全文获取类型
收费全文 | 152篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 4篇 |
地球物理 | 55篇 |
地质学 | 66篇 |
海洋学 | 21篇 |
天文学 | 9篇 |
综合类 | 1篇 |
自然地理 | 2篇 |
出版年
2024年 | 1篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 12篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 8篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 7篇 |
2007年 | 7篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 1篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有166条查询结果,搜索用时 421 毫秒
151.
Hoyle F. Wickramasinghe N. C. Al-Mufti S. Karim L. M. 《Astrophysics and Space Science》1985,114(2):303-309
Whereas data for the extinction of starlight in the visible show the interstellar grains must be partially hollow, data in the ultraviolet show the vesicular interiors must be irregular. In particular, the absorbing materials responsible for excess extinction over a band centred at 2175 Å are required to be concentrated in irregularly distributed chromophores with dimensions of the order of or less than one-tenth of the whole grain.The laboratory measurements of absorptions produced by microorganisms agree very closely with astronomical observations for a large number of early-type stars. Since the interior structures of microorganisms are indeed highly irregular, the laboratory measurements made with microorganisms suspended in a fluid, can reasonably be transferred to microorganismsin vacuo.The characteristic dimension for the scattering of visible light by rod-like grains has in the past been taken to be rod diameters. An alternate interpretation with the characteristic dimension taken instead to be rod-oengths may turn out to have advantages in respect of data in the ultraviolet, as well as agreeing in scale with bacteria-like objects found in meteorites, and possibly also, in particles entering the Earth's atmosphere from the zodiacal cloud. 相似文献
152.
153.
The Nador lagoon ecosystem (North-East of Morocco) displays a major socioeconomic interest. In fact, it is essential to evaluate consequences of anthropogenic activities in the lagoon especially by organic matter studies (nature and distribution) in the sedimentary compartment. Surface sediments show variable rates in total organic carbon and in sulfur, high in some cases (7.5 and 1.8% respectively). These high contents are recorded in the center of the lagoon. Their distributions are controlled by the hydrodynamism and the anthropogenic degree. The molecular biomarkers analyses and especially n-alkanes distribution reveal: a zone of marine influence; and a zone of continental influence. The occurrence of pentacyclic triterpanes with a typical distribution of a thermally mature organic matter reveals a contamination due to petroleum products in the entire lagoon except for the center. Coprostanol occurrence near cities indicates wastewater effluents inputs and reducing conditions underlined by high values of stanols/sterol ratios. Thus, the organic contamination (petroleum by-products and wastewater effluents) occurs in the vicinity of the cities whereas the littoral edge and center remain weakly affected by these contaminations. 相似文献
154.
Throughout the United Arab Emirates, the sand differs in color and composition, depending on its source. This study reports
the collection of 70 sediment samples from coastal district areas of seven emirates in the United Arab Emirates, namely, Abu
Dhabi, Dubai, Sharjah, Ajman, Umm Al Quwain, Ras Al-Khaimah, and Fujairah for the purposes of spectroscopic characterization
and color justification. The compositions of these naturally occurring sand samples obtained were tested using different spectroscopic
techniques. The techniques included both destructive instrumentation as scanning electron microscopy with energy dispersive
X-ray analysis and X-ray powder diffraction and nondestructive instrumentation as confocal Raman microscopy. It was concluded
that the sand can acquire various colors ranging from white to black due to the presence of certain chemical compounds. 相似文献
155.
Simulating spatiotemporal variability of blue and green water resources availability with uncertainty analysis 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Depeng Zuo Zongxue Xu Dingzhi Peng Jinxi Song Lei Cheng Shouke Wei Karim C. Abbaspour Hong Yang 《水文研究》2015,29(8):1942-1955
Due to rapid socioeconomic development, continuous population growth and urbanization, the world is facing a severe shortage of fresh water, particularly in arid and semi‐arid regions. A lack of water will put pressure on agricultural production, water pollution, as well as eco‐environmental degradation. Traditional water resources assessment mainly focused on blue water, ignoring green water. Therefore, analysis of spatiotemporal distribution of blue and green water resources in arid and semi‐arid regions is of great significance for water resources planning and management, especially for harmonizing agricultural water use and eco‐environmental water requirements. This study applied the Soil and Water Assessment Tool (SWAT) model and the Sequential Uncertainty Fitting algorithm (SUFI‐2) to calibrate and validate the SWAT model based on river discharges in the Wei River, the largest tributary of the Yellow River in China. Uncertainty analysis was also performed to quantify the blue and green water resources availability at different spatial scales. The results showed that most parts of the Wei River basin (WRB) experienced a decrease in blue water resources during the recent 50 years with a minimum value in the 1990s. The decrease is particularly significant in the most southern part of the WRB (the Guanzhong Plain), one of the most important grain production bases in China. Variations of green water flow and green water storage were relatively small both on spatial and temporal dimensions. This study provides strategic information for optimal utilization of water resources in arid and semi‐arid river basin. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
156.
