全文获取类型
收费全文 | 35321篇 |
免费 | 5809篇 |
国内免费 | 7290篇 |
专业分类
测绘学 | 3382篇 |
大气科学 | 4406篇 |
地球物理 | 5918篇 |
地质学 | 18703篇 |
海洋学 | 3819篇 |
天文学 | 4435篇 |
综合类 | 2260篇 |
自然地理 | 5497篇 |
出版年
2024年 | 166篇 |
2023年 | 431篇 |
2022年 | 1153篇 |
2021年 | 1316篇 |
2020年 | 1216篇 |
2019年 | 1599篇 |
2018年 | 1101篇 |
2017年 | 1300篇 |
2016年 | 1326篇 |
2015年 | 1511篇 |
2014年 | 1937篇 |
2013年 | 1938篇 |
2012年 | 2060篇 |
2011年 | 2203篇 |
2010年 | 1919篇 |
2009年 | 2471篇 |
2008年 | 2408篇 |
2007年 | 2465篇 |
2006年 | 2431篇 |
2005年 | 2338篇 |
2004年 | 2028篇 |
2003年 | 1931篇 |
2002年 | 1653篇 |
2001年 | 1459篇 |
2000年 | 1449篇 |
1999年 | 1289篇 |
1998年 | 1122篇 |
1997年 | 765篇 |
1996年 | 644篇 |
1995年 | 545篇 |
1994年 | 512篇 |
1993年 | 437篇 |
1992年 | 302篇 |
1991年 | 270篇 |
1990年 | 184篇 |
1989年 | 144篇 |
1988年 | 120篇 |
1987年 | 69篇 |
1986年 | 41篇 |
1985年 | 35篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 14篇 |
1977年 | 7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 89 毫秒
101.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1996,17(1-2):23-40
Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines
show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present
in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to
1992 相似文献
102.
位于华南褶皱带南缘的右江盆地,其发展可分为两个不同的阶段。它的轮廓和结构,与NW向及NE向同沉积断裂关系密切。盆地内的沉积物,分别由特征不同的非补偿性和补偿性沉积相组成两个双层结构。盆地内火山活动发育,也明显的分为两个阶段。海西期,古特提斯洋的发展使哀牢山洋盆开裂,导致了右江地区在拉张应力条件下出现若干NW向裂陷带,这时的盆地具有大陆边缘裂谷特点。东吴运动后开始的印支期,区域应力条件发生变化。滨大平洋构造的发生,使盆地轮廓和结构发生明显变化,与此同时开始的哀牢山洋盆向NE方向的俯冲消减作用,使盆地在新的挤压条件下再次发生张裂和拗陷。进入了弧后盆地发展阶段。印支期末,盆地封闭。 相似文献
103.
104.
Gert Finger Reinhold J. Dorn Alan W. Hoffman Hamid Mehrgan Manfred Meyer Alan F. M. Moorwood Joerg Stegmeier 《Experimental Astronomy》2002,14(2):117-127
Three different methods are presented to subtract thermal drifts and low-frequency noise from the signal of infrared array.
The first is dead pixels with open Indium bumps, the second is reference output as implemented on the Hawaii2 multiplexer,
and the third is dark pixels to emulate reference cells having a capacity connected to the gate of the unit cell field-effect
transistor (FET). The third method is the most effective and yields a reduction in readout noise from15.4–9.4 erms. A novel
method will be described to extend this readout technique to the Aladdin 1 K × 1 K InSb array.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
105.
106.
107.
L. I. Matveenko 《Astronomy Letters》2001,27(11):686-690
The core (injector) and the jet (relativistic plasma outflow) of AGN objects are surrounded by an ionized medium, an H II region observed in emission lines. The synchrotron radiation from the core and the jet is observed through a thin screen that cocoons the structure under consideration. The screen transparency depends on wavelength and distance from the injector. We consider the objects 3C 345 and 1803+784 whose core emission at decimeter wavelengths is absorption by more than 25 dB. The visible bright compact component is the bright nearby portion of the jet that extends outside the dense part of the screen. We explore the possibility of measuring the screen transparency from absorption in Hα recombination lines with different quantum numbers at centimeter wavelengths. 相似文献
108.
109.
110.
Jeremy Allington-Smith Graham Murray Robert Content George Dodsworth Bryan W. Miller James Turner Inger Jorgensen Isobel Hook 《Experimental Astronomy》2002,13(1):1-37
We describe the integral field unit (IFU) which converts the Gemini Multiobject Spectrograph (GMOS) installed on the Gemini-North telescope to an integral field spectrograph,which produces spectra over a contiguous field of view of 7 × 5 arcsec with spatial sampling of 0.2 arcsecover the wavelength range 0.4-1.0 μm.GMOS is converted to this mode by the remote insertion of the IFU into thebeam in place of the masks used for the multiobject mode. A separate fieldof half the area of the main field, but otherwise identical, is alsoprovided to improve background subtraction. The IFU contains 1500lenslet-coupled fibres and was the first facility of any type for integralfield spectroscopy employed on an 8/10 m telescope.We describe the design, construction and testing of the GMOS IFU and present measurements of the throughput both in the laboratory and at the telescope. We compare these with a theoretical prediction made before construction started. All are in good agreement with each other, with the on-telescope throughput exceeding 60% (averaged over wavelength). Finallywe show an example of data obtained during commissioning to illustrate the power of the device. 相似文献