全文获取类型
收费全文 | 1361篇 |
免费 | 66篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 26篇 |
大气科学 | 66篇 |
地球物理 | 495篇 |
地质学 | 550篇 |
海洋学 | 51篇 |
天文学 | 189篇 |
综合类 | 4篇 |
自然地理 | 51篇 |
出版年
2022年 | 12篇 |
2021年 | 27篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 70篇 |
2017年 | 51篇 |
2016年 | 82篇 |
2015年 | 53篇 |
2014年 | 80篇 |
2013年 | 100篇 |
2012年 | 60篇 |
2011年 | 77篇 |
2010年 | 70篇 |
2009年 | 69篇 |
2008年 | 45篇 |
2007年 | 38篇 |
2006年 | 34篇 |
2005年 | 36篇 |
2004年 | 22篇 |
2003年 | 22篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1986年 | 17篇 |
1985年 | 12篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 16篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 14篇 |
1973年 | 11篇 |
1971年 | 12篇 |
1968年 | 11篇 |
1957年 | 7篇 |
排序方式: 共有1432条查询结果,搜索用时 390 毫秒
951.
Discrimination of earthquakes and quarry blasts in the eastern Black Sea region of Turkey 总被引:1,自引:0,他引:1
In recent years, a large number of quarry blasts have been detonated in the eastern Black Sea region. When these blasts are recorded by seismic stations, they contaminate the regional earthquake catalog. It is necessary to discriminate quarry blast records from the earthquake catalogs in order to determine the real seismicity of the region. Earthquakes and quarry blasts can be separated through different methods. These methods should be applied concurrently in order to safely distinguish these events. In this study, we discriminated quarry blasts from earthquakes in the eastern Black Sea region of Turkey. We used 186 seismic events recorded by the Karadeniz Technical University and Bogaziçi University Kandilli Observatory Earthquake Research Institute stations which are Trabzon, Espiye, Pazar, Borçka, Ayd?ntepe, and Gümü?hane between years of 2002 and 2010. For the discrimination of quarry blasts from earthquakes, we used both, statistical methods (calculation of the maximum ratio of S to P waves (S/P), complexity (C)) and spectral methods (spectrogram calculation). These methods included measuring the maximum amplitude S/P, C, spectral ratio, and time-frequency analysis. We especially relied on two-dimensional time-frequency analysis methods to discriminate quarry blasts from earthquakes in Turkey. As a result of this study, 68 % of the examined seismic events were determined to be quarry blasts and 32 % to be earthquakes. The earthquakes occurring on land are related to small faults and the blasts are concentrated in large quarries. Nearly 40 % of the earthquakes occurred in the Black Sea, most of them are related to the Black Sea thrust belt, where the largest earthquake was observed in the time period studied. The areas with the largest earthquake potential in the eastern Black Sea region are in the sea. 相似文献
952.
Jérémy Piffady Éric Parent Yves Souchon 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(7):1719-1734
Global change calls for an understanding of how temperature and flow regimes influence aquatic ecosystems. Fish assemblages are a major component of river ecosystems and are thought to exhibit more integrative informative responses than single species to environmental variations, whether rare and sudden or gradual and continuous. The use of long-term datasets is thus of primary importance, allied to statistical modeling. For each of three previously identified species clusters, we performed Bayesian variable selection and inference within a hierarchical log Poisson Generalized Linear Model using a spike and slab normal prior to pinpoint which subset of environmental variables is of importance for each fish assemblage. Fish counts from electrofishing experiments are known to provide overdispersed data and, not surprisingly, the contribution of recorded environmental effects is found to be weak compared with those of other intra-assemblage sources of variation. The posterior distribution of the regression parameters is in coherence with what was expected from biological knowledge of the three species clusters. In particular, thermophilic species tend to benefit from warmer waters, whereas the recruitment of cold water species decreases due to global warming effects. Our study provides an example of the advantages of hierarchical modeling for quantifying interspecies ecological effects and selecting common environmental variables of importance. 相似文献
953.
