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151.
152.
冰芯钻取后,样品截取原则和环境记录的初步解释要求对年代-深度剖面有一初步了解,即要求建立冰体随深度变化的时间尺度。根据柯林斯冰帽一年多野外实测资料所揭示的小冰穹运动状况、温度分布、物质平衡和动力学特征,本文采用Dansgarrd-Johnsen模型和等温冰体流动模型(n=3),分别对一支80.2m冰芯的时间尺度进行初步估算。结果表明两种模型断代结果非常接近,在距冰床10m深度处,两模型分别给出1897年和1854年的冰龄。对比指出两种模型计算出的冰帽各深度冰龄最大误差不大于2%。与冰芯中上部含深褐色火山灰冰层的历史记录年代相比误差小于3%。 相似文献
153.
Deborah L. Elliott-Fisk 《自然地理学》2013,34(4):299-323
The White Mountains, astride the California-Nevada stateline, are the highest and westernmost of the Great Basin ranges. This range was extensively glaciated during the Quaternary Period. Glacial landforms and scattered erratics were identified in the field using primarily morpho-and lithostratigraphic criteria, and mapped on aerial photographs and topographic maps. Topographic characteristics of the glacial deposits were analyzed using standard statistical procedures. A sequence of glacial deposits was identified in terms of six glacial stages, these glaciations named according to type site, and relative ages inferred. With the exception of perched Stage I (early) deposits along the range crest, reconstructed equilibrium-line altitudes and elevation of the glacier termini increase to the present, with glacier length and inferred size decreasing through time. Preliminary data suggest that weathering and pedogenesis are also progressive, though environmental gradients mask some of these distinctions between deposits. It is hypothesized that the White Mountains have a similar glacial chronology to the adjacent Sierra Nevada, but that with the intensification of the Sierran rainshadow during the Quaternary, the extent of glaciation in the White Mountains apparently decreased through time owing to regional tectonic uplift. This had led to the preservation of a more complete sequence of glacial deposits than in the Sierra Nevada, making the delineation of multiple mid-Quaternary events possible in many valleys. Further radiometric and chronometric dating of these deposits is in progress. [Key words: Glaciation, Quaternary, glacial geomorphology, White Mountains, California, Nevada. 相似文献
154.
Compilation of the offshore and onshore altitudinal limits of the loess deposits of western France and southern England shows that they were deposited by low-level wind fields. These relate to (i) the deflation of silt-rich sediment extracted from the outwash plains of the not far distant British–Irish Ice Sheet and from the palaeo-rivers of the Channel, and (ii) the existence of north and north-western palaeo-winds deduced from particle size analysis and heavy mineral distribution, and suggest (iii) that loess particles were transported by strong katabatic winds blowing from the northern ice-covered regions towards Brittany and Normandy. Comparison between the main orientation of Neanderthal shelters and the direction of the katabatic winds shows that they were perpendicular to each other. The dominant orientation of the shelters was apparently ruled by these winds. A small-scale study concentrating on the penultimate glaciation shows that in contrast to Brittany and Normandy where loess deposits accumulated on north-facing cliffs, in England the same particles were deposited on the leeside of the hills. The existence of deflation zones, violently swept by Marine Isotope Stage 6 katabatic winds south of the British–Irish ice sheet, was probably at the origin of the restricted number of Neanderthals at that time in England. © 2021 John Wiley & Sons, Ltd. 相似文献
155.
156.
Lake ice supports a range of socio‐economic and cultural activities including transportation and winter recreational actives. The influence of weather patterns on ice‐cover dynamics of temperate lakes requires further understanding for determining how changes in ice composition will impact ice safety and the range of ecosystem services provided by seasonal ice cover. An investigation of lake ice formation and decay for three lakes in Central Ontario, Canada, took place over the course of two winters, 2015–2016 and 2016–2017, through the use of outdoor digital cameras, a Shallow Water Ice Profiler (upward‐looking sonar), and weekly field measurements. Temperature fluctuations across 0°C promoted substantial early season white ice growth, with lesser amounts of black ice forming later in the season. Ice thickening processes observed were mainly through meltwater, or midwinter rain, refreezing on the ice surface. Snow redistribution was limited, with frequent melt events limiting the duration of fresh snow on the ice, leading to a fairly uniform distribution of white ice across the lakes in 2015–2016 (standard deviations week to week ranging from 3 to 5 cm), but with slightly more variability in 2016–2017 when more snow accumulated over the season (5 to 11 cm). White ice dominated the end‐of‐season ice composition for both seasons representing more than 70% of the total ice thickness, which is a stark contrast to Arctic lake ice that is composed mainly of black ice. This research has provided the first detailed lake ice processes and conditions from medium‐sized north‐temperate lakes and provided important information on temperate region lake ice characteristics that will enhance the understanding of the response of temperate lake ice to climate and provide insight on potential changes to more northern ice regimes under continued climate warming. 相似文献
157.
