全文获取类型
收费全文 | 691篇 |
免费 | 27篇 |
国内免费 | 15篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 26篇 |
地球物理 | 165篇 |
地质学 | 357篇 |
海洋学 | 35篇 |
天文学 | 69篇 |
综合类 | 20篇 |
自然地理 | 32篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 20篇 |
2020年 | 29篇 |
2019年 | 23篇 |
2018年 | 71篇 |
2017年 | 53篇 |
2016年 | 70篇 |
2015年 | 36篇 |
2014年 | 56篇 |
2013年 | 75篇 |
2012年 | 30篇 |
2011年 | 39篇 |
2010年 | 35篇 |
2009年 | 28篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有733条查询结果,搜索用时 15 毫秒
681.
Hamid Zekri Ahmad Reza Mokhtari David R. Cohen 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(7):1947-1960
Common multivariate clustering techniques are ineffective in identifying subtle patterns of correlation, and clustering of variables or samples within complex geochemical datasets. This study compares the combination of singular value decomposition (SVD) and semi discrete decomposition (SDD), with that of hierarchical cluster analysis (HCA), to examine patterns within a multielement soil geochemical dataset from an agricultural area in the vicinity of Pb–Zn mining operations in central Iran. SVD was used to both identify patterns of correlation between variables and samples and to “denoise” the data, and SDD to simultaneously cluster the samples and variables. The results reveal various spatial associations of mining waste-associated metals As, Ba, Pb and Zn, and within the remaining elements whose distribution is largely controlled by the major oxides. SVD–SDD was found to be superior to HCA, in its ability to detect subtle clusters in soil geochemistry indicative of mine-related contamination in the study area. 相似文献
682.
Siavash?SoroushianEmail author E.?“Manos”?Maragakis Arash?E.?Zaghi Esmaeel?Rahmanishamsi Ahmad?M.?Itani Gokhan?Pekcan 《地震工程与工程振动(英文版)》2016,15(1):19-29
A full-scale, two-story, two-by-one bay, steel braced-frame was subjected to a number of unidirectional ground motions using three shake tables at the UNR-NEES site. The test-bed frame was designed to study the seismic performance of nonstructural systems including steel-framed gypsum partition walls, suspended ceilings and fire sprinkler systems. The frame can be configured to perform as an elastic or inelastic system to generate large floor accelerations or large inter story drift, respectively. In this study, the dynamic performance of the linear and nonlinear test-beds was comprehensively studied. The seismic performance of nonstructural systems installed in the linear and nonlinear test-beds were assessed during extreme excitations. In addition, the dynamic interactions of the test-bed and installed nonstructural systems are investigated. 相似文献
683.
Muhammad Sadiq Carl C. Tscherning Zulfiqar Ahmad 《Studia Geophysica et Geodaetica》2009,53(3):375-388
This paper deals with the analysis of gravity anomaly and precise levelling in conjunction with GPS-Levelling data for the
computation of a gravimetric geoid and an estimate of the height system bias parameter No for the vertical datum in Pakistan by means of least squares collocation technique. The long term objective is to obtain
a regional geoid (or quasi-geoid) modeling using a combination of local data with a high degree and order Earth gravity model
(EGM) and to determine a bias (if there is one) with respect to a global mean sea surface. An application of collocation with
the optimal covariance parameters has facilitated to achieve gravimetric height anomalies in a global geocentric datum. Residual
terrain modeling (RTM) technique has been used in combination with the EGM96 for the reduction and smoothing of the gravity
data. A value for the bias parameter No has been estimated with reference to the local GPS-Levelling datum that appears to be 0.705 m with 0.07 m mean square error.
The gravimetric height anomalies were compared with height anomalies obtained from GPS-Levelling stations using least square
collocation with and without bias adjustment. The bias adjustment minimizes the difference between the gravimetric height
anomalies with respect to residual GPS-Levelling data and the standard deviation of the differences drops from 35 cm to 2.6
cm. The results of this study suggest that No adjustment may be a good alternative for the fitting of the final gravimetric geoid as is generally done when using FFT methods. 相似文献
684.
Noor Azlinda Ahmad M. Fernando Z.A. Baharudin M. Rahman V. Cooray Ziad Saleh Joseph R. Dwyer Hamid K. Rassoul 《Journal of Atmospheric and Solar》2010,72(2-3):143-150
In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as ‘small’, ‘medium’ and ‘large’, depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same. 相似文献
685.
Wan Saime Wan Ngah Noorul Farhana Md Ariff Azhan Hashim Megat Ahmad Kamal Megat Hanafiah 《洁净——土壤、空气、水》2010,38(4):394-400
The removal of Malachite green (MG) from aqueous solutions by cross‐linked chitosan coated bentonite (CCB) beads was investigated and the CCB beads were characterized by Fourier Transform Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and X‐ray diffraction (XRD) analysis. Solubility and swelling tests were performed in order to determine the stability of the CCB beads in acidic solution, basic solution and distilled water. The amount of MG adsorbed was shown to be influenced by the initial pH of the solution, contact time and the initial MG concentration. A kinetic study indicated that a pseudo‐second‐order model agreed well with the experimental data. From the Langmuir isotherm model, the maximum adsorption capacity of MG was found to be 435.0 mg g–1. Desorption tests were carried out at different concentrations of EDTA, H2SO4 and NaOH. However, all desorbing solutions showed zero recovery of MG at all concentrations. 相似文献
686.
