全文获取类型
收费全文 | 269篇 |
免费 | 4篇 |
国内免费 | 3篇 |
专业分类
大气科学 | 41篇 |
地球物理 | 27篇 |
地质学 | 158篇 |
海洋学 | 12篇 |
天文学 | 6篇 |
自然地理 | 32篇 |
出版年
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 23篇 |
2012年 | 8篇 |
2011年 | 10篇 |
2010年 | 11篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 8篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 5篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 16篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 1篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有276条查询结果,搜索用时 15 毫秒
1.
2.
THOMAS C. GUSTAVSON 《Sedimentology》1978,25(3):401-426
All major streams draining the southwestern flank of the Edwards Plateau in south-central Texas transport large volumes of gravel and sandy muddy gravel and are developing meander lobe sequences consisting predominantly of coarse gravel. The largest of these streams, the Nueces River, has a sinuosity index of 1.3 and an average stream surface slope of 1.8 m/km in the study area. Stream discharge is variable and has ranged from no flow to more than 17,000 m3/s. Mean clast b-axis length for the ten largest clasts at thirteen sample sites ranged from 2.5 to 10.8 cm. Velocities of 2.7-4.4 m/s 1 m above the stream bed are required to transport these clasts. Stream velocities of these magnitudes occur about once in 8 years when discharge of the Nueces River exceeds 3300 m3/s. Mean grain size of Nueces River alluvium ranges from 1.2 to 3.4 cm. At a flow depth of 1 m, sediment of this size has a critical erosion velocity of 1.8-3 m/s. Velocities of this magnitude occur about once in two years when discharge exceeds 340 m3/s. Under these conditions flow is subcritical, with critical shear stresses on depositional surfaces ranging from 6.4 to 12.7 kg/m2. Gravel clasts are imbricated and channel bed forms are predominantly transverse gravel bars with slip faces ranging up to 2 m high and wavelengths in excess of 100 m. Stratification includes graded planar crossbeds and horizontal beds. Lower lateral accretion face sediments are also predominantly transverse bars; upper lateral accretion face deposits occur as longitudinal gravel ridges deposited in the lee of vegetation and, less commonly, as chute bars. Near the upper limit of meander lobes where vegetation is heavy, mud and muddy sand occur as overbank deposits; in these deposits sedimentary structures other than desiccation cracks are rare. Sedimentary sequences in gravel meander lobe systems deposited by low sinuosity streams are graded or non-graded horizontal beds and planar cross-beds overlain by mud and muddy sand interbedded with horizontally bedded gravels. Sequences may be several metres thick, but probably do not exceed 8-10 m in thickness. These deposits in turn are overlain by overbank deposits of mud and muddy sand. Similar sedimentary sequences occur in the extensive Quaternary terraces that parallel the Nueces River. 相似文献
3.
Late Pleistocene glacial and lake history of northwestern Russia 总被引:1,自引:0,他引:1
EILIV LARSEN KURT H. KJæR IGOR N. DEMIDOV SVEND FUNDER KARI GRØSFJELD MICHAEL HOUMARK-NIELSEN MARIA JENSEN HENRIETTE LINGE ASTRID LYSA 《Boreas: An International Journal of Quaternary Research》2006,35(3):394-424
Five regionally significant Weichselian glacial events, each separated by terrestrial and marine interstadial conditions, are described from northwestern Russia. The first glacial event took place in the Early Weichselian. An ice sheet centred in the Kara Sea area dammed up a large lake in the Pechora lowland. Water was discharged across a threshold on the Timan Ridge and via an ice-free corridor between the Scandinavian Ice Sheet and the Kara Sea Ice Sheet to the west and north into the Barents Sea. The next glaciation occurred around 75-70 kyr BP after an interstadial episode that lasted c. 15 kyr. A local ice cap developed over the Timan Ridge at the transition to the Middle Weichselian. Shortly after deglaciation of the Timan ice cap, an ice sheet centred in the Barents Sea reached the area. The configuration of this ice sheet suggests that it was confluent with the Scandinavian Ice Sheet. Consequently, around 70-65 kyr BP a huge ice-dammed lake formed in the White Sea basin (the 'White Sea Lake'), only now the outlet across the Timan Ridge discharged water eastward into the Pechora area. The Barents Sea Ice Sheet likely suffered marine down-draw that led to its rapid collapse. The White Sea Lake drained into the Barents Sea, and marine inundation and interstadial conditions followed between 65 and 55 kyr BP. The glaciation that followed was centred in the Kara Sea area around 55-45 kyr BP. Northward directed fluvial runoff in the Arkhangelsk region indicates that the Kara Sea Ice Sheet was independent of the Scandinavian Ice Sheet and that the Barents Sea remained ice free. This glaciation was succeeded by a c. 20-kyr-long ice-free and periglacial period before the Scandinavian Ice Sheet invaded from the west, and joined with the Barents Sea Ice Sheet in the northernmost areas of northwestern Russia. The study area seems to be the only region that was invaded by all three ice sheets during the Weichselian. A general increase in ice-sheet size and the westwards migrating ice-sheet dominance with time was reversed in Middle Weichselian time to an easterly dominated ice-sheet configuration. This sequence of events resulted in a complex lake history with spillways being re-used and ice-dammed lakes appearing at different places along the ice margins at different times. 相似文献
4.
