全文获取类型
收费全文 | 144篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 3篇 |
地球物理 | 26篇 |
地质学 | 117篇 |
海洋学 | 11篇 |
天文学 | 1篇 |
综合类 | 1篇 |
自然地理 | 12篇 |
出版年
2022年 | 1篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 7篇 |
2011年 | 5篇 |
2010年 | 14篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 7篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有176条查询结果,搜索用时 31 毫秒
91.
青藏高原大冰盖假说的提出与扬弃 总被引:5,自引:3,他引:2
M.Kuhle自20世纪80年代,提出青藏高原冰期发育大冰盖假说,连续发表20多篇文章,喧闹一时,吸引很多人注意,一批中国学者首先反对,不少欧、美、日等国学者专程为此问题上高原考察,结果均持异议。1991年第13届INQUA大会前后,很多学者参加的横贯青藏高原考察,未能看到冰盖假说的任何实证。IGCP计划253项为此问题设立的成问题冰盖工作组,工作组组长N.Rutter专文评论M.Kuhle假说中的许多错误,认为绝大多数学者均拒绝接受冰盖论,但M.Kuhle仍坚持其原先论点。现在可以说在科学讨论中大冰盖假说实际上被扬弃了 相似文献
92.
The 36Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the 36Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms 36Cl (g Ca)−1 yr−1 and are 228±18 atoms 36Cl (g K)−1 yr−1, respectively. The calculated ground-level secondary neutron production rate in air, Pf(0), inferred from thermal neutron absorption by 35Cl is 762±28 neutrons (g air)−1 yr−1 for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is 40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated 36Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated 14C ages, thereby supporting the validity of our 36Cl production rates integrated over the last 15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators. 相似文献
93.
Mass balance of the Lambert Glacier basin, East Antarctica 总被引:2,自引:1,他引:2
Since it is the largest glacier system in Antarctica, the Lambert Glacier basin plays an important role in the mass balance
of the overall Antarctic ice sheet. The observed data and shallow core studies from the inland traverse investigations in
recent years show that there are noticeable differences in the distribution and variability of the snow accumulation rate
between east and west sides. On the east side, the accumulation is higher on the average and has increased in the past decades,
while on the west side it is contrary. The ice movement measurement and the ice flux calculation indicate that the ice velocity
and the flux are larger in east than in west, meaning that the major part of mass supply for the glacier is from the east
side. The mass budget estimate with the latest data gives that the integrated accumulation over the upstream area of the investigation
traverse route is larger than the outflow ice flux by 13%, suggesting that the glacier basin is in a positive mass balance
state and the ice thickness will increase if the present climate is keeping. 相似文献
94.
Jan Mangerud Reidar LøvlieSteinar Gulliksen Anne-Karin HufthammerEiliv Larsen Vidar Valen 《Quaternary Research》2003,59(2):213-222
Two paleomagnetic excursions, the Skjong correlated with the Laschamp (about 41,000 GISP2 yr B.P.) and the Valderhaug correlated with the Mono Lake (about 34,000 GISP2 yr B.P.), have been identified in stratigraphic superposition in laminated clay deposited in ice-dammed lakes in three large caves in western Norway. During both periods the margin of the Scandinavian Ice Sheet advanced and reached the continental shelf beyond the outermost coastline. The mild, 4000-yr-long Ålesund interstade, when the coast and probably much of the hinterland were ice-free, separated the two glacial advances. The two paleomagnetic excursions have also been indirectly identified as increased fluxes of 36Cl and 10Be in the GRIP ice core, Greenland. This article presents a correlation between ice-margin fluctuations of the Scandinavian Ice Sheet and the stratigraphy of GRIP/GISP cores, using the paleomagnetic excursions and the 36Cl and 10Be peaks and thus circumventing the application of different dates or time scales. Some of the fluctuations of the Scandinavian Ice Sheet were of the “Allerød/Younger Dryas type” in the sense that its margin retreated during mild interstades on Greenland and readvanced during cold stades. However, some fluctuations were apparently not in phase with the Greenland climate. 相似文献
95.
本文以1:5万里庄幅为例,阐述了运用G1S系统对区调过程中各种资料的处理与编辑方法,并介绍了数字制图方法及工艺流程,提出了GIS系统在1:5万区调工作中的应用前景。 相似文献
96.
