全文获取类型
收费全文 | 39153篇 |
免费 | 6217篇 |
国内免费 | 10686篇 |
专业分类
测绘学 | 3009篇 |
大气科学 | 4968篇 |
地球物理 | 7350篇 |
地质学 | 21689篇 |
海洋学 | 4857篇 |
天文学 | 6709篇 |
综合类 | 2686篇 |
自然地理 | 4788篇 |
出版年
2024年 | 103篇 |
2023年 | 320篇 |
2022年 | 819篇 |
2021年 | 957篇 |
2020年 | 1144篇 |
2019年 | 1429篇 |
2018年 | 1067篇 |
2017年 | 1197篇 |
2016年 | 1223篇 |
2015年 | 1412篇 |
2014年 | 1827篇 |
2013年 | 2245篇 |
2012年 | 2110篇 |
2011年 | 2094篇 |
2010年 | 2006篇 |
2009年 | 2394篇 |
2008年 | 2593篇 |
2007年 | 2970篇 |
2006年 | 3036篇 |
2005年 | 2891篇 |
2004年 | 2624篇 |
2003年 | 2156篇 |
2002年 | 1929篇 |
2001年 | 1734篇 |
2000年 | 1773篇 |
1999年 | 1868篇 |
1998年 | 1772篇 |
1997年 | 1221篇 |
1996年 | 1153篇 |
1995年 | 999篇 |
1994年 | 892篇 |
1993年 | 991篇 |
1992年 | 769篇 |
1991年 | 642篇 |
1990年 | 423篇 |
1989年 | 309篇 |
1988年 | 255篇 |
1987年 | 140篇 |
1986年 | 78篇 |
1985年 | 92篇 |
1984年 | 62篇 |
1983年 | 64篇 |
1982年 | 48篇 |
1981年 | 29篇 |
1980年 | 37篇 |
1979年 | 20篇 |
1978年 | 25篇 |
1977年 | 29篇 |
1976年 | 14篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
81.
82.
83.
PatMoore 《成都信息工程学院学报》2002,17(4):289-299
尽管语法在交际教学法鼎盛时期一度遭到冷遇,但现在又重新被英语语言教学所接纳,作为一种新的语法教学方式,发现原则综合了传统归纳发和演绎法的长处,概述了发现原则的理论依据,指出发现原则旨在鼓励学习者积极参与而非被动接受,符合当前认知主义对二语学习的认识。 相似文献
84.
85.
1 IntroductionAnicecoreobtainedfrom polarglaciersoricesheetsisoneofthemostimportantarchivestoreconstructpaleoclimaticandpaleoatmosphericcondition .Informationonpale o environmentcanbeextractedfromicecoresaschemicaland/orphysicalsignals.Amongthechemicalsignals,heavymetalsarenotedassignalsofterrestrialenvironmentalchangeandanthropogenicpollution (e.g .Murozumietal.1 969;NgandPatterson 1 981 ;Hongetal.1 994) .SinceconcentrationsofmostofthemetalsinpolarsnowincentralGreen landareatorbelowthepptl… 相似文献
86.
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
87.
88.
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
89.
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
90.
Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and
for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities
coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In
addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets
and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric
device MIDI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献