首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   35篇
  免费   0篇
测绘学   1篇
大气科学   1篇
地球物理   2篇
地质学   7篇
海洋学   3篇
天文学   20篇
自然地理   1篇
  2022年   1篇
  2018年   2篇
  2016年   2篇
  2013年   4篇
  2012年   2篇
  2010年   2篇
  2009年   2篇
  2008年   5篇
  2007年   1篇
  2006年   2篇
  2005年   1篇
  2004年   1篇
  2003年   1篇
  2001年   1篇
  1998年   1篇
  1993年   1篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
排序方式: 共有35条查询结果,搜索用时 15 毫秒
21.
Lutz‐Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main‐sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson‐Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% (σπ ≤ 0.15). The calibration equations which provide the corrected absolute magnitude for optical and near‐infrared pass bands are valid for wide ranges of colours and absolute magnitudes: –0.18 < (BV)0 < 0.91, –1.6 < MV < 5.5 and –0.15 < (JH)0 < 0.50, –0.02 < (HKs)0 < 0.13, 0 < MJ < 4, respectively. The distances computed using the luminosity‐colours (LCs) relation with optical (BV) and near‐infrared (JHKs) observations were compared to the distances found from various other methods. The results show that new absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
22.
Hydrogeology Journal - The hydraulic conductivity of jointed rocks is one of the main input parameters to predict water inflow to engineering structures that are located in the jointed rocks....  相似文献   
23.
Subaerial weathering level, source area and tectonic environments were interpreted by using petrographic and geochemical characteristics of Eocene age sandstones found in the eastern Pontides. The thickness of Eocene age clastic rocks in the eastern Pontides ranges from 195 to 400 m. Mineralogical components of sandstones were mainly quartz, feldspar, rock fragments, and opaque and accessory minerals. Depending on their matrix and mineralogical content, Eocene age sandstones are identified as arkosic arenite-lithic arenite and feldspathic wacke-lithic wacke. CIA (Chemical Index of Alteration) values observed in the Eocene age sandstones (43–55) suggest that the source terrain of the sandstones was not affected by intense chemical weathering. Low CIW/CIA (Chemical Index of Weathering/Chemical Index of Alteration) values of the sandstones studied here suggest only slightly decomposed material and having undergone little transport until final deposition. Zr/Hf, Th/Sc, La/Sc and CIA ratios are low and demonstrate a mafic source; on the other hand, high LREE/HREE ratios and a slightly negative Eu anomaly indicate a subordinate fclsic source. Modal mineralogical and SiO2/Al2O3 and K2O/Na2O and Th, Zr, Co, Sc of Eocene age sandstone contents indicate that they are probably magmatic arc originated and deposited in the back arc basin.  相似文献   
24.
The properties of the hot zone in the accretion flow near the surface of a magnetized white dwarf have been studied. For this purpose, the aperiodic optical variability of LS Peg, one of the brightest intermediate polars in the northern sky, has been investigated. The main radiation of the hot zone, which is then reemitted in the optical band, results from the radiation of an optically thin plasma heated during the passage of the accretion flow of a standing shock. Recently, Semena and Revnivtsev (2012) have shown that the aperiodic variability (flickering) of accreting magnetized white dwarfs should have a characteristic feature in the range of Fourier frequencies corresponding to the plasma cooling time in this hot region. The photometric brightness measurements for LS Peg made with the RTT-150 telescope using a high-speed ANDOR iXon CCD array have allowed the break frequency in the power spectrum of the source’s variability to be constrained. Constraints on the geometry of the accretion column for the white dwarf in LS Peg and on the plasma parameters in it have been obtained.  相似文献   
25.
26.
