全文获取类型
收费全文 | 1784篇 |
免费 | 247篇 |
国内免费 | 292篇 |
专业分类
测绘学 | 58篇 |
大气科学 | 48篇 |
地球物理 | 488篇 |
地质学 | 1027篇 |
海洋学 | 197篇 |
天文学 | 111篇 |
综合类 | 73篇 |
自然地理 | 321篇 |
出版年
2024年 | 6篇 |
2023年 | 16篇 |
2022年 | 40篇 |
2021年 | 42篇 |
2020年 | 57篇 |
2019年 | 59篇 |
2018年 | 52篇 |
2017年 | 51篇 |
2016年 | 55篇 |
2015年 | 74篇 |
2014年 | 85篇 |
2013年 | 163篇 |
2012年 | 75篇 |
2011年 | 85篇 |
2010年 | 58篇 |
2009年 | 134篇 |
2008年 | 110篇 |
2007年 | 114篇 |
2006年 | 119篇 |
2005年 | 126篇 |
2004年 | 89篇 |
2003年 | 72篇 |
2002年 | 84篇 |
2001年 | 61篇 |
2000年 | 79篇 |
1999年 | 55篇 |
1998年 | 73篇 |
1997年 | 50篇 |
1996年 | 38篇 |
1995年 | 30篇 |
1994年 | 36篇 |
1993年 | 24篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 19篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1978年 | 1篇 |
1973年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有2323条查询结果,搜索用时 531 毫秒
961.
遵义断裂带是贵州省境内南北向最大的断层之一,对断裂带的宏观构造、微观构造及两侧沉积相研究表明,该断裂是形成于燕山期的盖层断裂,并非同沉积断裂。其活动演化与周缘构造单元之间存在明显的耦合性,控制着断裂两侧燕山期褶皱、断裂的展布形迹。结合流体包裹体测温和ESR定年的研究表明,断裂的变形以浅部的脆性为主,主要经历了三期活动:主燕山期(J3-K1)的主期变形,表现为强烈的高角度自东向西逆冲兼左行剪切,断裂基本定型;燕山晚期(K2-E),表现为正断层兼右行平移,控制K2-E红盆沉积,石英脉ESR定年约束该期活动在59~65Ma;喜山期(古近纪至今),表现为自西向东逆冲。断裂现今构造形迹为多期构造叠加的结果,它在整个活动历史中均表现为脆性,对黔中隆起后期构造格局起到明显的制约作用。 相似文献
962.
地球科学研究中的创造性思维 总被引:1,自引:0,他引:1
刘德长 《地球信息科学学报》2005,7(1):16-19
本文通过分析地质发展历史上的某些成就,着重探讨了地球科学研究中创造性思维的8个问题。 相似文献
963.
S. Meiners 《GeoJournal》2005,62(3-4):49-90
The most recent glacial history of the Bar Valley on the Batura south side of the great Karakorum main ridge shows a marked
retreat of the Kukuar and Baltar glaciers since 1915 by 8 km. This tendency is continuing. A great lateral moraine (GLM),
which shows the latest, historical maximum postglacial stage, is accompanied by a higher level, which reflects a neoglacial
glacier level whose ice margins no longer exist. An earth-pyramid moraine rising high above the glacier, as also occurs on
the northern declivities of the Batura, does not mark a specific level, but bears witness to a valley-filling glacier, for
which further indicators can be found along the valley flank. In the gorge-like narrow trough valley, the flanks of which
are covered by steep debris cones originating from the postglacial, numerous former glacial characteristics contrast with
the current glaciation of the far retreated Kukuar and Baltar glaciers. Moraine material found at the valley outlet at Chalt
and also on the Talmutz pass demonstrates complete ice filling of the Bar valley, also supported by the Daintar glacier. From
a glacial geomorphological perspective, this confirms a late to high glacial connection of the Bar glacier to a Hunza glacier,
as postulated by Kuhle (2005). 相似文献
964.
Stratigraphical investigations, geomorphological mapping, and diatom, plant macrofossil and pollen analyses were undertaken in and around two lakes in central Ireland to establish correlations between changes in lake conditions and catchment vegetation throughout the Holocene. Similar investigations of an adjacent mire reveal early Holocene changes in lake level and area. The palaeoecological data show high correlations related to variations in lake depth and area, catchment vegetation type, organic inputs and trophic status. Catchment‐scale deforestation is gradual and occurs through the Bronze and the Iron Ages, and the construction of a crannog in the early Medieval period (seventh century AD ) appears to be associated with a widespread increase in deforestation and mixed agriculture in the catchment. Both pollen and plant macrofossils suggest that one of the crannogs was used for crop storage in addition to domestic and any other activities. In the early to middle Holocene similarities in the proxy‐data appear to be climatically driven through changing lake levels and areal extent whereas the later Holocene record is clearly dominated by anthropogenic changes within the catchment and the construction of crannogs in the lakes. The advantages of combining multi‐proxy indicators of lake hydroecology with the vegetation record are illustrated. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
965.