Long-term behavior of lime-stabilized kaolinite clay 总被引:1,自引:1,他引:0
Clay soils create many problems for highway construction and they have to be replaced or improved by stabilization for satisfactory performance. Lime stabilization is a well-established technique to improve the performance of clays. Cementitious minerals form upon mixing of clay with lime causing an improvement in strength and durability. In the study, the changes in the microfabric of long-term cured lime-stabilized kaolinite clay using X-ray diffraction pattern, scanning electron microscope and unconfined compressive strength (UCS) is presented. Unconfined compression test samples at two different lime contents (4 and 12% by weight) were prepared and cured in a humidity room for long time curing. The UCS of pure kaolinite was originally 125 kPa, which increased to 1,015 kPa after 1 month and to 2,640 kPa (21 times the initial value) after 10 years for cured lime-stabilized kaolinite samples. Similar long-term strength increases were also observed for stabilized kaolinite with 12% lime. Calcium aluminate silicate hydrate minerals were detected in the structure of the kaolinite. This suggests pozzolanic reactions with lime stabilization may continue in the long-term for up to 10 years. 相似文献
954.
Pan-African magmatism in the Menderes Massif: geochronological data from leucocratic tourmaline orthogneisses in western Turkey 总被引:1,自引:1,他引:0
O. E. Koralay O. Candan F. Chen C. Akal R. Oberh?nsli M. Sat?r O. ?. Dora 《International Journal of Earth Sciences》2012,101(8):2055-2081
The Menderes Massif, exposed in western Anatolia, is a metamorphic complex cropping out in the Alpine orogenic belt. The metamorphic rock succession of the Massif is made up of a Precambrian basement and overlying Paleozoic-early Tertiary cover series. The Pan-African basement is composed of late Proterozoic metasedimentary rocks consisting of partially migmatized paragneisses and conformably overlying medium- to high-grade mica schists, intruded by orthogneisses and metagabbros. Along the southern flank of the southern submassif, we recognized well-preserved primary contact relationship between biotite and leucocratic tourmaline orthogneisses and country rocks as the orthogneisses represent numerous large plutons, stocks and vein rocks intruded into a basement of garnet mica schists. Based on the radiometric data, the primary deposition age of the precursors of the country rocks, garnet mica schist, can be constrained between 600 and 550?Ma (latest Neoproterozoic). The North Africa–Arabian-Nubian Shield in the Mozambique Belt can be suggested as the possible provenance of these metaclastics. The intrusion ages of the leucocratic tourmaline orthogneisses and biotite orthogneisses were dated at 550–540?Ma (latest Neoproterozoic–earliest Cambrian) by zircon U/Pb and Pb/Pb geochronology. These granitoids represent the products of the widespread Pan-African acidic magmatic activity, which can be attributed to the closure of the Mozambique Ocean during the final collision of East and West Gondwana. Detrital zircon ages at about 550?Ma in the Paleozoic muscovite-quartz schists show that these Pan-African granitoids in the basement form the source rocks of the cover series of the Menderes Massif. 相似文献
955.
Jér?me Lopez Saez Christophe Corona Markus Stoffel Laurent Astrade Frédéric Berger Jean-Philippe Malet 《Landslides》2012,9(2):189-203
The purpose of this study was to reconstruct spatiotemporal patterns of past landslide reactivation in a forested area of the Barcelonnette Basin (Bois Noir landslide, Southern French Alps). Analysis of past events was based on tree ring series from 79 heavily affected Mountain pine (Pinus uncinata Mill. ex Mirb) trees growing near or next to the landslide body. Dendrogeomorphic analysis focused on the presence of compression wood and growth reductions, with the first reaction being used for a dating of past reactivations with seasonal precision. A total of 151 growth disturbances were identified in the samples representing eight different stages of reactivation of the landslide body between 1874 and 2008. The spatiotemporal accuracy of the reconstruction is confirmed by historical records from neighboring sites and by aerial photographs. The onset of compression wood formation allows identifying five stages of landslide reactivation during the dormant season or the very beginning of the growing season of trees, i.e., between early October and late May, and three stages toward the end of the growth period. Monthly rainfall data from the HISTALP database demonstrate that the rainfall during four out of the eight reactivations are characterized by summer rainfall totals (July?CAugust) exceeding 200?mm, pointing to the important role of summer rainstorms in the triggering of events at the Bois Noir landslide body. 相似文献
956.
