全文获取类型
收费全文 | 1057篇 |
免费 | 37篇 |
国内免费 | 29篇 |
专业分类
测绘学 | 52篇 |
大气科学 | 50篇 |
地球物理 | 199篇 |
地质学 | 656篇 |
海洋学 | 39篇 |
天文学 | 75篇 |
综合类 | 10篇 |
自然地理 | 42篇 |
出版年
2023年 | 5篇 |
2022年 | 37篇 |
2021年 | 46篇 |
2020年 | 34篇 |
2019年 | 28篇 |
2018年 | 83篇 |
2017年 | 89篇 |
2016年 | 69篇 |
2015年 | 46篇 |
2014年 | 77篇 |
2013年 | 93篇 |
2012年 | 44篇 |
2011年 | 56篇 |
2010年 | 41篇 |
2009年 | 41篇 |
2008年 | 36篇 |
2007年 | 26篇 |
2006年 | 31篇 |
2005年 | 26篇 |
2004年 | 19篇 |
2003年 | 17篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有1123条查询结果,搜索用时 15 毫秒
991.
Bremer Leah L. Elshall Ahmed S. Wada Christopher A. Brewington Laura Delevaux Jade M.S. El-Kadi Aly I. Voss Clifford I. Burnett Kimberly M. 《Hydrogeology Journal》2021,29(5):1749-1765
Hydrogeology Journal - Groundwater sustainability initiatives, including sustainable yield and watershed policy protection policies, are growing globally in response to increasing demand for... 相似文献
992.
Stochastic analyses of maximum daily rainfall series recorded at two stations across the Mediterranean Sea 总被引:1,自引:1,他引:0
Independence, stationarity, homogeneity, trend, and periodicity tests are applied on 48-year-long complete and 79-year-long incomplete maximum daily rainfall series recorded at Alexandria, Egypt, and on 61-year-long maximum daily rainfall series recorded at Antalya, Turkey, which are located at the southeastern and northeastern shores of the Mediterranean Sea. The results indicate no significant trend and no periodicity in mean, and both series are independent and homogeneous. Linear regression trend test applied to the 10 % highest part of the Alexandria series indicated a significant increasing trend. Next, frequency analysis is applied on each of these series by the probability distributions of Gumbel, general extreme-values, three-parameter log-normal, Pearson-3, log-Pearson-3, log-logistic, generalized Pareto, and Wakeby. The distributions, except for the generalized Pareto and Wakeby, pass the χ 2 and Kolmogorov–Smirnov goodness-of-fit tests at 90 % probability. By visual inspection of the plots of histograms together with the probability density functions, and by the results of the χ 2, Kolmogorov–Smirnov, and probability plot correlation coefficient tests, the general extreme-value distribution whose parameters are computed by the method of probability-weighted moments is deemed to be suitable for these two maximum daily rainfall series. 相似文献
993.
994.
Ahmed Melegy 《Geotechnical and Geological Engineering》2010,28(5):549-558
Activated carbons have been proven to be effective adsorbents for the removal of Pb (II) and Zn (II) dissolved in aqueous
media. The study of adsorption of Pb (II) and Zn (II) on two different size fractions from a composite coal sample of Maghara
coal mine, C63 (63–125 μm) and C250 (125–250 μm) is presented in this paper. C63 and C250 were treated in water solutions of 50 mM lead and zinc acetates. X-ray photoelectron spectroscopy (XPS) was used to characterize
the starting and treated coal surfaces. The high surface area and surface functional groups (carboxy and phenolic) enable
activated bituminous coal of Maghara to act as efficient adsorbents for removing dissolved Pb (II) and Zn (II) in alkaline
medium. 相似文献
995.
