全文获取类型
收费全文 | 115篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 23篇 |
地球物理 | 17篇 |
地质学 | 40篇 |
海洋学 | 5篇 |
天文学 | 21篇 |
自然地理 | 8篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 6篇 |
2012年 | 7篇 |
2011年 | 5篇 |
2010年 | 3篇 |
2009年 | 8篇 |
2008年 | 3篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有117条查询结果,搜索用时 15 毫秒
111.
Vertical crustal motion observed in the BIFROST project 总被引:2,自引:0,他引:2
Hans-Georg Scherneck Jan M. Johansson Hannu Koivula Tonie van Dam James L. Davis 《Journal of Geodynamics》2003,35(4-5):425-441
This paper reports from investigations on the robustness of estimated rates of intraplate motion from the continuous GPS project BIFROST (Baseline Inferences from Fennoscandian Rebound Observations, Sealevel and Tectonics). We study loading effects due to ocean, atmosphere and hydrology and their impact on estimated rate parameters. We regularly find the admittance of a modelled perturbation at less than fifty percent of the full effect. We think that the finding relates to a difficult noise situation at all periods, and that a satisfying model for the dominating noise source has not been found yet. An additional reason for low admittance is found in the mapping process of the no-fiducial network solution into a conventional reference frame. 相似文献
112.
A. Johnsson D. Reiss E. Hauber M. Zanetti H. Hiesinger L. Johansson M. Olvmo 《Icarus》2012,218(1):489-505
On Earth, periglacial solifluction is a slow mass-wasting process related to freeze–thaw activity. We compare the morphology of small-scale lobate features on Mars to solifluction lobes in Svalbard to constrain their processes of formation. The analysis is based on high-resolution satellite imagery of Mars (HiRISE, ~25 cm/pxl), aerial images of Svalbard with a similar spatial resolution (HRSC–AX, ~20 cm/pxl) acquired through an air campaign in summer 2008, and ground truth obtained during two summer expeditions in 2009 and 2011 on Svalbard. We present a detailed study of two crater environments on Mars displaying two types of lobate forms, characterized as sorted (clast-banked) and non-sorted lobes. On both Svalbard and Mars such lobes typically occur as clusters of overlapping risers (lobe fronts), pointing to differential velocities in the soil. The martian small-scale lobes have well-defined arcuate risers and lobe treads (surface). Lobe widths range between 14 and 127 m and tread lengths between 13 and 105 m. Riser height is estimated to be approximately 1–5 m. The lobes on Mars share the plan view morphology of solifluction lobes on Svalbard and their morphometry is within the range of values of terrestrial solifluction lobes. The lobes are distinct from permafrost-creep landforms such as rock glaciers. We show the results of a survey of 53 HiRISE images covering latitudes between 59°N and 81°N. Similar to Svalbard, the studied lobate features on Mars occur in close spatial proximity to gullies and thermal contraction polygons. The widespread distribution of the lobate forms in the northern hemisphere and their close association to ground-ice and gullies are best explained by mass-wasting processes related to frost creep, gelifluction and/or plug-like flow. This suggests a protracted process (thousand to several thousands of years) of freeze–thaw activity at the northern high latitudes on Mars. Age constraints on lobe deposits and superposition relationships with gullies and polygons imply a process involving liquid water within the last few million years. 相似文献
113.
Julia Bosiö Christian Stiegler Margareta Johansson Herbert N. Mbufong Torben R. Christensen 《Climatic change》2014,127(2):321-334
This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots. 相似文献
114.
Seventy-eight molecules have been detected as a result of a spectral survey of the star-forming region DR21(OH) at 84–115
GHz. The abundances of most molecules are typical of those in the dense cores of molecular clouds. The rotational temperatures
derived using the lines of most molecules fall in the range 9–56 K, which is also typical for dense cores. However, emission
from high-lying levels of methanol and sulfur dioxide was detected; since the rotational temperatures for methanol and sulfur
dioxide are 252 and 186 K, this indicates the presence of hot regions. Another fact indicating the existence of hot regions
is the detection of CH3OCHO, CH3CH2OH, and CH3OCH3, which have thus far been observed only in hot cores and shock-heated regions. An interesting result is the tentative detection
of the J = 2 − 1, v = 1 SiO line, with the upper level energy of 1775 K. This is probably a maser line, similar to but weaker than the well-known
SiO masers in the star-forming regions Orion-KL,W51(N), and Sgr B2(N). 相似文献
115.
