全文获取类型
收费全文 | 439篇 |
免费 | 28篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 10篇 |
地球物理 | 104篇 |
地质学 | 232篇 |
海洋学 | 25篇 |
天文学 | 47篇 |
综合类 | 7篇 |
自然地理 | 39篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 35篇 |
2017年 | 32篇 |
2016年 | 33篇 |
2015年 | 21篇 |
2014年 | 38篇 |
2013年 | 48篇 |
2012年 | 16篇 |
2011年 | 26篇 |
2010年 | 16篇 |
2009年 | 18篇 |
2008年 | 19篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 15 毫秒
1.
The Feiran–Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S1, and is almost everywhere parallel to lithological layering, S0. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S0. S1 formed by coaxial pure shear flattening strain (Z normal to S0, i.e. vertical; with X and Y both extensional and lying in S1). This strain also produced chocolate tablet boudinage of some layers and S1-concordant sills and veins. S1 has a strong stretching lineation L1 with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L1-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F1 folds with hinges parallel to the stretching lineation. F1 fold asymmetry variations do not support previous models involving macroscopic F1 folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran–Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia. 相似文献
2.
Doaa Hassan Youssef 《Journal of Oceanography》2003,59(5):537-544
Concentrations of boron in seawater (from four regions along the Alexandria coastline, subjected to land disposal), brackish
water (Lake Edku) and drains water (e.g. El-Umum Drain) were determined during the period from February to August 2000. Boron
was determined spectrophotometrically by a modified curcumin method. For Lake Edku, boron concentration fluctuated between
0.023 and 0.105 mmol/l. There are several factors that affect the concentration of B in the Lake water: (a) effect of the
drainage water via El-Khairy and Barsiek Drains, (b) utilization of boron by hydrophytes, and (c) water exchange through the
sea-lake connection. It may be concluded that the level of boron in the Lake water cannot be considered a substantial hazard
to the Lake organisms. Boron concentration varied from 0.392 to 0.522 mmol/l in seawater samples and from 0.141 to 0.458 mmol/l
in the sites where the water from the drains (El-Umum Drain and El-Noubaria Canal) mixed with the seawater. The broader variation
of boron (mmol/l)/salinity ratios for seawater samples (0.0106–0.0138) may be due to that the samples were collected from
the upper seawater layers, where contributions from land run-off, atmospheric precipitation and differences in the biota affect
the concentration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
M. Hassan M. A. Haq M. Aslam M. Saleem K. P. Akhtar S. Sarwar Alam 《International Journal of Environmental Science and Technology》2006,2(4):319-325
Twenty four new strains were tested for their yield, quality and Leaf Curl Virus (ClCuV) resistance. NIAB-111/S, NIAB-98 and NIAB-999 were significantly high fruit bearing varieties at 90 days completing 59.54, 48.26 and 46.00% fruiting respectively. Seed cotton yield of VH-142 was highest with 5417 kgha?1 and 52 per plant boll bearing, DNH-57 and NIAB-999 remained second and third with 5234 and 5095 kg ha?1 seed cotton yield, respectively. BH-160 and CRIS-467 were found to be second and third highest boll bearing varieties with 50.97 and 40.20 per plant average bolls respectively. Plant height in CRIS-467, MNH-642 and SLH-224 was significantly higher in comparison to other varieties.NIAB-98, CIM-499 and CIM-506 were found short stature varieties in comparison with other but out of these NIAB-98 and CIM-506 were in high yielding position and CIM-499 was found medium yielder variety. GOT% of MNH-642 remained highest having value of 45.00%. While GOT%. of NIBGE-1, CRIS-168 and CRIS-467 was at lowest position with 35.73, 35.89 and 36.62% respectively. NIAB-111, CIM-499 and BH-160 were at first position in terms of fibre fineness with micronaire values 3.98, 4.00 and 4.07 ìg/inch having fibre length 28.53, 31.38 and 30.23 mm respectively. Out of 26 varieties, 16 varieties resulted maturity index in the range of 85.03% and 90.30% with highest maturity index in case of NIBGE-1 (i.e. 90.30%) followed by NIAB-999 and MNH-642 with 89.55 and 85.5% respectively.CRIS-168, CRIS-468 and CRIS-467 were found viral susceptible. 相似文献
4.
