全文获取类型
| 收费全文 | 27498篇 |
| 免费 | 4819篇 |
| 国内免费 | 5085篇 |
专业分类
| 测绘学 | 2234篇 |
| 大气科学 | 3413篇 |
| 地球物理 | 5596篇 |
| 地质学 | 11791篇 |
| 海洋学 | 3632篇 |
| 天文学 | 6610篇 |
| 综合类 | 1427篇 |
| 自然地理 | 2699篇 |
出版年
| 2024年 | 85篇 |
| 2023年 | 278篇 |
| 2022年 | 686篇 |
| 2021年 | 857篇 |
| 2020年 | 956篇 |
| 2019年 | 1043篇 |
| 2018年 | 933篇 |
| 2017年 | 1015篇 |
| 2016年 | 1023篇 |
| 2015年 | 1102篇 |
| 2014年 | 1657篇 |
| 2013年 | 1718篇 |
| 2012年 | 1786篇 |
| 2011年 | 1812篇 |
| 2010年 | 1728篇 |
| 2009年 | 2147篇 |
| 2008年 | 2012篇 |
| 2007年 | 2203篇 |
| 2006年 | 2037篇 |
| 2005年 | 1754篇 |
| 2004年 | 1510篇 |
| 2003年 | 1348篇 |
| 2002年 | 1103篇 |
| 2001年 | 998篇 |
| 2000年 | 936篇 |
| 1999年 | 853篇 |
| 1998年 | 752篇 |
| 1997年 | 493篇 |
| 1996年 | 490篇 |
| 1995年 | 351篇 |
| 1994年 | 348篇 |
| 1993年 | 317篇 |
| 1992年 | 238篇 |
| 1991年 | 145篇 |
| 1990年 | 152篇 |
| 1989年 | 104篇 |
| 1988年 | 102篇 |
| 1987年 | 63篇 |
| 1986年 | 58篇 |
| 1985年 | 40篇 |
| 1984年 | 35篇 |
| 1983年 | 24篇 |
| 1982年 | 22篇 |
| 1981年 | 12篇 |
| 1980年 | 24篇 |
| 1979年 | 6篇 |
| 1978年 | 13篇 |
| 1977年 | 16篇 |
| 1972年 | 2篇 |
| 1954年 | 8篇 |
排序方式： 共有10000条查询结果，搜索用时 109 毫秒
71.
72.
通过将车流量的增大或减小转化为路长权重的变化。将交通流量的动态问题转化为静态问题，用解决最短路问题的Dijkstra方法，给出交通流量实时最优控制的可行性模型及其有效算法。 相似文献
73.
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
74.
75.
76.
77.
78.
1 IntroductionAnicecoreobtainedfrom polarglaciersoricesheetsisoneofthemostimportantarchivestoreconstructpaleoclimaticandpaleoatmosphericcondition .Informationonpale o environmentcanbeextractedfromicecoresaschemicaland/orphysicalsignals.Amongthechemicalsignals,heavymetalsarenotedassignalsofterrestrialenvironmentalchangeandanthropogenicpollution (e.g .Murozumietal.1 969;NgandPatterson 1 981 ;Hongetal.1 994) .SinceconcentrationsofmostofthemetalsinpolarsnowincentralGreen landareatorbelowthepptl… 相似文献
79.
A. S. Oliveira J. E. Steiner D. Cieslinski 《Monthly notices of the Royal Astronomical Society》2003,346(3):963-967
The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no O vi emission has been reported. The Temporal Variance Spectrum – TVS – analysis of our data shows weak but strongly variable emission of O vi lines which is below the noise level in the intensity spectrum.
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is Pphot = 0.227(±14) d , while radial velocities suggest a period of P spec = 0.204(±13) d . One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P
In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the N v 4604 Å absorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR – quasi Wolf–Rayet – star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system. 相似文献
80.