全文获取类型
收费全文 | 36996篇 |
免费 | 5780篇 |
国内免费 | 7683篇 |
专业分类
测绘学 | 3435篇 |
大气科学 | 4522篇 |
地球物理 | 6084篇 |
地质学 | 19495篇 |
海洋学 | 4017篇 |
天文学 | 5207篇 |
综合类 | 2248篇 |
自然地理 | 5451篇 |
出版年
2024年 | 242篇 |
2023年 | 626篇 |
2022年 | 1272篇 |
2021年 | 1479篇 |
2020年 | 1345篇 |
2019年 | 1659篇 |
2018年 | 1174篇 |
2017年 | 1388篇 |
2016年 | 1429篇 |
2015年 | 1596篇 |
2014年 | 1991篇 |
2013年 | 1946篇 |
2012年 | 2090篇 |
2011年 | 2203篇 |
2010年 | 1921篇 |
2009年 | 2543篇 |
2008年 | 2437篇 |
2007年 | 2543篇 |
2006年 | 2481篇 |
2005年 | 2367篇 |
2004年 | 2080篇 |
2003年 | 2005篇 |
2002年 | 1733篇 |
2001年 | 1515篇 |
2000年 | 1522篇 |
1999年 | 1328篇 |
1998年 | 1209篇 |
1997年 | 769篇 |
1996年 | 655篇 |
1995年 | 565篇 |
1994年 | 529篇 |
1993年 | 442篇 |
1992年 | 316篇 |
1991年 | 283篇 |
1990年 | 189篇 |
1989年 | 172篇 |
1988年 | 132篇 |
1987年 | 82篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
53.
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
54.
S. Ó Tuairisg R. F. Butler A. Shearer R. M. Redfern D. Butler A. Penny 《Monthly notices of the Royal Astronomical Society》2003,345(3):960-980
We present the results of TRIFFID simultaneous V - and B -band observations of the cores of the globular clusters M15, M92 and NGC 6712. A variability search of their dense centres was made feasible through performing post-exposure image sharpening on the images, increasing the image resolution by a factor of ∼2. The isis implementation of the image subtraction technique developed by Alard & Lupton was then used to detect flux variations in our image sets. We have obtained periods for all observable variables (in our field of view) in NGC 6712 and we have found two new RR Lyrae variables (an RRab and an RRc). We have confirmed three variables in our field of view of the M92. For M15, we detect 48 variables in our field of view, 23 of which are new discoveries. We obtain periods and amplitudes for all variables and classify new ones based on the light-curve shape, the most significant period and the mean magnitude in the V band. Among the detected RR Lyrae we find 19 RRc, 12 RRab and two RRd types. In the subsequent analysis we find a marked increase in RRc over RRab variables in the core. In a refined procedure to search for fainter objects we find no dwarf novae in our field of view of M15. Simulations performed on the data set to quantify our sensitivity to such objects indicate that an upper limit of 10 dwarf novae (at 92 per cent probability) exist in our field of view. The implications this result has on globular clusters are discussed. 相似文献
55.
56.
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
57.
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
58.
59.
60.