Seismic profiles and well data from the Doukkala basin unravel the structure of the Palaeozoic basement and suggest that this coastal zone of western Morocco was affected by a compressive phase during the Frasnian. This resulted in the formation of upright, plurikilometric folds associated with reverse faults (North Doukkala), and of asymmetrical folds associated with mostly west verging ramps (South Doukkala). Folding involved all pre-Upper Frasnian formations and caused partial or total hiatus of Upper Frasnian–Strunian strata. This event can be correlated with the orogenic phase reported from more internal domains of the Morocco Hercynian belt, where it is referred to as the ‘Bretonne’ or ‘Eovariscan’ phase. To cite this article: H. Echarfaoui et al., C. R. Geoscience 334 (2002) 13–20 相似文献
5.
A two‐dimensional simulation model of travel distances of individual particles in a gravel‐bed river is presented. The model is based on a number of rules, which include particle size, entrainment, trajectory, distance of movement and entrapment. Particle interactions are controlled by resistance fields defined about each obstacle and critical elevation defined in the model. Resistance fields, particle dropping and critical elevation rules control particle interactions. The interaction rules cause the particles to develop pebble clusters, stone cells and transverse structures (transverse ribs). The simulated travel distances of individual particles are consistent with reported field results. Individual particle travel distances were simulated using two different models; one without interactions between the individual particles and the stationary bed and one with interactions. The case without interactions demonstrates the random nature of sediment transport, and narrow ranges of travel distances. Wider ranges of travel distances, similar to those for natural situations, were obtained for the cases with interactions. The more intense the interaction between the mobile stones and the stationary ones, the wider the range of distances of travel for a given particle size. Modelling the mean travel distance yielded a result similar to that published previously, which was based on empirical data. Well developed bed‐surface structures were obtained for relatively poorly sorted sediment with intense interactions between particles. Transverse structures developed when relatively large particles were allowed to move. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
6.
Hassan Ramadan Salameh 《GeoJournal》1997,41(3):255-266
This paper aims to investigate the geomorphological characteristics of theeastern coast of the Dead Sea as influenced by structural instability andclimatic changes. Aerial photos and map analyses served to distinguish mainmorphological features and slope classes, whereas geomorphological changesalong the cost, mainly those developed by the declining of the Dead Sealevels were located and examined in the field. The eastern coast of the DeadSea was considered an ultimate outcome of stream work practiced undercontrols of sea-level lowerings. Climatic, hydrological and structuralinstabilities characterizing the study coast put watersheds and wadisdraining into the sea under accelerated erosion that produced huge volumes ofsediments to be deposited in the upper levels of the subsiding former lakesof the Dead Sea. Retrogradation exposed subaqueous deltaic-fluviatileformations, contributing to coastal geomorphological development. Also,present climatic seasonal fluctuations, rejuvenating stream work, continue tosubject past depositional environments to denudation as the stream distanceof transport is increased, and newer subaqueous deltas are being formed.Weathering and mass-wasting processes added to such a development byenhancing the formation of karst, tofoni and pedestal features as well as thehigh erodibility rate of deltaic sediments which endagers constructionalprojects along the study coast. 相似文献
7.
The Wadi Badaa (WB) Upper Miocene clays, Cairo-Suez district, Egypt, represent materials for the ceramic production. The clay raw materials are composed mainly of smectite and kaolinite with minor quartz, calcite, and rare feldspar. The plasticity indices vary between 24 and 30%, suggesting that these clays are plastic raw materials. IR bands of the investigated clays were observed at 3695, 3619, 1032, 916, 794, 690, 534, 466, and 423 cm?1 for kaolinite; at 3436, 1635, 916, and 466 cm?1 for smectite; and at 1179, 1104, 794, 690, and 466 cm?1 for quartz. The <2 μm particle sizes of samples are relatively abundant in clays (~33%), which is adequate for uses of the ceramic products because of containing fine particle sizes. The studied WB clays contain 7.95 and 12.35% moisture water and interlayer water, respectively, with a maximum drying shrinkage of 7.87% at room temperature; therefore, the WB clays could be used in the ceramic manufacture. 相似文献
8.
