全文获取类型
| 收费全文 | 36470篇 |
| 免费 | 4523篇 |
| 国内免费 | 6621篇 |
专业分类
| 测绘学 | 4474篇 |
| 大气科学 | 3260篇 |
| 地球物理 | 6165篇 |
| 地质学 | 13343篇 |
| 海洋学 | 3554篇 |
| 天文学 | 7113篇 |
| 综合类 | 2420篇 |
| 自然地理 | 7285篇 |
出版年
| 2024年 | 123篇 |
| 2023年 | 314篇 |
| 2022年 | 1139篇 |
| 2021年 | 1289篇 |
| 2020年 | 1339篇 |
| 2019年 | 1664篇 |
| 2018年 | 1228篇 |
| 2017年 | 1417篇 |
| 2016年 | 1461篇 |
| 2015年 | 1603篇 |
| 2014年 | 1932篇 |
| 2013年 | 2450篇 |
| 2012年 | 2239篇 |
| 2011年 | 2380篇 |
| 2010年 | 2037篇 |
| 2009年 | 2676篇 |
| 2008年 | 2519篇 |
| 2007年 | 2661篇 |
| 2006年 | 2488篇 |
| 2005年 | 2083篇 |
| 2004年 | 1923篇 |
| 2003年 | 1620篇 |
| 2002年 | 1348篇 |
| 2001年 | 1133篇 |
| 2000年 | 1075篇 |
| 1999年 | 984篇 |
| 1998年 | 833篇 |
| 1997年 | 568篇 |
| 1996年 | 526篇 |
| 1995年 | 407篇 |
| 1994年 | 422篇 |
| 1993年 | 374篇 |
| 1992年 | 260篇 |
| 1991年 | 184篇 |
| 1990年 | 194篇 |
| 1989年 | 157篇 |
| 1988年 | 134篇 |
| 1987年 | 101篇 |
| 1986年 | 62篇 |
| 1985年 | 68篇 |
| 1984年 | 41篇 |
| 1983年 | 24篇 |
| 1982年 | 27篇 |
| 1981年 | 16篇 |
| 1980年 | 21篇 |
| 1979年 | 10篇 |
| 1978年 | 13篇 |
| 1977年 | 24篇 |
| 1976年 | 3篇 |
| 1954年 | 11篇 |
排序方式： 共有10000条查询结果，搜索用时 218 毫秒
51.
讨论了应用曲面拟合技术和利用离散的重力观测点的重力变化对特定研究区的重力场变化进行数值模拟以获取该区重力变化空间梯度场图像的具体方法;并应用该方法获得了2004年3月福建安溪3.6级地震前的重力变化空间梯度场图像,发现空间梯度场图像能清晰地反映出地震前重力场群体性变化的差异性;利用此方法对2005年6月~2006年3月间台湾海峡西岸重力场变化进行数值模拟,获得其空间梯度场图像。 相似文献
52.
Hai-Ning LiNational Astronomical Observatories Chinese Academy of Sciences Beijing lhnDepartment of Astronomy Beijing Normal University Beijing 《中国天文和天体物理学报》2003,3(5)
We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v < 100 GHz, but become non-negligible at high frequencies v > 350 GHz. Moreover, the corrections appear to be slightly smaller at higher l or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology. 相似文献
53.
54.
C. Dickinson R. D. Davies R. J. Davis 《Monthly notices of the Royal Astronomical Society》2003,341(2):369-384
A full-sky template map of the Galactic free–free foreground emission component is increasingly important for high-sensitivity cosmic microwave background (CMB) experiments. We use the recently published Hα data of both the northern and southern skies as the basis for such a template.
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area | b | < 5°, l = 260°–0°–160° and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a ≈6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed. 相似文献
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area | b | < 5°, l = 260°–0°–160° and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a ≈6 per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed. 相似文献
55.
Peter J. Wheatley Christopher W. Mauche Janet A. Mattei 《Monthly notices of the Royal Astronomical Society》2003,345(1):49-61
We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated.
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of 3 × 1015 g s−1 in quiescence, 1 × 1016 g s−1 when the boundary layer becomes optically thick, and ∼1018 g s−1 at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state. 相似文献
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of 3 × 10
56.
57.
58.
We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra. 相似文献
59.
60.