全文获取类型
收费全文 | 222篇 |
免费 | 15篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 8篇 |
地球物理 | 78篇 |
地质学 | 120篇 |
海洋学 | 21篇 |
天文学 | 6篇 |
自然地理 | 7篇 |
出版年
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 10篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 15篇 |
2013年 | 20篇 |
2012年 | 14篇 |
2011年 | 15篇 |
2010年 | 20篇 |
2009年 | 24篇 |
2008年 | 13篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有243条查询结果,搜索用时 281 毫秒
71.
Abdullah Kaygusuz Cem Yücel Mehmet Arslan İrfan Temizel Keewook Yi Youn-Joong Jeong 《International Geology Review》2020,62(11):1406-1432
ABSTRACT The Eastern Pontides orogenic belt in NE Turkey hosts numerous I-type plutons of Eocene epoch. Here, we report new U–Pb SHRIMP zircon ages and in situ zircon Lu-Hf isotopes along with bulk-rock geochemical and Sr-Nd-Pb-O isotope data from the Kemerlikda??, Ayd?ntepe and Pelitli plutons and mafic microgranular enclaves (MMEs) to constrain their parental melt source(s) and evolutionary processes. U-Pb SHRIMP zircon dating yielded crystallization ages between 45 and 44 Ma for the studied plutons and their MMEs. The plutons range from gabbro to granite and have I-type, medium to high-K calc-alkaline, and metaluminous to slightly peraluminous characteristics. On the primitive mantle-normalized multi-trace-element variations, the plutons and their MMEs are characterized by signi?cant enrichment in LILE/HFSE. Chondrite-normalized REE patterns of the plutons and their MMEs are close to each other and show moderate enrichment with variable negative Eu anomalies. The studied plutons have fairly homogeneous isotope composition (87Sr/86Sr(i) = 0.70502 to 0.70560; εNd(i) = +0.9 to – 1.4; δ18O = +5.0 to +8.7‰, εHf(i) = – 2.2 to +13.5). The MMEs show medium to high-K calc-alkaline and metaluminous character. Although the isotope signatures of the MMEs (87Sr/86Sr(i) = 0.70508 to 0.70542; εNd(i) = +0.9 to ?1.1; δ18O = +5.8 to +8.0, εHf(i) = +4.3 to +10.4) are very similar to those of the host rocks. Fractionation of plagioclase, amphibole, pyroxene and Fe-Ti oxides played an important role in the evolution of the plutons. The isotopic composition of the studied plutons and MMEs are similar to I-type plutons derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. The parental magma(s) of the studied plutons were generated from the enriched lithospheric mantle and then modified by fractional crystallisation, and lesser assimilation and mixing/mingling in the crustal magma chambers. 相似文献
72.
In the Sandıklı-Afyon area, the very low-grade metamorphic Sandıklı Basement Complex with clastic sediments and Late Neoproterozoic felsic igneous rocks are unconformably overlain by a cover succession with red continental clastic rocks, tholeiitic basalts and siliciclastic rocks with Early Cambrian trace fossils. Illite crystallinity studies reveal that both the basement and cover units were metamorphosed at high anchizonal to epizonal conditions ( 300 °C). Textural data together with the detailed evaluation of the P–T–b0 grid, however, indicate that this thermal event has multiple phases. The first tectonothermal event was realized at pressures of 4.2 kb on the basis of b0-data and resulted in development of blastomylonites. This is supported by the presence of dynamo-metamorphosed pebbles within the basal conglomerates of the Lower Paleozoic cover series. The second event is post-Ordovician–pre-Jurassic in age, occurred at lower pressures 3.2 kb and produced a weakly developed cleavage in the siliciclastic rocks of the cover. The mineralogical/textural data across the basement-cover boundary therefore indicate the removal of an entire metamorphic zone and thus a metamorphic hiatus.
These data suggest that the Taurides were affected by a Late Neoproterozoic event as part of the peri-Gondwana during the Cadomian orogeny. 相似文献
73.
This study concerns the correlation between burden and blast-induced vibrations in open-pit mines. For this purpose, two different
mines were studied. In these mines, the vibrations caused by explosions at burdens having widths ranging from 3 to 14 m were
measured from various distances. From the results, it was found for these cases that burden width has a significant impact
on vibrations. Consequently, it was proven that vibrations decrease as burden increases. 相似文献
74.
Dissolved oxygen is one of the most important water quality parameters. Aeration improves the water quality by maintaining good dissolved oxygen levels in water. Dissolved oxygen enters water by entrainment of air bubbles. A method of aeration that has become popular in recent years is the venturi aeration. In the present paper, experimental studies were conducted to investigate the effect of the location of the air hole in venturi tubes upon air injection. It was observed from the results that the location of the air hole playes a significant role for the air injection. The optimal air hole location that maximized the air injection in venturi aerators was determined. 相似文献
75.
Natural Resources Research - Geothermal fluids can be used for purposes such as power production, district heating/cooling, agriculture, and industrial and thermal tourism. Although using... 相似文献
76.