A spectral survey of the W51 e1/e2 star-forming region at 84–115 GHz has yielded detections of 105 molecules and their isotopic
species, from simple diatomic or triatomic molecules, such as CO, CS, HCN, up to complex organic compounds, such as CH3OCH3, CH3COCH3, and C2H5OOCH. Ninety-three lines that are absent from the Lovas list of molecular lines observed from space were detected, and approximately
half of these were identified. A significant number of the detectedmolecules are typical for hot cores. These include the
neutral molecules CH3OCHO, C2H5OH, CH3COCH3 etc., which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally
excited SiO, C4H, HCN, l-C3H, HCCCN, CH3CN, CH3OH, H2O, and SO2 lines with upper-level temperatures of several hundred Kelvin were found. Such lines can arise only in hot gas with temperatures
of the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (N2H+, HCO+, HCS+) usually exist in molecular clouds with high visual extinctions A
V
. At the same time, the CF+ ion should be observed in photon-dominated regions with A
V
values of about unity or lower. An interesting result is the tentative detection of two molecules that have thus far been
observed only in the atmospheres of late-type giant stars—MgCN and NaCN. This suggests that the conditions in the hottest
W51 regions (probably, in the vicinities of protostars) are close to those in the atmospheres of giant stars. It would be
desirable to search for other lines of these molecules to verify these tentative detections. Analysis of the radial velocities
of the detected molecules suggests that the contribution from the e2 core dominates the emission of some O-bearing molecules
(CH3OCHO, CH3CH2OH), while the contribution of the e1 core dominates the emission of some N-bearing molecules (e.g., CH3CH2CN). Thus, the molecular composition of the e2 core may be closer to the composition of the “Compact Ridge” in OMC-1, while
the composition of the e1 core is closer to that for the “Hot Core” in the same cloud. 相似文献
116.
Karin F. Helmens Jan Risberg Krister N. Jansson Jan Weckstrm Annika Berntsson Pivi Kaislahti Tillman Peter W. Johansson Stefan Wastegrd 《Quaternary Science Reviews》2009,28(19-20):1880-1894
Lake development at Sokli, northern Finland, is traced through the analysis of diatoms and other siliceous micro-fossils in a 2-meter thick minerogenic, laminated clay-silt deposit dated to the early part of Marine Isotope Stage (MIS) 3. Fluctuating water levels and changes in lake extent depicted by the siliceous micro-fossil record, together with lithology, suggest that an important part of the sediment sequence was deposited in a glacial lake. The proxy-based glacial lake evolution is tested using a Digital Elevation Model and geomorphologic evidence including eskers dated to the early MIS 3 Tulppio Interstadial at Sokli. Despite the apparent ice-dammed nature of the lake, the sediment is relatively rich in fossils and there are limited signs of re-deposition of older fossil material. The siliceous micro-fossil record together with data from other proxies previously analysed in the same sediment samples provides a coherent picture of past environmental changes around the Sokli site. This is most probably due to the sheltered position of the coring-site in a lake embayment. Quantitative climate reconstructions based on the diatom record show mean July air temperatures as high as present-day values at Sokli, and the temperature ranges indicated by the diatom record are in agreement with temperature reconstructions based on chironomids. The position of Sokli in the northeastern portion of the central area of the Scandinavian glaciations and the northern retreat pattern implies that an important part of eastern Fennoscandia was deglaciated during the early MIS 3 warming event. 相似文献
117.
Results from radiosoundings, performed both over land and over sea, show that the ascent rate of a radiosounding balloon, the vertical velocity of the balloon, can be used to determine the height of the boundary layer. In many cases the balloon has a higher ascent rate in the boundary layer and a lower, less variable, ascent rate above. The decrease in ascending velocity appears as a jump at the top of the boundary layer. Two examples of potential temperature profiles for unstable stratification and one profile for stable conditions are shown with the corresponding ascent rates. A comparison between the boundary-layer height determined from potential temperature profiles and from ascent rates is presented for a larger dataset. The different ascent rates of the balloon in the boundary layer and above can be explained by a decrease in drag on the balloon in combination with a lowering of the critical Reynolds number in the boundary layer caused by turbulence. Hence, by simply logging the time from release of a radiosonde, it is possible to obtain additional information that can be used to estimate the height of both the unstable and stable boundary layers. 相似文献