全文获取类型
收费全文 | 11666篇 |
免费 | 2473篇 |
国内免费 | 2798篇 |
专业分类
测绘学 | 431篇 |
大气科学 | 548篇 |
地球物理 | 926篇 |
地质学 | 10678篇 |
海洋学 | 1446篇 |
天文学 | 17篇 |
综合类 | 1088篇 |
自然地理 | 1803篇 |
出版年
2024年 | 102篇 |
2023年 | 313篇 |
2022年 | 598篇 |
2021年 | 614篇 |
2020年 | 548篇 |
2019年 | 599篇 |
2018年 | 474篇 |
2017年 | 504篇 |
2016年 | 597篇 |
2015年 | 617篇 |
2014年 | 889篇 |
2013年 | 704篇 |
2012年 | 802篇 |
2011年 | 759篇 |
2010年 | 763篇 |
2009年 | 762篇 |
2008年 | 683篇 |
2007年 | 817篇 |
2006年 | 800篇 |
2005年 | 703篇 |
2004年 | 608篇 |
2003年 | 536篇 |
2002年 | 508篇 |
2001年 | 496篇 |
2000年 | 379篇 |
1999年 | 372篇 |
1998年 | 302篇 |
1997年 | 235篇 |
1996年 | 192篇 |
1995年 | 161篇 |
1994年 | 115篇 |
1993年 | 104篇 |
1992年 | 94篇 |
1991年 | 55篇 |
1990年 | 31篇 |
1989年 | 30篇 |
1988年 | 8篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
1.
This paper describes the application of environmental isotopes and injected tracer techniques in estimating the contribution of storms as well as annual precipitation to groundwater recharge and its circulation, in the semi‐arid region of Bagepalli, Kolar district, Karnataka. Environmental isotopes 2H, 18O and 3H were used to study the effect of storms on the hydrological system, and an isotope balance was used to compute the contribution of a storm component to the groundwater. Some of the groundwater samples collected during the post‐storm periods were highly depleted in stable isotope content with higher deuterium excess relative to groundwater from the pre‐storm periods. Significant variation in deuterium excess in groundwater from the same area, collected in two different periods, indicates the different origin of air masses. The estimated recharge component of a storm event of 600 mm to the groundwater was found to be in the range of 117–165 mm. There was no significant variation in environmental tritium content of post‐storm and pre‐storm groundwater, indicating the fast circulation of groundwater in the system. After completion of the environmental isotope work, an injected radiotracer 3H technique was applied to estimate the direct recharge of total precipitation to the groundwater. The estimated recharge to the groundwater is 33 mm of the 550 mm annual precipitation during 1992. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
2.
本文根据胜利二号极浅海步行坐底钻井平台的作业和工作环境特点,进行了防腐措施研究,设计了切合实际的防腐措施。该平台在海上作业近四年进坞修理,经观测防腐情况良好。 相似文献
3.
Delayed Geochemical Hazard (DGH briefly) presents the whole process of a kind of serious ecological and environmental hazard caused by sudden reactivation and sharp release of long-term accumulated pollutant from stable species to active ones in soil or sediment system due to the change of physical-chemical conditions (such as temperature, pH, Eh, moisture, the concentrations of organic matters, etc.) or the decrease of environment capacity. The characteristics of DGH are discussed. The process of a typical DGH can be expressed as a nonlinear polynomial. The points where the derivative functions of the first and second orders of the polynomial reach zero, minimum and maximum are keys for risk assessment and harzard pridication.The process and mechanism of the hazard is due to the transform of pollutant among different species principally. The concepts of "total releasable content of pollutant", TRCP, and "total concentration of active specie", TCAS, are necessarily defined to describe the mechanism of DGH. The possibility of the temporal and spatial propagation is discussed. Case study shows that there exists a transform mechanism of "gradual release" and "chain reaction" among the species of the exchangeable and the bounds to carbonate, iron and manganese oxides and organic matter, thus causing the delayed geochemical hazard. 相似文献
4.
5.
以GIS空间数据处理为平台,在层次分析法的基础上对攀西矿区的矿山地质环境构建了评价指标体系,综合各评价指标所占权重对攀西矿区的地质环境作了评价分级,该评价分级结果反映出研究区的矿山地质环境状况并分析了问题原因,为攀西矿区的地质环境管理和恢复治理提供了依据。 相似文献
6.
介绍了UASMaster对低空无人机航摄影像的数据处理,并针对无人机应急保障的快拼影像制作和大比例尺测图数据生产的技术流程进行了探讨。 相似文献
7.
8.
数字水印技术与算法实现 总被引:6,自引:0,他引:6
综述了数字水印技术的起源、概念、特点和应用;提出了数字水印处理技术的基本框架;列出了一些主要的基于图像的水印嵌入算法和水印检测算法;并展望了水印处理技术的未来发展趋势;最后给出了一种基于DCT变换的水印嵌入与检测算法。 相似文献
9.
A long-term Global LAnd Surface Satellite (GLASS) data-set for environmental studies 总被引:1,自引:0,他引:1
《International Journal of Digital Earth》2013,6(6):5-33
Recently, five Global LAnd Surface Satellite (GLASS) products have been released: leaf area index (LAI), shortwave broadband albedo, longwave broadband emissivity, incident short radiation, and photosynthetically active radiation (PAR). The first three products cover the years 1982–2012 (LAI) and 1981–2010 (albedo and emissivity) at 1–5 km and 8-day resolutions, and the last two radiation products span the period 2008–2010 at 5 km and 3-h resolutions. These products have been evaluated and validated, and the preliminary results indicate that they are of higher quality and accuracy than the existing products. In particular, the first three products have much longer time series, and are therefore highly suitable for various environmental studies. This paper outlines the algorithms, product characteristics, preliminary validation results, potential applications and some examples of initial analysis of these products. 相似文献
10.
运用高分一号卫星进行江西樟树市地质灾害评价对于科学防治地质灾害,提高国产卫星应用水平具有重要意义。本文通过正射校正、影像融合、几何校正等步骤对高分一号影像进行预处理,然后对处理后的影像进行地质灾害解译,获取樟树市地质灾害分布情况。在进行地质灾害评价过程中采用小流域评价单元,选取灾害点密度、地表水文、构造断裂带、工程活动、岩土类型、地形坡度等6个评价因子,并运用层次分析法确定因子权重,通过加权平均法最终获得樟树市地质灾害易发性综合评价图,其精度为78%。结果表明樟树市易发生地质灾害的地区占全市总面积的34.68%,易发程度最高的地区主要分布在东南部,占全市总面积的7.82%。 相似文献