全文获取类型
收费全文 | 12483篇 |
免费 | 2808篇 |
国内免费 | 1813篇 |
专业分类
测绘学 | 1269篇 |
大气科学 | 232篇 |
地球物理 | 4269篇 |
地质学 | 6832篇 |
海洋学 | 1394篇 |
天文学 | 1614篇 |
综合类 | 919篇 |
自然地理 | 575篇 |
出版年
2024年 | 20篇 |
2023年 | 138篇 |
2022年 | 415篇 |
2021年 | 578篇 |
2020年 | 490篇 |
2019年 | 540篇 |
2018年 | 413篇 |
2017年 | 487篇 |
2016年 | 507篇 |
2015年 | 528篇 |
2014年 | 731篇 |
2013年 | 683篇 |
2012年 | 728篇 |
2011年 | 665篇 |
2010年 | 564篇 |
2009年 | 813篇 |
2008年 | 822篇 |
2007年 | 841篇 |
2006年 | 857篇 |
2005年 | 696篇 |
2004年 | 766篇 |
2003年 | 661篇 |
2002年 | 561篇 |
2001年 | 512篇 |
2000年 | 508篇 |
1999年 | 425篇 |
1998年 | 408篇 |
1997年 | 288篇 |
1996年 | 283篇 |
1995年 | 241篇 |
1994年 | 216篇 |
1993年 | 181篇 |
1992年 | 151篇 |
1991年 | 78篇 |
1990年 | 64篇 |
1989年 | 70篇 |
1988年 | 49篇 |
1987年 | 42篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 24篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1954年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
本文介绍了瞬变电磁法在煤矿水文地质勘探中的具体应用效果.采用瞬变电磁法对落差较大断层的含(导)水性进行测量,不仅可有效地控制断层的空间位置,而且可定性地判断断层的富水性,其测量结果与已知水文地质资料吻合较好. 相似文献
42.
43.
介绍了自动高精度测距系统。该系统能以5×10-7的测距精度测定多个观测点的形变,可作为跨断层动态连续观测的新仪器。 相似文献
44.
Boli basin, between Yishu fracture belt and Dunmi fracture belt, is the biggest Mesozoic coal basin in the east of Heilongjiang Province. Now it is a fault - fold remnant basin. The basin' s shape is generally consistent with the whole distribution of the cover folds, an arc protruding southwards. The basement of the basin can be divided into three fault blocks or structural units. The formation and evoluation of the basin in Mesozoic was determined by the basement fault blocks' displacement features rusulted from by the movement of the edge faults and the main basement faults. 相似文献
45.
M. V. Sazhin V. E. Zharov T. A. Kalinina 《Monthly notices of the Royal Astronomical Society》2001,323(4):952-964
Parallax measurements allow distances to celestial objects to be determined. Together with measurements of their position on the celestial sphere, they give a full three-dimensional picture of the location of the objects relative to the observer. The distortion of the parallax value of a distant source affected by weak microlensing is considered. This means that the weak microlensing leads to distortion of the distance scale. The gravitational deflection causes a retrograde apparent motion of the image, which is revealed as a negative parallax. It is shown that the distortions may significantly change the parallax values when they amount to several microseconds of arc. In particular, at this level many measured values of parallaxes should be negative. 相似文献
46.
R.G. Sharp R.G. McMahon M.J. Irwin S.T. Hodgkin 《Monthly notices of the Royal Astronomical Society》2001,326(4):L45-L49
We report the first results of an observational programme designed to determine the luminosity density of high-redshift quasars quasars) using deep multicolour CCD data. We report the discovery and spectra of three high-redshift quasars, including one with . At , this is the fourth highest redshift quasar currently published. Using these preliminary results we derive an estimate of the quasar space density in the redshift range of . When completed, the survey will provide a firm constraint on the contribution to the ionizing UV background in the redshift range from quasars by determining the faint-end slope of the quasar luminosity function. The survey uses imaging data taken with the 2.5-m Isaac Newton Telescope as part of the Public Isaac Newton Group Wide Field Survey (WFS). This initial sample of objects is taken from two fields of effective area ∼12.5 deg2 from the final ∼100 deg2 . 相似文献
47.
48.
49.
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
50.
Itziar Aretxaga Elena Terlevich † Roberto J. Terlevich ‡ Garret Cotter Ángeles I. Díaz 《Monthly notices of the Royal Astronomical Society》2001,325(2):636-648
We present optical spectra of the nuclei of seven luminous ( P 178 MHz ≳1025 W Hz−1 Sr−1 ) nearby ( z <0.08) radio galaxies, which mostly correspond to the FR II class. In two cases, Hydra A and 3C 285, the Balmer and λ 4000-Å break indices constrain the spectral types and luminosity classes of the stars involved, revealing that the blue spectra are dominated by blue supergiant and/or giant stars. The ages derived for the last burst of star formation in Hydra A are between 7 and 40 Myr, and in 3C 285 about 10 Myr. The rest of the narrow-line radio galaxies (four) have a λ 4000-Å break and metallic indices consistent with those of elliptical galaxies. The only broad-line radio galaxy in our sample, 3C 382, has a strong featureless blue continuum and broad emission lines that dilute the underlying blue stellar spectra. We are able to detect the Ca ii triplet in absorption in the seven objects, with good quality data for only four of them. The strengths of the absorptions are similar to those found in normal elliptical galaxies, but these values are consistent both with stellar populations of roughly similar ages (as derived from the Balmer absorption and break strengths) and with mixed young+old populations. 相似文献