G. Sharaf H. Hassan 《International Journal of Environmental Science and Technology》2014,11(6):1581-1590
The batch removal of copper(II) ions from aqueous solution under different experimental conditions using alkali-leached silica and activated charcoal was investigated in this study. The copper(II) uptake was dependent on varying time, pH, copper concentration and temperature. Copper sorption was found fast reaching equilibrium within 1 h with better performance for alkali-leached silica than charcoal. Copper sorption was low at low pH values and increased with rise in initial pH-value until 6.7. Sorption fits well the Langmuir and Freundlich equations with higher uptake by increasing temperature. According to Langmuir equation, the maximum uptake of Cu(II) ions by alkali-leached SiO2 and charcoal was found to be 242.5 and 94.4 mmol/g at temperature 60 °C and pH 6. Thermodynamic studies confirm that the process was spontaneous and endothermic nature. Kinetic data for Cu(II) sorption was found to follow pseudo-second-order model. 相似文献
9.
Muhammad Hassan Agheem Mohammad Tahir Shah Tahseenullah Khan Mamoru Murata Muhammad Arif Humaira Dars 《Arabian Journal of Geosciences》2014,7(9):3801-3814
A variety of gemstones is being mined in the Shigar valley, Skardu, Pakistan. These include beryl (goshenite and aquamarine), tourmaline (schorl), garnet (almandine–spessartine), apatite, topaz, fluorite, zoisite, clinozoisite, and axinite, mostly occurring in complex or zoned pegmatites and metamorphic rocks. These have been analyzed using electron probe micro-analyzer and X-ray diffractometer. The mineral chemistry of each gemstone is similar to its respective typical gemstone variety with homogenous chemical composition. Field and chemical characteristics suggest that beryl, tourmaline, garnet, apatite, topaz, and fluorite are occurring in zoned pegmatites which are largely formed by magmatic hydrothermal fluids in the cavities and vugs within the intermediate zone. However, zoisite, clinozoisite, and axinite may have a metamorphic and/or metasomatic origin. 相似文献
10.
MERVATSAIDHASSAN SAYEDMAHMOUDSALEM 《中国地球化学学报》2001,20(2):120-129
Clay minerals from different Cretaceous stratigraphic successions of Egypt were investigated using XRD,DTA,dissolution analysis(DCB),IR,Moessbauer and X-ray Electron Spin Resonance(ESR) spectroscopes.The purity of the samples and the degree of their structural order were determined by XRD.The location of Fe in the octahedral sheet is characterized by absorption bands at-875cm^-1 assigned as Al-OH-Fe which persist after chemical dissolution of free iron.The Moessbauer spectra of these clays show two doublets with isomer shift and quadrupole splitting typical of octahedrally coordinated Fe^3 ,in addition to third doublet with hyperfine parameter typical of Fe^2 in the spectra of Abu-Had kaolinite (H) sample.Six-lines magnetic hyperfine components which are consistent with those of hematite are confirmed in the spectra of both Isel and Rish kaolinite samples.Goethite was confirmed by both IR and DTA.Multiple nature of ESR of these clays suggested structural Fe in distorted octahedral symmetry as well as non-structural Fe.Little dispersion and low swelling indices as well as incomplete activation of the investigated montmorillonite samplas by NaCO3 appear to be due to incomplete disaggregation of montmorillonite particles.This can be explained by the ability of Fe-gel to aggregate the montmorillonite into pseudo-particles and retard the rigid-gel structure.However,extraction of this ferric amorphous compound by dithonite treatment recovers the surface properties of the montmorillonite samples.On the other hand,the amount and site occupation of Fe associated with kaolinite samples show an inverse correlation with the parameters used to describe the degree of crystallinity perfection,color,brightness and vitrification range of these kaolinite samples. 相似文献