Outcrops of pebbly mud (diamict) at Scarborough in Southern Ontario, Canada (the so-called Sunnybrook ‘Till’) are associated with the earliest incursion of the Laurentide Ice Sheet (LIS) into mid-continent North America some 45,000 years ago. The Sunnybrook is a blanket-like deposit containing deepwater ostracodes and occurs conformably within a thick (100 m) succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake. Contextual evidence (associated facies, sedimentary structures, deposit geometry and landforms) indicates a low energy depositional setting in an ice-dammed ancestral Lake Ontario in which scouring by floating ice masses was an important process. U-shaped, iceberg-cut scours (with lateral berms) up to 7 m deep, occur on the upper surface of the Sunnybrook and are underlain by ‘sub-scour’ structures that extend several meters below the scour base. Ice-rafted concentrations of clasts (‘clast layers’), grooved surfaces formed by floating ice glissading over a muddy lake floor (‘soft sediment striations’) and melanges of sand and mud mixed by grounding ice keels (‘ice keel turbates’) are present and are all well known from modern cold environments. The wider significance of this depositional model is that the LIS margin lay east of Scarborough and did not overrun Southern Ontario. This finding is in agreement with recent data from the Erie Basin of Canada, Ohio, and Indiana where deposits formerly correlated with the Sunnybrook (and thus implying an extensive early Wisconsin ice sheet) are now regarded as Illinoian. A speculative hypothesis is proposed that relates deposition of the Sunnybrook and two younger deposits of similar sedimentology, to surge-like instabilities of the southern LIS margin. 相似文献
97.
98.
Single grain optical dating of glacigenic deposits 总被引:4,自引:0,他引:4
Determining the age of glacigenic sediments is difficult for many geochronological methods because of the lack of suitable materials for analysis. Luminescence dating can be applied to the mineral grains making up the glacigenic sediments. However a major source of uncertainty in previous studies has been whether the mineral grains were exposed to sufficient daylight prior to deposition for the luminescence signal to be reset. Measurements of the optically stimulated luminescence signal from single sand-sized quartz grains offers the potential for explicitly identifying if a sediment contains grains that were not exposed to sufficient daylight to reset their signal. Statistical analysis of the resulting data can then reject those grains to allow the age of the sample to be determined. This study is the first to apply single grain optical dating to glacigenic sediments, and demonstrates the issues involved by analysis of samples from Chile and Scotland. Ages from 2.4±0.5 to 17.3±1.5 ka are produced. Comparison of the results with independent age control suggests that the ages are reliable. The results also show that the extent of bleaching at deposition varies considerably from one sample to another. For the most incompletely bleached sample, luminescence measurements based on the average of many hundreds or thousands of grains would have overestimated the age of the sample by 60 ka, but the single grain method proposed here was able to reliably date it. 相似文献
99.
Sheet flows occur widely in natural free-surface flows including rivers in flood, tidal estuaries and coastal waters in storm conditions when bed shear stress becomes sufficiently high. Particle volumetric concentration in sheet flows normally follows a linear distribution with the Rouse [Rouse H. Modern conceptions of the mechanics of fluid turbulence. Trans ASCE, 1937;102:463–543] distribution applicable in the dilute water column above the sheet-flow layer. However, a well-verified formula for determining particle velocity distribution in sheet flows is still lacking. This paper presents formulas to describe the particle velocity profile in steady or oscillatory sheet flows. They compare well with measured data. In particular, the novel formula for determining the particle velocity at the top of bedload–sediment-dominated sublayer in sheet flows is also well verified with measured data. 相似文献
100.
以1∶5万高炉集幅为研究对象,在6个点/km 2及4个点/km 2两种采样密度条件下,土壤元素在地球化学参数特征及空间分布上均相近,表明该图幅内采样密度4个点/km 2可以满足1∶5万土地质量调查评价工作的要求。基于不同采样密度下土壤元素地球化学特征的对比分析,提出淮北平原覆盖区地质背景相对单一的连片耕地区开展1∶5万土地质量调查时可采用最低采样密度(4个点/km 2)。土壤环境质量评价结果显示,区内土壤环境质量优良,以优先保护类土壤为主,安全利用类土壤仅零星分布,影响土壤环境质量的指标为Cd,研究结果可为该地区实施绿色无公害产业发展提供科学依据。 相似文献