全文获取类型
收费全文 | 351篇 |
免费 | 3篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 28篇 |
地球物理 | 50篇 |
地质学 | 149篇 |
海洋学 | 6篇 |
天文学 | 102篇 |
自然地理 | 7篇 |
出版年
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2016年 | 4篇 |
2014年 | 7篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 7篇 |
1999年 | 6篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1948年 | 3篇 |
1938年 | 4篇 |
1937年 | 7篇 |
1936年 | 4篇 |
1935年 | 3篇 |
1934年 | 3篇 |
1933年 | 4篇 |
1928年 | 3篇 |
排序方式: 共有354条查询结果,搜索用时 15 毫秒
41.
Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates 总被引:2,自引:0,他引:2
Dorothee Hippler Dieter Buhl Detlev K. Richter 《Geochimica et cosmochimica acta》2009,73(20):6134-2836
This study presents magnesium stable-isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species, seawater samples collected from the western Dutch Wadden Sea, and reference materials. The aim of this study is to explore the influence of mineralogy, taxonomy and environmental factors (e.g., seawater isotopic composition, temperature, salinity) on magnesium-isotopic (δ26Mg) ratios of skeletal carbonates. Using high-precision multi-collector inductively coupled plasma mass spectrometry, we observed that the magnesium-isotopic composition of seawater from the semi-enclosed Dutch Wadden Sea is identical to that of open marine seawater. We further found that a considerable component of the observed variability in δ26Mg values of marine skeletal carbonates can be attributed to differences in mineralogy. Furthermore, magnesium-isotope fractionation is species-dependent, with all skeletal carbonates being isotopically lighter than seawater. While δ26Mg values of skeletal aragonite and high-magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences, the δ26Mg values of echinoids, brachiopods and bivalves likely result from a taxon-specific level of control on Mg-isotope incorporation during biocalcification. Moreover, no resolvable salinity and temperature effect were observed for coralline red algae and echinoids. In contrast, Mg-isotope data of bivalves yield ambiguous results, which require further validation. The data presented here, point to a limited use of Mg isotopes as temperature proxy, but highlight the method’s potential as tracer of seawater chemistry through Earth’s history. 相似文献
42.
Max Richter 《International Journal of Earth Sciences》1941,32(1-2):93-105
Ohne Zusammenfassung 相似文献
43.
Max Richter 《International Journal of Earth Sciences》1937,28(1-2):135-136
Ohne Zusammenfassung 相似文献
44.
45.
46.
H. Richter 《International Journal of Earth Sciences》1934,25(2):144
Ohne Zusammenfassung 相似文献
47.
Ohne Zusammenfassung 相似文献
48.
We analyze radio observations, magnetograms and extrapolated field line maps, Hα filtergrams, and X-ray observations of two
flare events (6 February 1992 in AR 7042 and 25 October 1994 in AR 7792) and study properties, evolution and energy release
signatures of sigmoidal loop systems. During both events, the loop configuration seen in soft X-ray (SXR) images changes from
a preflare sigmoidal shape to a relaxed post-flare loop system. The underlying magnetic field system consists of a quadrupolar
configuration formed by a sheared arcade core and a remote field concentration. We demonstrate two possibilities: a sigmoidal
SXR pattern can be due to a single continuous flux tube (the 1992 event). Alternatively, it can be due to a set of independent
loops appearing like a sigmoid (the 1994 event). In both cases, the preflare and post-flare loops can be well reproduced by
a linear force-free field and potential field, respectively, computed using preflare magnetograms. We find that thermal and
non-thermal flare energy release indicators of both events become remarkably similar after applying spatial and temporal scale
transformations. Using the spatial scaling between both events we estimated that the non-thermal energy release in the second
event liberated about 1.7 times more energy per unit volume. A two-and-a-half times faster evolution indicates that the rate
of the energy release per unit volume is more than four times higher in this event. A coronal type II burst reveals ignition
and propagation of a coronal shock wave. In contrast, the first event, which was larger and released about a 10 times more
energy during the non-thermal phase, was associated with a CME, but no type II burst was recorded. During both events, in
addition to the two-ribbon flare process an interaction was observed between the flaring arcade and an emerging magnetic flux
region of opposite polarity next to the dominant leading sunspot. The arcade flare seems to stimulate the reconnection process
in an `emerging flux-type' configuration, which significantly contributes to the energy release. This regime is characterized
by the quasiperiodic injection of electron beams into the surrounding extended field line systems. The repeated beam injections
excite pulsating broadband radio emission in the decimetric-metric wavelength range. Each radio pulse is due to a new electron
beam injection. The pulsation period (seconds) reflects the spatial scale of the emerging flux-type field configuration. Since
broadband decimetric-metric radio pulsations are a frequent radio flare phenomenon, we speculate that opposite-polarity small-scale
flux intrusions located in the vicinity of strong field regions may be an essential component of the energy release process
in dynamic flares. 相似文献
49.
Razumovskiy A. A. Novikov I. A. Ryazantsev A. V. Rud’ko S. V. Kuznetsov N. B. Yashunskiy Yu. V. 《Doklady Earth Sciences》2020,495(2):867-871
Doklady Earth Sciences - U–Th–Pb (SHRIMP II) isotopic dating of accessory zircons from Vendian (Ediacaran) ash tuffs of the Basa formation section (Asha Group, Southern Ural) was... 相似文献
50.
On September 22, 2001 the Deep Space 1 spacecraft performed a flyby at comet 19P/Borrelly at a solar distance of 1.36 AU leading the Earth by 74° in longitude. The spacecraft-comet distance at closest approach was 2171 km. The bow shock had a magnetic compression ratio of 2.5 at a distance of 147 100 km from the nucleus. Deep Space 1 first entered the sheath region essentially from the north polar region. Fluctuations from the cometary ion pickup were present throughout the sheath region and even well upstream of the shock, as expected. The magnetic field pileup region had a peak field strength of 83 nT and was shown to be consistent with a pressure equal to the solar wind ram pressure. The peak field location was offset from the time of closest approach. It is uncertain whether this is a spatial or temporal variation. Draping of magnetic fields around the nucleus was sought, but evidence for this was not apparent in the data. A possible explanation is that the interplanetary solar wind was composed of turbulent short-scale fields, and thus the fields were not symmetric about the point of closest approach. During the flyby phase there were in general few intervals of ACE data where there were large scale Parker spiral fields. With the addition of plasma data, the shock properties are investigated. The characteristics of magnetic draping, pileup and fluctuations are explored. These comet 19P/Borrelly results are contrasted with other cometary flyby results. 相似文献