全文获取类型
| 收费全文 | 34947篇 |
| 免费 | 6263篇 |
| 国内免费 | 8719篇 |
专业分类
| 测绘学 | 3847篇 |
| 大气科学 | 6325篇 |
| 地球物理 | 7212篇 |
| 地质学 | 17024篇 |
| 海洋学 | 4073篇 |
| 天文学 | 5529篇 |
| 综合类 | 2351篇 |
| 自然地理 | 3568篇 |
出版年
| 2024年 | 94篇 |
| 2023年 | 404篇 |
| 2022年 | 1012篇 |
| 2021年 | 1282篇 |
| 2020年 | 1352篇 |
| 2019年 | 1590篇 |
| 2018年 | 1285篇 |
| 2017年 | 1449篇 |
| 2016年 | 1516篇 |
| 2015年 | 1737篇 |
| 2014年 | 2315篇 |
| 2013年 | 2297篇 |
| 2012年 | 2428篇 |
| 2011年 | 2657篇 |
| 2010年 | 2414篇 |
| 2009年 | 2821篇 |
| 2008年 | 2649篇 |
| 2007年 | 2847篇 |
| 2006年 | 2660篇 |
| 2005年 | 2236篇 |
| 2004年 | 2001篇 |
| 2003年 | 1668篇 |
| 2002年 | 1302篇 |
| 2001年 | 1238篇 |
| 2000年 | 1083篇 |
| 1999年 | 1005篇 |
| 1998年 | 828篇 |
| 1997年 | 648篇 |
| 1996年 | 529篇 |
| 1995年 | 461篇 |
| 1994年 | 452篇 |
| 1993年 | 388篇 |
| 1992年 | 290篇 |
| 1991年 | 209篇 |
| 1990年 | 157篇 |
| 1989年 | 171篇 |
| 1988年 | 116篇 |
| 1987年 | 73篇 |
| 1986年 | 53篇 |
| 1985年 | 46篇 |
| 1984年 | 28篇 |
| 1983年 | 23篇 |
| 1982年 | 26篇 |
| 1981年 | 12篇 |
| 1980年 | 21篇 |
| 1979年 | 7篇 |
| 1978年 | 11篇 |
| 1977年 | 18篇 |
| 1954年 | 13篇 |
| 1875年 | 1篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
91.
92.
基于蚁群算法的城市可持续发展综合评价 总被引：1，自引：0，他引：1
在可持续发展体系分类的基础上，应用蚁群算法对可持续发展各分类指数公式和综合指数公式进行优化，建立可持续发展评价模型。将该模型应用于乌鲁木齐市可持续发展水平评价，评价结果与现状分析一敛。结果表明该模型简单适用、有良好的通用性。 相似文献
93.
94.
95.
在目前常用的周跳探测与修复方法基础上 ,提出了首先将观测资料按照观测历元不连续分成若干小弧段 ,然后利用差分法进行周跳探测 ,根据差分后周跳放大的特性判断周跳和野值 ,并确定其位置利用宽带组合和电离层组合的方法解算周跳大小。通过实例验证了其有效性。 相似文献
96.
97.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
98.
99.
We present the results of a systematic investigation of spectral evolution in the Z source GX 349+2, using data obtained during 1998 with the Proportional Counter Array (PCA) on-board the RXTE satellite. The source traced a extended normal branch (NB) and flaring branch (FB) in the colour–colour diagram (CD) and the hardness-intensity diagram (HID) during these observations. The spectra at different positions of the Z-track were best fitted by a model consisting of a disc blackbody and a Comptonized spectrum. A broad (Gaussian) iron line at ∼6.7 keV is also required to improve the fit. The spectral parameters showed a systematic and significant variation with the position along the Z-track. The evolution in spectral parameters is discussed in view of the increasing mass accretion rate scenario, proposed to explain the motion of Z sources in the CD and the HID. 相似文献
100.
We investigate the role of seasonal variations of Titan’s stratospheric composition on the temperature. We use a general circulation model coupled with idealized chemical tracers that reproduce variations of ethane (C2H6), acetylene (C2H2), and hydrogen cyanide (HCN). Enhancement of the mole fractions of these compounds, at high latitudes in the winter hemisphere relative to their equatorial values, induces a relative decrease in temperature above approximately 0.2 mbar, with a peak amplitude around −20 K, and a relative increase in temperature below, around 1 mbar, with a peak amplitude around +7 K. These thermal effects are mainly due to the variations of the cooling to space induced by the varying distributions. The ethane, acetylene, and hydrogen cyanide variations affect the cooling rates in a similar way, with the dominant effect being due to ethane, though its latitudinal variations are small. 相似文献