全文获取类型
收费全文 | 289篇 |
免费 | 11篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 16篇 |
地球物理 | 68篇 |
地质学 | 62篇 |
海洋学 | 66篇 |
天文学 | 66篇 |
综合类 | 4篇 |
自然地理 | 14篇 |
出版年
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 14篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有308条查询结果,搜索用时 31 毫秒
61.
Based on high-resolution analysis to a 280-cm long sediment core obtained from the muddy area in the central Yellow Sea, we examined the provenance of muddy sediments and discussed the changing marine sedimentary environment since the middle Holocene. The results indicated that fine-grained sediments in the muddy area were mainly derived from the Huanghe(Yellow River) and Changjiang(Yangtze River) with considerable stepwise variations during the past 6.6 kyr. The Yellow Sea Warm Current was initiated at 6 kyr when the sea level was high together with the enhanced East Asian Winter Monsoon. These in combination established the framework of shelf circulation in the Yellow Sea that began to trap the river-derived fine-grained sediments. From 4.9 kyr to 2.8 kyr, both the Kushiro Current and East Asian Monsoon were significantly weakened, reducing the delivery of Changjiang sediments to the muddy area. As a result, the sediments were mainly originated from the Huanghe. From 2.8 kyr to 1.5 kyr the continuously weakened East Asian Winter Monsoon and enhanced Yellow Sea Warm Current entrapped more fine-grain sediments. Whereas the enhanced East Asian Winter Monsoon and the human caused increase in sediment load of the Huanghe since 1.5 kyr, and direct delivery of Huanghe sediments to the Yellow Sea during 1128–1855 AD might dominated the sedimentation in the study area. The stepwise variations of the sediment provenance and composition of the Central Yellow Sea muddy sediments are of importance to understanding the formation of muddy deposit in the central Yellow Sea and the associated variations of marine environment since the middle Holocene. 相似文献
62.
Sedimentation rates and heavy metals in a macrotidal salt marsh: Bay of Fundy,Canada 总被引:1,自引:0,他引:1
Ray Kostaschuk Zhongyuan Chen Yoshiki Saito Zhangqiao Wang 《Environmental Geology》2008,55(6):1291-1298
Macrotidal salt marshes play an important role in sedimentary processes in estuaries and can act as a sink for fine sediments
and contaminants. This study examines sedimentation rates and the history of heavy metal accumulation in the Allen Creek salt
marsh in the Bay of Fundy, Canada. Pb-210 and Cs-137 measurements and accelerated mass spectrometer (AMS) dating indicate
a sedimentation rate of about 1.1 cm/year, which is consistent with independent observations. Elevated normalized concentrations
of As in the upper section of the deposit may reflect an increase in organic matter content while a consistent decrease in
Mn toward the surface of the section may be due to a decrease in natural supply. A peak in metal concentrations in the early
to mid twentieth century is attributed to inputs from local foundries. 相似文献
63.
Saito Susumu Sunda Surendra Lee Jiyun Pullen Sam Supriadi Slamet Yoshihara Takayuki Terkildsen Michael Lecat Frédéric 《GPS Solutions》2017,21(4):1937-1947
GPS Solutions - We investigated characteristics of anomalous spatial gradients in ionospheric delay on GNSS signals in the Asia-Pacific (APAC) low-magnetic latitude region in the context of the... 相似文献
64.
65.