Some earthquakes in the Eastern Mediterranean are tsunamigenic and some of their tsunamis affected the coastal area of the
Gulf of Fethiye, SW Turkey. Recent trenching surveys on the low-lying coastal areas of Dalaman delta beach across the Rhodes
Pass revealed three probable tsunami impacts as a result of the historical earthquakes of 1303, 1481 and 1741. Yet, there
have been relatively few studies of the processes associated with tsunami sediment transport, their deposition and nature
in geological record. In addition to the interpretation of sedimentary features, accurate paleoenvironmental assessments might
be possible by distinctive biogeochemical researches on marine-sourced organic matters, geochemical properties, quantitative
amounts of marine-sourced biomarkers and deterministic ratios. The identification of major lipid biomarkers (fatty acids and
sterols) in the samples recovered from the sidewalls of the studied trench, for example, indicated biogenic contributions
due to the presence of phytoplankton, zooplankton, dinoflagellates and bacteria. Quantitative estimation of biomarkers and
deterministic ratios also indicated some evidences for marine-sourced organic matters, implying that biomarkers can be used
to answer the open questions in tsunami and paleotsunami researches. 相似文献
957.
Agnese Fazio Massimo D'Orazio Luigi Folco Jérôme Gattacceca Corinne Sonzogni 《Meteoritics & planetary science》2013,48(12):2451-2468
Northwest Africa (NWA) 6583 is a silicate‐bearing iron meteorite with Ni = 18 wt%. The oxygen isotope composition of the silicates (?′17O = ?0.439 ‰) indicates a genetic link with the IAB‐complex. Other chemical, mineralogical, and textural features of NWA 6583 are consistent with classification as a new member of the IAB‐complex. However, some unique features, e.g., the low Au content (1.13 μg g?1) and the extremely reducing conditions of formation (approximately ?3.5 ?IW), distinguish NWA 6583 from the known IAB‐complex irons and extend the properties of this group of meteorites. The chemical and textural features of NWA 6583 can be ascribed to a genesis by impact melting on a parent body of chondritic composition. This model is also consistent with one of the most recent models for the genesis of the IAB‐complex. Northwest Africa 6583 provides a further example of the wide lithological and mineralogical variety that impact melting could produce on the surface of a single asteroid, especially if characterized by an important compositional heterogeneity in space and time like a regolith. 相似文献
958.
Stephen Pintér 《Astrophysics and Space Science》1986,123(1):209-211
We have proposed a mechanism of arise of transient magnetic disturbances from solar flare explosion which can lead to understanding of observed pulsations of type IV radio emission with period of 0.3–3.0 s. According to the proposed mechanism the pulsation activity of the radio emission results from MHD waves accompanying the expanding diamagnetic plasma produced by the explosive flare material. 相似文献
959.
The devastating zmit and Düzce earthquakes were followed by theOrta intra-plate earthquake (MS = 6.1) occurred in the central Anatolianblock on June 6, 2000. The focal mechanism, aftershock distribution andthe field studies (Emre et al., 2000) suggest a movement on a 21-km longDodurga fault striking nearly N-S where the sense of motion is left-lateralstrike-slip with considerable amount of normal component. We applied theconstrained linear finite-fault inversion method of Hartzell and Heaton(1983) to the teleseismic P and SH waveforms to derive a coseismic slipdistribution model for the earthquake. Time windows approach is appliedallowing variable rise times and rupture velocities. The source-rise timefunction is discretized into consecutive time intervals that stand for slipcontribution of individual subfaults. Although no clear surface ruptureswere associated with the earthquake, the resulting slip model suggestscoseismic slip in the order of several tens of centimetres. Our coseismicslip distribution model identifies two slip patches with the followingmaximum slip values: (1) the larger one (42 cm) is located to the southof the hypocenter at depth range of 4–8 km and (2) the smaller one(31 cm) is located just above and north of the hypocenter. Theslip-model yield a seismic moment of 1.0 × 1018 Nm, most of whichis released from the rupture over the depth of 8 km. 相似文献
960.