全文获取类型
| 收费全文 | 233篇 |
| 免费 | 12篇 |
| 国内免费 | 12篇 |
专业分类
| 测绘学 | 24篇 |
| 大气科学 | 14篇 |
| 地球物理 | 89篇 |
| 地质学 | 103篇 |
| 海洋学 | 7篇 |
| 天文学 | 1篇 |
| 综合类 | 4篇 |
| 自然地理 | 15篇 |
出版年
| 2024年 | 1篇 |
| 2023年 | 2篇 |
| 2022年 | 12篇 |
| 2021年 | 13篇 |
| 2020年 | 18篇 |
| 2019年 | 10篇 |
| 2018年 | 30篇 |
| 2017年 | 24篇 |
| 2016年 | 30篇 |
| 2015年 | 15篇 |
| 2014年 | 26篇 |
| 2013年 | 30篇 |
| 2012年 | 11篇 |
| 2011年 | 12篇 |
| 2010年 | 7篇 |
| 2009年 | 3篇 |
| 2008年 | 3篇 |
| 2006年 | 3篇 |
| 2005年 | 1篇 |
| 2004年 | 1篇 |
| 2002年 | 1篇 |
| 2001年 | 1篇 |
| 2000年 | 2篇 |
| 1990年 | 1篇 |
排序方式： 共有257条查询结果，搜索用时 343 毫秒
101.
ABSTRACTThe problem of estimation of suspended load carried by a river is an important topic for many water resources projects. Conventional estimation methods are based on the assumption of exact observations. In practice, however, a major source of natural uncertainty is due to imprecise measurements and/or imprecise relationships between variables. In this paper, using the Multivariate Adaptive Regression Splines (MARS) technique, a novel fuzzy regression model for imprecise response and crisp explanatory variables is presented. The investigated fuzzy regression model is applied to forecast suspended load by discharge based on two real-world datasets. The accuracy of the proposed method is compared with two well-known parametric fuzzy regression models, namely, the fuzzy least-absolutes model and the fuzzy least-squares model. The comparison results reveal that the MARS-fuzzy regression model performs better than the other models in suspended load estimation for the particular datasets. This comparison is done based on four goodness-of-fit criteria: the criterion based on similarity measure, the criterion based on absolute errors and the two objective functions of the fuzzy least-absolutes model and the fuzzy least-squares model. The proposed model is general and can be used for modelling natural phenomena whose available observations are reported as imprecise rather than crisp.
Editor D. Koutsoyiannis; Associate editor H. Aksoy 相似文献
102.
Ali Olad Ali Reza Amani‐Ghadim Mir Saeed Seyed Dorraji Mohammad Hosein Rasoulifard 《洁净——土壤、空气、水》2010,38(4):401-408
The removal of Alphazurine FG (AF) dye from water by an electrocoagulation process has been studied. The effect of some operational parameters, such as anode material, current density, initial dye concentration, pH of solution, conductivity, and inter‐electrode distance, on the removal efficiency was investigated. Iron and aluminum were used as anodes in the electrocoagulation cell. It was found that the efficiency of the iron anode was better than that of the aluminum anode for AF removal. The factors that affected the removal efficiency were the current density and the initial dye concentration. The removal efficiency increased from about 35% at 25 A m–2 to about 97% at 100 A m–2, during 4 min of electrocoagulation. The results exhibited pseudo‐first‐order kinetics for AF removal by electrocoagulation. In addition, a mathematical model was successfully established for predicting the removal efficiency. A comparison between the model results and experimental data gave a high correlation coefficient (R2 = 0.9925), which indicates that the model is able to predict the removal efficiency of AF. 相似文献
103.
In this experimental study,the effect of suspended sediment concentration on the characteristics of a submerged hydraulic jump in a rectangular channel has been investigated,based on the sediment conce... 相似文献
104.
Spatial distribution and biodiversity of macrofauna in the southeast of the Caspian Sea, Gorgan Bay in relation to environmental conditions 总被引：1，自引：0，他引：1
Mehrshad Taheri Maryam Yazdani Foshtomi Majid Noranian Seyed Sahab Mira 《Ocean Science Journal》2012,47(2):113-122
Spatial distribution and biodiversity of macrofauna in the Gorgan Bay, southeast of the Caspian Sea, were studied at fifteen stations in June 2010. Also, depth, temperature, salinity, dissolved oxygen, total organic matter content and sediment particle size were measured in each station. A total 3,356 individuals belonged to eight families and ten species were identified. Polychaeta were numerically dominated groups and Streblospio gynobranchiata, was constant and dominant species with 60.28% of total individuals but Bivalvia with four species had highest species number, though the density of them were low. The maximum density (4,500 ind/m2) was obtained at station 1 while the minimum (411 ind/m2) was observed at station 6. There was not significant correlation between the density of macrofauna with all environmental conditions. In total, six feeding group were considered but surface deposit feeder and deposit feeder were dominant in all stations. The maximum mean species number, diversity, richness, and evenness were obtained, 6.33, 1.46, 1.38 and 0.87, respectively. Based on the M-AMBI and the AMBI classification it seems that bentic environment in Gorgan Bay was not bad but the results of Shannon-Wiener, Margalef and Simpson indices the results were vice versa. In general, the values of the mentioned indices decreased from the western to the eastern part of the bay. Furthermore, the nonmetric multidimensional scaling (nMDS) showed that the structure of the macrofaunal assemblages was divides to six groups. 相似文献
105.
