全文获取类型
收费全文 | 1538篇 |
免费 | 69篇 |
国内免费 | 64篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 52篇 |
地球物理 | 338篇 |
地质学 | 958篇 |
海洋学 | 102篇 |
天文学 | 82篇 |
综合类 | 12篇 |
自然地理 | 72篇 |
出版年
2023年 | 4篇 |
2022年 | 35篇 |
2021年 | 42篇 |
2020年 | 60篇 |
2019年 | 36篇 |
2018年 | 137篇 |
2017年 | 121篇 |
2016年 | 134篇 |
2015年 | 72篇 |
2014年 | 115篇 |
2013年 | 186篇 |
2012年 | 65篇 |
2011年 | 94篇 |
2010年 | 71篇 |
2009年 | 73篇 |
2008年 | 53篇 |
2007年 | 33篇 |
2006年 | 36篇 |
2005年 | 27篇 |
2004年 | 27篇 |
2003年 | 23篇 |
2002年 | 35篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有1671条查询结果,搜索用时 15 毫秒
991.
Abdelrahman Mohamed Abdelgawad Kunio Watanabe Mebruk Mohammed Shinji Takeuchi 《Environmental Earth Sciences》2010,60(3):449-462
High levels of fluoride concentration were observed in deep groundwater of the Mizunami area in Central Japan. Fluoride occurs
mainly due to the reaction between granitic basement rock and groundwater. Granites were collected, crushed to powder, and
then allowed to react with purified water for 80 days. Water–rock interaction results showed that the major factor affecting
fluoride concentration is the residence time of the groundwater. Coexisting ions have also some contribution toward fluoride
concentration. The groundwater residence time in the Mizunami area was estimated by applying results of water–rock interaction
to correspond with field data. A regression model relating fluoride concentration, residence time, and coexisting ions was
developed. The parameters of the regression model were determined using the genetic algorithms technique. Residence time was
estimated by extrapolating experimental data to correspond with filed data. Near the recharge area, residence times in the
potential fluoride source rock varied between 1 and 2,000 years, whereas near the discharge area residence times were in excess
of tens of thousands of years. The groundwater residence time was also estimated by the groundwater particle-tracking-flow
model. The estimates of groundwater residence time based on geochemical regression model were often larger than estimates
of groundwater residence time developed by particle-tracking analysis using a groundwater flow model. There were large uncertainties—on
the order of 10–10,000 years—in the estimates based on geochemical data. 相似文献
992.
Mohamed E. Hereher 《Environmental Earth Sciences》2010,59(5):1119-1127
Wind action is the most dominant agent for erosion and deposition in the vast Western Desert of Egypt. Analysis of wind data
from seven meteorological stations distributed along the Western Desert reveals that this desert is characterized by high-energy
wind environments along the northern and southern edges and low-energy wind environments throughout the rest of the desert.
Accordingly, sand drift potential follows the pattern of wind energy. Maximum sand drift potential was observed at the southern
edge (571 vector units, which equals 40 m3/m width/year). Sand drift direction was observed towards the southeast except at the southern part of the desert where the
trend of sand movement was towards southwest. The major dune type recognized on satellite images was the simple linear type.
Linear dunes are generally associated with bimodal wind regime. Rates of sand drift potential and sand dune migration were
greatest at East of Owinate region at the extreme southern part of the desert. Measurements of crescentic sand dune advance
from two satellite images reveal a maximum advance rate of about 9 m/year at the southern part of the desert. Dune movement
creates potential hazard to the infrastructures in this open desert. 相似文献
993.
The role of the Najd Fault System in the tectonic evolution of the Hammamat molasse sediments,Eastern Desert,Egypt 总被引:1,自引:1,他引:0
Mohamed A. Abd El-Wahed 《Arabian Journal of Geosciences》2010,3(1):1-26
The Hammamat molasse sediments of the Eastern Desert of Egypt were deposited in isolated basins formed during an initial stage
of orogen parallel N–S extension (650–580 Ma) in the Neoproterozoic time. Supply of sediments to the molasse basins began
after the eruption of Dokhan volcanics (602–593 Ma), exhumation of core complexes (650–550 Ma), and intrusion of late tectonic
granites (610–550 Ma). The late Neoproterozoic structures in the molasse sediments include: (1) NNW-directed thrusts due to
NNW–SSE shortening (650–640 Ma), indicated by the presence of NE-, ENE-, and WSW-trending folds and NNW-directed thrusts.
(2) SW- and NE-directed thrusts due to ENE–WSW constriction during oblique convergence and arc accretion at around 640–620 Ma.
