全文获取类型
收费全文 | 12368篇 |
免费 | 127篇 |
国内免费 | 75篇 |
专业分类
测绘学 | 281篇 |
大气科学 | 794篇 |
地球物理 | 2390篇 |
地质学 | 4785篇 |
海洋学 | 1213篇 |
天文学 | 2549篇 |
综合类 | 52篇 |
自然地理 | 506篇 |
出版年
2022年 | 155篇 |
2021年 | 213篇 |
2020年 | 205篇 |
2019年 | 237篇 |
2018年 | 542篇 |
2017年 | 444篇 |
2016年 | 501篇 |
2015年 | 208篇 |
2014年 | 433篇 |
2013年 | 644篇 |
2012年 | 493篇 |
2011年 | 589篇 |
2010年 | 579篇 |
2009年 | 690篇 |
2008年 | 599篇 |
2007年 | 602篇 |
2006年 | 518篇 |
2005年 | 348篇 |
2004年 | 332篇 |
2003年 | 299篇 |
2002年 | 290篇 |
2001年 | 262篇 |
2000年 | 263篇 |
1999年 | 178篇 |
1998年 | 196篇 |
1997年 | 186篇 |
1996年 | 122篇 |
1995年 | 138篇 |
1994年 | 122篇 |
1993年 | 102篇 |
1992年 | 76篇 |
1991年 | 102篇 |
1990年 | 102篇 |
1989年 | 71篇 |
1988年 | 83篇 |
1987年 | 106篇 |
1986年 | 83篇 |
1985年 | 110篇 |
1984年 | 98篇 |
1983年 | 107篇 |
1982年 | 86篇 |
1981年 | 84篇 |
1980年 | 97篇 |
1979年 | 88篇 |
1978年 | 87篇 |
1977年 | 78篇 |
1976年 | 60篇 |
1975年 | 66篇 |
1974年 | 71篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
461.
Seismic facies and architecture of ice-contact submarine fans in high-relief fjords, Troms, Northern Norway 总被引:1,自引:0,他引:1
ASTRID LYSÅ TORE O. VORREN 《Boreas: An International Journal of Quaternary Research》1997,26(4):309-328
During the Late Weichselian, large marginal moraines were deposited in the Norwegian fjords. In Troms County these features are termed the Skarpnes and Tromsø-Lyngen moraines, respectively, and have been mapped from land into the marine environment where they were formed as ice-contact submarine fans. High-resolution seismic data from several fjords have been studied and reveal a typical sediment thickness of 150–320 m for these ice-contact systems. All of the ice-contact submarine fans were formed under similar climatic conditions, but display wide variation in geometry, architecture and seismic pattern. This variation is related to differences in sediment supply, the nature of the subsurface of the fan (e.g. position of thresholds), basin geometry and basin depth. Based on interpretation of the different seismic facies and the architecture of the fans, former ice-front positions have been suggested and a model has been presented for the formation of different types of ice-contact submarine fans dependent upon variation in local basin condition. 相似文献
462.
Anifowoshe TO 《GeoJournal》1990,20(3):243-247
This paper reviews the different problems associated with food production in relation to population growth. A number of solutions are put forward to improve the situation. 相似文献
463.
464.
The giant lenticular galaxy NGC 80, which is the brightest member of a rich group, possesses a central evolutionarily-distinct region: the stars in the nucleus and in a circumnuclear ring of radius 5″t–7″ have a mean age of only 7 Gyr, whereas the stellar population of the bulge is older than 10 Gyr. The nucleus of NGC 80 is also chemically distinct: it is a factor of 2–2.5 richer in metals than its immediate neighborhood and is characterized by a high magnesium-to-iron abundance ratio [Mg/Fe]≈+0.3. The global stellar disk of NGC 80 has a two-tiered structure: its outer part has an exponential scale length of 11 kpc and normal surface density, while the inner disk, which is also exponential and axisymmetric, is more compact and brighter. Although the two-tiered structure and the chemically distinct nucleus obviously have a common origin and owe their existence to some catastrophic restructuring of the protogalactic gaseous disk, the origin of this remains unclear, since the galaxy lacks any manifestations of perturbed morphology or triaxiality. 相似文献
465.
