全文获取类型
| 收费全文 | 14081篇 |
| 免费 | 2767篇 |
| 国内免费 | 2922篇 |
专业分类
| 测绘学 | 603篇 |
| 大气科学 | 962篇 |
| 地球物理 | 4015篇 |
| 地质学 | 7238篇 |
| 海洋学 | 2007篇 |
| 天文学 | 2009篇 |
| 综合类 | 710篇 |
| 自然地理 | 2226篇 |
出版年
| 2024年 | 39篇 |
| 2023年 | 172篇 |
| 2022年 | 417篇 |
| 2021年 | 462篇 |
| 2020年 | 517篇 |
| 2019年 | 596篇 |
| 2018年 | 523篇 |
| 2017年 | 526篇 |
| 2016年 | 548篇 |
| 2015年 | 610篇 |
| 2014年 | 720篇 |
| 2013年 | 699篇 |
| 2012年 | 771篇 |
| 2011年 | 852篇 |
| 2010年 | 692篇 |
| 2009年 | 1000篇 |
| 2008年 | 923篇 |
| 2007年 | 1005篇 |
| 2006年 | 997篇 |
| 2005年 | 850篇 |
| 2004年 | 850篇 |
| 2003年 | 847篇 |
| 2002年 | 667篇 |
| 2001年 | 627篇 |
| 2000年 | 592篇 |
| 1999年 | 517篇 |
| 1998年 | 570篇 |
| 1997年 | 334篇 |
| 1996年 | 316篇 |
| 1995年 | 299篇 |
| 1994年 | 272篇 |
| 1993年 | 225篇 |
| 1992年 | 198篇 |
| 1991年 | 118篇 |
| 1990年 | 79篇 |
| 1989年 | 87篇 |
| 1988年 | 55篇 |
| 1987年 | 64篇 |
| 1986年 | 42篇 |
| 1985年 | 21篇 |
| 1984年 | 7篇 |
| 1983年 | 4篇 |
| 1982年 | 4篇 |
| 1981年 | 5篇 |
| 1980年 | 6篇 |
| 1979年 | 10篇 |
| 1978年 | 4篇 |
| 1977年 | 5篇 |
| 1976年 | 5篇 |
| 1954年 | 14篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
31.
32.
银晕中天琴RR变星金属丰度的测定对于研究银河系晕的形成和演化具有重要的意义．在当前的技术条件下,高分辨光谱的方法难以测量银晕中较暗的天琴RR变星的金属丰度．高分辨光谱测定金属丰度的方法对恒星大气模型的依赖性较高,而恒星脉动引起的复杂大气状况对于建立正确的大气模型本身就是挑战．△S光谱方法、Caby测光方法和光变曲线的参数方法则弥补了高分辨光谱方法的不足,将能测量更远距离上的天琴RR变星的金属丰度．着重介绍了这3种方法发展的历史、具体的观测流程以及需要注意的问题。通过比较这3种方法的优劣,为实际观测时方法的选用提供借鉴。 相似文献
33.
刘升 《广东海洋大学学报》2006,26(2):44-46
个人所得税是与每个人联系都很紧密的税种,它的完善与否,直接体现了我国法制建设的完善程度及居民素质的高低。但现行税制由于内外原因,存在各种缺陷。因此有必要在理论中找到对策,并在实践中寻求答案逐步完善个人所得税制度。 相似文献
34.
35.
36.
Andreas Just 《Astrophysics and Space Science》2003,284(2):727-730
There is a long term dynamical heating of stellar populations with age observed in the age – velocity dispersion – relation
(AVR). This effect allows a determination of the star formation history SFR(t) from local kinematical data of main sequence stars. Using a self-consistent disk model for the vertical structure of the
disk, we find from the kinematics of the stars in the solar neighbourhood that the SFR shows a moderate star burst about 10 Gyr ago followed by a continuous decline to the present day value consistent with the
observed number of OB stars. The gravitational potential of the gas component and of the Dark Matter Halo is included and
the effect of chemical enrichment, finite lifetime of the stars and mass loss of the stellar component are taken into account.
The scale heights for main sequence stars together with the SFR is then used to determine constistently the IMF from the observed local luminosity function. The main new result is that the power law break in the present day mass function
(PDMF) around 1 M
⊙ is entirely due to evolutionary effects of the disk and does not appear in the IMF.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
37.
38.
39.
40.
The frequent use of soils and earth materials for hydraulic capping and for geo‐environmental waste containment motivated our interest in detailed modelling of changes in size and shape of macro‐pores to establish links between soil mechanical behaviour and concurrent changes in hydraulic and transport properties. The objective of this study was to use finite element analysis (FEA) to test and extend previous analytical solutions proposed by the authors describing deformation of a single macro‐pore embedded in linear viscoplastic soil material subjected to anisotropic remote stress. The FEA enables to consider more complex pore geometries and provides a detailed picture of matrix yield behaviour to explain shortcomings of approximate analytical solutions. Finite element and analytical calculations agreed very well for linear viscous as well as for viscoplastic materials, only limited for the case of isotropic remote stress due to the simplifications of the analytical model related to patterns and onset of matrix‐yielding behaviour. FEA calculations were compared with experimental data obtained from a compaction experiment in which pore deformation within a uniform modelling clay sample was monitored using CAT scanning. FEA predictions based on independently measured material properties and initial pore geometry provided an excellent match with experimentally determined evolution of pore size and shape hence lending credence to the potential use of FEA for more complex pore geometries and eventually connect macro‐pore deformation with hydraulic properties. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献