全文获取类型
收费全文 | 60篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 3篇 |
地球物理 | 20篇 |
地质学 | 18篇 |
海洋学 | 5篇 |
天文学 | 15篇 |
自然地理 | 1篇 |
出版年
2019年 | 1篇 |
2018年 | 1篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1991年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有63条查询结果,搜索用时 31 毫秒
31.
Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm 总被引:2,自引:0,他引:2
The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F2 region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O+ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min. 相似文献
32.
Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand. 相似文献
33.
34.
We present the X-ray light curve in the 0.2–2.4 keV band based on fiveROSAT observations of SN1978K in NGC 1313. The X-ray emission is believed to arise from the interaction of the reverse shock and the expanding debris from the supernova. The reverse shock becomes established after the outgoing shock runs into circumstellar matter. 相似文献
35.
A 30 ka paleo-climate record of the Boise area, Idaho, USA has been delineated using groundwater stable isotopic compositions. Groundwater ages are modern (cold batholith), 5-15 ka (thermal batholith) , 10-20 ka (frontal fault) , and 20-30 ka (Snake River plain thermal). The stable isotopic composition of groundwaters have been used as a surrogate for the stable isotopic composition of precipitation. Using δ2H and δ18O compositions, local groundwater lines (LGWL's) were defined for each system. Each LGWL has been evaluated with defined slopes of 6.94 and 8, respectively, and resulting deuterium excess values (d) were found for each groundwater system for each slope. Time dependent changes in moisture source humidity and temperature, and Boise area recharge temperatures, calculated from stable isotopic data and the deuterium excess factors, agree with previous paleo-climate studies. Results indicate that from the last glacial maximum to the present time the humidity over the ocean moisture source increased by 9%, sea surface temperature at the moisture source increased 6-7°C, and local Boise temperature increased by 4-5°C. A greater increase of temperature at the moisture source as compared to the Boise area may impart be due to a shift in the moisture source area. 相似文献
36.
利用1988~1999年欧洲非相干散射EISCAT(European Incoherent Scatter)雷达观测数据,对不同太阳活动周相、不同季节的极光椭圆区电离层F区电子密度进行统计分析,研究其气候学特征,并与IRI 2001模式比较.EISCAT观测到的电子密度显示出显著的太阳活动高年“冬季异常”和太阳活动低年半年变化等现象.EISCAT实测电子密度随时间和高度的平均二维分布和500 km高度以下总电子含量TEC,从总体来看与IRI 2001模式预测结果符合较好.但高年在TEC达到最大值前后,IRI 2001模式预测的电子密度高度剖面与EISCAT观测结果有显著差别:F2峰以上IRI 2001模式预测的电子密度过大,造成TEC明显高于雷达观测值.另外,在太阳活动下降相,EISCAT观测显示出明显的半年周期季节变化特征,但IRI 2001模式未能预测出此下降相季节变化. 相似文献
37.
Large-Eddy Simulation of Inhomogeneous Canopy Flows Using High Resolution Terrestrial Laser Scanning Data 总被引:1,自引:1,他引:0
Fabian Schlegel Jörg Stiller Anne Bienert Hans-Gerd Maas Ronald Queck Christian Bernhofer 《Boundary-Layer Meteorology》2012,142(2):223-243
The effect of sub-tree forest heterogeneity in the flow past a clearing is investigated by means of large-eddy simulation
(LES). For this purpose, a detailed representation of the canopy has been acquired by terrestrial laser scanning for a patch
of approximately 190 m length in the field site “Tharandter Wald”, near the city of Dresden, Germany. The scanning data are
used to produce a high resolution plant area distribution (PAD) that is averaged over approximately one tree height (30 m)
along the transverse direction, in order to simplify the LES study. Despite the smoothing involved with this procedure, the
resulting two-dimensional PAD maintains a rich vertical and horizontal structure. For the LES study, the PAD is embedded in
a larger domain covered with an idealized, horizontally homogeneous canopy. Simulations are performed for neutral conditions
and compared to a LES with homogeneous PAD and recent field measurements. The results reveal a considerable influence of small-scale
plant distribution on the mean velocity field as well as on turbulence data. Particularly near the edges of the clearing,
where canopy structure is highly variable, usage of a realistic PAD appears to be crucial for capturing the local flow structure.
Inside the forest, local variations in plant density induce a complex pattern of upward and downward motions, which remain
visible in the mean flow and make it difficult to identify the “adjustment zone” behind the windward edge of the clearing. 相似文献
38.