Many of the map- and mesoscopic-scale NW-trending folds in the core complexes, the molasse sediments, and the Neoproterozoic
nappes in the Eastern Desert are related to this event. Sinistral shearing along the Najd Fault System (650–540 Ma) resulted
in the development of subvertical foliation, subhorizontal stretching lineation, and NW-trending tight folds overprinting
earlier folds. Stretched pebbles are oriented NW–SE and WNW–ESE in the molasse basins localized within the Najd Fault System,
and NE–SW in the basins outside the influence zone of this NW-trending fault system. Strain estimated using pebbles from nine
molasse basins indicate that the amount of strain differs from one basin to another and from one place to another within the
same basin. Weak tectonic strain (Rs = 2.16–2.24) is obtained from post-orogenic basins; moderate strains are reported from
foreland basins (Rs = 2.37–3.18), whereas moderate to high tectonic strains are recorded from the intermontane basins (Rs = 2.40–4.36).
The obtained tectonic strain and K values indicate that the flattening strain prevails in the post-orogenic and foreland basins, whereas as both constrictional
and flattening strains are recorded in intermontane basins. Strain variation from one basin to another and within the individual
basin is attributed to presence of thrust and sinistral shear zones. Away from the deformed zones, the pebbles show no significant
stretching. Two phases of thrusting and an episode of transpressional sinistral shearing are the latest structure features
of the East African orogeny in the Arabian–Nubian Shield. 相似文献
994.
The littoral fringe ranging between the capes of Bizerte and Ras Ettarf (north-eastern of Tunisia) represents an unstable
and complex system of the Tunisian littoral. The instability of this zone is dependent, on one hand, on natural phenomena
contributing to the destabilization of certain sectors to which are added the induced effects of anthropic factors on the
other hand. This study was carried out from grain size analysis and a simulation of swell plans. This led the authors to highlight
the increasing grain size classification from the zones of the Capes towards the sandy low coasts and to quantify the moved
volumes under the effect of the dominant swells in order to simulate the fattening and erosion zones in this sector. A littoral
transit of direction north–south is able to transport 45,000 m3/year of sediment which are participating in the fattening of the beach of Sidi Salem; 6,000 m3/year of sandy sediments are directed towards the beach of R'mel and 12,000 m3/year are participating in the fattening of the beaches of Chatt Mami (Ras Jebel) and Lahmmari (Raf Raf). 相似文献
995.
A near-surface seismic refraction survey was conducted at a new mining area located in southeast Cairo, Egypt, to explore the subsurface clay layer for future economic use in mining and cement industry. The purpose of the survey has been to provide geological and geophysical information because no borehole was existent in the area under investigation. The aim of study had been to explain the main characteristics of the subsurface layers. For this purpose, a new technique has been used to acquire and process the data. This technique provides critical information to determine the depth of the subsurface layers, as well as morphology, stratigraphy, and potential locations of the clay layer for future economic use. The thickness and general shape of the clay layer in the whole area were determined and are illustrated in maps. 相似文献
996.
Sayang Mohd Deni Jamaludin Suhaila Wan Zawiah Wan Zin Abdul Aziz Jemain 《Theoretical and Applied Climatology》2010,99(3-4):357-371
This study aims to trace changes in the dry spells over Peninsular Malaysia based on the daily rainfall data from 36 selected rainfall stations which include four subregions, namely northwest, west, southwest, and east for the periods of 1975 to 2004. Six dry spell indices comprising of the main characteristics of dry spells, the persistency of dry events, and the frequency of the short and long duration of dry spells will be used to identify whether or not these indices have increased or decreased over Peninsular Malaysia during the monsoon seasons. The findings of this study indicate that the northwestern areas of the Peninsular could be considered as the driest area since almost all the indices of dry spells over these areas are higher than in the other regions during the northeast (NE) monsoon. Based on the individual and the field significant trends, the results of the Mann–Kendall test indicate that as the total number of dry days, the maximum duration, the mean, and the persistency of dry days are decreased, the trend of the frequency of long dry spells of at least 4 days is also found to decrease in almost all the stations over the Peninsula; however, an increasing trend is observed in the frequency of short spells in these stations during the NE monsoon season. On the other hand, during the southwest monsoon, a positive trend is observed in the characteristics of dry spells including the persistency of two dry days in many stations over the Peninsula. The frequency of longer dry periods exhibits a decreasing trend in most stations over the western areas during both monsoon seasons for the periods of 1975 to 2004. 相似文献
997.
The frequency analysis of many log data permits to verify that their stochastic component show ‘power-law-type’ spectral densities, characteristic of noise. They can be modelled by fractional Brownian motions. Continuous Wavelet Transformation (CWT) provides us with very efficient methods to determine the local spectral exponents of these scaling laws. These new attributes are related to the local fractality of these signals. We first present some theoretical results and an application to a fractional Brownian motion. The second application concerns a dataset recorded in the MAR203 borehole. We show that clustering of these new pseudo-logs leads to a good resolution between different lithofacies. To cite this article: N. Zaourar et al., C. R. Geoscience 338 (2006). 相似文献
998.
