全文获取类型
收费全文 | 1492篇 |
免费 | 134篇 |
国内免费 | 171篇 |
专业分类
测绘学 | 157篇 |
大气科学 | 128篇 |
地球物理 | 123篇 |
地质学 | 366篇 |
海洋学 | 45篇 |
天文学 | 910篇 |
综合类 | 37篇 |
自然地理 | 31篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 29篇 |
2021年 | 39篇 |
2020年 | 30篇 |
2019年 | 29篇 |
2018年 | 16篇 |
2017年 | 30篇 |
2016年 | 44篇 |
2015年 | 39篇 |
2014年 | 39篇 |
2013年 | 35篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 49篇 |
2009年 | 97篇 |
2008年 | 90篇 |
2007年 | 78篇 |
2006年 | 99篇 |
2005年 | 112篇 |
2004年 | 100篇 |
2003年 | 106篇 |
2002年 | 96篇 |
2001年 | 93篇 |
2000年 | 92篇 |
1999年 | 91篇 |
1998年 | 87篇 |
1997年 | 34篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 2篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1971年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1797条查询结果,搜索用时 109 毫秒
991.
J. P. Phillips G. Ramos-Larios 《Monthly notices of the Royal Astronomical Society》2009,396(4):1915-1928
We present mid-infrared (MIR) photometry for 367 Galactic disc, bulge and Large Magellanic Cloud (LMC) planetary nebulae (PNe), determined using data acquired with the Spitzer Space Telescope , and through the Legacy Programs GLIMPSE II (Galactic Legacy Infrared Mid-plane Survey Extraordinaire II) and SAGE (Surveying the Agents of the Galaxy's Evolution). This has permitted us to make a comparison between the luminosity functions of bulge and LMC PNe, and between the MIR colours of all three categories of source. It is determined that whilst the 3.6 μm luminosity functions of the LMC and bulge sources are likely to be closely similar, the [3.6]–[5.8] and [5.8]–[8-0] indices of LMC nebulae are different from those of their disc and bulge counterparts. This may arise because of enhanced 6.2 μm polycyclic aromatic hydrocarbon emission within the LMC sources, and/or as a result of further, and more radical differences between the spectra of LMC and Galactic PNe. We also determine that the more evolved disc sources listed in the Macquarie/AAO/Strasbourg (MASH) catalogues of Parker et al. and Miszalski et al. have similar colours to those of the less evolved (and higher surface brightness) sources in the catalogue of Acker et al., a result which appears at variance with previous studies of these sources. 相似文献
992.
J. P. Phillips D. Zepeda-García 《Monthly notices of the Royal Astronomical Society》2009,394(4):1875-1886
We have analysed the near-infrared (NIR) and far-infrared (FIR) colours of MASH I and MASH II (the Macquarie/AAO/Strasbourg surveys) planetary nebulae (PNe), using data deriving from the Two-Micron All-Sky Survey and Infrared Astronomical Satellite . We were able to identify ∼5 per cent of the sources in the NIR, and a slightly larger fraction (∼12 per cent) in the FIR. It is concluded that whilst the NIR colours of these nebulae are consistent with those of less evolved (and higher surface brightness) PNe, their FIR colours are markedly different. This disparity is likely to arise as a result of an evolution in dust temperatures, in their line emission characteristics, and in the relative contributions of the 8.6 and 11.3 μm polycyclic aromatic hydrocarbon emission features. A rump of ∼9 per cent of the detected sources have values log[ F (25 μm)/ F (60 μm)] which are lower than can be explained in terms of normal nebular evolution, however. If these are comparable in nature to the undetected PNe, then this would argue that ∼1 in 10 of MASH I and II nebulae may represent galactic H ii regions, Stromgren spheres, symbiotic nebulae or other unrelated categories of source. 相似文献
993.
For this paper, we collected almost all of the type II quasars so far discovered. Among them, 485 sources have photometric data at JHK bands, mainly from Two-Micron All-Sky Survey observations, 65 sources have IRAS photometric data in at least one of the three IRAS bands at 25, 60 and 100 μm and 15 sources have IRAS photometric data in all three IRAS bands. We find that in nearly half of all type II quasars, both the near- and far-infrared radiations are dominated by starlight or thermal reprocessing of starlight by dust in the underlying galaxy. The infrared radiation of the other group (slightly over half) is dominated by a non-thermal radiation in the near-infrared, and mostly in the far-infrared also (although there is a mixture particularly for the longer wavelengths). It is proposed that for the later group, hidden broad lines may exist in the infrared. On the basis of our and previous results, we also discuss the possibility that there are two distinct classes of type II quasars: 'true' type II quasars without a broad-line region and heavily obscured type I quasars, in full analogy with the case for type II Seyfert galaxies. No relationships can be found for either the near-infrared or the far-infrared colours and the redshift. Correlations between absolute magnitude in the near- and far-infrared with redshift are found, but could be due to a flux limit (Malmquist bias). 相似文献
994.
