全文获取类型
收费全文 | 17179篇 |
免费 | 2954篇 |
国内免费 | 3059篇 |
专业分类
测绘学 | 1396篇 |
大气科学 | 1207篇 |
地球物理 | 4589篇 |
地质学 | 7473篇 |
海洋学 | 2123篇 |
天文学 | 2237篇 |
综合类 | 947篇 |
自然地理 | 3220篇 |
出版年
2024年 | 102篇 |
2023年 | 308篇 |
2022年 | 636篇 |
2021年 | 659篇 |
2020年 | 678篇 |
2019年 | 796篇 |
2018年 | 611篇 |
2017年 | 693篇 |
2016年 | 730篇 |
2015年 | 739篇 |
2014年 | 838篇 |
2013年 | 836篇 |
2012年 | 916篇 |
2011年 | 949篇 |
2010年 | 783篇 |
2009年 | 1111篇 |
2008年 | 1026篇 |
2007年 | 1107篇 |
2006年 | 1066篇 |
2005年 | 932篇 |
2004年 | 959篇 |
2003年 | 942篇 |
2002年 | 764篇 |
2001年 | 695篇 |
2000年 | 664篇 |
1999年 | 567篇 |
1998年 | 618篇 |
1997年 | 381篇 |
1996年 | 351篇 |
1995年 | 327篇 |
1994年 | 296篇 |
1993年 | 263篇 |
1992年 | 216篇 |
1991年 | 138篇 |
1990年 | 95篇 |
1989年 | 109篇 |
1988年 | 74篇 |
1987年 | 73篇 |
1986年 | 45篇 |
1985年 | 21篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1954年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
P. Jean M. Hernanz J. Gómez-Gomar J. José 《Monthly notices of the Royal Astronomical Society》2000,319(2):350-364
Models of Galactic 1.275‐MeV emission produced by the decay of the radionuclide 22 Na have been computed. Several frequency–spatial distributions of novae have been investigated using recent results of nova rates and spatial distributions of novae in our Galaxy. These models allow us to estimate the lower limit of the 22 Na mass ejected per ONe nova detectable with the future spectrometer (SPI) of the INTEGRAL observatory as a function of the frequency–spatial distribution of ONe novae in the Galaxy. Calculations using recent estimations of the expected 22 Na mass ejected per ONe nova show that the detection of the Galactic emission of 1.275‐MeV photons will be difficult with the future spectrometer of the INTEGRAL observatory, whereas the cumulative emission around the Galactic Centre has some chance of being detected during the deep survey of the central radian of the Galaxy. 相似文献
963.
Lesley I. Onuora Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2000,319(2):614-618
The alignment of clusters of galaxies with their nearest neighbours and between clusters within a supercluster is investigated using simulations of 5123 dark matter particles for ΛCDM and τ CDM cosmological models. Strongly significant alignments are found for separations of up to 15 h −1 Mpc in both cosmologies, but for the ΛCDM model the alignments extend up to separations of 30 h −1 Mpc. The effect is strongest for nearest neighbours, but is not significant enough to be useful as an observational discriminant between cosmologies. As a check of whether this difference in alignments is present in other cosmologies, smaller simulations with 2563 particles are investigated for four different cosmological models. Because of poor number statistics, only the standard CDM model shows indications of having different alignments from the other models. 相似文献
964.
In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the absolute proper motions of more than 11000 stars with respect to 3000 galaxies and their stellar magnitudes in the B, V Johnson system are determined in two sky regions near the North Galactic Pole (NGP) by means of Tautenburg Schmidt plates. The limiting and completing apparent stellar magnitudes are B = 20.4 and 18.3 mag, the overall and the investigated sky areas are 16.4 and 14.6 square degrees, respectively. Distances have been determined using the stellar magnitudes, colours, proper motions and reduced proper motions. Stellar kinematics, eccentricities of Galactic orbits, spatial distribution and changes of these characteristics with Z-distance from the Galactic plane are obtained up to 15 kpc. Four subsystems distinguished in the NGP direction, respectively with semithicknesses of 0.25, 0.38, 0.67, 1.48 kpc and density ellipsoid axial ratios of 0.09, 0.20, 0.28, 0.49 show mean velocities in the Galactic rotation direction relative to the LSR of 5.6 ± 0.6, − 11.0 ± 0.6, − 62.5 ± 1.2, − 181.6 ± 4.4 km/s, and ages of 0.1, 0.4, 0.9, 1 of the Galaxy age. 相似文献
965.
本文利用紫金山天文台赣榆站太阳精细结构望远镜拍得的高分辨率色球H_α照片,分析了三个典型活动区。文中利用并检验了七十年代获得的磁图推导法则,应用自己的数值模拟知识和Zwaan对AFS系新浮流区概括的特征,参考七十和九十年代总结的有关耀斑和EllermanBomb的出现规律,逐日分析活动区发展,定出其内部的中性线位置,提出简单和复合中性线的区分,由AFS系和亮谱斑同时出现判断新浮流区,从近离带图找等离子体不稳定点,从远离带图找普遍的磁场流场分布,由H_α结构的综合迹象推测磁场变化。总结出有关活动区H_α结构、磁场及等离子体性质关系的几点启示。 相似文献
966.
967.
968.
969.
970.
Tao Kiang Yong-Feng Wu Xing-Fen Zhu Dunsink Observatory Dublin Institute for Advanced Studies Dublin Ireland Center for Astrophysics University of Science Technology of China Hefei 《中国天文和天体物理学报》2004,4(3):209-220
Rhombic cell analysis as outlined in the first paper of the present seriesis applied to samples of varying depths and liming luminosities of the IRAS/PSCzCatalogue. Numerical indices are introduced to summarize essential information.Because of the discrete nature of the analysis and of the space distribution of galax-ies, the indices for a given sample must be regarded as each having an irreduciblescatter. Despite the scatter, the mean indices show remarkable variations acrossthe samples. The underlying factor for the variations is shown to be the limitingluminosity rather than the sampling depth. As samples of more and more luminousgalaxies are considered over a range of some 2.5 magnitudes (a factor of some 75in space density), the morphology of the filled and empty regions defined by thegalaxies degrades steadily towards insignificance, and the degrading is faster for thefilled than the empty region. 相似文献