全文获取类型
| 收费全文 | 6213篇 |
| 免费 | 869篇 |
| 国内免费 | 1188篇 |
专业分类
| 测绘学 | 1760篇 |
| 大气科学 | 1531篇 |
| 地球物理 | 1574篇 |
| 地质学 | 695篇 |
| 海洋学 | 881篇 |
| 天文学 | 902篇 |
| 综合类 | 643篇 |
| 自然地理 | 284篇 |
出版年
| 2024年 | 31篇 |
| 2023年 | 74篇 |
| 2022年 | 206篇 |
| 2021年 | 271篇 |
| 2020年 | 279篇 |
| 2019年 | 297篇 |
| 2018年 | 201篇 |
| 2017年 | 331篇 |
| 2016年 | 295篇 |
| 2015年 | 366篇 |
| 2014年 | 351篇 |
| 2013年 | 460篇 |
| 2012年 | 407篇 |
| 2011年 | 406篇 |
| 2010年 | 315篇 |
| 2009年 | 418篇 |
| 2008年 | 371篇 |
| 2007年 | 424篇 |
| 2006年 | 392篇 |
| 2005年 | 350篇 |
| 2004年 | 352篇 |
| 2003年 | 322篇 |
| 2002年 | 202篇 |
| 2001年 | 186篇 |
| 2000年 | 153篇 |
| 1999年 | 122篇 |
| 1998年 | 127篇 |
| 1997年 | 102篇 |
| 1996年 | 86篇 |
| 1995年 | 69篇 |
| 1994年 | 89篇 |
| 1993年 | 60篇 |
| 1992年 | 46篇 |
| 1991年 | 29篇 |
| 1990年 | 18篇 |
| 1989年 | 15篇 |
| 1988年 | 11篇 |
| 1987年 | 10篇 |
| 1986年 | 5篇 |
| 1985年 | 4篇 |
| 1984年 | 3篇 |
| 1983年 | 2篇 |
| 1982年 | 2篇 |
| 1980年 | 3篇 |
| 1979年 | 1篇 |
| 1978年 | 3篇 |
| 1954年 | 3篇 |
排序方式： 共有8270条查询结果，搜索用时 390 毫秒
1.
本文简要介绍了陆地系列地球资源卫星的轨道特征，并以陆地—５号资源卫星为例，根据南山站的座标计算出该站对陆地—５号资源卫星的可观测范围及以该站为中心的卫星的覆盖区域。 相似文献
2.
本文介绍了ＧＤＪ跟踪打印经纬仪在人造卫星的观测中如何应用计算机对多圈卫星的目视观测资料进行实时采集、处理等工作过程的原理和方法。 相似文献
3.
4.
在GPS数据处理中 ,存在着误差影响、影响波的干扰、周跳和数据量大等问题。误差影响和影响波的干扰实质是在接收卫星信号时受到其它因素的影响 ;周跳是由于卫星信号的失锁而造成信号的不连续 ;数据量大是因为GPS观测需要采样间隔小又连续观测所致。由于小波理论具有时频分析、波形分解、特征提取和快速小波变换等特性 ,应用小波变换和波形分解可以解决误差影响和影响波的干扰的问题 ;应用特征提取可以解决周跳检测问题 ;应用快速小波变换可进行数据压缩 相似文献
5.
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
6.
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
7.
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
8.
利用 12年的Lageos 1卫星激光测距资料 (1990 - 2 0 0 1)解算得到了地球定向参数 (EOP) ,将该序列的结果与同期的EOP(IERS)C0 4进行比较 ,其外符精度为 :极移XP— 0 .4 0mas,YP— 0 .4 2mas ,日长变化Dr— 0 .0 35ms。 相似文献
9.
小行星自转参数的资料不仅可以为小行星碰撞演化提供数据,还可以为太阳系的演化研究提供依据．利用云南天文台1米望远镜对主带碳类小行星(360)Carlova进行了新的CCD测光观测,结合前人的测光资料,利用Epoch-方法对(360)的自转参数进行了反演计算,得到该小行星自转的恒星周期为0．25780417±0．00000003天,自转轴的黄道坐标为(95°±3,°40°±1°)．新的结果与前人的结果相比较为一致,其精度稍高于以前的估算结果． 相似文献
10.
形变大地测量学的进展、问题与地震预报 总被引：12，自引：7，他引：5
简要概括了形变大地测量学的革命性进展，研讨了它的科学特色、功能和定义以及对地球科学和防灾减灾的推动。形变大地测量学有助于从根本上击破多年来制约地震预报的“瓶颈”，但也存在不少急待解决的问题。着重研讨了在21世纪前10年，形变大地测量学如何依托多年的学科积累并充分受益于人造卫星和数字化等新技术，开展创新性研究和试验以推进地震预报。为此，对当前的研究工作提出了12条科学技术途径。最后对学科名称提出了建议。 相似文献