伊朗锡斯坦地区沙漠灾害区划(英文) 总被引：1，自引：1，他引：0
Desertification process as a great problem affects most of the countries in the world.This process has a high rate in arid and semiarid areas.Today,human societies are encountering the desertification phenomenon as a serious problem which causes various irreparable damages to economic and social sectors.In order to assess desertification results in production of different regional models for their application in another region the indices should be re-investigated and adjusted to local conditions.Several models have been developed for desertification evaluation.The present study,attempts to assess quantitatively the desertification process has in an area located at Sistan plain of Iran(Niatak region as a case study) by using Modified MEDALUS method.The obtained results indicated that of the whole studied region(comprising 4819.6 acres),2651.56 acres(55%) are located in medium desertification intensity class,1269.48 acres(26.34%) are positioned in severe desertification intensity class,and 898.54 acres(18.64%) are placed in vary severe desertification intensity class. 相似文献
106.
107.
108.
A multi-technique approach for characterizing the SVN49 signal anomaly, part 1: receiver tracking and IQ constellation 总被引：3，自引：1，他引：2
André Hauschild Oliver Montenbruck Steffen Thoelert Stefan Erker Michael Meurer Javad Ashjaee 《GPS Solutions》2012,16(1):19-28
A characterization of the signal anomaly of SVN49 is presented. A mathematical model is developed to relate the observed multipath
to the internal signal reflection. The analyses provided are based on measurements, which have been collected during a dedicated
tracking campaign with a 30-m dish antenna. Data on the L1 and L2 frequency have been collected with four different receivers.
In addition, IQ samples have been recorded directly with a spectrum analyzer. The multipath combination of the receiver measurements
on L1 and L2 is analyzed to demonstrate the effect of the signal reflections on different correlator spacing. The capability
to suppress the signal reflection with receiver multipath mitigation methods is demonstrated. Finally, preliminary estimates
of the attenuation, delay, and phase shift over elevation are obtained from an IQ sample analysis. 相似文献
109.
Masoumeh Molaei Seyed Hamid Vaziri Morteza Taherpour-Khalil-Abad Jafar Taheri 《Arabian Journal of Geosciences》2017,10(14):317
Neotrocholina Reichel, 1956 is one of the most important benthic foraminifera in Early Cretaceous. Some of the species of this genus are indexes in biostratigraphy especially for this interval (e.g., Neotrocholina friburgensis: Late Barremian–Early Aptian; Neotrocholina aptiensis: Early Aptian). In order to conduct accurate paleontological investigations, sampling from the carbonate units of the Tirgan Formation in Kopet Dagh sedimentary basin is done. According to the occurrence level in the studied stratigraphic sections as well as biometric interpretations, two species of this genus (N. friburgensis and Neotrocholina valdensis) are pointed out. 相似文献
110.
This paper examines the influence of porous media deformation on water-table wave dispersion in an unconfined aquifer using a numerical model which couples Richards’ equation to the poro-elastic model. The study was motivated by the findings of Shoushtari et al. (J Hydrol 533:412–440, 2016) who were unable to reproduce the observed wave dispersion in their sand flume data with either numerical Richards’ equation models (assuming rigid porous media) or existing analytic solutions. The water-table wave dispersion is quantified via the complex wave number extracted from the predicted amplitude and phase profiles. A sensitivity analysis was performed to establish the influence of the main parameters in the poro-elastic model, namely Young’s modulus (E) and Poisson’s ratio (ν). For a short oscillation period (T?=?16.4 s), the phase lag increase rate (k i) is sensitive to the chosen values of E and ν, demonstrating an inverse relationship with both parameters. Changes in the amplitude decay rate (k r), however, were negligible. For a longer oscillation period (T?=?908.6 s), variations in the values of E and ν resulted in only small changes in both k r and k i. In both the short and long period cases, the poro-elastic model is unable to reproduce the observed wave dispersion in the existing laboratory data. Hence porous media deformation cannot explain the additional energy dissipation in the laboratory data. Shoushtari SMH, Cartwright N, Perrochet P, Nielsen P (2016) The effects of oscillation period on groundwater wave dispersion in a sandy unconfined aquifer: sand flume experiments and modelling. J Hydrol 533:412–440. 相似文献