全文获取类型
收费全文 | 1572篇 |
免费 | 316篇 |
国内免费 | 469篇 |
专业分类
测绘学 | 145篇 |
大气科学 | 346篇 |
地球物理 | 392篇 |
地质学 | 909篇 |
海洋学 | 211篇 |
天文学 | 40篇 |
综合类 | 153篇 |
自然地理 | 161篇 |
出版年
2024年 | 7篇 |
2023年 | 37篇 |
2022年 | 55篇 |
2021年 | 73篇 |
2020年 | 72篇 |
2019年 | 84篇 |
2018年 | 97篇 |
2017年 | 79篇 |
2016年 | 90篇 |
2015年 | 88篇 |
2014年 | 111篇 |
2013年 | 80篇 |
2012年 | 100篇 |
2011年 | 100篇 |
2010年 | 93篇 |
2009年 | 85篇 |
2008年 | 91篇 |
2007年 | 95篇 |
2006年 | 69篇 |
2005年 | 69篇 |
2004年 | 54篇 |
2003年 | 47篇 |
2002年 | 49篇 |
2001年 | 54篇 |
2000年 | 59篇 |
1999年 | 77篇 |
1998年 | 65篇 |
1997年 | 65篇 |
1996年 | 69篇 |
1995年 | 55篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 24篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1958年 | 1篇 |
排序方式: 共有2357条查询结果,搜索用时 15 毫秒
51.
本文论述了宇宙中子、反射宇宙中子的形成过程和反射宇宙中子测量装置的研制。对入射宇宙中子流和反射宇宙中子流的测量与研究 ,可为揭示大气环境和解决工程地质问题提供一种新的方法和手段 相似文献
52.
53.
南堡凹陷沉积岩化学元素分布特征及多元统计方法研究 总被引:2,自引:0,他引:2
对南堡凹陷Ed1亚段、Ng下、Ng上、Nm底地层的75个沉积岩样品进行了主量、微量元素分析,结果表明粒度效应造成砂岩和泥岩元素丰度明显不同,砂岩除富集K、Na、Sr、Ba、Si外,其余元素均较泥岩亏损.根据地层垂向上元素丰度由高—低—高的变化规律,可将这4个亚段分为Ed1、Ng下和Ng上、Nm底3个阶段,与凹陷构造演化特征响应.因子分析、聚类分析等多元统计方法表明,表生环境中元素具有不同的迁移富集规律,Ca、Na、Sr等具有较强的活动性,Zr、Hf等少数元素则在粗粒级中含量较高,而其余元素则多在黏土粒级中富集.元素在表生环境中地球化学行为的不同主要受化学结构特征控制,沉积环境对其也有影响. 相似文献
54.
Yu Liu Hiroki Kurokawa Chang Liu David H. Brooks Jingping Dun Takako T. Ishii Hongqi Zhang 《Solar physics》2007,240(2):253-262
Vector magnetograms taken at Huairou Solar Observing Station (HSOS) and Mees Solar Observatory (MSO) reveal that the super
active region (AR) NOAA 10486 was a complex region containing current helicity flux of opposite signs. The main positive sunspots
were dominated by negative helicity fields, while positive helicity patches persisted both inside and around the main positive
sunspots. Based on a comparison of two days of deduced current helicity density, pronounced changes associated with the occurrence
of an X10 flare that peaked at 20:49 UT on 29 October 2003 were noticed. The average current helicity density (negative) of
the main sunspots decreased significantly by about 50%. Accordingly, the helicity densities of counter-helical patches (positive)
were also found to decay by the same proportion or more. In addition, two hard X-ray (HXR) “footpoints” were observed by the
Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during the flare in the 50 – 100 keV energy range. The cores
of these two HXR footpoints were adjacent to the positions of two patches with positive current helicity that disappeared
after the flare. This strongly suggested that the X10 flare on 29 October 2003 resulted from reconnection between magnetic
flux tubes having opposite current helicity. Finally, the global decrease of current helicity in AR 10486 by ∼50% can be understood
as the helicity launched away by the halo coronal mass ejection (CME) associated with the X10 flare.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
55.
早侏罗世托阿尔期早期大洋缺氧事件(Toarcian Oceanic Anoxic Event,~183.8 Ma)是一次全球性的多幕式生物—环境事件,其在四川盆地下侏罗统自流井组大安寨段亦有显示。对采集自川东北地区大安寨段的鱼粪化石进行形态学描述和内含物分析,发现鱼粪化石中含有大量的磷质成分,多为未经消化的鱼骨化石,另有大量介壳类化石与有机质混杂在一起。据露头岩性和显微薄片特征认为: (1)粪化石呈螺旋状,生产该粪化石的鱼类为大型肉食性鱼类,其喜食小型鱼类和软体动物等,推测可能是肺鱼类(角齿鱼);(2)鱼粪化石形成于开放型淡水湖泊中的半深湖—深湖区,其中湖泊表层含氧量丰富,主要由生产者、消费者构成了研究区早侏罗世托阿尔期大型湖泊生态系统,食物链较为复杂,而湖底为水动力条件较弱的还原环境。该研究成果可为早侏罗世托阿尔期大洋缺氧事件在湖泊中的沉积响应及生态影响研究提供依据。 相似文献
56.
57.
葛焕称 《地震学报(英文版)》1995,8(1):57-63
OnsomeproblemsofseismiccrustalphaseHuan-ChengGE(葛焕称)(SeismologicalBureauofJiangsuProvince,Nanjing210014,China)Abstract:Inthis... 相似文献
58.
59.
Yajie Zhang Yao Li Jing Ge Gaopeng Li Zhisheng Yu Haishan Niu 《Environmental Earth Sciences》2018,77(12):462
Drought monitoring is a key topic in environmental monitoring and assessment although there is still a need to determine the correlation between drought monitoring indices and remote sensing products. We analyzed the correlation between the self-calibrating Palmer Drought Severity Index (sc_PDSI), the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index (SPEI) and terrestrial water storage monitored through the Gravity Recovery and Climate Experiment (GRACE) on a monthly timescale from 2002 to 2015 in China. As a consequence of anomalies in the soil water budget, the highly significant correlation between the sc_PDSI and the GRACE satellite-observed terrestrial water storage suggested that these two datasets are the most suitable for use in monitoring droughts. In comparing the three drought indices, the sc_PDSI was introduced as a means of drought monitoring in the Yangtze, Pearl, Huaihe, Southeast and Songhua River Basins, whereas the SPEI was found to be more applicable to other major river basins, such as the Inland River Basin. These diverse spatial behaviors are caused by the differences between the hydrological droughts characterized by these three drought indices. 相似文献
60.