全文获取类型
收费全文 | 1541篇 |
免费 | 327篇 |
国内免费 | 400篇 |
专业分类
测绘学 | 61篇 |
大气科学 | 451篇 |
地球物理 | 429篇 |
地质学 | 708篇 |
海洋学 | 212篇 |
天文学 | 121篇 |
综合类 | 147篇 |
自然地理 | 139篇 |
出版年
2024年 | 5篇 |
2023年 | 27篇 |
2022年 | 56篇 |
2021年 | 58篇 |
2020年 | 49篇 |
2019年 | 57篇 |
2018年 | 56篇 |
2017年 | 59篇 |
2016年 | 73篇 |
2015年 | 63篇 |
2014年 | 56篇 |
2013年 | 78篇 |
2012年 | 81篇 |
2011年 | 88篇 |
2010年 | 82篇 |
2009年 | 82篇 |
2008年 | 79篇 |
2007年 | 108篇 |
2006年 | 84篇 |
2005年 | 49篇 |
2004年 | 43篇 |
2003年 | 62篇 |
2002年 | 44篇 |
2001年 | 47篇 |
2000年 | 72篇 |
1999年 | 99篇 |
1998年 | 91篇 |
1997年 | 73篇 |
1996年 | 74篇 |
1995年 | 54篇 |
1994年 | 52篇 |
1993年 | 53篇 |
1992年 | 29篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 31篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2268条查询结果,搜索用时 31 毫秒
171.
172.
δ18O of a stalagmite collected from Shihua Cave, 50 km southwest of Beijing is analyzed. The uppermost 2 cm was sampled at about
3-year intervals by a computer-controlled microsampling device. A total of 133 samples were analyzed, covering the last 480
years. A comparison of the δ18O record with the instrumentally recorded precipitation in Beijing and Tianjin back to 1840 AD shows that high precipitation
correlates with negative δ18O peaks. The long-term δ18O trend records temperature changes. Between 1620 and 1900 AD, the temperature was cooler than the average value for the 480-year
record, corresponding to the Little Ice Age. Temperatures warmer than the average prevailed during 1520–1620 and 1900—present.
Superimposed on the long-term trend are about 14 δ18O cycles of 30–40-year periodicity, with wet periods centered around 1985, 1955, 1910, 1880, 1840, 1800, 1760, 1730, 1690,
1660, 1630, 1600, 1560 and 1530 AD.
Project supported by the National Natural Science Foundation of China (Grant No. 9615875). 相似文献
173.
北淮阳盆岭构造带是大别造山带的重要组成部分。佛子岭岩群代表了早古生代扬子地块北缘大别古岛弧弧前海盆的火山沉积建造,在加里东运动陆块对接过程中变形变质。石炭系梅山群具磨拉石建造特征。在华力西印支期陆内俯冲褶皱带的基础上,燕山期沿桐柏桐城断裂伸展北移,近东西向断陷盆地发育,形成盆岭构造景观。南侧大别山强烈隆升,铸就了现今大别山变质核杂岩构造格局。中生代岩浆活动是区内重要铀源,具有成矿潜力的地质体是响洪甸正长岩体和北带粗面质火山碎屑岩 相似文献
174.
Mingcai Yan Chunshu Wang Tiexin Gu Qinghua Chi Zhong Zhang 《Geostandards and Geoanalytical Research》1998,22(2):235-246
Unlike the situation for other elements, few reference materials certified for the platinum-group elements are currently available. Therefore, the GPt1-7 series of PGE geochemical CRMs, prepared by the IGGE, represent an important addition and comprise a range of matrix types, including a soil, stream sediment, Mg-rich ultramafic rock, Fe-rich ultramafic rock, platinoid ore depleted in Cu, Ni and Fe, and a chromitite. The concentration of PGE in these samples ranges over 4-5 orders of magnitude and the samples were shown to have good homogeneity as assessed by a variance test. Analytical methods based on different principles were used in sample certification, including several fire assay and wet chemical procedures used for decomposition and preconcentration. Certified values for the elements Pt, Pd, Os, Ru, Ir, Rh and Au were determined by AAS, catalytic colourimetry (COL), catalytic polarography (POL), atomic emission spectrometry (AES), ICP-MS and NAA. Recently, the GPt1-7 samples were approved as national primary CRMs by the State Bureau of Technical Supervision of China. 相似文献
175.
In this paper, we report our preliminary results on enhanced star formation activity in Seyfert 2 galaxies. By re-analysing
the Tully-Fisher relation for Whittle's (1992) sample and for a Seyfert 2s' sample selecting from Veron-Cetty and Veron (1996),
we find that (1) almost all Seyfert 2 galaxies with circumnuclear star formation have a ratio of far infrared (FIR) to blue
luminosities (LFIR/LB) to be larger than 1/3; (2) for Seyfert 2 galaxies with LFIR/LB > 1/3, the Tuly-Fisher relation is similar to that of the normal spiral galaxies; while for those with LFIR/LB ≥ 1/3, they are significantly different from the normal ones, which confirms Whittle's suggestion of enhanced star formation
activities in the circumnuclear regions of these Seyfert 2 galaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
176.
1987~1995年对降水、黑河水和古日乃草原地下水作了定位观测,在巴丹吉林沙漠水文探险中采集了沙漠和戈壁地下水及湖水.降水同位素组成δD~δ18O与Craig线相同,但发现了地下水的δD~δ18D关系平行于降水线且有氘盈余为负且达-22‰的异常,其成因不明.由地表、地下水环境同位素组成,分析了黑河治理规划实施后可能对地下水资源产生的工程影响,它近期不会成为古日乃草原沙漠化进程的因素,但对额济纳绿洲的影响却不容忽视. 相似文献
177.
地幔对流及其对地壳表层拉张盆地的影响 总被引:4,自引:0,他引:4
回顾近十年来在地幔对流方面的最新研究进展,阐述了板块俯冲后在地幔中的演化特征,以及地幔上升流即地幔柱的驱动机制和地质效应。特别介绍了地幔柱对地壳表层拉张盆地形成和充填过程的影响。进一步探讨了地幔柱活动在济阳坳陷的地质表现及其引发的火山岩浆活动、碎屑充填特征。认为盆地演化的阶段性间接反映了地幔对流的阶段性。 相似文献
178.
179.
P.Y. Gillot J. Labeyrie C. Laj G. Valladas G. Guérin G. Poupeau G. Delibrias 《Earth and Planetary Science Letters》1979,42(3):444-450
The reverse paleomagnetism of the lava flows of Laschamp and Olby, already discovered by Bonhommet and Babkine, is confirmed. The ages of these flows, measured by14C, thermoluminescence and K-Ar dating are respectively36,000 ± 4000 and42,000 ± 5000years. VGP's comparison of the “Laschamp event” with those of the 30,000-year Lake Mungo excursion does not show evidence of coincidence between these two events. 相似文献
180.