全文获取类型
收费全文 | 89005篇 |
免费 | 14938篇 |
国内免费 | 19948篇 |
专业分类
测绘学 | 7992篇 |
大气科学 | 11177篇 |
地球物理 | 18203篇 |
地质学 | 49289篇 |
海洋学 | 10590篇 |
天文学 | 7221篇 |
综合类 | 5821篇 |
自然地理 | 13598篇 |
出版年
2024年 | 527篇 |
2023年 | 1417篇 |
2022年 | 2827篇 |
2021年 | 3225篇 |
2020年 | 3269篇 |
2019年 | 3783篇 |
2018年 | 2928篇 |
2017年 | 3364篇 |
2016年 | 3597篇 |
2015年 | 3877篇 |
2014年 | 4807篇 |
2013年 | 4740篇 |
2012年 | 5176篇 |
2011年 | 5514篇 |
2010年 | 4745篇 |
2009年 | 5922篇 |
2008年 | 5729篇 |
2007年 | 6204篇 |
2006年 | 5989篇 |
2005年 | 5424篇 |
2004年 | 4974篇 |
2003年 | 4744篇 |
2002年 | 4094篇 |
2001年 | 3683篇 |
2000年 | 3499篇 |
1999年 | 3119篇 |
1998年 | 2830篇 |
1997年 | 2292篇 |
1996年 | 2025篇 |
1995年 | 1739篇 |
1994年 | 1721篇 |
1993年 | 1433篇 |
1992年 | 1141篇 |
1991年 | 823篇 |
1990年 | 677篇 |
1989年 | 558篇 |
1988年 | 435篇 |
1987年 | 305篇 |
1986年 | 188篇 |
1985年 | 130篇 |
1984年 | 56篇 |
1983年 | 43篇 |
1982年 | 40篇 |
1981年 | 32篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1978年 | 52篇 |
1977年 | 30篇 |
1976年 | 11篇 |
1954年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
93.
The study of the chemical stability of vitreous material in aqueous media is well‐established. There has to date been little consideration of the implications of variations in the chemical durability of tephra in Quaternary tephrochronology. Chemical alteration can take the form of cationic leaching from the matrix, or complete destruction of the silica network, either of which could constrain the ability to chemically identify distal tephra. Here we apply established models of vitreous durability to the published chemical analyses of a large number of Icelandic tephras in order to predict their relative durabilities under equivalent conditions. This suggests that some important tephras have relatively poor chemical stability, and that rhyolitic tephras are, in general, more stable than basaltic. We conclude that tephras should be expected to show predictable differential chemical stability in the post‐depositional environment. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
94.
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
95.
96.
A. V. Bogomolov A. P. Ignat’ev K. Kudela S. N. Kuznetsov Yu. I. Logachev O. V. Morozov I. N. Myagkova S. N. Oparin A. A. Pertsov S. I. Svertilov B. Yu. Yushkov 《Astronomy Letters》2003,29(3):199-204
We consider temporal, spectral, and polarization parameters of the hard X-ray and gamma-ray radiation observed during the solar flare of May 20, 2002, in the course of experiments with the SONG and SPR-N instruments onboard the Coronas-F spacecraft. This flare is one of the most intense gamma-ray events among all of the bursts of solar hard electromagnetic radiation detected since the beginning of the Coronas-F operation (since July 31, 2001) and one of the few gamma-ray events observed during solar cycle 23. A simultaneous analysis of the Coronas-F and GOES data on solar thermal X-ray radiation suggests that, apart from heating due to currents of matter in the the flare region, impulsive heating due to the injection of energetic electrons took place during the near-limb flare S21E65 of May 20, 2002. These electrons produced intense hard X-ray and gamma-ray radiation. The spectrum of this radiation extends up to energies ≥7 MeV. Intense gamma-ray lines are virtually unobservable against the background of the nonthermal continuum. The polarization of the hard X-ray (20–100 keV) radiation was estimated to be ≤15–20%. No significant increase in the flux of energetic protons from the flare under consideration was found. At the same time, according to ACE data, the fluxes of energetic electrons in interplanetary space increased shortly (~25 min) after the flare. 相似文献
97.
98.
99.
Andreas Just 《Astrophysics and Space Science》2003,284(2):727-730
There is a long term dynamical heating of stellar populations with age observed in the age – velocity dispersion – relation
(AVR). This effect allows a determination of the star formation history SFR(t) from local kinematical data of main sequence stars. Using a self-consistent disk model for the vertical structure of the
disk, we find from the kinematics of the stars in the solar neighbourhood that the SFR shows a moderate star burst about 10 Gyr ago followed by a continuous decline to the present day value consistent with the
observed number of OB stars. The gravitational potential of the gas component and of the Dark Matter Halo is included and
the effect of chemical enrichment, finite lifetime of the stars and mass loss of the stellar component are taken into account.
The scale heights for main sequence stars together with the SFR is then used to determine constistently the IMF from the observed local luminosity function. The main new result is that the power law break in the present day mass function
(PDMF) around 1 M
⊙ is entirely due to evolutionary effects of the disk and does not appear in the IMF.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
100.
Larisa A. Yakovina Yakiv V. Pavlenko Carlos Abia 《Astrophysics and Space Science》2003,288(3):279-286
Lithium abundances in the atmospheres of the super Li-rich C-giants WZ Cas and WX Cyg are derived by the spectral synthesis
technique using the Li I resonance line at λ670.8 nm and three subordinate lines at λλ 812.6, 610.4 and 497.2 nm. The differences
between the Li abundances derived from the λ670.8 nm line and the λλ 497.2, 812.6 nm lines do not exceed ±0.5 dex. The lithium
line at λ610.4 nm provides typically lower abundances than the resonance line (by ≈ 1 dex). The mean LTE and NLTE Li abundances
from three Li I lines (excluding λ610.4 nm) are 4.7, 4.9 for WZ Cas, and 4.6, 4.8 for WX Cyg, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献