Mehmet Yesiltas Timothy D. Glotch Steven Jaret Alexander B. Verchovsky Richard C. Greenwood 《Meteoritics & planetary science》2019,54(7):1495-1511
As of today, the Sariçiçek (SC) meteorite is the newest howardite and the only confirmed fall among the 17 known howardites. In this study, we present isotopic, infrared, and Raman data on three distinct pieces of the SC meteorite. Our oxygen isotopic measurements show that Δ17O values of the pieces are close to each other, and are in good agreement with other howardites, eucrites, and diogenites. The carbon isotopic measurements, which were conducted by combusting terrestrial contamination selectively at temperatures lower than 500–600 °C, show the presence of indigenous carbon in the SC specimens. The matrix of these specimens, investigated via infrared microspectroscopy, appears to be dominated by clinopyroxene/orthopyroxene, forsterite, and fayalite, with minor contributions from ilmenite, plagioclase, and enstatite. Carbon‐rich regions were mapped and studied via Raman imaging microspectroscopy, which reveals that both amorphous and graphitic carbon exist in these samples. Synchrotron‐based infrared microspectroscopy data show the presence of very little aliphatic and aromatic hydrocarbons. The SC meteorite is suggested to be originating from the Antonia impact crater in the Rheasilvia impact basin on 4 Vesta (Unsalan et al. 2019). If this is in fact the case, then the carbon phases present in the SC samples might provide clues regarding the impactor material (e.g., carbonaceous chondrites). 相似文献
77.
Ali Kiliçoğlu Ahmet Direnç Hasan Yildiz Murat Bölme Bahadir Aktuğ Mehmet Simav Onur Lenk 《Studia Geophysica et Geodaetica》2011,55(4):557-578
Turkish regional geoid models have been developed by employing a reference earth gravitational model, surface gravity observations
and digital terrain models. The gravimetric geoid models provide a ready transformation from ellipsoidal heights to the orthometric
heights through the use of GPS/leveling geoid heights determined through the national geodetic networks. The recent gravimetric
models for Turkish territory were computed depending on OSU91 (TG-91) and EGM96 (TG-03) earth gravitational models. The release
of the Earth Gravitational Model 2008 (EGM08), the collection of new surface gravity observations, the advanced satellite
altimetry-derived gravity over the sea, and the availability of the high resolution digital terrain model have encouraged
us to compute a new geoid model for Turkey. We used the Remove-Restore procedure based on EGM08 and applied Residual Terrain
Model (RTM) reduction of the surface gravity data. Fast Fourier Transformation (FFT) was then used to obtain the residual
quasigeoid from the reduced gravity. We restored the individual contributions of EGM08 and RTM to the whole quasi-geoid height
(TQG-09). Since the Helmert orthometric height system is adopted in Turkey, the quasi-geoid model (TQG-09) was then converted
to the geoid model (TG-09) by making use of Bouguer gravity anomalies and digital terrain model. After all we combined a gravimetric
geoid model with GPS/leveling geoid heights in order to obtain a hybrid geoid model (THG-09) (or a transformation surface)
to be used in GPS applications. The RMS of the post-fit residuals after the combination was found to be ± 0.95 cm, which represents
the internal precision of the final combination. And finally, we tested the hybrid geoid model with GPS/leveling data, which
were not used in the combination, to assess the external accuracy. Results show that the external accuracy of the THG-09 model
is ± 8.4 cm, a precision previously not achieved in Turkey until this study. 相似文献
78.
Earthquake Engineering and Engineering Vibration - For more than 20 years, the concept of near-fault pulse-like ground motion has been a topic of great interest due to its distinct characteristics,... 相似文献
79.
Mehmet Baran Ulak Ayberk Kocatepe Lalitha Madhavi Konila Sriram Eren Erman Ozguven Reza Arghandeh 《Natural Hazards》2018,92(3):1489-1508
Natural disasters have devastating effects on the infrastructure and disrupt every aspect of daily life in the regions they hit. To alleviate problems caused by these disasters, first an impact assessment is needed. As such, this paper focuses on a two-step methodology to identify the impact of Hurricane Hermine on the City of Tallahassee, the capital of Florida. The regional and socioeconomic variations in the Hermine’s impact were studied via spatially and statistically analyzing power outages. First step includes a spatial analysis to illustrate the magnitude of customers affected by power outages together with a clustering analysis. This step aims to determine whether the customers affected from outages are clustered or not. Second step involves a Bayesian spatial autoregressive model in order to identify the effects of several demographic-, socioeconomic-, and transportation-related variables on the magnitude of customers affected by power outages. Results showed that customers affected by outages are spatially clustered at particular regions rather than being dispersed. This indicates the need to pinpoint such vulnerable locations and develop strategies to reduce hurricane-induced disruptions. Furthermore, the increase in the magnitude of affected customers was found to be associated with several variables such as the power network and total generated trips as well as the demographic factors. The information gained from the findings of this study can assist emergency officials in identifying critical and/or less resilient regions, and determining those demographic and socioeconomic groups which were relatively more affected by the consequences of hurricanes than others. 相似文献
80.
Pumice is a porous rock, which is formed as a result of volcanic activity and does not include any crystal water. Its porous structure makes it lightweight and provides advantage for heat and sound isolation. Foam concrete is a type of lightweight concrete. Foam concrete is obtained by adding the foam obtained from the agent to the mixture of cement, water, and aggregate. Foam concrete is an environmentally friendly structure and insulation material which provides light, heat, and impact sound insulation that can be used in place of the building elements used in the interior-exterior walls and floors of all buildings. Because of the lack of coarse aggregate in the foam concrete mix, it has some structural problems and this limits its usage area. In this study, four different types of pumice aggregates and stone powder were used to overcome the structural problems of foam. The cement dosages (250 kg/m3), aggregate amounts (250 kg/m3), fresh concrete densities and w/c ratio (0.45) were kept constant in all foamed concrete mixtures. Then, physical, mechanical, and thermal conductivity properties of the resulting foam concretes were investigated. When the findings were evaluated, the most suitable type of lightweight aggregates for use in foam concrete have been determined in terms of compressive strength and thermal conductivity properties. In all aggregate groups, Nevsehir Pumice has the highest compressive strength while Karaman Pumice has the lowest thermal conductivity. However, when both properties were evaluated together, it was determined that the most favorable lightweight aggregate was Nevsehir Pumice. 相似文献