Sid Ahmed Benahmed Daho 《Comptes Rendus Geoscience》2010,342(2):87-94
The main purpose of this article is to discuss the use of GPS positioning together with a gravimetrically determined geoid, for deriving orthometric heights in the North of Algeria, for which a limited number of GPS stations with known orthometric heights are available, and to check, by the same opportunity, the possibility of substituting the classical spirit levelling. For this work, 247 GPS stations which are homogeneously distributed and collected from the international TYRGEONET project, as well as the local GPS/Levelling surveys, have been used. The GPS/Levelling geoidal heights are obtained by connecting the points to the levelling network while gravimetric geoidal heights were interpolated from the geoid model computed by the Geodetic Laboratory of the National Centre of Spatial Techniques from gravity data supplied by BGI. However, and in order to minimise the discordances, systematic errors and datum inconsistencies between the available height data sets, we have tested two parametric models of corrector surface: a four parameter transformation and a third polynomial model are used to find the adequate functional representation of the correction that should be applied to the gravimetric geoid. The comparisons based on these GPS campaigns prove that a good fit between the geoid model and GPS/levelling data has been reached when the third order polynomial was used as corrector surface and that the orthometric heights can be deducted from GPS observations with an accuracy acceptable for the low order levelling network densification. In addition, the adopted methodology has been also applied for the altimetric auscultation of a storage reservoir situated at 40 km from the town of Oran. The comparison between the computed orthometric heights and observed ones allowed us to affirm that the alternative of levelling by GPS is attractive for this auscultation. 相似文献
996.
Ahmed Saif Al-Mikhlafi 《Arabian Journal of Geosciences》2010,3(2):193-205
One hundred thirty boreholes of volcanic aquifers in rural Yemen Highland Groundwaters (YHGs) were chemically investigated to assess the suitability of water for drinking. Focus is to identify inorganic constituents of significant risk to health that occur in groundwaters of this area. Results showed that a number of boreholes contain, apart from fluoride, levels of nitrate, some heavy metals, total dissolved solids, and sulfates that could pose a health risk for consumers. The lateral variations of major ions with depth varied within the same aquifer based on the dynamic equilibrium of groundwater and hydrogeological conditions. The main inorganic groundwater contaminant in volcanic YHG is fluoride which is attributed to groundwater lithology and water type. Fluoride appears high in Ca-poor groundwater and where cation exchanges of Ca for Na are dominant. High F concentration in YHG is an extension of East African fluoride-rich groundwater. Majority of tube wells show that Fe concentration exceeds WHO guideline many folds. Much of the iron and manganese in groundwaters are naturally occurring, since the source rocks are enriched in ferromagnesian minerals. NO 3 ? and Cl? concentrations that have been detected in some wells may indicate sewage and/or agricultural runoff. Elevated concentration of chemical constituents in groundwater is a sign of groundwater degradation. 相似文献
997.
Geochemical stream sediments survey was conducted in the northwestern part of Wadi Allaqi area, Eastern Desert, Egypt. The
area comprises Precambrian metasediments, intermediate metavolcanics, gabbro, and serpentinites, with intrusive masses of
granites and quartz-porphyry and invaded by several quartz veins. The −1.0-mm size fraction is analyzed for As, Cu, S, Mo,
Pb, Zn, Co, Ni, Rb, Ba, Sr, Nb, V, U, Th, Cr, Zr, La, Ce, Nd, and Y. The geochemical survey is supported by heavy minerals
study in the −0.125 + 0.0625-mm fraction. The geochemical data were statistically investigated using Q-mode cluster and R-mode
factor analyses as well as the enrichment factor. Factors 1 (Zr, Nb, Nd, La, and Y), 2 (V, Sr, and Zn), and 4 (Ba and Rb)
are mainly controlled by the lithological characters of the rocks hosting Au-sulfide mineralizations and their accompanied
hydrothermal alteration zones. In the mineralization Factor 3 (Cu, S, As, Ce, and Mo), arsenic, Cu, S, and Mo are direct indicators,
while Ce is indirect one for the Au-sulfide mineralizations. The Cu–S–As–Mo association with Pb and Zn anomalies in the stream
sediments draining the quartz-porphyry point to its porphyry copper mineralization. Cobalt and Ni (Factor 5) are pathfinders
for the Fe- and Cu-sulfides, whereas Zn and Pb of Factor 8 are additional pathfinders for the Au-sulfide mineralizations.
