全文获取类型
收费全文 | 55234篇 |
免费 | 684篇 |
国内免费 | 1281篇 |
专业分类
测绘学 | 2521篇 |
大气科学 | 4351篇 |
地球物理 | 10638篇 |
地质学 | 22123篇 |
海洋学 | 3482篇 |
天文学 | 9180篇 |
综合类 | 2285篇 |
自然地理 | 2619篇 |
出版年
2021年 | 283篇 |
2020年 | 285篇 |
2019年 | 330篇 |
2018年 | 5355篇 |
2017年 | 4599篇 |
2016年 | 3515篇 |
2015年 | 816篇 |
2014年 | 1044篇 |
2013年 | 1710篇 |
2012年 | 1960篇 |
2011年 | 3816篇 |
2010年 | 2975篇 |
2009年 | 3567篇 |
2008年 | 2996篇 |
2007年 | 3409篇 |
2006年 | 1234篇 |
2005年 | 1173篇 |
2004年 | 1254篇 |
2003年 | 1256篇 |
2002年 | 1094篇 |
2001年 | 818篇 |
2000年 | 794篇 |
1999年 | 687篇 |
1998年 | 644篇 |
1997年 | 630篇 |
1996年 | 570篇 |
1995年 | 536篇 |
1994年 | 511篇 |
1993年 | 435篇 |
1992年 | 390篇 |
1991年 | 419篇 |
1990年 | 414篇 |
1989年 | 391篇 |
1988年 | 365篇 |
1987年 | 440篇 |
1986年 | 368篇 |
1985年 | 447篇 |
1984年 | 484篇 |
1983年 | 473篇 |
1982年 | 457篇 |
1981年 | 380篇 |
1980年 | 378篇 |
1979年 | 315篇 |
1978年 | 308篇 |
1977年 | 297篇 |
1976年 | 266篇 |
1975年 | 256篇 |
1974年 | 287篇 |
1973年 | 310篇 |
1972年 | 196篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
124.
M. J. Carson J. C. Davies E. Daw R. J. Hollingworth V. A. Kudryavtsev T. B. Lawson P. K. Lightfoot J. E. McMillan B. Morgan S. M. Paling M. Robinson N. J. C. Spooner D. R. Tovey 《Astroparticle Physics》2004,21(6):667-687
Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10−9–10−10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector. 相似文献
125.
126.
127.
Wimbush M. Chiswell S.M. Lukas R. Donohue K.A. 《Oceanic Engineering, IEEE Journal of》1990,15(4):380-383
A four-year record from an inverted echo sounder deployed near Palmyra Island at 6°N in the central Pacific Ocean is compared with a simultaneous record of subsurface pressure from this island lagoon. A factor m , converting round-trip acoustic travel time to surface dynamic height relative to a deep pressure level, was estimated from the ratio of the spectra of the two records in the energetic synoptic oscillation band. Year-to-year variation in m was not statistically significant. For the overall record, m was found to be -70±8 dynamic m/s, where the error bounds represent a 90% confidence interval. This is consistent with first-baroclinic-mode excitation 相似文献
128.
129.
130.
C. Tadhunter K. Wills R. Morganti T. Oosterloo R. Dickson 《Monthly notices of the Royal Astronomical Society》2001,327(1):227-232
We present new spectroscopic observations of the southern radio galaxy . Despite the flat-spectrum character of the radio emission from this source, our optical spectra show no sign of the broad permitted lines and non-stellar continuum characteristic of quasar nuclei and broad-line radio galaxies. However, the high-ionization forbidden lines, including [O iii ] λλ 5007, 4959, are unusually broad for a narrow-line radio galaxy , and are blueshifted by 600 km s−1 relative to the low-ionization lines such as [O ii ] λλ 3726,3729. The [O ii ] lines are also considerably narrower than the [O iii ] lines, and have a redshift consistent with that of the recently detected H i 21-cm absorption-line system. Whereas the kinematics of the [O iii ] emission lines are consistent with outflow in an inner narrow-line region, the properties of the [O ii ] emission lines suggest that they are emitted by a more extended and quiescent gaseous component. We argue that, given the radio properties of the source, our line of sight is likely to be lying close to the direction of bulk outflow of the radio jets. In this case it is probable that the quasar nucleus is entirely obscured at optical wavelengths by the material responsible for the H i absorption-line system. The unusually broad [O iii ] emission lines suggest that the radio source is intrinsically compact. Overall, our data are consistent the idea that is a radio source in an early stage of evolution. 相似文献