全文获取类型
收费全文 | 6267篇 |
免费 | 551篇 |
国内免费 | 763篇 |
专业分类
测绘学 | 251篇 |
大气科学 | 1009篇 |
地球物理 | 1408篇 |
地质学 | 2632篇 |
海洋学 | 535篇 |
天文学 | 1040篇 |
综合类 | 280篇 |
自然地理 | 426篇 |
出版年
2023年 | 53篇 |
2022年 | 137篇 |
2021年 | 146篇 |
2020年 | 134篇 |
2019年 | 142篇 |
2018年 | 227篇 |
2017年 | 251篇 |
2016年 | 279篇 |
2015年 | 184篇 |
2014年 | 302篇 |
2013年 | 345篇 |
2012年 | 282篇 |
2011年 | 358篇 |
2010年 | 302篇 |
2009年 | 354篇 |
2008年 | 289篇 |
2007年 | 285篇 |
2006年 | 321篇 |
2005年 | 224篇 |
2004年 | 193篇 |
2003年 | 185篇 |
2002年 | 164篇 |
2001年 | 138篇 |
2000年 | 164篇 |
1999年 | 176篇 |
1998年 | 192篇 |
1997年 | 193篇 |
1996年 | 170篇 |
1995年 | 121篇 |
1994年 | 104篇 |
1993年 | 135篇 |
1992年 | 76篇 |
1991年 | 84篇 |
1990年 | 54篇 |
1989年 | 61篇 |
1988年 | 63篇 |
1987年 | 61篇 |
1986年 | 65篇 |
1985年 | 51篇 |
1984年 | 58篇 |
1983年 | 51篇 |
1982年 | 53篇 |
1981年 | 41篇 |
1980年 | 34篇 |
1979年 | 36篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1975年 | 23篇 |
1974年 | 20篇 |
1973年 | 23篇 |
排序方式: 共有7581条查询结果,搜索用时 15 毫秒
991.
992.
Observations of AGNs and microquasars by ASCA, RXTE, Chandra and XMM-Newton indicate the existence of broad X-ray emission lines of ionized heavy elements in their spectra. Such spectral lines were discovered also in X-ray spectra of neutron stars and X-ray afterglows of GRBs. Recently, Zakharov et al. [MNRAS 342 (2003) 1325] described a procedure to estimate an upper limit of the magnetic fields in regions from which X-ray photons are emitted. The authors simulated typical profiles of the iron Kα line in the presence of magnetic field and compared them with observational data in the framework of the widely accepted accretion disk model. Here we further consider typical Zeeman splitting in the framework of a model of non-flat accretion flows, which is a generalization of previous consideration into non-equatorial plane motion of particles emitting X-ray photons. Using perspective facilities of space borne instruments (e.g., Constellation-X mission) a better resolution of the blue peak structure of iron Kα line will allow to evaluate the magnetic fields with higher accuracy. 相似文献
993.
M. Mikolajewski C. Galan K. Gazeas P. Niarchos S. Zola M. Kurpinska-Winiarska M. Winiarski A. Majewska M. Siwak M. Drahus W. Waniak A. Pigulski G. Michalska Z. Kolaczkowski T. Tomov M. Gromadzki D. Graczyk J. Osiwala A. Majcher M. Hajduk M. Cikala A. Zajczyk D. Kolev D. Dimitrov E. Semkov B. Bilkina A. Dapergolas L. Bellas-Velidis B. Csak B. Gere P. Nemeth G. Apostolovska 《Astrophysics and Space Science》2005,296(1-4):445-449
We report multicolour photometric observations of the 2003 eclipse of the long-period (5.6 yr) eclipsing binary EE Cep. Measurements
were obtained with ten telescopes at eight observatories in four countries. In most cases, UBV(RI)C broad band filters have been used. The light curve shape shows that the obscuring body is an almost dark disk around a low-luminosity
central object. However, variations of the colour indices during the eclipse indicate that the obscuring body emits a considerable
amount of radiation in the near infrared. 相似文献
994.
995.
996.
997.
C. Íbanoğlu E.R. Pekünlü V. KESKÍn Z. Tunca S. Evren M.C. Akan 《Astrophysics and Space Science》1997,257(1):11-21
The peculiar chromospherically active binary system RT Lac was observed in B and V bands between 1989 and 1992. The four-year photoelectric B and V light curves are presented. The light and colour variations in the four special regions of the light curve between 1978 and 1992 are discussed. The available photometry obtained by the present authors defines at least three consecutive maxima in the variation of the brightness of the system at second maximum and in mid-primary eclipse. The behaviour of the light and colour changes in mid-primary and at second maximum harmonizes with the common property of the RS CVn-type binaries. However, the light changes at first maximum do not resemble either at second maximum or in mid-primary minimum. Therefore, we conclude that the observed features cannot be attributed to the spottedness of the more massive component alone. The signs of the starspots are masked by the matter in front of the more massive component at the first maximum. The present data indicate that the magnetic cycle in RT Lac is about 12 years, which is analogous to the Sun's 11-year sunspot cycle. 相似文献
998.
Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550−564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with
the well-known Sedov evolutionary phase R∝ t
2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gamma-ray burst remnants, is shown to
be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around
the source is well below the canonical value n
ISM∼1 cm−3. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically
expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important
when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta. 相似文献
999.
Contribution to diffuse gamma-rays in the Galactic Centre region from unresolved millisecond pulsars
W. Wang Z. J. Jiang K. S. Cheng 《Monthly notices of the Royal Astronomical Society》2005,358(1):263-269
Diffuse gamma-rays in the Galactic Centre region have been studied. We propose that there exists a population of millisecond pulsars in the Galactic Centre, which emit GeV gamma-rays through synchrotron-curvature radiation as predicted by outer gap models. These GeV gamma-rays from unresolved millisecond pulsars probably contribute to the diffuse gamma-ray spectrum detected by EGRET which displays a break at a few GeV. We have used a Monte Carlo method to obtain simulated samples of millisecond pulsars in the Galactic Centre region covered by EGRET (∼ 15) according to the different period and magnetic field distributions from observed millisecond pulsars in the Galactic field and globular clusters, and superposed their synchrotron-curvature spectra to derive the total GeV flux. Our simulated results suggest that there probably exist about 6000 unresolved millisecond pulsars in the region of angular resolution of EGRET, the emissions of which could contribute significantly to the observed diffuse gamma-rays in the Galactic Centre. 相似文献
1000.