全文获取类型
收费全文 | 1477篇 |
免费 | 115篇 |
国内免费 | 104篇 |
专业分类
测绘学 | 124篇 |
大气科学 | 45篇 |
地球物理 | 294篇 |
地质学 | 252篇 |
海洋学 | 41篇 |
天文学 | 745篇 |
综合类 | 73篇 |
自然地理 | 122篇 |
出版年
2024年 | 6篇 |
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 24篇 |
2018年 | 15篇 |
2017年 | 30篇 |
2016年 | 28篇 |
2015年 | 30篇 |
2014年 | 31篇 |
2013年 | 63篇 |
2012年 | 29篇 |
2011年 | 36篇 |
2010年 | 44篇 |
2009年 | 81篇 |
2008年 | 92篇 |
2007年 | 157篇 |
2006年 | 93篇 |
2005年 | 78篇 |
2004年 | 85篇 |
2003年 | 77篇 |
2002年 | 92篇 |
2001年 | 58篇 |
2000年 | 74篇 |
1999年 | 57篇 |
1998年 | 54篇 |
1997年 | 78篇 |
1996年 | 38篇 |
1995年 | 39篇 |
1994年 | 34篇 |
1993年 | 26篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有1696条查询结果,搜索用时 781 毫秒
491.
J. Höpfner 《Journal of Geodesy》2000,74(3-4):335-358
Recently, effective atmospheric-angular-momentum (AAM) functions as calculated from National Centers for Environmental Prediction
(NCEP) (formerly National Meteorological Center, NMC) and National Center for Atmospheric Research (NCAR) Reanalyses have
become available for the years 1958 to 1998. Concerning the wind terms, the top level in the atmosphere used here is 10 hPa.
Compared with earlier NMC model versions, which incorporate wind fields up to 100 hPa since 1976 and up to 50 hPa since 1981,
the reanalyses have produced improved data series over a longer period than before. The axial AAM component χ3 is associated with changes in length of day (LOD). Motivated by better quality and continuity of the series AAM (NCEP) Reanalysis,
the problem of the seasonal imbalances in the solid Earth–atmosphere axial angular momentum budget is re-examined. To assess
better the estimates of the annual and semiannual oscillations in LOD and AAM and of the residual oscillations derived as
difference series between LOD and AAM, the series of LOD data from three analysis centers [International Earth Rotation Service
(IERS), GeoForschungZentrum Potsdam (GFZ) and Jet Propulsion Laboratory Pasadena (JPL)] and of AAM data in terms of χ3(W), χ3(P) and χ3(P+IB) from four meteorological centers [NCEP, Japan Meteorological Agency (JMA), European Centre for Medium-Range Weather
Forecasts (ECMWF) and the UK Meteorological Office (UKMO)] are used in this study. The main analysis steps were removing gaps,
filtering out the seasonal oscillations, calculating optimal estimates of the parameters of the oscillations and calculating
the difference series between the LOD and AAM systems as well as the residuals in the axial angular momentum budget in the
LOD–AAM systems. The results derived as difference series between the different LOD, AAM and LOD–AAM systems show to what
extent the variations reflect systematic differences and significant signals, respectively, which is important for future
activities in this field.
Received: 2 February 1999 / Accepted: 30 November 1999 相似文献
492.
TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL)1 AppelE ,M櫣llerR ,WidderRW .PalaeomagneticresultsfromtheTibetanSedimentarySeriesoftheManangarea (northcentralnepal) [J].GeophysJInt ,1991,10 4:2 5 5~ 2 6 6 .
2 AppelE ,PatzeltA ,ChoukerC .SecondarypalaeoremanenceofTethyansedimentsfromtheZanskarRange (NWHimalaya)[J].GeophysJInt,1995 ,12 2 :2 2 7~ 2 42 .
3 B… 相似文献
493.
R. Brajša H. Wöhl D. Ruždjak B. Vršnak G. Verbanac L. Svalgaard J.-F. Hochedez 《Astronomische Nachrichten》2007,328(10):1013-1015
The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set (1878–1981) and a series of full-disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998–2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
494.
全球陆地水储量对地球自转变化的激发作用 总被引:5,自引:2,他引:3
用美国环境预测中心和美国大气研究中心(NCEP/NCAR)40年重新分析计划气候数据同化系统(CDAS)所得到的全球陆地水储量(土壤湿度和积雪水当量)数据,对地球自转变化(极移和日长)的激发作用作了分析.结果表明,陆地水储量对周年地极移动正频分量的激发为17.8mas,与大气激发相当,相位滞后约48°.其中,积雪水当量的激发结果与用人卫遥感技术所得到的积雪水当量激发的正、负频率分量的振幅和相位都符合得很好.
用陆地水储量数据得到对日长变化周年分量的激发作用约49μs,约占观测激发的15%,相位滞后约23°;对日长变化半年分量的激发作用约9μs,约占观测激发的3%,相位滞后约122°. 相似文献
495.
J. Javaraiah 《Journal of Astrophysics and Astronomy》2000,21(3-4):167-170
Using the data on sunspot groups compiled during 1879–1975, we determined variations in the differential rotation
coefficientsA andB during the solar cycle. The variation in the equatorial rotation rateA is found to be significant only in the odd numbered cycles, with an amplitude ∼ 0.01 μ rads-1. There exists a good anticorrelation between the variations of the differential rotation rateB derived from the odd and even numbered cycles, suggesting existence of a ‘22-year’ periodicity inB. The amplitude of the variation ofB is ∼ 0.05 μ rad s-1. 相似文献
496.
回顾了恒星表面结构多普勒成像研究工作的发展历史,重点评述了该项技术在类太阳活动恒星研究领域的应用。介绍了该项技术在国际上的发展现状,给出了恒星表面黑子结构形态的多普勒成像技术的基本原理,讨论了该项技术对观测仪器、观测过程和观测对象的要求,并对未来这一领域的研究工作进行了展望。 相似文献
497.
498.
499.
500.
对挡土墙背离填土绕墙脚转动时墙后滑裂土体的应力状态进行了详细分析,建立了墙后滑裂体水平土层墙面反力、滑裂面反力、土层间剪力和土层竖向土压力强度之间的关系式。为了考虑挡土墙绕墙脚转动时墙脚局部土体并未达到极限状态,对墙面摩擦角、滑裂面土体的内摩擦角予以折减。在水平土层单元法的基础上,考虑水平土层间剪力作用、每一土层的墙面摩擦角和滑裂面水平倾角等的变化,建立了土层竖向土压力强度的逐层渐近的计算方法,并给出了挡土墙主动土压力强度、土压力合力及其作用位置的计算公式。经比较表明:挡土墙主动土压力分布曲线与试验结果基本一致,计算得的主动土压力系数与试验结果很接近,比库仑解大;计算得出的滑裂面为一曲面,其顶部开裂宽度比库仑滑裂面小,与工程实际相符。 相似文献