ACOSTA-VIGIL ANTONIO; LONDON DAVID; DEWERS THOMAS A.; MORGAN GEORGE B. VI 《Journal of Petrology》2002,43(10):1885-1908
The mechanisms and kinetics of equilibration between peraluminousminerals and granitic melt were investigated experimentallyby the dissolution of corundum and andalusite into H2O-saturatedmetaluminous haplogranitic melt at 800°C and 200 MPa. Mineraland haplogranitic glass rods were juxtaposed inside platinumcapsules, and then subjected to experimental conditions fortimes ranging from 12 to 2900 h. Upon melting, the mineral meltinterface retreats with the square root of time. The compositionof the melt at the interface changes with time, but its ASI[aluminum saturation index = molar Al2O3/(CaO + Na2O + K2O)]remains constant at 相似文献
5.
Fluid-absent Melting of High-grade Semi-pelites: P-T Constraints on Orthopyroxene Formation and Implications for Granulite Genesis 总被引:4,自引:0,他引:4
Rocks of semi-pelitic composition are common in high-grade terranes.The first appearance of orthopyroxene in these rocks marks thetransition from amphibolite- to granulite-facies conditions,and is commonly attributed to the process of fluid-absent partialmelting. We have conducted fluid-absent melting experimentson two natural semi-pelitic rocks (quartz, plagioclase, alkalifeldspar, biotite and garnet) with the specific objective ofdetermining the pressuretemperature conditions necessaryto produce orthopyroxene. In contrast to previous experimentalstudies, our starting materials were obtained from a transitionalamphibolitegranulite terrane. Importantly, the high TiO2(>5 wt %) and F (>1 wt %) contents of biotite in our experimentsare more representative of biotite found in rocks on the vergeof granulite-facies conditions than those used in earlier studies.Experiments were conducted in a piston-cylinder apparatus at8001050°C and 715 kbar. We reversed the firstappearance of orthopyroxene in two-stage experiments at 7 and10 kbar. Fluid-absent melting of biotite began at 相似文献
6.
Neotectonics, sea-level changes and biological evolution in the Fennoscandian Border Zone of the southern Kattegat Sea 总被引:1,自引:0,他引:1
JØRN BO JENSEN KAJ STRAND PETERSEN PETER KONRADI ANTOON KUIJPERS OLE BENNIKE WOLFRAM LEMKE RUDOLF ENDLER 《Boreas: An International Journal of Quaternary Research》2002,31(2):133-150
Shallow seismic data and vibrocore information, sequence stratigraphic and faunal evidence have been used for documentation of Late Weichselian reactivation of faulting in the south central Kattegat, southern Scandinavia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciation fast isostatic rebound resulted in reactivation of a NW-SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previously reported late Weichselian sea-level highstand, which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostatic rebound in early Preboreal. Our findings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nordberg 1992) may have been triggered by tectonic activity in this region. 相似文献
7.
8.