This paper covers the detailed version of the potential raw material deposits at Darukhula and the adjacent areas of Nizampur,
the manufacturing of high-strength Portland cement samples from the same material and comparison of the physical and chemical
parameters for resulting cement with British and Pakistan standard specifications, which include compressive strength, setting
time, consistency, lechatelier expansion, Blaine and insoluble residue. It was found that the raw material available in the
study area meets the standard specifications and the area is feasible for the cement plant installation. The area can provide
raw material which is quite sufficient for the running of a cement plant. 相似文献
999.
We conduct shear wave splitting measurements on waveform data from the Hi-net and the broadband F-net seismic stations in Kanto and SW Japan generated by shallow and intermediate-depth earthquakes occurring in the subducting Philippine Sea and Pacific slabs. We obtain 1115 shear wave splitting parameter pairs. The results are divided into those from the shallow (depth < 50 km) and the deep (depth > 50 km) events. The deep events beneath Kanto are further divided into PHS1 and PHS2 (upper and lower planes of the double seismic zone in the Philippine Sea slab, respectively), PAC1 and PAC2 (western and eastern Pacific slab, respectively) events. The results from the shallow events represent the crustal anisotropy, and their fast directions are more or less aligned in the σHmax directions, implying that the anisotropy is produced by the alignment of the vertical cracks in the crust induced by the compressive stresses. In Kanto, Kii Peninsula and Kyushu regions, the results from the deep events suggest a contribution from the mantle wedge anisotropy. Events from all groups beneath Kanto show NW, NE and EW fast directions. This complex pattern seems to be produced by the corner flows induced by both the WNW PAC plate subduction and the oblique NNW PHS slab subduction with the associated olivine lattice-preferred orientations (LPOs), and the anisotropy frozen in the PHS slab. The deep events beneath Kii Peninsula show NE and NW fast directions and may be produced by the corner flow produced by the NNW PHS slab subduction with the associated olivine LPOs. The NE directions might also be produced by the segregated melts in the thin layers parallel to the PHS slab subduction. The deep events beneath N Kyushu show NNW fast directions, which may result from the southeastward flow in the upper mantle inferred from the stresses in the upper plate. Results from the deep events beneath middle-south Kyushu show dominantly E–W fast directions, in both the fore- and back-arcs. They may be produced by the corner flow of the westward PHS slab subduction with the olivine LPOs. Because the source regions with multiple fast directions are not resolved in this study, further detailed analyses of shear wave splitting are necessary for a better understanding of the stress state, the induced mantle flow, and the melt-segregation processes. 相似文献
1000.
B. C. Prabhakar M. Jayananda Mohamed Shareef T. Kano 《Journal of the Geological Society of India》2009,74(2):171-188
In this paper we document widespread coeval felsic-mafic magma interaction and progressive hybridization near Gurgunta in
the northern part of Eastern Dharwar Craton (EDC) where mafic magma pulses have injected into a 2.5 Ga granite pluton. The
pluton contains voluminous pink porphyritic facies with minor equigranular grey facies. The mafic body shows compositional
variation from diorite to meladiorite with hornblende as the chief mafic mineral with lesser clinopyroxene and biotite. The
observed variation on binary diagrams suggests that granite was evolved by fractional crystallization. Chemical characteristics
such as higher Al2O3 and moderate to high CaO, Mg#, Ni, Cr, Co and V are interpreted by slab-melting. Mafic bodies show lower SiO2, Na2O and K2O; but higher CaO, Mg#, FeO, Cr, Ni and V; higher LREE with moderate to higher HREE which suggest their derivation from mantle.
A major active shear zone has played an important role at the time of synplutonic mafic injection and hybridization process.
Field evidences suggest that the synplutonic mafic body has injected into the crystallizing felsic magma chamber in successive
stages. The first stage injection has resulted in extensive mixing and hybridization due to the liquidus state of resident
felsic magma to which hot mafic magma was injected. However, progressive mixing produced heterogeneity as the xenocrysts started
mechanically dispersed into hybrid magma. The second stage injection, after a time gap, encountered colder and viscous hybrid
magma in the magma chamber, which inhibited free injection. As a consequence, the mafic magma spread into magma chamber as
flows, producing massive mafic bodies. However, with the continued mafic pulses and the heat gradient, the viscosity contrasts
of mafic magma and felsic magma were again lowered resulting in second stage mixing. This episode was followed by mingling
when the granite was almost crystallized, but still viscous enough to accommodate lamellar and ribbon like mafic penetrations
to produce mingling. The successive mixing and mingling processes account for the observed heterogeneity in the granite pluton. 相似文献