Eker  Zeki 《Solar physics》2003,212(2):277-300
Assuming the clouds as plane parallel structures above the photosphere, center-to-limb contrast variations of various cloud models for solar faculae with approximations such as optically thin or thick, hot or cold, and with or without surface reflections, have been investigated. It has been found that the observed facular contrast data from Frazier (1971) and Taylor et al. (1998) at the 525 nm continuum is best represented by a cloud which is 230 K hotter than the undisturbed photosphere, with an optical depth =0.4283, and with isotropic surface reflections causing 11% of the background photons to be lost before penetrating into the cloud. This model and some other cloud models are shown to provide a fit better than the other physical and non-physical facular models presented previously.  相似文献   
27.
A data base of 111 filter-collected marine atmospheric particulates is used to describe the distribution of lead over the North and South Atlantic, the Mediterranean Sea, the Red Sea, the Gulf of Aden and the northern and central Arabian Sea. The distribution of atmospheric Pb is assessed in terms of enrichment factor diagrams, and it is shown that over the marine regions studied in both the Northern and Southern Hemispheres the distribution of Pb in the atmosphere is controlled by the mixing of a background component, or components, with crustal material within certain concentration limits. For the Northern Hemisphere samples used in the investigation there is a reasonably well-defined Pb concentration minimum of ~ 0.6 ng m?3 of air; however, this will be severely decreased in more remote Northern Hemisphere marine regions. Geometric average Pb atmospheric concentrations vary from one marine region to another, ranging from ~ 0.98 ng m?3 of air for the South Atlantic westerlies to ~ 15 ng m?3 of air in the North Atlantic westerlies; although the latter reduces to ~ 7 ng m?3 of air when ‘polluted’ samples are excluded. Lead sea-surface deposition fluxes are calculated on the basis of two deposition velocities (0.25 and 1 cm s?1), the largest flux (220 ng Pb cm?2 yr?1) being found for the westerlies over the eastern margins of the North Atlantic. The distribution of lead over the North Atlantic is assessed in terms of the global lead budget and it is estimated that a maximum of ~ 24% of the total ‘natural’ lead injected annually into the World atmosphere, and ~ 3.5% of the anthropogenic lead injected annually into the Northern Hemisphere atmosphere, are deposited over the North Atlantic sea surface.  相似文献   
28.
An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the chemically peculiar (CP) star HD 26385. Model parameters were determined from H-profile and photometric data. Its pattern of abundance shows that HD 26385 is typically Ap Si-star.  相似文献   
29.
The secular evolution of the orbital angular momentum (OAM), the systemic mass  ( M = M 1+ M 2)  and the orbital period of 114 chromospherically active binaries (CABs) were investigated after determining the kinematical ages of the subsamples which were set according to OAM bins. OAMs, systemic masses and orbital periods were shown to be decreasing by the kinematical ages. The first-order decreasing rates of OAM, systemic mass and orbital period have been determined as     per systemic OAM,     per systemic mass and     per orbital period, respectively, from the kinematical ages. The ratio of d log  J /d log  M = 2.68, which were derived from the kinematics of the present sample, implies that there must be a mechanism which amplifies the angular momentum loss (AML)     times in comparison to isotropic AML of hypothetical isotropic wind from the components. It has been shown that simple isotropic mass loss from the surface of a component or both components would increase the orbital period.  相似文献   
30.
RASAT Earth Observation Satellite is the second remote sensing satellite of The Scientific and Technological Research Council of Turkey (TUBITAK) Space Technologies Search Institute (TUBITAK Space). Generally, the first step to utilize the satellite imagery in GIS applications is the accurate geometric correction of the imagery. But, the geometric correction process of RASAT images is somewhat difficult due to insufficient orbit data and lack of satellite imagery processing software with RASAT model. Although the geolocation of RASAT images is investigated in some recent studies, subpixel accuracies cannot be achieved. In this study, different geometric correction methods and combination of them are tested with a more interactive workflow that uses the results of other approaches. Results show that these approaches can be used for the geometric correction of RASAT like pushbroom satellite images with insufficient orbit data and better geolocation accuracies can be achieved by different geometric correction approaches.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号