V. O. Davydova V. D. Shcherbakov P. Yu. Plechov 《Moscow University Geology Bulletin》2018,73(5):444-450
Intrusion of magma of contrasting composition into a magma chamber often triggers eruptions of arc volcanoes. Application of the diffusion chronometry method allowed us to determine the time when fresh magma was supplied to the shallow chamber of Bezymianny volcano in the case of six eruptions in 2006–2012 and to compare them to the recorded seismic activity of this volcano. Two types of eruptions of Bezymianny volcano were distinguished, with a contrasting orthopyroxene rim being formed in the respective magmas (a) up to 3 years and (b) up to 2 months before the beginning of an eruption. It was shown that these differences are caused by two different paths of magma supply to the shallow chamber of Bezymianny volcano. 相似文献
466.
V. Alves Martins C. Patinha E. Ferreira da Silva J.-M. Jouanneau O. Weber F. Rocha 《Journal of Geochemical Exploration》2006,88(1-3):408
A multiproxy approach (textural characteristics, heavy metal concentrations and benthic foraminifera data) was adopted to study the OMEX core KSGX 40, collected at the Galicia Mud Deposit (NW Iberian outer continental shelf) and recording the last ca. 4.8 ka cal BP. Geochemical profiles of Fe, Mn, Zn, Co, Cr, Cu, Ni, Pb, Al and Ca show significant temporal variations. Benthic foraminifera productivity proxy suggests that the recorded muddy events were contemporaneous of a higher Corg flux to the marine benthic environment. The higher flux of organic matter, following a long-term intensification of the upwelling and coinciding with a finer sedimentation, led to depressed levels of oxygen beneath the water-sediments interface and to early diagenetic processes of several redox-sensitive elements. 相似文献
467.
Imogen O.H. Fielding Simon P. Johnson Sebastien Meffre Jianwei Zi Stephen Sheppard Ross R. Large Birger Rasmussen 《地学前缘(英文版)》2019,10(1):89-105
Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events.Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However,the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada,with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP UeP b dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean~(207) Pb*/~(206) Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820 -1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking. 相似文献
468.
Paleoproterozoic accretion in the Northeast Siberian craton: Isotopic dating of the Anabar collision system 总被引:1,自引:0,他引:1
O. M. Rosen L. K. Levskii D. Z. Zhuravlev A. Ya. Rotman Z. V. Spetsius A. F. Makeev N. N. Zinchuk A. V. Manakov V. P. Serenko 《Stratigraphy and Geological Correlation》2006,14(6):581-601
Geochronological database considered in the work and characterizing the Anabar collision system in the Northeast Siberian craton includes coordinated results of Sm-Nd and Rb-Sr dating of samples from crustal xenoliths in kimberlites, deep drill holes, and bedrock outcrops. As is inferred, collision developed in three stages dated at 2200–2100, 1940–1760, and 1710–1630 Ma. The age of 2000–1960 Ma is established for substratum of mafic rocks, which probably originated during the lower crust interaction with asthenosphere due to the local collapse of the collision prism. Comparison of Sm-Nd and Rb-Sr isochron dates shows that the system cooling from ≈700 to ≈300°C lasted approximately 300 m.y. with a substantial lag relative to collision metamorphism and granite formation. It is assumed that accretion of the Siberian craton resulted in formation of a giant collision mountainous structure of the Himalayan type that was eroded by 1.65 Ga ago, when accumulation of gently dipping Meso-to Neoproterozoic (Riphean) platform cover commenced. 相似文献
469.
Groundwater recharge in irrigated semi-arid areas: quantitative hydrological modelling and sensitivity analysis 总被引:3,自引:0,他引:3
Joaquín Jiménez-Martínez Lucila Candela Jorge Molinero Karim Tamoh 《Hydrogeology Journal》2010,18(8):1811-1824
For semi-arid regions, methods of assessing aquifer recharge usually consider the potential evapotranspiration. Actual evapotranspiration rates can be below potential rates for long periods of time, even in irrigated systems. Accurate estimations of aquifer recharge in semi-arid areas under irrigated agriculture are essential for sustainable water-resources management. A method to estimate aquifer recharge from irrigated farmland has been tested. The water-balance-modelling approach was based on VisualBALAN v. 2.0, a computer code that simulates water balance in the soil, vadose zone and aquifer. The study was carried out in the Campo de Cartagena (SE Spain) in the period 1999–2008 for three different groups of crops: annual row crops (lettuce and melon), perennial vegetables (artichoke) and fruit trees (citrus). Computed mean-annual-recharge values (from irrigation+precipitation) during the study period were 397 mm for annual row crops, 201 mm for perennial vegetables and 194 mm for fruit trees: 31.4, 20.7 and 20.5% of the total applied water, respectively. The effects of rainfall events on the final recharge were clearly observed, due to the continuously high water content in soil which facilitated the infiltration process. A sensitivity analysis to assess the reliability and uncertainty of recharge estimations was carried out. 相似文献