全文获取类型
收费全文 | 179篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 12篇 |
地球物理 | 41篇 |
地质学 | 75篇 |
海洋学 | 4篇 |
天文学 | 18篇 |
综合类 | 1篇 |
自然地理 | 5篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 14篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 10篇 |
2013年 | 18篇 |
2012年 | 8篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1991年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 2篇 |
1962年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有191条查询结果,搜索用时 359 毫秒
41.
We report here results from a study of X-ray bursts from 3 magnetar candidates (SGR 1806-20, SGR 1900+14 and AXP 1E 2259+586).
We have searched for a pulse phase dependence of the X-ray burst rate from these sources. X-ray light curves were obtained
with the Proportional Counter Array on-board the Rossi X-ray Timing Explorer during the periods of intense burst activity
in these sources. On detailed analysis of the three sources, we found a very significant burst rate for all pulsar phases.
However, some locations appear to produce bursts slightly more often, rendering the non-isotropic distribution. Only in the
case of SGR 1900+14, there is a clear pulse phase dependence of burst rate. 相似文献
42.
43.
44.
Tophel Amir Walker Jeffrey P. Dutta Troyee Tanu Kodikara Jayantha 《Acta Geotechnica》2022,17(8):3479-3497
Acta Geotechnica - This paper introduces a theory-guided machine learning (TGML) framework, which combines a theoretical model (TM) and a machine learning (ML) algorithm to predict compaction... 相似文献
45.
Sandip K. Chakrabarti Broja G. Dutta P. S. Pal 《Monthly notices of the Royal Astronomical Society》2009,394(3):1463-1468
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot regions embedded in Keplerian discs. Observational evidence of evolutions of QPOs would therefore be very important as they throw lights on the dynamics of the hotter region. Our aim is to find systems in which there is a well-defined correlation among the frequencies of the QPOs over a range of time so as to understand the physical picture. In this paper, we concentrate on the archival data of XTE J1550−564 obtained during 1998 outburst, and study the systematic drifts during the rising phase from the 1998 September 7 to the 1998 September 19, when the QPO frequency increased monotonically from 81 mHz to 13.1 Hz. Immediately after that, QPO frequency started to decrease and on the 1998 September 26, the QPO frequency became 2.62 Hz. After that, its value remained almost constant. This frequency drift can be modelled satisfactorily with a propagatory oscillating shock solution where the post-shock region behaves as the Comptonized region. Comparing with the nature of a more recent 2005 outburst of another black hole candidate GRO 1655−40, where QPOs disappeared at the end of the rising phase, we conjecture that this so-called 'outburst' may not be a full-fledged outburst. 相似文献
46.
Prasun Dutta Ayesha Begum Somnath Bharadwaj Jayaram N. Chengalur 《Monthly notices of the Royal Astronomical Society》2009,398(2):887-897
We estimate the power spectrum of H i intensity fluctuations for a sample of eight galaxies (seven dwarf and one spiral). The power spectrum can be fitted to a power-law for six of these galaxies, indicating turbulence is operational. The estimated best-fitting value for the slope ranges from ∼−1.5 (AND IV, NGC 628, UGC 4459 and GR 8) to ∼−2.6 (DDO 210 and NGC 3741). We interpret this bi-modality as being due to having effectively 2D turbulence on length-scales much larger than the scale-height of the galaxy disc and 3D otherwise. This allows us to use the estimated slope to set bounds on the scale-heights of the face-on galaxies in our sample. We also find that the power-law slope remains constant as we increase the channel thickness for all these galaxies, suggesting that the fluctuations in H i intensity are due to density fluctuations and not velocity fluctuations, or that the slope of the velocity structure function is ∼0. Finally, for the four galaxies with '2D turbulence' we find that the slope α correlates with the star formation rate (SFR) per unit area, with larger SFRs leading to steeper power laws. Given our small sample size, this result needs to be confirmed with a larger sample. 相似文献
47.
Chetana Jain Biswajit Paul Kaustubh Joshi Anjan Dutta Harsha Raichur 《Journal of Astrophysics and Astronomy》2007,28(4):175-184
We report here results from a new search for orbital motion of the accretion powered X-ray pulsar 4U 1626–67 using two different
analysis techniques. X-ray light curve obtained with the Proportional Counter Array of the Rossi X-ray Timing Explorer during
a long observation carried out in February 1996, was used in this work. The spin period and the local period derivative were
first determined from the broad 2–60 keV energy band light curve and these were used for all subsequent timing analysis. In
the first technique, the orbital phase dependent pulse arrival times were determined for different trial orbital periods in
the range of 500 to 10,000 s. We have determined a 3σ upper limit of 13 lt-ms on the projected semimajor axis of the orbit of the neutron star for most of the orbital period range,
while in some narrow orbital period ranges, covering about 10% of the total orbital period range, it is 20lt-ms. In the second
method, we have measured the pulse arrival times at intervals of 100 s over the entire duration of the observation. The pulse
arrival time data were used to put an upper limit on any periodic arrival time delay using the Lomb-Scargle periodogram. We
have obtained a similar upper limit of 10 lt-ms using the second method over the orbital period range of 500–10,000 s. This
puts very stringent upper limits for the mass of the compact object except for the unlikely case of a complete face-on orientation
of the binary system with respect to our line-of-sight. In the light of this measurement and the earlier reports, we discuss
the possibility of this system being a neutron star with a supernovae fall-back accretion disk. 相似文献
48.
Sujay Dutta S.A. Sharma A.P. Khera Ajai M. Yadav R.S. Hooda K.E. Mothikumar M.L. Manchanda 《ISPRS Journal of Photogrammetry and Remote Sensing》1994,49(6)
The accuracy of cotton crop classification using satellite data has been assessed with respect to a detailed land cover map prepared by field survey. The effect of spatial resolution on classification accuracy was studied using LISS-I (spatial resolution 72.6 m) and LISS-II data (spatial resolution 36.25 m) of the Indian remote sensing satellite IRS-1B. The performances of the maximum likelihood and the minimum distance to mean as classifiers have also been assessed. LISS-II data have been found to give a higher classification accuracy. The estimate of cotton acreage using LISS-II data was closer to that obtained from the base map. The maximum likelihood classifier (MXL) and the minimum distance to mean (MDM) classifier performed equally well. 相似文献
49.
50.
Scrap tyres can be shredded into chips and can easily be mixed with granular soils. To assess the behaviour of the admixtures,
compressibility and triaxial compression tests were carried out by varying chip size and chip content. The results demonstrated
that sand–tyre chip mixtures up to 20% could be a potential material for highway construction and embankment construction
up to around 10 m height. 相似文献