全文获取类型
收费全文 | 133篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 1篇 |
地球物理 | 5篇 |
地质学 | 1篇 |
海洋学 | 12篇 |
天文学 | 115篇 |
出版年
2024年 | 4篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 9篇 |
2011年 | 5篇 |
2010年 | 1篇 |
2009年 | 12篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1987年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有142条查询结果,搜索用时 31 毫秒
21.
We present the UV spectroscopy and timing of three nearby pulsars (Vela, B0656+14 and Geminga) recently observed with the
Space Telescope Imaging Spectrograph. We also review the optical and X-ray properties of these pulsars and establish their
connection with the UV properties. We show that the multiwavelengths properties of neutron stars (NSs) vary significantly
within the sample of middle-aged pulsars. Even larger differences are found between the thermal components of Geminga and
B0656+14 as compared to those of radio-quiet isolated NSs. These differences could be attributed to different properties of
the NS surface layers.
This work was supported by STScI grants GO-9182 and GO-9797 and NASA grant NAG5-10865. 相似文献
22.
We make a statistical analysis of the periodsP and period-derivativesP of pulsars using a model independent theory of pulsar flow in theP-P diagram. Using the available sample ofP andP values, we estimate the current of pulsars flowing unidirectionally along theP-axis, which is related to the pulsar birthrate. Because of radio luminosity selection effects, the observed pulsar sample
is biased towards lowP and highP. We allow for this by weighting each pulsar by a suitable scale factor. We obtain the number of pulsars in our galaxy to
be 6.05−2.80
+3.32 × 105 and the birthrate to be 0.048−0.011
+0.014 pulsars yr−1 galaxy−1. The quoted errors refer to 95 per cent confidence limits corresponding to fluctuations arising from sampling, but make no
allowance for other systematic and random errors which could be substantial. The birthrate estimated here is consistent with
the supernova rate. We further conclude that a large majority of pulsars make their first appearance at periods greater than
0.5 s. This ‘injection’, which runs counter to present thinking, is probably connected with the physics of pulsar radio emission.
Using a variant of our theory, where we compute the current as a function of pulsar ‘age’ (1/2P/P), we find support for the
dipole braking model of pulsar evolution upto 6 × 106 yr of age. We estimate the mean pulsar braking index to be 3.7−0.8
+0.8. 相似文献
23.
最近,一个困扰人们达十几年之久的γ射线源Geminga被证认为X、γ射线脉冲星,其光学对应体也被确定为一颗光谱偏蓝的25等星。对Geminga脉冲星的确证说明存在着一类没有射电辐射的脉冲单星。 相似文献
24.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2009,395(3):1723-1732
The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron–positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field and gives rise to the scattered component nearly antiparallel to the streaming velocity of the scattering particles. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside the MP can be explained in terms of our model. 相似文献
25.
Optical polarization of the Crab pulsar: precision measurements and comparison to the radio emission
A. Sowikowska G. Kanbach M. Kramer A. Stefanescu 《Monthly notices of the Royal Astronomical Society》2009,397(1):103-123
The linear polarization of the Crab pulsar and its close environment was derived from observations with the high-speed photopolarimeter Optical Pulsar TIMing Analyser at the 2.56-m Nordic Optical Telescope in the optical spectral range (400–750 nm). Time resolution as short as 11 μs, which corresponds to a phase interval of 1/3000 of the pulsar rotation, and high statistics allow the derivation of polarization details never achieved before. The degree of optical polarization and the position angle correlate in surprising details with the light curves at optical wavelengths and at radio frequencies of 610 and 1400 MHz. Our observations show that there exists a subtle connection between presumed non-coherent (optical) and coherent (radio) emissions. This finding supports previously detected correlations between the optical intensity of the Crab and the occurrence of giant radio pulses. Interpretation of our observations requires more elaborate theoretical models than those currently available in the literature. 相似文献
26.
脉冲星时间尺度及其TOA预报初步分析 总被引:2,自引:0,他引:2
在简述国际天文学会(IAU)定义的几种不同时间尺度的基础上,重点讨论脉冲星计时观测中时间坐标相对论转换问题。脉冲星计时观测资料分析应该参考地球时TT,并将TT转换为质心坐标时TCB或质心力学时TDB。基于IAU重新定义的TDB,讨论和比较了时间坐标转换的解析算法和利用太阳系天体历表的数值积分算法。分析了TCB和TDB对脉冲星自转参数测量的影响。最后,以毫秒脉冲星PSR B1855+09的计时模型为例,初步分析了脉冲星脉冲到达时间的预报问题。 相似文献
27.
28.
Houshang Ardavan ArzhangArdavan John Singleton Mario R. Perez 《Monthly notices of the Royal Astronomical Society》2008,388(2):873-883
We show that the proportionately spaced emission bands in the dynamic spectrum of the Crab pulsar fit the oscillations of the square of a Bessel function whose argument exceeds its order. This function has already been encountered in the analysis of the emission from a polarization current with a superluminal distribution pattern: a current whose distribution pattern rotates (with an angular frequency ω) and oscillates (with a frequency Ω > ω differing from an integral multiple of ω) at the same time. Using the results of our earlier analysis, we find that the dependence on frequency of the spacing and width of the observed emission bands can be quantitatively accounted for by an appropriate choice of the value of the single free parameter Ω/ω . In addition, the value of this parameter, thus implied by Hankins & Eilek's data, places the last peak in the amplitude of the oscillating Bessel function in question at a frequency (∼Ω3 /ω2 ) that agrees with the position of the observed ultraviolet peak in the spectrum of the Crab pulsar. We also show how the suppression of the emission bands by the interference of the contributions from differing polarizations can account for the differences in the time and frequency signatures of the interpulse and the main pulse in the Crab pulsar. Finally, we put the emission bands in the context of the observed continuum spectrum of the Crab pulsar by fitting this broad-band spectrum (over 16 orders of magnitude of frequency) with that generated by an electric current with a superluminally rotating distribution pattern. 相似文献
29.
The Crab Pulsar was observed at 1540 MHz with the 25m radio telescope at Urumqi with a filterbank de-dispersion backend. A total of 2436 giant pulses with pulse energies larger than 4300 Jy μs were detected in two observing sets. All of these giant pulses are located in the main pulse (MP) and inter pulse (IP) windows of the average profile of the Crab Pulsar. The ratio of the numbers of giant pulses detected in the IP and MP windows is about 0.05. Our results show that, at 1540 MHz, the emission in the IP is contributed by giant and normal pulses, while that in the MP is almost dominated by giant pulses. The distribution of energy of the 2436 giant pulses at 1540 MHz can be described by a power-law with index α=3.13±0.09. The intrinsic threshold of giant pulse energy in the MP window is about 1400 Jy μs at 1540 MHz. 相似文献
30.