Temperatures of Granulite-facies Metamorphism: Constraints from Experimental Phase Equilibria and Thermobarometry Corrected for Retrograde Exchange 总被引:17,自引:7,他引:17
PATTISON DAVID R. M.; CHACKO THOMAS; FARQUHAR JAMES; MCFARLANE CHRISTOPHER R. M. 《Journal of Petrology》2003,44(5):867-900
This study assesses temperatures of formation of common granulitesby combining experimental constraints on the PT stabilityof granulite-facies mineral associations with a garnetorthopyroxene(GrtOpx) thermobarometry scheme based on Al-solubilityin Opx, corrected for late FeMg exchange. We appliedthis scheme to 414 granulites of mafic, intermediate and aluminousbulk compositions. Our findings suggest that granulites aremuch hotter than traditionally assumed and that the PTconditions of the amphibolitegranulite transition portrayedin current petrology textbooks are significant underestimatesby over 100°C. For aluminous and intermediate granulites,mean corrected temperatures based on our method are 890 ±17 and 841 ± 11°C, respectively (uncertainties reportedas 95% confidence limits on the mean), consistent with minimumtemperatures for orthopyroxene production by fluid-absent partialmelting in these bulk compositions. In contrast, mean temperaturesbased on GrtOpx FeMg exchange equilibria, usingthe same thermodynamic data, are 732 ± 22 and 723 ±11°C, respectively, well below the minimum temperaturesfor Opx stability. For mafic granulites, the mean correctedtemperature using our method is 816 ± 12°C, similarto the mean temperature of 793 ± 13°C from FeMgexchange. Reasons for the differences between the mafic granulitesand aluminousintermediate granulites are unclear butmay be due to the lower Al concentrations in Opx in the maficrocks and possible deficiencies in the thermodynamic modellingof these low concentrations. We discuss a number of well-knowngranulite terrains in the context of our findings, includingthe Adirondacks, the Acadian granulites of New England, theincipient charnockites of southern India and Sri Lanka, andthe Kerala Khondalite Belt. Our findings carry implicationsfor thermotectonic models of granulite formation. A computerprogram to perform our thermobarometry calculations, RCLC, isavailable from the Journal of Petrology website at http://www.petrology.oupjournals.orgor from the authors at http://www.geo.ucalgary.ca/~pattison/drm_pattison-rclc.htm. KEY WORDS: granulite-facies metamorphism; thermobarometry; garnet; orthopyroxene 相似文献
9.
During a 3-year study, gaseous hydrogenperoxide (H2O2) concentrations were measuredas part of the SANA project at the Melpitz FieldResearch Station and in the city of Leipzig. Typicaldaily mean H2O2 mixing ratios on sunny dayswere 0.15 to 0.25 ppbv with maximum values of 0.3 to0.5 ppbv at Melpitz, and 0.3 to 0.6 ppbv with maximumvalues of 0.4 to 1.0 ppbv in Leipzig. Over the entireperiod of the project the maximum hourly mean valueswere 2.1 ppbv and 5.3 ppbv in Melpitz and Leipzig,respectively. The data were not complete enough to show a trend.Linear regression analysis shows, that ozone(O3), temperature and solar radiation arepositively correlated with H2O2, whereasnitrogen oxides (NOx), carbon monoxide (CO) andrelative humidity are negatively correlated. Negativecorrelation between H2O2 and CO is caused byjoint occurrence of CO with NOx in exhaust gases.Negative correlation between H2O2 andrelative humidity is not necessarily in contradictionto the accelerating effect of water vapour onH2O2 formation. The strong positivecorrelation of H2O2 with the dew pointdifference however seems to better reflect theinfluence of water vapour. Multiple linear regression analysis (MLRA) of thecomponents measured, indicates the great influence of CO on the formation of H2O2 in the gasphase. 相似文献
10.
Columnar structured horizons have been recognized in ancient coastal palaeosols of several Lower Permian (Asselian) stratigraphic units of north-central Kansas. These strongly developed columnar, polygonal-shaped peds are characteristic of sodium-influenced (natric) argillic horizons, and are commonly indicative of semi-arid to arid environments. Evaporite features above and below these palaeosols support the conclusion for a dry palaeoclimate. The columnar peds are typically 3–15 cm in diameter and exhibit domed tops. Fine clay fills the cracks between the columnar peds, and is generally of a darker colour than the peds. Each natric horizon has a low value and chroma colour, apparently the result of carbonate accumulation. The natric horizons in these Permian palaeosols appear to have been partially influenced by sodium-rich groundwaters. Root traces and root moulds are found between peds in all natric horizons, indicating plant succession after columnar ped formation. These sodium-influenced palaeosol profiles occur as part of a spectrum of palaeosol types that indicate cyclical climate change associated with glacioeustatic sea-level fluctuations. 相似文献