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881.
Michael G. Loso 《Journal of Paleolimnology》2009,41(1):117-128
For the heavily glaciated mountains of southern Alaska, few high-resolution, millennial-scale proxy temperature reconstructions
are available for comparison with modern temperatures or with the history of glacier fluctuations. Recent catastrophic drainage
of glacier-dammed Iceberg Lake, on the northern margin of the Bagley Icefield, exposed subaerial outcrops of varved lacustrine
sediments that span the period 442–1998 AD. Here, an updated chronology of varve thickness measurements is used to quantitatively
reconstruct melt-season temperature anomalies. From 1958 to 1998, varve thickness has a positive and marginally significant
correlation with May–June temperatures at the nearest coastal measurement stations. Varve sensitivity to temperature has changed
over time, however, in response to lake level changes in 1957 and earlier. I compensate for this by log-transforming the varve
thickness chronology, and also by using a 400-year-long tree-ring-based temperature proxy to reconstruct melt-season temperatures
at Iceberg Lake. Regression against this longer proxy record is statistically weak, but spans the full range of occupied lake
levels and varve sensitivities. Reconstructed temperature anomalies have broad confidence intervals, but nominally span 1.1°C
over the last 1500+ years. Maximum temperatures occurred in the late twentieth century, with a minimum in the late sixth century.
The Little Ice Age is present as three cool periods between 1350 and 1850 AD with maximum cooling around 1650 AD. A Medieval
Warm Period is evident from 1000 to 1100 AD, but the temperature reconstruction suggests it was less warm than recent decades—an
observation supported by independent geological evidence of recent glacier retreat that is unprecedented over the period of
record.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Michael G. LosoEmail: |
882.
Áslaug Geirsdóttir Gifford H. Miller Thorvaldur Thordarson Kristín B. Ólafsdóttir 《Journal of Paleolimnology》2009,41(1):95-115
The sediment fill of Haukadalsvatn, a lake in northwest Iceland, preserves a record of environmental change since deglaciation,
13 ka ago. The rapid sedimentation rate over the past 2 ka (ca. 4 m ka−1) provides a high-resolution archive of late Holocene environmental change. Physical and chemical environmental proxies extracted
from cores from the Haukadalsvatn sediment fill provide a reconstruction of sub-decadal-scale climate variability in Iceland
over the past 2 ka. Over this interval biogenic silica (BSi) reflects warm April–May temperatures, whereas total organic carbon
(TOC) peaks represent an increased flux of carbon to the lake from eolian-derived soil erosion following periods of cold summers
accompanied by dry, windy winters. The proxy-based temperature reconstructions show a broad interval of warmth through Medieval
times, but this warmth is punctuated by multi-decadal cold intervals. The transition into the Little Ice Age occurred in two
steps, with initial summer cooling 1250–1300 AD, and a more severe drop in summer temperatures between 1450 and 1500 AD; both
are periods of severe explosive volcanism. Multi-decadal patterns of cold and warm conditions have some characteristics of
a North Atlantic Oscillation (NAO)-like signal, but instrumental records and proxy-based reconstructions of the NAO index
contain little power in the frequencies most strongly expressed in our data set. Although severe soil erosion in Iceland is
frequently equated with settlement, our reconstructions indicate that soil erosion began several centuries before settlement,
whereas for several centuries after settlement, when summer temperatures were relatively high, there was little or no soil
erosion. Only during the transition into and during the Little Ice Age did soil erosion become a major feature of the record.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Kristín B. ólafsdóttirEmail: |
883.
The effects of intra-seasonal wind forcing on the mean field of the tropical Pacific Ocean has been studied using an ocean general circulation model (GCM). Idealized intra-seasonal zonal wind forcing with zero mean, which propagates eastward, induces net eastward jets at the equator that shift the warm water pool to the east. The mean temperature of the upper 200 m of the ocean increases off the equator and decreases at the equator. The change is independent of the propagation speed of the intra-seasonal wind forcing. The magnitude of the change depends on the amplitude and the period of the forcing, and the ocean structure, while the spatial pattern is independent of these parameters. A simple shallow water model is used to explain these changes. It is found that the term responsible for the enhanced eastward Equatorial jet is the Reynolds stress term, which arises from a phase shift of the zonal current due to friction. The resultant convergence of eastward momentum on the equator and geostrophic adjustment of the interface to the change of zonal current brings about the thermal redistribution of the upper ocean seen in the GCM. 相似文献
884.
