrode-sleeve geometry were studied using this method that led to the final electrode-sleeve design. The electrode sleeve reduces the response of the transverse couplings to eccentering in a conductive borehole. Quantitative agreement was found between the measurements and calculations. Using the FD software we study the tool response to various effects of 3D geometry. 相似文献
40.
针对目前基于近景摄影测量方法构建建筑物立面模型过程中因密集影像匹配(DIM)点云噪声所引起的建筑物立面TIN网格模型畸变问题,本文借鉴机器学习中样本学习的思想,对建筑物立面进行了分类并对DIM点云提出了相应的滤波方法,以达到去除DIM点云噪声和改善其TIN网格模型畸变的目的。其中,针对平面结构立面,采取先对点云样本进行学习计算构建数学立面模型所需参数,再对该立面模型设定阈值并对其点云进行滤波处理的方法;针对曲面结构立面,则结合DIM点云特性先将点云样本分类标记归为立面点与非立面点,再进行样本特征值学习,使用Logistic回归算法迭代计算求解最佳回归系数,从而构建滤波分类器的方法对立面点云进行滤波处理。试验结果表明,本文滤波处理方法能将立面DIM点云噪声有效识别并去除,而且使用该方法处理后所得点云构建的建筑物立面TIN网格模型精细化程度得到有效提高,模型质量得到明显改善。 相似文献