全文获取类型
收费全文 | 5181篇 |
免费 | 544篇 |
国内免费 | 156篇 |
专业分类
测绘学 | 234篇 |
大气科学 | 587篇 |
地球物理 | 1928篇 |
地质学 | 2103篇 |
海洋学 | 266篇 |
天文学 | 334篇 |
综合类 | 187篇 |
自然地理 | 242篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 17篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 433篇 |
2017年 | 372篇 |
2016年 | 249篇 |
2015年 | 149篇 |
2014年 | 112篇 |
2013年 | 113篇 |
2012年 | 647篇 |
2011年 | 420篇 |
2010年 | 113篇 |
2009年 | 129篇 |
2008年 | 116篇 |
2007年 | 109篇 |
2006年 | 125篇 |
2005年 | 830篇 |
2004年 | 871篇 |
2003年 | 651篇 |
2002年 | 172篇 |
2001年 | 69篇 |
2000年 | 43篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1962年 | 1篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1951年 | 2篇 |
1948年 | 2篇 |
1925年 | 1篇 |
排序方式: 共有5881条查询结果,搜索用时 547 毫秒
511.
Emplacement of a giant submarine slide complex, offshore of South Kona, Hawaii Island, was investigated in 2001 by visual observation and in-situ sampling on the bench scarp and a megablock, during two dives utilizing the Remotely Operated Vehicle (ROV) Kaiko and its mother ship R/V Kairei. Topography of the bench scarp and megablocks were defined in 3-D perspective, using high-resolution digital bathymetric data acquired during the cruise. Compositions of 34 rock samples provide constraints on the landslide source regions and emplacement mechanisms. The bench scarp consists mainly of highly fractured, vesiculated, and oxidized aa lavas that slumped from the subaerial flank of ancestral Mauna Loa. The megablock contains three units: block facies, matrix facies, and draped sediment. The block facies contains hyaloclastite interbedded with massive lava, which slid from the shallow submarine flank of ancestral Mauna Loa, as indicated by glassy groundmass of the hyaloclastite, low oxidation state, and low sulfur content. The matrix facies, which directly overlies the block facies and is similar to a lahar deposit, is thought to have been deposited from the water column immediately after the South Kona slide event. The draped sediment is a thin high-density turbidite layer that may be a distal facies of the Alika-2 debris-avalanche deposit; its composition overlaps with rocks from subaerial Mauna Loa. The deposits generated by the South Kona slide vary from debris avalanche deposit to turbidite. Spatial distribution of the deposits is consistent with deposits related to large landslides adjacent to other Hawaiian volcanoes and the Canary Islands. 相似文献
512.
Information included in this summary is based on more detailed reports published in the Bulletin of the Global Volcanism Network, vol. 28, No. 9, September 2003 (on the Internet at ). Edited by scientists at the Smithsonian, this bulletin includes reports provided by a worldwide network of correspondents. The reports contain the names and contact information for all sources. Please note that these reports are preliminary and subject to change as events are studied in more detail. The Global Volcanism Program welcomes further reports of current volcanism, seismic unrest, monitoring data, and field observations. 相似文献
513.
Instability of exogenous lava lobes during intense rainfall 总被引:1,自引:1,他引:0
On many volcanoes, there is evidence of a relationship between dome collapse and periods of high precipitation. We propose a mechanism for this relationship and investigate the conditions that optimize failure by this process. Observations of elongate lobes that evolve through exogenous growth of lava domes reveal that they commonly develop tensile fractures perpendicular to the direction of motion. These cracks can increase in depth by localized cooling and volumetric contraction. During periods of high rainfall, water can fill these cracks, and the increase in fluid pressure on the base of the lobes and within the crack can trigger the collapse of the hot exogenous lava domes. Using limit-equilibrium analysis, it is possible to calculate the water and vapor forces acting on the rear and base of the potentially unstable part of the lobe. The model presented is rectangular in cross-section, with material properties representative of andesitic dome rocks. Vapor pressures at the base of cracks are sealed by the penetrating rainfall, which forms a saturated cap within the lobe. This leads to an increase in fluid pressurization both through the underlying gas pressure and the downslope component of the liquid water cap. Fluid pressurization increases as the penetration depth increases. This rainfall penetration depth is dependent on the thermal properties of the rocks, antecedent temperature, lobe geometry, and the intensity and duration of precipitation. Dominant parameters influencing the stability of the lobe are principally lobe thickness, duration and intensity of rainfall, and antecedent lobe temperature. Our modeling reveals that thicker lobes are intrinsically more unstable due to the amplification of downslope forces in comparison to cohesive strength. The increase in the duration and intensity of rainfall events also increases the potential for collapse, as it leads to deeper liquid penetration. Deeper penetration depths are also achieved through lower antecedent temperatures since less fluid is lost through vaporization. Thus, the potential for rain-triggered collapse increases with time from emplacement.Editorial responsibility: D. Dingwell 相似文献
514.
