全文获取类型
收费全文 | 647篇 |
免费 | 45篇 |
国内免费 | 74篇 |
专业分类
测绘学 | 84篇 |
大气科学 | 198篇 |
地球物理 | 32篇 |
地质学 | 4篇 |
海洋学 | 8篇 |
天文学 | 409篇 |
综合类 | 21篇 |
自然地理 | 10篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 16篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 9篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 23篇 |
2013年 | 27篇 |
2012年 | 21篇 |
2011年 | 21篇 |
2010年 | 15篇 |
2009年 | 46篇 |
2008年 | 32篇 |
2007年 | 48篇 |
2006年 | 52篇 |
2005年 | 54篇 |
2004年 | 42篇 |
2003年 | 38篇 |
2002年 | 33篇 |
2001年 | 35篇 |
2000年 | 34篇 |
1999年 | 28篇 |
1998年 | 33篇 |
1997年 | 1篇 |
1996年 | 8篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1980年 | 4篇 |
1978年 | 2篇 |
排序方式: 共有766条查询结果,搜索用时 523 毫秒
11.
W. Bednarek 《Monthly notices of the Royal Astronomical Society》2003,345(3):847-853
We argue that γ-ray sources observed in the direction of the Cygnus OB2 association in the GeV and TeV energy range are due to a pulsar that was created by a supernova a few tens of thousands of years ago. The GeV emission is produced by a middle-aged pulsar, a factor of 2 older than the Vela pulsar. The TeV emission is produced by high-energy hadrons and/or leptons accelerated in pulsar wind nebulae. We suggest, moreover, that the excess of cosmic rays at ∼1018 eV observed from the direction of the Cygnus region can also be related to the appearance of this very energetic pulsar in the Cyg OB2 association. Some of the relativistic hadrons, captured in strong magnetic fields of a high-density region of Cyg OB2, produce neutrons and γ-rays in collisions with matter. These neutrons can arrive from Cyg OB2, creating an excess of cosmic rays. 相似文献
12.
Frédéric Zagury 《Monthly notices of the Royal Astronomical Society》2006,370(4):1763-1770
The hypothesis of an extended red emission (ERE) in diffuse Galactic light (DGL) has been put forward in 1998 by Gordon, Witt & Friedmann who found that scattered starlight was not enough to explain the amount of DGL in the R band, in some high Galactic latitude directions. This paper re-investigates, for high Galactic latitudes, the brightnesses and colours of DGL, integrated star and galaxy light (ISGL), and of the total extrasolar light (ISGL+DGL) measured by Pioneer. Under the traditional assumption that DGL is forward scattering of background starlight by interstellar dust on the line of sight, ISGL and Pioneer have very close colours, as it is found by Gordon, Witt & Friedmann. Pioneer observations at high |b| thus accept an alternative and simple interpretation, with no involvement of ERE in DGL. 相似文献
13.
I.A. Crawford 《Astrophysics and Space Science》2003,285(3-4):661-675
I review the recent discoveries of variable interstellar absorption lines, widely taken to imply the existence of very small
scale(10–100 AU) structure in the interstellar medium. Possible origins of this structure are discussed, and attention is
drawn to the fact that most known examples seem to be associated with interstellar shells and bubbles of various kinds. On
the other hand, in at least one case (κ Velorum),the variation appears to occur in the supposedly quiescent cold neutral medium,
consistent with earlier studies of small scale structure in atomic hydrogen probed at radio wavelengths. Further work is urgently
required to determine the prevalence, mode of formation, and the physical and chemical state of these enigmatic structures.
Only then will their implications for our wider understanding of the interstellar medium become apparent.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
15.
There are ten channels in the FY-1C polar-orbiting meteorological satellite of China.Thesechannels cover visible,near-infrared and infrared spectral bands.Based on simulating analysis ofsingle layer and multilayer clouds that cirrus clouds possibly overlap low water clouds,the casestudy using FY-1C data is performed.Results show that FY-1C data can be used to analyzemultilayer clouds,especially for the ease of low water cloud overlaid by cirrus. 相似文献
16.