Modern sediment characteristics and accumulation rates from the delta front to prodelta of the Yellow River (Huanghe) 总被引:2,自引:0,他引:2
Liangyong Zhou Jian Liu Yoshiki Saito Maosheng Gao Shaobo Diao Jiandong Qiu Shaofeng Pei 《Geo-Marine Letters》2016,36(4):247-258
Since 1976, the main channel of the Yellow River (Huanghe) has been on the east side of the delta complex, and the river has prograded a broad new delta lobe in Laizhou Bay of the Bohai Sea. In 2012, extensive bathymetric and high-resolution seismic profiles were conducted and sediment cores were collected off the new delta lobe. This study examined delta sedimentation and morphology along a profile across the modern subaqueous Yellow River delta and into Laizhou Bay, by analyzing sediment radionuclides (137Cs, 210Pb and 7Be), sedimentary structure, grain-size composition, organic carbon content, and morphological changes between 1976 and 2012. The change in the bathymetric profile, longitudinal to the river’s course, reveals subaqueous delta progradation during this period. The subbottom boundary between the new delta lobe sediment and the older seafloor sediment (before the 1976 course shift) was identified in terms of lithology and radionuclide distributions, and recognized as a downlap surface in the seismic record. The accumulation rate of the new delta lobe sediment is estimated to be 5–18.6 cm year–1 on the delta front slope, 2 cm year–1 at the toe of the slope, and 1–2 cm year–1 in the shelf areas of Laizhou Bay. Sediment facies also change offshore, from alternations of gray and brown sediment in the proximal area to gray bioturbated fine sediment in the distal area. Based on 7Be distribution, the shorter-term deposition rate was at least 20 cm year–1 in the delta front. 相似文献
66.
A post flare loop system was observed on the west limb at the total solar eclipse of February 16, 1980 in Kenya. Analyzing the monochromatic images and the flash spectra, we obtained the following results: (1) the lower part of the post flare loop system is characterized mainly by distinct cool loops of H and Fe x 6374. Fe x 6374 emitting plasma (T
e = 1.0 × 106 K) is highly concentrated in the loops. The 6374 loops are broader in diameter and located very close to but a little higher than the corresponding H loops. The electron densities of the dense part in H and Fe x 6374 loops are 1011 cm-3 and 6 × 109cm-3, respectively; (2) the Ca xv emitting region (3.5 × 106 K) is confined to the upper part of the post flare loops. The electron density of this hot region is estimated as 8 × 109 cm-3 from the Ca xv line intensity ratio, I(5694)I(5445). These observational results led us to construct an empirical model of the post flare loop system which is consistent with the reconnection model of Kopp and Pneuman (1976).Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 267. 相似文献
67.
The C-13 and proton NMR spectra of marine humic and fulvic acids isolated from sediments of Sagami and Suruga Bays and Aldrich humic acid were obtained using pulse Fourier transform mode. The C-13 and proton NMR spectra, which clarified the differences in chemical characteristics among the various humic substances, showed that the marine humic acids had more aliphatic and less aromatic character than the Aldrich humic acid, and the marine fulvic acids had polysaccharide-like character. The C-13 NMR spectra of the marine humic substances, in particular, had many relatively well-resolved peaks with significant intensities, indicating the presence of variously bonded carbon atoms in them. 相似文献
68.
69.
The elemental composition and oxygen-containing functional groups contents in the marine humic acids from the five sediment samples from Sagami Bay and Suruga Bay were determined. Kumada's method of classification of soil humic acids was applied to the marine humic acids. The carbon, nitrogen, hydrogen, oxygen and sulfur contents of the marine humic acids were, on average, 52.96, 5.12, 5.79, 34.99 and 1.13%, respectively, without wide variation. In comparison with terrestrial humic acids, the marine ones had relatively lower carbon content and higher hydrogen and nitrogen contents. It is suggested that the marine humic acids have more aliphatic and less aromatic character, as expected from their possible origins, e.g., phytoplankton. The total acidity, carboxyl, phenolic and alcoholic hydroxyl, carbonyl and methoxyl group contents in the marine humic acids were, on average, 5.80, 3.27, 2.53, 2.53, 3.09 and 0.41 milliequivalents per gram of dry ash-free humic acid (me g–1), respectively. From quantitative data on the elemental composition and functional groups of the average marine humic acid, its empirical formula was calculated to be C107H138O20(COOH)9(OH)7
phenolic (OH)7
alcoholic (CO)9(OCH)3N10S. The marine humic acids were similar to the so-called B type of soil humic acids with regard to the distribution of functional groups and spectroscopic properties. 相似文献
70.