M. B. Danard M. C. Rasmussen T. S. Murty R. F. Henry Z. Kowalik S. Venkatesh 《Natural Hazards》1984,2(2):153-171
Storm surges in the Beaufort Sea present a severe problem for navigation as well as for offshore oil drilling activities. Influence of ice cover on storm surges in the Beaufort Sea is examined making use of a numerical model as well as a set of observations.The automated shallow-water model of Henry has been modified to incorporate ice cover and is adapted to the Beaufort Sea. The leading edge of the permanent ice is calculated from the loci of identifiable points. Generalized similarity theory is employed to compute wind stresses. Simulations are made using model-predicted ice concentrations and observed ice concentrations. Ice motion is relatively small in units of model grid distance (approximately 18 km) during surges. Spherical effects are important and should be included in future adaptations of the model. Comparison of the computed surges with observed surges for eight different events showed reasonable agreement. 相似文献
158.
喜马拉雅山南坡冬季暴雪对高原南部冰芯中稳定同位素记录的影响 总被引:3,自引:0,他引:3
聂拉木气象站降水中 δ18O的变化表明 ,夏季降水中 δ18O为一低值阶段 ;冬季降水中 δ18O总的来说为一高值阶段 ,但冬季暴风雪中δ18O的值和夏季强的季风活动中降水的δ18O一样很低。由于该地区冬季降水十分活跃 ,冬季降水中 δ18O的变化对该地区冰芯记录将产生重要的影响。首先是用δ18O的季节变化来对冰芯定年产生一定的困难 ,其次喜马拉雅山中段冰芯中的δ18O记录不仅包括了夏季季风活动的强弱信息 ,而且冬季强的暴风雪过程也记录在内。 相似文献
159.
Ute C. Herzfeld Craig S. Lingle Cecily Freeman Chris A. Higginson Michael P. Lambert Li-Her Lee Vera A. Voronina 《Mathematical Geology》1997,29(6):859-890
The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar
sea represent its gateways to the world’s oceans. Satellite radar altimeter data provide an opportunity for mapping surface
elevation at kilometerresolution with meteraccuracy. Geostaristical methods have been developed for the analysis of these
data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert
Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives
of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter
time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that
one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is
the key for a limeseries analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire
Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics
of the ice-stream/iceshelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice.
In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps
may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric
problem. 相似文献
160.
HuiJun Jin XiaoLi Chang DongLiang Luo RuiXia He LanZhi L SiZhong Yang DongXin Guo XueMei Chen Stuart A. Harris 《寒旱区科学》2016,8(4):269-296
In Northeast China, permafrost advanced and retreated several times under the influences of fluctuating paleo-climates and paleo-environments since the Late Pleistocene. During the last 60 years, many new data were obtained and studies were conducted on the evolution of permafrost in Northeast China, but so far no systematic summary and review have been made. Based on sedimentary sequences, remains of past permafrost, paleo-flora and-fauna records, and dating data, permafrost evolution since the Late Pleistocene has been analyzed and reconstructed in this paper. Paleo-temperatures reconstructed from the remains of past permafrost and those from paleo-flora and-fauna are compared, and thus the southern limit of permafrost(SLP) in each climate period is inferred by the relationship of the permafrost distribution and the mean annual air/ground temperatures(MAAT/MAGT). Thus, the evolutionary history of permafrost is here divided into five stages:(1) the Late Pleistocene(Last Glaciation, or LG)(65 to 10–8.5 ka), the Last Glaciation Maximum(LGM, 21–13 ka) in particular, the coldest period in the latest history with a cooling of about 6~10 ?C, characterized by extensive occurrences of glaciation, flourishing Mammathas-Coelodonta Faunal Complex(MCFC), widespread aeolian deposits, and significant sea level lowering, and permafrost greatly expanded southwards almost to the coastal plains(37?N–41?N);(2) the Holocene Megathermal Period(HMP, 8.5–7.0 to 4.0–3.0 ka), 3~5 ?C warmer than today, permafrost retreated to about 52°N;(3) the Late Holocene Cold Period(Neoglaciation)(4.0–3.0 to 1.0–0.5 ka), a cooling of 1~3 ?C, some earlier thawed permafrost was refrozen or attached, and the SLP invaded southwards to 46?N;(4) the Little Ice Age(LIA, 500 to 100–150 a), the latest cold period with significant permafrost expansion; and(5) climate warming since the last century, during which Northeast China has undergone extensive permafrost degradation. The frequent and substantial expansions and retreats of permafrost have greatly impacted cold-region environments in Northeast China. North of the SLP during the HMP, or in the present continuous permafrost zone, the existing permafrost was largely formed during the LG and was later overlapped by the permafrost formed in the Neoglaciation. To the south, it was formed in the Neoglaciation. However, many aspects of permafrost evolution still await further investigations, such as data integration, numerical reconstruction, and merging of Chinese permafrost history with those of bordering regions as well as collaboration with related disciplines. Of these, studieson the evolution and degradation of permafrost during the past 150 years and its hydrological, ecological, and environmental impacts should be prioritized. 相似文献