豫西崤山早元古代中酸性侵入岩锆石/斜锆石U-Pb测年及其对熊耳火山岩系时限的约束 总被引:5,自引:4,他引:1
熊耳火山岩系是华北克拉通早元古代晚期重要的岩浆记录,其火山作用时限的厘定对于揭示华北该时期的构造格局与演化历史有重要意义。对侵入到熊耳火山岩系顶层马家河组的石英闪长岩体中的斜锆石与锆石和花岗斑岩体中的锆石进行了高精度SIMSU-Pb定年。三个样品共58个测点,石英闪长岩体中的斜锆石207Pb/206Pb平均年龄为1789±4Ma,锆石207Pb/206Pb平均年龄1778±12Ma,花岗斑岩体中的锆石207Pb/206Pb平均年龄为1786±8Ma。这些年龄数据表明石英闪长岩体从生成到侵位是一个短暂而连续的过程,这一岩体与花岗斑岩岩体基本同期。同时,由于这两个岩体侵入到了熊耳火山岩系最顶部的马家河组,因此可以限定熊耳火山岩系的上限。结合前人的年代学数据,我们提出熊耳火山岩系的岩浆作用时限在1770~1800Ma之间,峰期为1780Ma。这一研究结果从年代学上支持熊耳火山岩系形成于快速拉张的裂谷环境。 相似文献
39.
Russell J. Smith † J.R. Lucey D.J. Schlegel ‡ Michael J. Hudson § Glenn Baggley Roger L. Davies 《Monthly notices of the Royal Astronomical Society》2001,327(1):249-264
We present new R -band photometric data for 447 galaxies, gathered for the 'Streaming Motions of Abell Clusters' (SMAC) project. The data comprise 629 individual measurements of the Fundamental Plane (FP) parameters effective radius ( R e ) and surface brightness (〈 μ 〉e ), derived from r 1/4 -law profile fitting. More than a third of the galaxies were observed more than once. The photometric precision is ∼0.02 mag as judged from comparisons of aperture photometry between repeat observations of galaxies. The combination which enters into the Fundamental Plane relation, has internal uncertainties of ∼0.008, corresponding to < 2 per cent in estimated distance. Taken individually, the (correlated) internal errors in R e and 〈 μ 〉e are ∼8 per cent and ∼0.12 mag respectively. Comparisons with literature data constrain the external random errors to ≲5 per cent in distance (per observation), which is small in comparison to the ∼20 per cent scatter in the FP. The data will form part of a merged catalogue of FP parameters, presented in a companion paper. 相似文献
40.
Rainer Dähn André M ScheideggerAlain Manceau Michel L Schlegel Bart BaeyensMichael H Bradbury Magali Morales 《Geochimica et cosmochimica acta》2002,66(13):2335-2347
Wet chemistry kinetics and powder and polarized extended X-ray absorption fine structure (EXAFS and P-EXAFS) spectroscopy were combined to investigate the mechanism of Ni uptake on montmorillonite, at pH 8, high ionic strength (0.2 M Ca(NO3)2), initial Ni concentration of 660 μM, and solid concentration of 5.3 g/L. Approximately 20% of Ni sorbed within the first 24 h; thereafter, the Ni uptake rate slowed, and 12% of the initial Ni concentration remained in solution after 206 d of reaction time. Powder EXAFS spectra collected on wet pastes at 1, 14, 90, and 206 d showed the presence of Ni-Ni pairs at ∼3.08 Å in an amount that gradually increased with time. Results were interpreted by the nucleation of a Ni phase having either an α-Ni-hydroxide- or a Ni-phyllosilicate-like local structure. The latter possibility was confirmed by recording P-EXAFS spectra of a highly textured, self-supporting montmorillonite film prepared in the same conditions as the wet samples and equilibrated for 14 d. The orientation distribution of the c*-axes of individual clay particles off the film plane, as measured by quantitative texture analysis, was 32.8° full width at half maximum, and this value was used to correct from texture effect the effective numbers of Ni and Si nearest neighbors determined by P-EXAFS. Ni atoms were found to be surrounded by 2.6 ± 0.5 Ni atoms at 3.08 Å in the in-plane direction and by 4.2 ± 0.5 Si atoms at 3.26 Å in the out-of-plane direction. These structural parameters, but also the orientation and angular dependence of the Ni and Si shells, strongly support the formation of a Ni phyllosilicate having its layers parallel to the montmorillonite layers. The neoformation of a phyllosilicate on metal uptake on montmorillonite, documented herein for the first time, has important geochemical implications because this dioctahedral smectite is overwhelmingly present in the environment. The resulting sequestration of sorbed trace metals in sparingly soluble phyllosilicate structure may durably decrease their migration and bioavailability at the Earth’s surface and near surface. 相似文献