Diffuse CO<Subscript>2</Subscript> degassing at Vesuvio,Italy 总被引:1,自引:0,他引:1
Francesco?FrondiniEmail author Giovanni?Chiodini Stefano?Caliro Carlo?Cardellini Domenico?Granieri Guido?Ventura 《Bulletin of Volcanology》2004,66(7):642-651
At Vesuvio, a significant fraction of the rising hydrothermal–volcanic fluids is subjected to a condensation and separation process producing a CO2–rich gas phase, mainly expulsed through soil diffuse degassing from well defined areas called diffuse degassing structures (DDS), and a liquid phase that flows towards the outer part of the volcanic cone. A large amount of thermal energy is associated with the steam condensation process and subsequent cooling of the liquid phase. The total amount of volcanic–hydrothermal CO2 discharged through diffuse degassing has been computed through a sequential Gaussian simulation (sGs) approach based on several hundred accumulation chamber measurements and, at the time of the survey, amounted to 151 t d–1. The steam associated with the CO2 output, computed assuming that the original H2O/CO2 ratio of hydrothermal fluids is preserved in fumarolic effluents, is 553 t d–1, and the energy produced by the steam condensation and cooling of the liquid phase is 1.47×1012 J d–1 (17 MW). The location of the CO2 and temperature anomalies show that most of the gas is discharged from the inner part of the crater and suggests that crater morphology and local stratigraphy exert strong control on CO2 degassing and subsurface steam condensation. The amounts of gas and energy released by Vesuvio are comparable to those released by other volcanic degassing areas of the world and their estimates, through periodic surveys of soil CO2 flux, can constitute a useful tool to monitor volcanic activity.Editorial responsibility: H. Shinohara 相似文献
515.
LIU Shuwen GUO Zhaojie ZHANG Zhicheng LI Qiugen & ZHENG Haifei The Key Laboratory of Orogenic Belts Crustal Evolution Ministry of Education China School of Earth Space Sciences Peking University Beijing China 《中国科学D辑(英文版)》2004,47(12):1085-1094
The Central Tianshan Tectonic Zone (CTTZ) is anarrow domain between an early Paleozoic southernTianshan passive continental margin and a late Paleo-zoic northern Tianshan arc zone, which is character-ized by the presence of numerous Precambrian meta-morphic basement blocks. Proterozoic granitoidgneisses and metamorphic sedimentary rocks,namely Xingxingxia and Kawabulag and Tianhugroups, are the most important lithological assem-blages in these metamorphic basement blocks, and alittle of … 相似文献
516.
Zonal propagation of kinetic energy and convection in the South China Sea and Indian monsoon regions in boreal summer 总被引:7,自引:0,他引:7
CHEN Longxun GAO Hui HE Jinhai TAO Shiyan & JIN Zuhui .Chinese Academy of Meteorological Sciences Beijing China .Nanjing Institute of Meteorology Nanjing China .Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2004,47(12):1076-1084
As early as in the 1980s, Chinese scientists hadfirst proposed that there exits two summer monsoonsystems in Asia, namely the East Asian summer mon-soon (EASM) and the Indian summer monsoon(ISM)[1-4]. The two monsoon systems are quite dif-ferent in characteristics. Since then, such issue andconclusion had been documented and approved by alot of studies in the past two decades, and was appliedin the guideline of the South China Sea summer mon-soon experiment (SCSMEX), which was undertak… 相似文献
517.