966.
Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake‐level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb‐2, first part of the Bølling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake‐level. A weak rise occurred during this zone. The Juniperus–Hippophaë to Betula zone transition coincided with a lake‐level lowering, interrupted by a short‐lived but marked phase of higher lake‐level recorded at the neighbouring site of Hauterive‐Champréveyres, but not present at Hauterive/Rouges‐Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb‐3, second part of the Bølling, ca 14 450–14 000 cal. yr BP), a marked rise in lake‐level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake‐level associated with raised values in Artemisia and other non‐arboreal pollen. The last part of RPAZ CHb‐3 saw a fall in lake‐level. The lower lake‐levels during RPAZ CHb‐2 to early RPAZ CHb‐3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake‐level punctuating the GI 1e might be linked to the so‐called Intra‐Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen‐isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges‐Terres lake‐level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb‐4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb‐4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake‐levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges‐Terres lake‐level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake‐level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
967.
采用RAPD方法研究了洪湖微齿眼子菜种群的遗传多样性,并初步探讨了它的遗传结构及影响因素。在97个RAPD标记中有28条(28.87%)是多态性标记,Shannon信息多样性指数分析表明该种群总的遗传多样性为0.193,说明洪湖微齿眼子菜种群的遗传多样性水平较低。研究发现距离和种群发展历史对洪湖微齿眼子菜种群的遗传结构有重要影响。 相似文献
968.
有效古温标的缺乏制约了碳酸盐岩层系热史的研究,团簇同位素作为一种新兴古温标,对碳酸盐岩层系热史重建具有重要意义。四川盆地二叠系是天然气勘探开发的重点层系,本文通过对川东地区二叠系碳酸盐岩样品进行团簇同位素测试,联合镜质组反射率重建了二叠纪以来的热史,在此基础上明确了二叠系烃源岩的热演化,并讨论了峨眉山地幔柱对川东热体制的影响。川东地区碳酸盐岩的团簇同位素温度在101. 7~178. 7℃,利用交换/扩散模型进行热史模拟认为:川东地区晚白垩世古温度最高,最高古温度在213~225℃,古地温梯度在23~33 ℃/km;川东地区二叠纪古热流最高,最高古热流约为55~70 mW/m 2,二叠纪之后热流逐渐降低至现今大地热流。烃源岩热演化分析认为:川东地区二叠系烃源岩热演化具有阶段性,热演化受控于构造运动,受印支期运动和燕山 喜马拉雅期运动影响存在两期热演化停滞,晚白垩世达到最高古温度后停止生烃,现今处于生气阶段。川东地区二叠纪热流值和烃源岩热演化主要受到地壳拉张减薄作用的影响,受峨眉山地幔柱的影响较小且具有局限性。 相似文献
969.
970.
利用机载Ka波段云雷达(Airborne Ka-Band Precipitation Cloud Radar, KPR)和粒子测量系统(Droplet Measurement Technologies, DMT),分析了2018年4月22日黄淮气旋背景系统下积层混合云中对流泡的动力和微物理特征。首先,对Ka波段云雷达观测的山东地区春季36个对流泡样本按照回波强度、水平尺度、回波顶高三个参量进行统计,结果表明平均回波强度为20~30 dBZ的对流泡占69%。对流泡水平尺度为15~30 km,占61%。对流泡最大回波顶高集中在6~8 km,比周边层云高2~4 km。之后,对4月22日积层混合云中的对流泡个例微物理参数进行统计,结果表明对流泡内部以上升气流为主,最大上升气流速度达到1.35 m s?1,平均上升气流速度为0.22 m s?1;对流泡内过冷水含量比较高,最大含水量为0.34 g m?3,平均含水量为0.15 g m?3。对流泡内冰晶数浓度是泡外的5.5倍,平均直径是泡外的1.7倍。结合云粒子图像探头,发现对流泡前沿和尾部冰粒子以柱状和辐枝状为主,而对流泡核心区域冰粒子以聚合体形式存在。冰粒子通过凇附过程和碰并过程增长,过冷水含量不足时冰粒子的凇附增长形成柱状粒子,含量充足时可迅速凇附成霰粒子。对流泡内降水形成的微物理机制不完全相同,主要依赖过冷水含量。当云中有充足的过冷水分布时,高层冰晶通过凇附增长形成霰粒子,通过融化层后形成降水;当云中缺少过冷水时,降水的形成主要通过水汽凝华过程形成冰雪晶,然后雪晶通过聚合过程实现增长。 相似文献