全文获取类型
收费全文 | 51759篇 |
免费 | 5457篇 |
国内免费 | 7752篇 |
专业分类
测绘学 | 2582篇 |
大气科学 | 8443篇 |
地球物理 | 11555篇 |
地质学 | 25714篇 |
海洋学 | 4377篇 |
天文学 | 3047篇 |
综合类 | 4900篇 |
自然地理 | 4350篇 |
出版年
2024年 | 123篇 |
2023年 | 536篇 |
2022年 | 1224篇 |
2021年 | 1480篇 |
2020年 | 1262篇 |
2019年 | 1308篇 |
2018年 | 5842篇 |
2017年 | 5055篇 |
2016年 | 3926篇 |
2015年 | 1524篇 |
2014年 | 1881篇 |
2013年 | 1582篇 |
2012年 | 2430篇 |
2011年 | 4102篇 |
2010年 | 3533篇 |
2009年 | 3801篇 |
2008年 | 3148篇 |
2007年 | 3555篇 |
2006年 | 1208篇 |
2005年 | 1233篇 |
2004年 | 1202篇 |
2003年 | 1187篇 |
2002年 | 1078篇 |
2001年 | 848篇 |
2000年 | 1060篇 |
1999年 | 1465篇 |
1998年 | 1244篇 |
1997年 | 1304篇 |
1996年 | 1086篇 |
1995年 | 1002篇 |
1994年 | 898篇 |
1993年 | 783篇 |
1992年 | 638篇 |
1991年 | 464篇 |
1990年 | 318篇 |
1989年 | 349篇 |
1988年 | 292篇 |
1987年 | 199篇 |
1986年 | 165篇 |
1985年 | 121篇 |
1984年 | 101篇 |
1983年 | 78篇 |
1982年 | 76篇 |
1981年 | 76篇 |
1980年 | 69篇 |
1979年 | 31篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1958年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
John Clinton Aldo Zollo Alexandru Marmureanu Can Zulfikar Stefano Parolai 《Bulletin of Earthquake Engineering》2016,14(9):2441-2458
European researchers and seismic networks are active in developing new approaches to earthquake early warning (EEW), implementing and operating test EEW systems, and in some cases, offering operational EEW to end users. We present the key recent developments in EEW research in Europe, describe the networks and regions where EEW is currently in testing or development, and highlight the two systems in Turkey and Romania that currently provide operational systems to a limited set of end users. 相似文献
962.
济南北部地热田地热资源类型属于层状裂隙岩溶型,热源是北部齐河-广饶断裂的沟通导热,盖层是第四系、新近系、石炭-二叠系、侏罗系.可利用的、具有开发价值的热储层为奥陶系灰岩热储,该热储层顶板埋深在700~2500m左右,热储层厚度由南向北逐渐增大,单井涌水量2000m3/d左右,孔口水温一般在38~57℃,地热田东部地热水矿化度1.4~3.5g/L左右,西部5.1~7.2g/L左右,地热水中富含氟、锶、偏硅酸等微量元素,具腐蚀性,结垢性弱,具较好的开发利用价值.经计算奥陶系热储层单井可采资源量为7.3×105m3/a,合理井间距为5000m. 相似文献
963.
Variation of albedo to soil moisture for sand dunes and biological soil crusts in arid desert ecosystems 总被引:1,自引:0,他引:1
Ya-feng Zhang Xin-ping Wang Rui Hu Yan-xia Pan Hao Zhang 《Environmental Earth Sciences》2014,71(3):1281-1288
Surface albedo plays a crucial role in the energy balance of soils. The surface albedo and surface soil moisture of bare sand and biological soil crusts (BSCs) were concurrently observed on field plots of shifting sand dune and in revegetated desert ecosystems at Shapotou, northwestern China, to study relationships between surface albedo, solar elevation angle, and surface soil moisture. Results indicated that rainfall exerted a remarkable lowering effect on the variation of surface albedo by increasing surface soil moisture. Surface albedo was an exponential function of solar elevation angle, and the normalized surface albedo (solar elevation angle effect was removed) decreased exponentially with the increase of surface soil moisture. Sand surface had a higher albedo (0.266) than BSCs (0.226) when the surfaces were very dry. However, sand surface albedo became increasingly lower than that of BSCs when the surfaces were in wet conditions and when the soil moisture exceeded a critical value. The changes in soil surface albedo from sand dune to BSCs after revegetation in shallow soil profiles associated with the variation of the surface soil moisture can be seen as an indicator of the degree of sand dune stabilization when compared with the original shifting sand dune soil. 相似文献
964.
The main purpose of this paper is to describe ways to improve the microstructure of expansive soil by adding nanomaterials. Mechanical tests were done to explore the changes in shear strength and compression index of expansive soil that was modified by adding different amounts of two kinds of nanomaterials (nano-alumina and nano-silica). The test results show that adding 1.2% nano-alumina and about 2% nano-silica to expansive soil provides the optimal compression index. The test results show that adding 1.2% nano-alumina and about 1.5% nano-silica to expansive soil provides the optimal unconfined compression stress. Scanning electron microscopy of the microstructure of expansive soil modified by nanomaterials provided a deeper understanding of the effects of nanomaterials on improving expansive soil. 相似文献
965.