The southern stream sediments having high U/Th ratios with U–Mo association and draining granites traversed by pegmatites,
as well as the stream sediments draining Um Garayat area and the quartz-porphyry stock with high abundance of monazite, zircon,
epidote, sphene, and ilmenite, could signify sources of U and Th (Factor 7). Two watershed areas have distinct enrichment
factors for arsenic suggesting unexplored extensions of Au-sulfide mineralization linked to the Allaqi shear-zone. The enrichment
of the mineralization Factor 3 in the drainage system is mainly controlled by the prevailed mechanical dispersion for the
hosting heavy minerals in such arid region with minor role of hydromorphic dispersion. The chemistry and mineralogy of the
stream sediments are evidently allied to the drained bedrocks and their hosted mineralizations that signify a promising area
for detailed exploration. 相似文献
998.
999.
Asuri Sridharan Ahmed El-Shafei Norihiko Miura 《Marine Georesources & Geotechnology》2013,31(1):21-50
The soft clay of Ariake Bay, in western Kyushu, Japan covers several hundred square kilometers. Ariake clay consists of the principal clay minerals namely smectite, illite, kaolinite and vermiculite, and other minerals in lesser quantity. The percentage of the principal clay mineral can vary significantly. The percent clay size fraction and the salt concentration can also vary significantly. In view of the importance of undrained shear strength in geotechnical engineering practice, its behavior has been studied with respect to variation in salt concentration. Basically two mechanisms control the undrained strength in clays, namely (a) cohesion or undrained strength is due to the net interparticle attractive forces, or (b) cohesion is due to the viscous nature of the double layer water. Concept (a) operates primarily for kaolinitic soil, and concept (b) dominates primarily for montmorillonitic soils. In Ariake clay, different clay minerals with different exchangeable cations and varying ion concentration in the pore water and varying nonclay size fraction are present. In view of this while both concepts (a) and (b) can coexist and operate simultaneously, one of the mechanisms dominates. For Isahaya clay, concept (a), factors responsible for an increase in level of flocculation and attractive forces result in higher undrained strength. Increase in salt concentration increases the remolded undrained strength at any moisture content. For Kubota and Kawazoe clays, concept (b) factors responsible for an expansion of diffuse double layer thickness, resulting in higher viscous resistance, increase the undrained shear strength, that is, as concentration decreases, the undrained strength increases at any moisture content. The liquid limit of Isahaya clay increases with increase in ion concentration and a marginal decrease is seen for both Kubota and Kawazoe clays, and their behavior has been explained satisfactorily. 相似文献
1000.
Noureddine Della Mostefa Belkhatir Ahmed Arab Jean Canou Jean-Claude Dupla 《Marine Georesources & Geotechnology》2013,31(6):487-495
A series of undrained monotonic triaxial compression tests were performed on natural, medium-dense (relative density (RD) = 50%) Chlef sand containing 0.5% of non-plastic fines, under different confining pressures of 50 kPa, 100 kPa, and 200 kPa. This article focuses on distinctive states of the monotonic undrained response of sands, namely the critical state, the phase transformation state, the quasi-steady state, and the state of undrained instability (onset of flow liquefaction). Specimens were prepared using dry funnel pluviation and wet deposition to investigate the effect of the initial sand fabric on these states. The present data suggest that the initial fabric of the sand appears to have a significant effect on the undrained behavior in the early stages of shearing, with its influence vanishing at large strains. Wet deposition specimens demonstrate considerably larger undrained instability state strength than their dry funnel pluviation counterparts, and a unique critical state locus is reached by both dry funnel pluviation and wet deposition. 相似文献