中国及周边海域对流云团的水平和垂直尺度 总被引:1,自引:0,他引:1
利用2007年1月-2010年12月CloudSat-CALIPSO二级云产品2B-CLDCLASS-LIDAR,统计中国及其周边海域对流云的发生频率,根据对流云发生频率的分布特征将中国及周边海域划分为青藏高原(TP)、东部陆地(EC)、南部海域(SO)和西北太平洋(WP)4个子区域,并研究了4个子区域积云团和深对流云团的水平尺度和垂直尺度。统计结果表明,海洋积云团的水平尺度约为2 km,陆地积云团的水平尺度约为1 km,海洋下垫面热力性质均匀,积云团尺度更大;陆地下垫面非均匀性强,积云团分布更为零散。深对流云团的水平尺度为10-50 km,东部陆地最大,约为45 km,西北太平洋最小,约为30 km。陆地深对流云团水平尺度较海洋上大,且多尺度特征显著,应该与深对流云发生的复杂天气背景有关。积云团的垂直尺度范围为0.24-2 km,4个区域无明显差异。垂直尺度海洋深对流云团大于陆地云团,其中在南部海域地区最大,约为15 km,青藏高原最小,约为10 km。与陆地云团相比,海洋深对流云团表现为水平尺度更小、垂直尺度更大的中尺度对流体特征。 相似文献
17.
18.
利用河北省邢台市皇寺国家观测站布设的Ka波段云雷达、微波辐射计和微雨雷达以及地面雨量计等观测资料,对2017年5月3日一次西南涡天气过程的降水云系进行了综合分析,结果表明:本次降水过程为稳定性层状云过程,云内粒子下落速度由高空向地面逐渐增大,第一轮降水出现在云的发展阶段,第二轮降水出现在云的成熟阶段,每次降水开始前云内的相对湿度、水汽含量、液态水含量和温度曲线同时出现跃增和峰值,各指标在降水结束后出现较明显下降,之后得到恢复,出现第二三次峰值并产生降水;利用微波辐射计资料在时间和空间上连续反演计算云中水汽压和冰面饱和水汽压差值场("e—E_i"差值场),当云中过冷水和过冷水汽大值区与"e—E_i"差值场的正值区重合时,冷云中贝吉龙过程较强,有利于精细化定量判断强降水出现和人工增雨潜力区位置,综合以上遥感探测资料分析结果,可以认为本次天气过程有利的人工增雨作业时机出现两次,第一次在13:45降水刚刚开始至云顶下降到6 km前;第二次时间较长,云层条件更为有利,即17:40—21:15云顶高度维持在8~10 km的时段;作业适宜高度为4~8 km(-20~0℃)。 相似文献
19.
利用常规观测资料、区域自动站资料和“葵花8号”气象卫星资料,对2016年4—9月甘肃省陇东南地区出现的43次强对流天气过程进行分析,确立了强对流云团识别指标、追踪方法及预报指标,并对2018年部分个例进行效果检验。结果表明:(1)利用卫星B13通道(10.4μm)亮温值TBB≤238 K或B08通道(6.2μm)与B13通道亮温差△TBB<0 K双阈值作为强对流云团识别指标,可以准确识别出陇东南地区的强对流天气云团;(2)利用“逆向搜索法”、“面积重叠法”及对云团重心的计算,可以对强对流云团进行准确定位、追踪及移动路径外推预报;(3)建立的强对流天气落区判别指标对该地区短时强降水及冰雹落区具有一定的预报能力。 相似文献
20.
The role of Arctic clouds in the recent rapid Arctic warming has attracted much attention. However, Arctic cloud water paths(CWPs) from reanalysis datasets have not been well evaluated. This study evaluated the CWPs as well as LWPs(cloud liquid water paths) and IWPs(cloud ice water paths) from five reanalysis datasets(MERRA-2,MERRA, ERA-Interim, JRA-55, and ERA5) against the COSP(Cloud Feedback Model Intercomparison Project Observations Simulator Package) output for MODIS from the MERRA-2 CSP(COSP satellite simulator) collection(defined as M2 Modis in short). Averaged over 1980–2015 and over the Arctic region(north of 60°N), the mean CWPs of these five datasets range from 49.5 g/m~2(MERRA) to 82.7 g/m~2(ERA-Interim), much smaller than that from M2 Modis(140.0 g/m~2). However, the spatial distributions of CWPs, show similar patterns among these reanalyses, with relatively small values over Greenland and large values over the North Atlantic. Consistent with M2 Modis, these reanalyses show larger LWPs than IWPs, except for ERA-Interim. However, MERRA-2 and MERRA underestimate the ratio of IWPs to CWPs over the entire Arctic, while ERA-Interim and JRA-55 overestimate this ratio. ERA5 shows the best performance in terms of the ratio of IWPs to CWPs. All datasets exhibit larger CWPs and LWPs in summer than in winter. For M2 Modis, IWPs hold seasonal variation similar with LWPs over the land but opposite over the ocean. Following the Arctic warming, the trends in LWPs and IWPs during 1980~2015 show that LWPs increase and IWPs decrease across all datasets, although not statistically significant. Correlation analysis suggests that all datasets have similar interannual variability. The study further found that the inclusion of re-evaporation processes increases the humidity in the atmosphere over the land and that a more realistic liquid/ice phase can be obtained by independently treating the liquid and ice water contents. 相似文献