全文获取类型
收费全文 | 1630篇 |
免费 | 109篇 |
国内免费 | 42篇 |
专业分类
测绘学 | 85篇 |
大气科学 | 45篇 |
地球物理 | 92篇 |
地质学 | 40篇 |
海洋学 | 16篇 |
天文学 | 1468篇 |
综合类 | 25篇 |
自然地理 | 10篇 |
出版年
2024年 | 7篇 |
2023年 | 16篇 |
2022年 | 18篇 |
2021年 | 20篇 |
2020年 | 10篇 |
2019年 | 22篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 13篇 |
2015年 | 12篇 |
2014年 | 31篇 |
2013年 | 20篇 |
2012年 | 26篇 |
2011年 | 29篇 |
2010年 | 19篇 |
2009年 | 107篇 |
2008年 | 90篇 |
2007年 | 134篇 |
2006年 | 107篇 |
2005年 | 123篇 |
2004年 | 160篇 |
2003年 | 104篇 |
2002年 | 105篇 |
2001年 | 100篇 |
2000年 | 90篇 |
1999年 | 86篇 |
1998年 | 114篇 |
1997年 | 32篇 |
1996年 | 22篇 |
1995年 | 28篇 |
1994年 | 24篇 |
1993年 | 8篇 |
1992年 | 22篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有1781条查询结果,搜索用时 281 毫秒
501.
L. K. Pollack G. B. Taylor S. W. Allen 《Monthly notices of the Royal Astronomical Society》2005,359(4):1229-1236
We present 5-, 8-, and 15-GHz total intensity and polarimetric observations of the radio source PKS 2322−123 taken with the Very Large Array (VLA). This small (11 kpc) source is located at the centre of the cooling-core cluster Abell 2597. The inner X-ray structure, the radio morphology and the steep spectral index (α=−1.8) in the lobes all suggest that the radio emission is confined by the ambient X-ray gas. We detect a small region of polarized flux in the southern lobe and are able to calculate a Faraday rotation measure (RM) of 3620 rad m−2 over this region. Based on these observations and Chandra X-ray data, we suggest that the southern lobe has been deflected from its original south-western orientation to the south and into our line of sight. Using the observed rotation measures (RMs) and our calculated electron density profiles, and assuming both a uniform and tangled magnetic field topology, we estimate a lower limit of the line-of-sight cluster magnetic field, B ∥ = 2.1 μG . 相似文献
502.
Josep M. Paredes J. Martí D. F. Torres G. E. Romero J. A. Combi V. Bosch-Ramon J. García-Sáanchez 《Astrophysics and Space Science》2005,297(1-4):223-233
We present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most
variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the γ-ray sources (any of the
radio emitters in the field) varies in time with similar timescales as the γ-ray variation. If the γ-rays are produced in
a jet-like source, as we have modelled theoretically, synchrotron emission is also expected at radio wavelengths. Such radio
emission should appear variable in time and correlated with the γ-ray variability. 相似文献
503.
In the course of the formation of cosmological structures, large shock waves are generated in the intracluster medium (ICM). In analogy to processes in supernova remnants, these shock waves may generate a significant population of relativistic electrons which, in turn, produce observable synchrotron emission. The extended radio relics found at the periphery of several clusters and possibly also a fraction of radio halo emission may have this origin. Here, we derive an analytic expression for (i) the total radio power in the downstream region of a cosmological shock wave, and (ii) the width of the radio-emitting region. These expressions predict a spectral slope close to −1 for strong shocks. Moderate shocks, such as those produced in mergers between clusters of galaxies, lead to a somewhat steeper spectrum. Moreover, we predict an upper limit for the radio power of cosmological shocks. Comparing our results to the radio relics in Abell 115, 2256 and 3667, we conclude that the magnetic field in these relics is typically at a level of 0.1 μG. Magnetic fields in the ICM are presumably generated by the shocks themselves; this allows us to calculate the radio emission as a function of the cluster temperature. The resulting emissions agree very well with the radio power–temperature relation found for cluster haloes. Finally, we show that cosmic accretion shocks generate less radio emission than merger shock waves. The latter may, however, be detected with upcoming radio telescopes. 相似文献
504.
505.
506.
Jarken Esimbek 《中国天文和天体物理学报》2007,7(2):297-303
Injecting phase calibration (PCAL) signals to the feed horn of the observation sys- tem and analyzing the output response signals of the spectrometer, we measured the working performance of a 4096-channel digital autocalibration spectrometer. The results demonstrate that the spectrometer has a fine working performance: (1) the channels are distributed uni- formly in the spectrometer; (2) line drift produces little effect on the observation results; (3) spectral resolution shows little changes with observation time. The distribution of the fre- quency resolution in an 80 MHz bandwidth was measured. A trial observation on the two molecular spectral lines of H2CO and H110α taken with this spectrometer is described. 相似文献
507.
508.
High speed photometry during the lunar occultation of a stellar system provides an effective means of achieving high angular
resolution in one dimension at the sub arc second level which is well suited for resolving close binary projected separations
in the range of 10–100 milliarc seconds. An optical fast photometer designed for such a purpose is described and some results
from the initial observations taken with the system including the resolution of a projected separation of 55 milli arcsecond
in one binary system are detailed. 相似文献
509.
Nissim Kanekar Ravi Subrahmanyan Jayaram N Chengalur Vicky Safouris 《Monthly notices of the Royal Astronomical Society》2003,346(4):L57-L61
We report high-spectral-resolution Australia Telescope Compact Array (ATCA) H i 21-cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two extragalactic radio sources, PKS 1814−637 and PKS 0407−658. The two lines of sight were selected on the basis of the simplicity of their absorption profiles and the strength of the background sources; the high velocity resolution of the spectra then enabled us to estimate the kinetic temperatures of the absorbing gas by fitting multiple Gaussians to the absorption profiles. Four separate WNM components were detected towards the two sources, with peak optical depths τmax = (1.0 ± 0.08) × 10−2 , (1.4 ± 0.2) × 10−3 , (2.2 ± 0.5) × 10−3 and (3.4 ± 0.5) × 10−3 and kinetic temperatures T k = 3127 ± 300, 3694 ± 1595, 3500 ± 1354 and 2165 ± 608 K , respectively. All four components were thus found to have temperatures in the thermally unstable range 500 < T k < 5000 K ; this suggests that thermal equilibrium has not been reached throughout the WNM. 相似文献
510.
This paper presents observations of SiO maser emission from 161 Mira variables distributed over a wide range of intrinsic
parameters like spectral type, bolometric magnitude and amplitude of pulsation. The observations were made at 86.243 GHz,
using the 10-4 m millimeter-wave telescope of the Raman Research Institute at Bangalore, India. These are the first observations
made using this telescope. From these observations, we have established that the maser emission is restricted to Miras having
mean spectral types between M6 and M10. The infrared period-luminosity relation for Mira variables is used to calculate their
distances and hence estimate their maser luminosities from the observed fluxes. The maser luminosity is found to be correlated
with the bolometric magnitude of the Mira variable. On an H-R diagram, the masing Mira variables are shown to lie in a region
distinct from that for the non-masing ones. 相似文献