995.
996.
“珍珠”台风卫星红外通道亮温的数值模拟 总被引:6,自引:0,他引:6
热带地区云的覆盖率高, 卫星辐射资料特别是红外通道的数值模拟容易受到云的影响, 提高台风等热带天气系统卫星亮温资料的模拟能力, 有助于热带地区数值模式的检验以及提高卫星资料直接同化的水平。首先, 利用天气研究和预报模式(Weather Research and Forecasting Model, 简称WRF) 对 “珍珠” 台风的三维气象场, 包括云结构特征, 进行了模拟, 并诊断分析了总云量、云顶气压等物理量; 然后, 结合快速辐射传输模式 (fast radiative transfer model for TOVS, 简称RTTOV) 8.7版对 “珍珠” 台风的高分辨率红外辐射探测仪3型 (High Resolution Infrared Radiation Sounder, 简称HIRS/3) 红外辐射亮温进行了模拟, 并且比较了有云和无云条件下的模拟结果。结果表明, 如果不考虑云的影响, RTTOV模式无法模拟出台风的结构特征; 结合三维云特征的模拟量, RTTOV模式可以较好地模拟出HIRS/3第4~10、13~19通道的辐射亮温。加入云结构特征对峰值能量高度在云层以下的红外通道的模拟有正面影响, 该方案既可以作为检验模式模拟的一种手段, 同时也表明红外资料在热带天气系统的资料同化领域具有潜在的应用能力。 相似文献
997.
Penélope Serrano-Ortiz Andrew S. Kowalski Francisco Domingo Borja Ruiz Lucas Alados-Arboledas 《Boundary-Layer Meteorology》2008,126(2):209-218
Errors in the estimation of CO2 surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol
Soc 106:85–100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65–85,
(2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements
of absolute CO2 density (ρ
c
). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance
system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to
reliably report ρ
c
and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively
large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ρ
c
in a semi-arid climate with large sensible heat fluxes (H
s
) and (wet) mineral deposition. When ρc is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO2 uptake. 相似文献
998.
利用局部二值模式(Local Binary Patterns,LBP),结合局部云图的方差信息(VAR),对全天空红外测云系统获得的红外云图进行了分类研究。首先建立了器测云状分类与传统分类的对应关系,其次分析了层状云、积状云、波状云、卷云和晴空5种类型天空的LBP谱和VAR特征,最后对274个样本进行了分类识别,并与人工观测结果比较,结果表明,层状云、积状云、波状云、卷云和晴空的识别正确率分别为100.0%、84.2%、70.3%、64.7%、99.0%,平均正确率达到87.2%。 相似文献
999.
为了对全天空红外测云系统获得的红外图像进行云类自动识别, 提出了基于模糊纹理光谱结合云物理属性的全天空云类识别方法。首先根据不同滤波窗口的模糊纹理光谱图像特征, 确定了滤波窗口大小, 然后通过分析不同天空类型下的FUTS谱 (fuzzy uncertainty texture spectrum) 以及同一种天空类型下的FUTS谱, 考察了FUTS进行云类识别的适用性, 最后利用最小距离分类法和云基本物理属性对全天空红外图像进行了分类测试。在200个测试样本中, 层状云、积云、高积云、卷云和晴空的识别率分别为100%, 100%, 90%, 100%, 100%, 平均识别率达到98%。基于模糊纹理光谱的云分类算法对单一云空具有很好的分类效果, 可进一步应用于全天空红外图像的云分类识别。 相似文献
1000.
用于地表温度场与断裂构造关系分析的分段均值法——以江山-绍兴断裂金衢段为例 总被引:1,自引:0,他引:1
提出了一种用于地表温度场与断裂构造关系分析的分段均值法.方法以已知断裂带中心线为准,向两侧一定范围作等间距划分,统计各等分带内的平均地表温度和平均距离,通过绘制平均地表温度与平均距离之间的相关性曲线来描述地表温度场与断裂构造之间的关系.在江山-绍兴断裂金衙段的实际应用中,方法以Landsat 7 ETM+热红外遥感影像为数据源,描述了研究区地表温度场与深大断裂带之间的关系.认为地表温度场与北东走向的江山-绍兴断裂带、常山-漓渚断裂带和球川-萧山断裂带的相关性明显,区域特征稳定.在各断裂带影响范围内,距离断裂带越近,地表温度越高;北西走向的淳安-温州断裂带和东西走向的衙州一天台断裂带均处于地表温度梯度变化带,断裂带两侧可能分属不同的地表温度场. 相似文献