太湖14000年以来古环境演变的湖泊记录 总被引:6,自引:0,他引:6
本文根据东西太湖短柱岩芯的沉积物的物理、化学、生物指标的综合分析,讨论了该区距今14ka来的古气候变化过程,结果表明14.3-13.3kaBP,太湖水位低,环境指标甚至表现为暴露特征,反映了气候干旱:13.3-12.4kaBP,为偏暖湿的过渡阶段;该孔柱270-280cm (11.5kaBP左右)各类指标均明显反映冷干特征,可能是YoungerDrays事件的记录,与我国东部其它地区有可比性;约10.9-10kaBP,这一时期是整个研究时段内一个较显著的温暖期。表现为还原沉积环境和水位相对较深;约10-7.2kaBP为冷暖交替的过渡带;7.2-5.737kaBP为暖湿气候;5.05kaBP多项分析指标发生突变,反映物源发生显著变化,可能存在沉积间断;表层沉积物则呈现现代环境的特征,西太湖藻类生长茂盛,偏氧化的沉积环境。目前湖泊生产力较高,富营养化程度高,表现为藻型湖泊特征;东太湖有机质来源以东太湖中生长较为茂盛的维管水生植物为主,目前湖泊生产力较低,富营养化程度低,表现为典型的草型湖泊特征。 相似文献
966.
利用通用地球系统模式CESM的过去2000年气候模拟试验资料,在与历史气候重建资料、观测/再分析资料及其他模式模拟资料进行对比验证的基础上,分析了中国中世纪暖期(Medieval Warm Period,简称MWP)地表温度年代际变化特征并初步探讨了其成因。结果表明:在公元801~1250年的中国中世纪暖期期间,在年代际尺度上,中国地表温度EOF第一模态的空间分布为全区一致型,并且北部的变率大于南部,最大的变率中心位于中国东北部;EOF第二模态反映出研究区内南北反向的空间分布特征。40°N以北地区温度变化一致;40°N以南青藏高原-云贵高原-东南沿海地区与华北地区呈反相变化,最大的变率中心位于青藏高原东部。中世纪暖期地表温度EOF第一模态主要归因于太阳辐射的影响,火山活动也是影响因子之一;EOF第二模态主要受气候系统内部变率的影响,其他外强迫因子的影响较小。但是,温室气体、土地利用/覆盖两个外强迫因子对气候系统内部变率具有一定的调制作用。在中国,中世纪暖期太阳活动剧烈、火山活动较少,下垫面吸收更多的太阳短波辐射,地表净辐射通量增大,是中世纪暖期形成的主要原因。 相似文献
967.
Spatial and temporal variations of albedo on nine glaciers in western China from 2000 to 2011 下载免费PDF全文
This research demonstrates the spatiotemporal variations of albedo on nine glaciers in western China during 2000–2011, by the albedo derived from two types of datasets: Landsat TM/ETM + images and MOD10A1 product. Then, the influence factors of glacier albedo and its relationship with glacier mass balance are also analyzed by the correlation approach, which is frequently used in geostatistics. The paper finds that there are different spatiotemporal variations over the glaciers in western China: (1) For a single glacier, the albedo varies gently with altitude on its tongue and increases fast in the middle part, while in the accumulation zones, the albedo value appears in the form of fluctuation. This could provide a quantitative method to retrieve the snowline by determining the threshold albedo value of snowpack and bare ice. (2) For the glaciers in western China, the albedo decreases with distance to the center of Tibetan Plateau (TP). This may relate to the elevation of glacier, for the speed of glacier retreat highly depends on air temperature. (3) In the summer period, albedo on most glaciers declines over the last 12 years, and it decreases much faster in southeastern TP than other regions, for which air temperature overwhelms the black carbon concentration. In addition, the trend of glacier albedo in summer is greatly correlated with that of measured glacier mass balance, which implies that the long‐term albedo datasets by remote sensing technology could be used to monitor and predict the change of glacier mass balance in the future. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
968.
近20年来河西-祁连山东部地区三条规模较大的北东向构造带在区域垂直形变图上反映明显。因受区域应力场强度的控制,其垂直形变表现出随时间波浪状演化式。区域垂直形变图像与莫霍面等深线相似,说明这几条北东向构造带的深部成因机制。它们对区内的中强地震起着很强的控制作用,与北西西及北北西向断裂构造共同构成了本区的控震构造网络。 相似文献
969.
970.
The discrimination between distinct remote compressions and multiple local stress deviations within a single compressive stress field has been carried out in the central-eastern Iberian Chain, by using structural criteria, computing palaeostress directions, identifying and ‘filtering’ stress deviations, and analysing time relationships. A probabilistic analysis based on a systematic comparison of real and expected frequencies of coexistence of two compressions is applied by means of the χ 2 Test. This allows us to identify those tectonic compressions that behave as independent events from the probabilistic point of view. The results suggest that among five initially defined compression directions only three can be considered as representative of distinct (although partially superposed) externally applied intraplate stress fields: Iberian s.l. (NE-SW), Betic s.l. (NW-SE), and Pyrenean (N-S to NNE-SSW). 相似文献