全文获取类型
收费全文 | 40433篇 |
免费 | 6627篇 |
国内免费 | 9135篇 |
专业分类
测绘学 | 4417篇 |
大气科学 | 4533篇 |
地球物理 | 7803篇 |
地质学 | 23120篇 |
海洋学 | 4212篇 |
天文学 | 3382篇 |
综合类 | 3021篇 |
自然地理 | 5707篇 |
出版年
2024年 | 267篇 |
2023年 | 724篇 |
2022年 | 1436篇 |
2021年 | 1677篇 |
2020年 | 1583篇 |
2019年 | 1931篇 |
2018年 | 1388篇 |
2017年 | 1637篇 |
2016年 | 1699篇 |
2015年 | 1874篇 |
2014年 | 2285篇 |
2013年 | 2250篇 |
2012年 | 2391篇 |
2011年 | 2562篇 |
2010年 | 2191篇 |
2009年 | 2786篇 |
2008年 | 2655篇 |
2007年 | 2739篇 |
2006年 | 2677篇 |
2005年 | 2487篇 |
2004年 | 2217篇 |
2003年 | 2108篇 |
2002年 | 1829篇 |
2001年 | 1580篇 |
2000年 | 1594篇 |
1999年 | 1388篇 |
1998年 | 1210篇 |
1997年 | 914篇 |
1996年 | 772篇 |
1995年 | 647篇 |
1994年 | 617篇 |
1993年 | 521篇 |
1992年 | 377篇 |
1991年 | 311篇 |
1990年 | 223篇 |
1989年 | 179篇 |
1988年 | 148篇 |
1987年 | 90篇 |
1986年 | 52篇 |
1985年 | 36篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
J. C. A. Miller-Jones R. P. Fender E. Nakar 《Monthly notices of the Royal Astronomical Society》2006,367(4):1432-1440
We present a collation of the available data on the opening angles of jets in X-ray binaries, which in most cases are small (≲10°). Under the assumption of no confinement, we calculate the Lorentz factors required to produce such small opening angles via the transverse relativistic Doppler effect. The derived Lorentz factors, which are in most cases lower limits, are found to be large, with a mean >10, comparable to those estimated for active galactic nuclei (AGN) and much higher than the commonly assumed values for X-ray binaries of 2–5. Jet power constraints do not, in most cases, rule out such high Lorentz factors. The upper limits on the opening angles show no evidence for smaller Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those sources in which deceleration has been observed (notably XTE J1550−564 and Cygnus X-3), some confinement of the jets must be occurring, and we briefly discuss possible confinement mechanisms. It is however possible that all the jets could be confined, in which case the requirement for high bulk Lorentz factors can be relaxed. 相似文献
42.
43.
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
44.
45.
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
46.
47.
昆仑山口大地震与地形变异常的讨论 总被引:7,自引:5,他引:2
针对昆仑山口大地震,总结了多种地形变(大地测量)手段所显示的异常变化及其时空分布,结果显示:8.1级大震前存在空间尺度大,时间尺度的地形变前兆异常,简要介绍了相关的异常图像,给出了初步解释,并对未来震情的发展进行了探讨,认为近期内强震活动向华北迁移的可能性不大。 相似文献
48.
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
49.
韩玲 《地球科学与环境学报》2003,25(1):74-75
提出了一种基于格网DEM的粗差检测及剔除方法,其基本思想是对每个表面上的点,在坡度上,高程或突变量引起的形状不连续,可能被怀疑有误差,通过坡度上每个点,应用坡度逼近或改变量来计算,考虑坡度变化的相对值,并以这些相对值计算一个统计值为判断该点合法性的阈值,使计算结果更为可靠。 相似文献
50.