全文获取类型
收费全文 | 237篇 |
免费 | 8篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 47篇 |
地球物理 | 52篇 |
地质学 | 82篇 |
海洋学 | 14篇 |
天文学 | 39篇 |
综合类 | 4篇 |
自然地理 | 12篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 19篇 |
2015年 | 15篇 |
2014年 | 23篇 |
2013年 | 27篇 |
2012年 | 16篇 |
2011年 | 10篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 12篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 15 毫秒
251.
In recent years, data assimilation techniques have been applied to an increasingly wider specter of problems. Monte Carlo
variants of the Kalman filter, in particular, the ensemble Kalman filter (EnKF), have gained significant popularity. EnKF
is used for a wide variety of applications, among them for updating reservoir simulation models. EnKF is a Monte Carlo method,
and its reliability depends on the actual size of the sample. In applications, a moderately sized sample (40–100 members)
is used for computational convenience. Problems due to the resulting Monte Carlo effects require a more thorough analysis
of the EnKF. Earlier we presented a method for the assessment of the error emerging at the EnKF update step (Kovalenko et
al., SIAM J Matrix Anal Appl, in press). A particular energy norm of the EnKF error after a single update step was studied.
The energy norm used to assess the error is hard to interpret. In this paper, we derive the distribution of the Euclidean
norm of the sampling error under the same assumptions as before, namely normality of the forecast distribution and negligibility
of the observation error. The distribution depends on the ensemble size, the number and spatial arrangement of the observations,
and the prior covariance. The distribution is used to study the error propagation in a single update step on several synthetic
examples. The examples illustrate the changes in reliability of the EnKF, when the parameters governing the error distribution
vary. 相似文献
252.
Gijs A. Verdoes Kleijn Andrey N. Belikov John P. McFarland 《Experimental Astronomy》2013,35(1-2):187-201
In this paper we describe the way the Astro-WISE information system (or simply Astro-WISE) supports the data from a wide range of instruments and combines multiple surveys and their catalogues. Astro-WISE allows ingesting of data from any optical instrument, survey or catalogue, processing of this data to create new catalogues and bringing in data from different surveys into a single catalogue, keeping all dependencies back to the original data. Full data lineage is kept on each step of compiling a new catalogue with an ability to add a new data source recursively. With these features, Astro-WISE allows not only combining and retrieving data from multiple surveys, but performing scientific data reduction and data mining down to the rawest data in the data processing chain within a single environment. 相似文献
253.
From a simple text interface to a graphical user interfaces—Astro-WISE provides the user with a wide range of possibilities to interact with the information system according to the user’s tasks and use cases. We describe a general approach to the interfacing of a scientific information system. We use this approach to create a number of services, which allows the user to browse the data stored in the system, to process the data and to exchange the newly created images and catalogs with the users within the system and wider astronomical community. Reusability of interfaces and services is another important feature of our approach. It reduces the time and resources spent to interface other information systems created from Astro-WISE. 相似文献
254.
Andrey Linhares Bezerra de Oliveira Júlio Carlos Afonso Lilian da Silva Arnaldo Alcover Neto Manuel Castro Carneiro Lílian Irene Dias da Silva Maria Inês Couto Monteiro 《Geostandards and Geoanalytical Research》2019,43(4):689-699
Rare earth elements (REEs) are very important to technological development as well as to geochemical and environmental studies. In this work, hydrofluoric acid (HF) was replaced by condensed phosphoric acid (CPA) in the digestion of geological samples, and the quantification of REEs was performed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Six international reference materials (RMs), named DC86318, CGL 111, CGL 124, CGL 126, OKA‐2 and COQ‐1 and three Brazilian ore samples, named Araxá, Catalão and Pitinga were analysed. Only zircon and xenotime, which are potential REE‐bearing minerals, were not completely dissolved. Nevertheless, no REE associated with zircon was detected. The investigated digestion method presented many advantages: It was relatively fast (3 h), avoided fluoride precipitation, it was less hazardous because handling diluted H3PO4 is safer than HF, NH4F or NH4HF2 aqueous solutions, it preserved the quartz fittings of the measurement equipment and the final solution contained lower levels of total dissolved solids than those produced by the fusion method. 相似文献
255.
Using a One-and-a-Half Order Closure Model of the Atmospheric Boundary Layer for Surface Flux Footprint Estimation 总被引:3,自引:1,他引:3
A knowledge of the distribution of the contribution of upwind sources to measurements of vertical scalar flux densities is
important for the correct interpretation of eddy covariance data. Several approaches have been developed to estimate this
so-called footprint function. Here a new approach based on the ensemble-averaged Navier—Stokes equations is presented. Comparisons
of numerical results using this approach with results from other studies under a range of environmental conditions show that
the model predictions are robust. Moreover, the approach outlined here has the advantage of a potential wide applicability,
due to an ability to take into account the heterogeneous nature of underlying surfaces. For example, the model showed that
any variations in surface drag, such as must occur in real life heterogeneous canopies, can exert a marked influence of the
shape and extent of flux footprints. Indeed, it seems likely that under such circumstances, estimates of surface fluxes will
be weighted towards areas of highest foliage density (and therefore quite likely higher photosynthetic rates) close to the
measurement sensor.
Three-dimensional footprints during the day and night were also determined for a mixed coniferous forest in european Russia.
A marked asymmetry of the footprint in the crosswind direction was observed, this being especially pronounced for non-uniform
plant distributions involving vegetation types with different morphological and physiological properties. The model also found
that, other things being equal, the footprint peak for forest soil respiration is typically over twice the distance from the
above canopy measurement sensor compared to that for canopy photosynthesis. This result has important consequences for the
interpretation of annual ecosystem carbon balances by the eddy covariance method. 相似文献
256.
Recently, new on‐shore acquisition designs have been presented with multi‐component sensors deployed in the shallow sub‐surface (20 m–60 m). Virtual source redatuming has been proposed for these data to compensate for surface statics and to enhance survey repeatability. In this paper, we investigate the feasibility of replacing the correlation‐based formalism that undergirds virtual source redatuming with multi‐dimensional deconvolution, offering various advantages such as the elimination of free‐surface multiples and the potential to improve virtual source repeatability. To allow for data‐driven calibration of the sensors and to improve robustness in cases with poor sensor spacing in the shallow sub‐surface (resulting in a relatively high wavenumber content), we propose a new workflow for this configuration. We assume a dense source sampling and target signals that arrive at near‐vertical propagation angles. First, the data are preconditioned by applying synthetic‐aperture‐source filters in the common receiver domain. Virtual source redatuming is carried out for the multi‐component recordings individually, followed by an intermediate deconvolution step. After this specific pre‐processing, we show that the downgoing and upgoing constituents of the wavefields can be separated without knowledge of the medium parameters, the source wavelet, or sensor characteristics. As a final step, free‐surface multiples can be eliminated by multi‐dimensional deconvolution of the upgoing fields with the downgoing fields. 相似文献