Geospatial-temporal analysis of land-use changes in the Yellow River Delta during the last 40 years 总被引:5,自引:0,他引:5
Qinghua?YeEmail author Gaohuan?Liu Guoliang?Tian Shenliang?Chen Chong?Huang Shupeng?Chen Qingshen?Liu Jun?Chang Yanan?Shi 《中国科学D辑(英文版)》2004,47(11):1008-1024
Research on land use/land cover changes (LUCC)has been the core project of the Global EnvironmentalChanges since the 1990s[1—6]. Scientists at home andabroad have been laying emphasis on integrationstudies on land-use change by “space and process”features[7—10] as researches on LUCC are in a greatdeal. It is of paramount important for us to studyLUCC at various spatial-temporal scales and build aquantitative assessment of land-use conversion by in-tegrated spatial-temporal features. … 相似文献
518.
Environmental records of lacustrine sediments in different time scales: Sediment grain size as an example 总被引:2,自引:0,他引:2
CHEN Jing’an WAN Guojiang David Dian Zhang ZHANG Feng & HUANG Ronggui . State Key Laboratory of Environmental Geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang China . Department of Geography Geology University of Hong Kong Pokfulam Road Hong Kong China 《中国科学D辑(英文版)》2004,47(10):954-960
Understanding the past is the key to know thepresent and to predict the future. As a core project ofthe International Geosphere Biosphere Program, PastGlobal Changes (PAGES) aims to reconstruct theevolution history of global climate, global environ-ment and global ecosystem with resort to all kinds ofnatural records, so as to reveal the change rules(change processes, change amplitude and change rate)of the global environment and thus provide scientificbasis for predicting climate changes p… 相似文献
519.
Discovery of agglutinated foraminifers from the Longzhaogou Group in eastern Heilongjiang Province 总被引:1,自引:1,他引:0
LI Gang & YU Shanmao. State Key Laboratory of Paleobiology Stratigraphy Nanjing Institute of Geology Paleontology Chinese Academy of Sciences Nanjing China .th Coal-prospecting Team of Geological Bureau NE China Inner Mongolia Coal Company Jixi China Correspondence should be addressed to Li Gang 《中国科学D辑(英文版)》2004,47(2):122-127
The low diversity agglutinated foraminifers are recovered from the Qihulin Formation of the Longzhaogou Group in eastern Heilongjiang, China. The foraminiferal fauna consists of 9 species of 5 genera. The common members are Cribrostomoides nonioninoides (Reuss), Haplophragmoides concavus (Chapman), H. gigas minor Nauss. Although the diagnostic zonal taxa are absent in the agglutinated fauna, according to the global stratigraphic distribution of the above-mentioned species, and the associated Pseudohaploceras ammonite fauna, the foraminiferal fauna may be of a Barremian-Aptian (Early Cretaceous) age. 相似文献
520.
Ore-forming fluid and mineralization of Caijiaying and Dajing polymetallic ore deposits 总被引:3,自引:0,他引:3
WANG Lijuan WANG Jingbin WANG Yuwang & ZHU Heping. Key Laboratory of Mineral Resources Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Beijing Institute of Geology for Mineral Resources Beijing China Correspondence should be addressed to Wang Lijuan 《中国科学D辑(英文版)》2004,47(2):97-107
Fluid inclusions from the Dajing and Caijiaying deposits have nearly the same ho-mogenization temperature. Correlation between temperature and salinity shows that both Sn-and Cu-bearing fluids Sn and Cu were present in the Dajing deposit but only one kind of fluids continuously evolved in the Caijiaying deposit. Study on rare earth elements (REE) in ancient fluid from the inclusions indicates that the fluid of Sn mineralizing stage in Dajing was derived from remelting magma of the continental crust, and the fluid of Cu-Pb-Zn mineralizing stage in the Dajing deposit and the fluid of Cu-Pb-Zn mineralization in the Caijiaying deposit were derived from the mantle. It is concluded that the Cu-Pb-Zn mineralizations in the Dajing and Caijiaying deposits resulted from the identical tectono-thermal event of magma-fluids induced by Mesozoic tectonic transition and extension in the eastern part of North China Craton. 相似文献