885.
天然气藏与油藏形成机理及分布特征的异同 总被引:13,自引:3,他引:10
作为流体矿藏气藏与油藏的形成和分布具有相似性,都需要经过由分散到富集的成藏过程。天然气来源的广泛性和易于溶解、运移、散失的特性,决定了天然气双石油具有更多的运聚成藏方式和时空分布的广泛性。水溶对流运移、多源复合成藏、溶解气脱溶成藏、运聚动平衡成藏,是天然气运聚成藏的重要特点。 相似文献
886.
887.
近期在塔里木盆地顺托果勒地区顺9井发现了下志留统柯坪塔格组下段原生油藏。通过岩心、测井和三维地震综合解释认为:柯坪塔格组下段沉积期间,顺托果勒地区经历了半深海-浅海-三角洲沉积过程,油层砂岩属于柯坪塔格组下段上部的由北向南的三角洲河口坝与分流河道沉积。南部附近的塔中隆起虽然距顺9井较近,但并未提供陆源碎屑物质。由于后期构造南抬北降,所以油藏区现今构造属于北倾缓坡背景,其上局部发育低幅度构造。圈闭类型主要为三角洲砂体岩性圈闭,其次为低幅度构造圈闭和岩性构造复合圈闭。有利圈闭区位于三角洲前缘主砂体发育带和局部构造圈闭叠合区。 相似文献
888.
Douglas M. Thompson 《地球表面变化过程与地形》2012,37(2):223-239
Studies on pool morphologies include reports of over 80% or 90% of pools being associated with structural controls and large obstructions that include boulders, bedrock outcrops and large woody debris (LWD). A Monte Carlo simulation approach and developmental computer model was created to predict pool formation, spacing and the percentage length covered by pools, riffles, scour holes and runs based on input data that include channel slope, width, the number of small and large boulders, and the number of 10–30 cm, 30–60 cm and >60 cm pieces of wood. The statistical‐empirical model is founded on the idea that boulders, bedrock outcrops and large woody debris provide a physical framework that then controls local water‐surface slopes, velocity patterns and the locations of pools and riffles. The spacing values of individual types and sizes of obstructions are modeled as log‐normal distributions with separate distributions for each obstruction type. Pools are assigned different probabilities of development depending on the obstruction type. Pool and riffle lengths used to create the subsequent morphology follow their own slope‐dependent, log‐normal trends. A minimum distance develops between successive pools because of the backwater and turbulent conditions needed for pool formation. The total number and spacing of pools, riffles and scour holes thus reflects the number and locations of obstructions and characteristics of the pool–riffle couplet. The simulation model accurately captures the number of pools in the modeled data range at 65% of all the verification field sites, and 86% of the verification field sites with a more limited range of width and slope characteristics. Lower levels of prediction capabilities are associated with modeled numbers of scour holes and log jams. The model accurately mimics some statistical attributes of pool spacing, and future versions of the model could be developed to improve overall predictive capabilities. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
889.
利用卫星遥感资料反演出的海洋大气参数,应用目前世界较为先进的通量算法(CORAER 3.0),计算了西太平洋区域海-气热通量(感热通量和潜热通量)。首先分析了海-气热通量的多年平均场和气候场变化的基本特征,以及年际和年代际变化特征;进而对其与南海夏季风爆发之间的关系进行了初步探讨。结果表明,西太平洋海-气热通量具有明显的时空分布特征,感热通量的最大值出现在黑潮区域,潜热通量的最大值出现在北赤道流区和黑潮区域。在气候平均场中,黑潮区域的感热通量和潜热通量最大值均出现在冬季,最小值出现在夏季;暖池区域感热通量除了春季较小外,冬、夏和秋季基本相同,而潜热通量最大值出现在秋、冬季,最小值出现在春、夏季。另外,海-气热通量还具有显著的年际变化和年代际变化,感热通量和潜热通量均存在16 a周期,与南海夏季风爆发存在相同的周期。由相关分析可知,4月份暖池区域的海-气热通量与滞后3 a的南海夏季风爆发之间存在密切相关关系,这种时滞相关性,可以用于进行南海夏季风爆发的预测,为我国汛期降水预报提供科学依据。基于以上结论,建立多元回归方程对2012年的南海夏季风爆发进行了预测,预测2012年南海夏季风爆发将偏晚1~2候左右。 相似文献
890.