全文获取类型
收费全文 | 21470篇 |
免费 | 1399篇 |
国内免费 | 2177篇 |
专业分类
测绘学 | 808篇 |
大气科学 | 3075篇 |
地球物理 | 4679篇 |
地质学 | 9041篇 |
海洋学 | 2009篇 |
天文学 | 3242篇 |
综合类 | 756篇 |
自然地理 | 1436篇 |
出版年
2023年 | 138篇 |
2022年 | 354篇 |
2021年 | 397篇 |
2020年 | 342篇 |
2019年 | 442篇 |
2018年 | 1055篇 |
2017年 | 974篇 |
2016年 | 957篇 |
2015年 | 642篇 |
2014年 | 875篇 |
2013年 | 1047篇 |
2012年 | 865篇 |
2011年 | 1027篇 |
2010年 | 798篇 |
2009年 | 1032篇 |
2008年 | 844篇 |
2007年 | 777篇 |
2006年 | 798篇 |
2005年 | 1189篇 |
2004年 | 1295篇 |
2003年 | 1033篇 |
2002年 | 540篇 |
2001年 | 503篇 |
2000年 | 547篇 |
1999年 | 652篇 |
1998年 | 550篇 |
1997年 | 555篇 |
1996年 | 537篇 |
1995年 | 443篇 |
1994年 | 367篇 |
1993年 | 345篇 |
1992年 | 268篇 |
1991年 | 257篇 |
1990年 | 212篇 |
1989年 | 232篇 |
1988年 | 192篇 |
1987年 | 193篇 |
1986年 | 169篇 |
1985年 | 142篇 |
1984年 | 152篇 |
1983年 | 127篇 |
1982年 | 134篇 |
1981年 | 125篇 |
1980年 | 99篇 |
1979年 | 96篇 |
1978年 | 53篇 |
1977年 | 71篇 |
1976年 | 74篇 |
1975年 | 62篇 |
1973年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Z. Balog † A. J. Delgado ‡ A. Moitinho G. Frész † G. Kaszás † J. Vinkó E. J. Alfaro 《Monthly notices of the Royal Astronomical Society》2001,323(4):872-886
CCD photometry in Johnson UBV and Strömgren uvby systems and medium-resolution spectroscopy of the galactic open cluster NGC 7128 are presented. Spectral types of the brightest 12 stars in the cluster field were determined based on equivalent widths of the H α and the He i 6678-Å line. The spectroscopic observations also revealed two obvious and one probable Be-type stars showing H α emission. The analysis of the photometric diagrams gave a colour excess of E ( B − V )=1.03±0.06 mag, a distance modulus DM =13.0±0.2 mag and an age above 10 Myr. Time-resolved photometric observations obtained on one night resulted in the detection of short time-scale light variations of seven new and three already known variable stars in the cluster field. 相似文献
42.
With a new theory on the 1PN celestial mechanics recently developed by Damour, Soffel and Xu (1991,1992,1993,1994), definitions
and expressions of the 1PN spin angular momentum are investigated and analysed. The total spin angular momentum of a system
of extended bodies such as the solar system is calculated and expressed as the function of local parameters and observables
under reasonable assumptions, which would find its application in the evolution and dynamics of systems of celestial bodies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
44.
45.
Pittichovâ J. Sekenina Z. Birkle K. Boehnhardt J. Engels D. Keller P. 《Earth, Moon, and Planets》1997,78(1-3):329-338
The Sekanina-Farrell particle fragmentation model for the striated tails of dust comets is successfully applied to two images
of comet Hale-Bopp to study the motions of 12 striae in a time span of March 12–15, 1997. There is evidence for recurring
outbursts with a periodicity of 11h21m, consistent with results based on analysis of dust jets. The ejecta in all the striae appear to have been released from one
source on the nucleus between the end of January and the second half of February 1997, some 60 to 40 days before perihelion.
The parent particles were subjected to a radiation pressure acceleration of βp ≃ 0.55 and their fragmentation lifetimes in 11 of the 12 striae were practically constant and equal to 13–15 days, when normalized
to 1 AU from the Sun. Brief analysis of Watanabe et al.'s measurements of striae on their images from March 5–9, 1997 shows
even shorter fragmentation lifetimes for the parent particles, mostly about 7–11 days at1 AU.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
46.
We have studied the optical historical light curves of two Active Galactic Nuclei (AGNs): OJ287 and 3C345. We find a linear
dependence between the magnitude and the logarithm of the length of the time the objects stay below this magnitude. The relation
may originate from a fractal structure of the light curve.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
使用中国科学院紫金山天文台青海站13.7米射电望远镜于1996年12月至1997年1月对富碳拱星IRC 10216和CIT6的CO J=1-0跃迁(115GHz)进行了观测。在观测谱线的基础上得到了IRC 10216的视向速度和膨胀速度分别为一26.1km s~(-1)和14.8km s~(-1),CIT6的视向速度和膨胀速度分别为0.6km s~(-1)和13.8kms~(-1)。并对望远镜的射束及指向精度进行了研究。 相似文献
48.
Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations. 相似文献
49.
In this paper, two factors — the redistribution of the density and the variation in the angular velocity of the Earth rotation, that affect the adopted value of the flattening for equidensity surface within the Earth, are discussed. The computational results show that the contribution of the redistribution of the density in the Earth interior (especially in the core) on the change of the flattening at the core-mantle boundary (CMB) is marginal, and that the calculated value of the flattening at the CMB can be in good agreement with the VLBI observed value so long as the fact that the angular velocity of the Earth rotation has undergone the tidal evolution is taken into account. As a result, this paper presents a set of recommended values of the dynamical parameters of the Earth (see Table III) for computing Earth's forced nutation series. 相似文献
50.
Yi-Zhong Fan Zi-Gao Dai Yong-Feng Huang Tan Lu Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2002,2(5):449-453
The optical flash accompanying GRB 990123 is believed to be powered by the reverse shock of a thin shell. With the best-fit physical parameters for GRB 990123 and the assumption that the parameters in the optical flash are the same as in the afterglow, we show that: 1) the shell is thick rather than thin, and we have provided the light curve for the thick shell case which coincides with the observation; 2) the theoretical peak flux of the optical flash accounts for only 3×10~-4 of the observed. In order to remove this discrepancy, the physical parameters, the electron energy and magnetic ratios, εe and εB, should be 0.61 and 0.39, which are very different from their values for the late afterglow. 相似文献