Ground motion selection for scenario ruptures using the generalised conditional intensity measure (GCIM) method 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《地震工程与结构动力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper, the generalised conditional intensity measure (GCIM) method is extended to ground motion selection for scenario earthquake ruptures. The selection algorithm is based on generating random realisations of the considered intensity measure (IM) distributions for a specific rupture scenario and then finding the prospective ground motions that best fit the realisations using an optimal amplitude scale factor. Using different rupture scenarios and site conditions, two important aspects of the GCIM methodology are scrutinised: (i) different weight vectors for the various IMs considered and (ii) quantifying the importance of replicate selections for ensembles with different numbers of desired ground motions. It is demonstrated that considering only spectral acceleration (SA) ordinates in the selection process, as is common in many conventional selection procedures, may result in selected motions with a biased representation for duration and cumulative ground motion effects. In contrast, considering IMs other than SA ordinates (in particular, significant duration, cumulative absolute velocity, and Arias intensity) results in ensembles with an appropriate representation of these IMs, without a practically significant effect on SA ordinates. The benefit of conducting replicate selections to obtain a suite of motions with an improved representation for the distribution of the considered IMs is demonstrated, and a minimum number of replicates are suggested for different ground motion ensemble sizes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
157.
A pushover procedure with a load pattern based on the height-wise distribution of the combined modal story shear and torsional moment is proposed to estimate the seismic response of 3D asymmetric-plan building frames. Contribution of the higher modes and torsional response of asymmetric-plan buildings are incorporated into the proposed load pattern. The proposed pushover method is a single-run procedure, which enables tracing the nonlinear response of the structure during the analysis and averts the elusiveness of conducting multiple pushover analyses. The proposed method has been used to estimate the response of two moment-resisting building frames with 9 and 20 stories. The obtained results indicate the appropriate accuracy and efficiency of the proposed procedure in estimating the trend of the drift profiles of the structures resulted from nonlinear time history analyses. 相似文献
158.
Hydrological models have been widely used for water resources management. Successful application of hydrological models depends on careful calibration and uncertainty analysis. Spatial unit of water balance calculations may differ widely in different models from grids to hydrological response units (HRU). The Soil and Water Assessment Tool (SWAT) software uses HRU as the spatial unit. SWAT simulates hydrological processes at sub-basin level by deriving HRUs by thresholding areas of soil type, land use, and slope combinations. This may ignore some important areas, which may have great impact on hydrological processes in the watershed. In this study, a hierarchical HRU approach was developed in order to increase model performance and reduce computational complexity simultaneously. For hierarchical optimization, HRUs are first divided into two-HRU types and are optimized with respect to some relevant influence parameters. Then, each HRU is further divided into two. Each child HRU inherits the optimum parameter values of the parent HRU as its initial value. This approach decreases the total calibration time while obtaining a better result. The performance of the hierarchical methodology is demonstrated on two basins, namely Sarisu-Eylikler and Namazgah Dam Lake Basins in Turkey. In Sarisu-Eylikler, we obtained good results by a combination of curve number (CN2), soil hydraulic conductivity, and slope for generating HRUs, while in Namazgah use of only CN2 gave better results. 相似文献
159.
Karim Saheb Ettabaa Manel Ben Salem Med Salim Bouhlel 《Arabian Journal of Geosciences》2017,10(18):412
Segmentation-based anomaly detectors proceeds to the clustering of the hyperspectral image as a first step. However, most of the well-known clustering methods cluster anomalous pixels as a part of the background. This paper presents a new hyperspectral image clustering approach based on the betweenness centrality measure. The proposed approach starts by the construction of an adaptive spatial and spectral neighborhood for each pixel. This neighborhood is based on the selection of the nearest spectral and spatial neighbors in multiple windows around each pixel to allow well-suited representation of the image features. In the next step, this neighborhood is clustered based on the edge betweenness measure algorithm that splits the image into regions sharing similar features. This approach (1) allows the reduction of intercluster relationship, (2) favors intracluster relations, and (3) preserves small clusters that can hold anomalous pixels. Experimental results show that the proposed approach is efficient for clustering and overcomes the state of the art approaches. 相似文献
160.
Ahmed Makaoui Abdelattif Orbi Karim Hilmi Soukaina Zizah Jamila Larissi Mohammed Talbi 《Comptes Rendus Geoscience》2005,337(16):1518
The pelagic ecosystem of the Moroccan Atlantic coast is influenced by the spatiotemporal variability of upwelling. The changes in the physicochemical and biological parameters as well as their interrelationship and regrouping by the principal components analysis allowed us to subdivide the Atlantic coast in four active areas: two areas located at the north of Cape Juby (28°N), characterised by a summery activity and two areas located at the south, active permanently, with a variable intensity. To cite this article: A. Makaoui et al., C. R. Geoscience 337 (2005). 相似文献