Ahmad Neyamadpour W. A. T. Wan Abdullah Samsudin Taib 《Studia Geophysica et Geodaetica》2010,54(2):299-311
The objective of this paper is to investigate the applicability of four-electrode arrays in 3D electrical resistivity imaging
survey. A 3D resistivity imaging survey was carried out along fourteen parallel lines using dipole-dipole, Wenner-Schlumberger,
and Wenner arrays with 2 m minimum electrode spacings. Roll-along measurements using a line spacing of 1 m were carried out
covering a grid of 20 × 14 electrodes. The 3D least squares algorithm, based on the robust inversion method, was used in the
inversion of the 3D apparent resistivity data sets. The results show that the 3D electrical resistivity imaging survey using
the Wenner-Schlumberger and the dipole-dipole arrays, or the Wenner and the dipole-dipole arrays, in combination with an appropriate
3D inversion method, can be highly useful when the site conditions do not allow using the pole-pole or pole-dipole arrays. 相似文献
687.
Majid Dehghani Bahram Saghafian Firoozeh Rivaz Ahmad Khodadadi 《Arabian Journal of Geosciences》2017,10(12):266
In this study, application of a class of stochastic dynamic models and a class of artificial intelligence model is reported for the forecasting of real-time hydrological droughts in the Black River basin in the USA. For this purpose, the Standardized Hydrological Drought Index (SHDI) was adopted in different time scales to represent the hydrological drought index. Six probability distribution functions (PDF) were fitted to the discharge time series to obtain the best fit for SHDI calculation. Then, a dynamic linear spatio-temporal model (DLSTM) and artificial neural network (ANN) were used to forecast SHDI. Although results indicated that both models were able to forecast SHDI in different time scales, the DLSTM was far superior in longer lead times. The DLSTM could forecast SHDI up to 6 months ahead while ANN was only capable of forecasting SHDI up to 2 months ahead appropriately. For short lead times (1–6 months), the DLSTM has performed nearly perfect in test phase and CE oscillates between 0.97 and 0.86 while for ANN modeling, CE is between 0.72 and 0.07. However, the performance of DLSTM and ANN reduced considerably in medium lead times (7–12 months). Overall, the DLSTM is a powerful tool for appropriately forecasting SHDI at short time scales; a major advantage required for drought early warning systems. 相似文献
688.
Mehdi Veiskarami Mir Ahmad Lashteh Neshaei Mehran Karimpour Fard Tina Pourramezan 《Marine Georesources & Geotechnology》2017,35(1):42-51
Marine structures which cover a wide range of offshore and onshore structures are often subjected to different external and internal forces against which a proper design should be performed. Among many, breakwaters constructed over a relatively loose agglomerate of granular soils are much prone to deep seated failure extended beneath the foundation. This type of failure has been given less attention in conventional design approaches. Stability analysis of such failures is the main subject of this research which includes both the static and the seismic stability of breakwaters over granular marine soils. As the subsoil strata in sea beds often comprise loose sand deposits, it is more convenient to assume a rather small angle of dilation, at least at failure, which certainly reduces the potential to resist geotechnical instabilities. The method of stress characteristics along with slight modifications to handle this issue has been used to assess the overall stability of breakwaters against deep seated failures. Investigations revealed that while even under static condition, there is certain potential of failure, under seismic condition, the risk is quite very high. A series of design charts are also developed presenting the factor of stability as a measure of safety against such failure. 相似文献
689.
The Asmari Formation consists of shallow marine sedimentary rocks deposited on ramp setting .Lar-ger benthic foraminifera collected from Asmri Formation are dominated by hyaline and porcelanouse forms , in-cluding Amphistegina, Nummulites, Archaias, Astrotrillina, Miogypsinella, Miogypsinoides, Lepidocyclina, Operculina, Spiroclypeous and Miliolids.The presence of Nummulites cf.vascus in the lower part of the forma-tion allows the age to be determined as Rupelian .The occurrence of Borelis pygmae is an index taxon of the Ru-pelian-Chattian and indicates Early Chattian of SBZ 21-22 in the study section .The first appearance of Mio-gypsinella akadagensis shows Late Chattian ( SBZ 23) and defines the upper boundary of the SBZ 21-22.The new data are the first evidences showing that the shallow marine Asmari Formation is attributed to Oligocene (Rupelian-Chattian) age for this region. 相似文献
690.
Michael Fuchs Adnan A. Awan Sardar S. Akhtar Ijaz Ahmad Simon Sadiq Asif Razzak Naghmah Haider 《山地科学学报》2017,14(5):948-963
In the frame of landslide susceptibility assessment, a spectral library was created to support the identification of materials confined to a particular region using remote sensing images. This library, called Pakistan spectral library (pklib) version 0.1, contains the analysis data of sixty rock samples taken in the Balakot region in Northern Pakistan. The spectral library is implemented as SQLite database. Structure and naming are inspired by the convention system of the ASTER Spectral Library. Usability, application and benefit of the pklib were evaluated and depicted taking two approaches, the multivariate and the spectral based. The spectral information were used to create indices. The indices were applied to Landsat and ASTER data to support the spatial delineation of outcropping rock sequences in stratigraphic formations. The application of the indices introduced in this paper helps to identify spots where specific lithological characteristics occur. Especially in areas with sparse or missing detailed geological mapping, the spectral discrimination via remote sensing data can speed up the survey. The library can be used not only to support the improvement of factor maps for landslide susceptibility analysis, but also to provide a geoscientific basis to further analyze the lithological spot in numerous regions in the Hindu Kush. 相似文献