全文获取类型
收费全文 | 3628篇 |
免费 | 519篇 |
国内免费 | 287篇 |
专业分类
测绘学 | 47篇 |
大气科学 | 26篇 |
地球物理 | 793篇 |
地质学 | 1371篇 |
海洋学 | 248篇 |
天文学 | 1482篇 |
综合类 | 118篇 |
自然地理 | 349篇 |
出版年
2024年 | 9篇 |
2023年 | 27篇 |
2022年 | 43篇 |
2021年 | 64篇 |
2020年 | 64篇 |
2019年 | 93篇 |
2018年 | 69篇 |
2017年 | 70篇 |
2016年 | 86篇 |
2015年 | 93篇 |
2014年 | 173篇 |
2013年 | 186篇 |
2012年 | 162篇 |
2011年 | 154篇 |
2010年 | 147篇 |
2009年 | 273篇 |
2008年 | 260篇 |
2007年 | 335篇 |
2006年 | 245篇 |
2005年 | 218篇 |
2004年 | 180篇 |
2003年 | 180篇 |
2002年 | 157篇 |
2001年 | 136篇 |
2000年 | 155篇 |
1999年 | 148篇 |
1998年 | 146篇 |
1997年 | 91篇 |
1996年 | 94篇 |
1995年 | 59篇 |
1994年 | 54篇 |
1993年 | 39篇 |
1992年 | 46篇 |
1991年 | 19篇 |
1990年 | 45篇 |
1989年 | 30篇 |
1988年 | 30篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有4434条查询结果,搜索用时 15 毫秒
991.
The velocity profiles and properties of proto-magnetar winds are investigated.It is found that the corotation of wind matter with magnetic field lines significantly affects r-process nucleosynthesis and could lead to long duration γ-ray bursts and hyper-energetic supernovae. 相似文献
992.
993.
白垩纪气候环境研究对认识现今全球环境格局的形成具有重要意义,现有的白垩纪环境变化记录均来自海洋沉积物,本文通过对我国中部六盘山地区六盘山群地层沉积与岩石磁化率测量分析,获得了128.15~115.82Ma期间陆相沉积物记录的气候变化信息。结果显示磁化率值总体较低,以125Ma为界大致可以分为前低后高两个阶段;结合岩石磁学测量及沉积相、岩石中铁含量与磁化率变化关系分析,认为岩石磁化率主要与源区磁性矿物的种类及含量有关,据此揭示六盘山地区在该时间段气候总体为干热环境,并可分为128.15~125Ma间气候相对湿热和125~115.82Ma间气候相对温湿两个阶段。磁化率记录的这种气候转变与海洋沉积物记录的全球海平面温度变化趋势一致,但相对海平面温度由升高到降低的转折时间提前约1.7Ma。 相似文献
994.
995.
大比例尺高精度航磁异常查证方法的探讨 总被引:1,自引:0,他引:1
大比例尺、高精度航空磁测具有飞行高度低、定位误差小,磁测精度高的特点。在寻找深部隐伏矿时,查证高精度航磁异常可以省去地面面积性磁测环节,节省异常查证费用和加快异常查证速度。 相似文献
996.
997.
998.
<正>This study examined spatial variations in the concentration,grain size and heavy mineral assemblages on Cedar Beach(Lake Erie,Canada).Magnetic studies of heavy mineral-enriched,dark-reddish sands present on the beach showed that magnetite(~150μm) is the dominant magnetic mineral.Surficial magnetic susceptibility values defined three zones:a lakeward region close to the water line(Zone 1),the upper swash zone(Zone 2) and the region landwards of the upper swash zone (Zone 3).Zone 2 showed the highest bulk and mass susceptibility(κ,χ) and the highest mass percentage of smaller grain-size(250μm) fractions in the bulk sand sample.Susceptibility(i.e.κandχ) values decreased and grain size coarsened from Zone 2 lakewards(into Zone 1) and landwards (into Zone 3),and correlated with the distribution of the heavy mineral assemblage,most probably reflecting preferential separation of large,less dense particles by waves and currents both along and across the beach.The eroded western section of Cedar Beach showed much higher concentrations of heavy minerals including magnetite,and finer sand grain sizes than the accreting eastern section, suggesting that magnetic techniques could be used as a rapid,cost-effective way of examining erosion along sensitive coastline areas. 相似文献
999.
Ian D. Howarth Nolan R. Walborn Danny J. Lennon Joachim Puls Yaël Nazé K. Annuk I. Antokhin D. Bohlender H. Bond J.-F. Donati L. Georgiev D. Gies D. Harmer A. Herrero I. Kolka D. McDavid T. Morel I. Negueruela G. Rauw P. Reig 《Monthly notices of the Royal Astronomical Society》2007,381(2):433-446
We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f?pe–O8fp). The Balmer and He i lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. He ii absorptions and metal lines (including many selective emission lines but excluding He ii λ4686 Å emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with P orb = 1542 d, e = 0.45 . We conduct a model-atmosphere analysis of the spectrum, and find that the system is consistent with a ∼O8 giant with a ∼B1 main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying 'clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint. 相似文献
1000.
The stability problem for small magnetohydrodynamic (MHD) perturbations in an optically thin, perfectly conducting uniform plasma with a cosmic abundance of elements is solved in the linear approximation. The electron heat conduction along the magnetic field and the proton heat conduction across the field are taken into account. We have shown for the first time that the entropy waves can grow exponentially, while the magnetosonic waves are damped in a wide range of physical conditions closest to the conditions in stellar coronae with the proper allowance for radiative losses. Slow magnetosonic waves are damped particularly rapidly. For the solar corona, the calculated damping decrement of slow magnetosonic waves agrees well with the averaged one in 11 quasi-periodic events observed from the TRACE satellite in extreme ultraviolet radiation. Other possible astrophysical applications of the results obtained are briefly discussed. 相似文献