全文获取类型
收费全文 | 581篇 |
免费 | 67篇 |
国内免费 | 42篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 64篇 |
地球物理 | 148篇 |
地质学 | 278篇 |
海洋学 | 68篇 |
天文学 | 67篇 |
综合类 | 22篇 |
自然地理 | 24篇 |
出版年
2024年 | 2篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 15篇 |
2018年 | 3篇 |
2017年 | 15篇 |
2016年 | 10篇 |
2015年 | 23篇 |
2014年 | 26篇 |
2013年 | 26篇 |
2012年 | 20篇 |
2011年 | 32篇 |
2010年 | 24篇 |
2009年 | 36篇 |
2008年 | 54篇 |
2007年 | 40篇 |
2006年 | 47篇 |
2005年 | 29篇 |
2004年 | 35篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 23篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有690条查询结果,搜索用时 31 毫秒
31.
利用基于密度泛函理论的第一性原理全势线性缀加平面波方法,研究了立方反ReO3结构Cu3N在零温(0 K)零压下的平衡晶格常数、体弹模量及其对压强的一阶导数,计算结果与其他实验及理论结果基本相符. 同时得出Cu3N的弹性常数,Poisson比等,并分析出Cu3N在零温零压下是稳定的. 通过准谐Debye模型计算Cu3N的热力学性质,得到了Cu3N的晶格常数、等压比热容、等容比热 相似文献
32.
本文以澜沧江下游流域边坡稳定性评价为实例,对模糊评判模型的应用问题和处理技术进行了论述。认为该模型简便实用、效果稳健、适应性强,是边坡稳定性评价工作中适宜推广的一个实用模型。此外,文中还提出了用于模糊评判模型的信息检验法,讨论了这一方法在遴选有效评价因子和优化模型效能中的作用。 相似文献
33.
本文叙述了国产半米平面光栅光程短、光强好、谱线锐度佳的特点,通过最佳条件选择,改进分析方法,使其测金灵敏度为3×10~(-9)g,取样10g可测定含金量范围为0.3—1000ppb,取得了很好的效果。 相似文献
34.
本文研究了磁层顶等离子体的一个基本模型,得到了一新的非线性常微分方程组.数值分析表明,在一定的磁Reynolds数范围内,系统呈现混沌行为,相轨道趋向于奇异吸引子. 相似文献
35.
36.
37.
Oxygen deficient perovskites in the system CaSiO3–CaAlO2.5 and implications for the Earth’s interior
U. W. Bläß F. Langenhorst D. J. Frost F. Seifert 《Physics and Chemistry of Minerals》2007,34(6):363-376
Oxygen deficient perovskites of the system CaSiO3–CaAlO2.5 have been synthesised at high-pressure and -temperature conditions relevant to the Earth’s transition zone in order to investigate
their stabilities in the Earth’s mantle and determine structural properties associated with vacancy incorporation. Two polysomes
of thermodynamically stable defect perovskites with Ca(Al0.4Si0.6)O2.8 and Ca(Al0.5Si0.5)O2.75 stoichiometry have been identified. The ordering of oxygen defects into pseudo-cubic (111) layers results in well-ordered
ten- or eightfold superstructures, respectively. At all other compositions examined, a metastable formation of perovskites
has been observed instead, which are assumed to grow initially disordered. These are now characterised by tiny domains, formed
due to subsequent ordering of vacancies along various pseudo-cubic {111} layers. Both ordered defect perovskites show a large
P–T stability field ranging from about 9–18 GPa and 4–12 GPa, respectively. Microstructural TEM analyses revealed the presence
of growth and ferroelastic twins, which indicate a phase transition from rhombohedral to monoclinic symmetry during quenching.
Electron energy loss spectroscopy of Si and Al K edges point at the presence of tetrahedral, octahedral and maybe some pentacoordinated silicon, whereas aluminium is predominantly
octahedrally coordinated with minor fractions in lower coordination. Observed properties are interpreted in terms of a new
structural model, explaining the observed phase transition and formation of different twin laws as well as giving reasons
for the development of such large superstructures. With respect to phase relations of the transition zone, the potential occurrence
of such defect perovskites in the Earth’s interior is discussed. 相似文献
38.
39.
文中讨论了在局地热平衡情况下简单模式中的热带海气耦合扰动 ,指出参数 KH,KS和α决定着耦合扰动性质 ,并研究了使用抛物线柱函数展开时所截项数多寡对耦合扰动性质的影响以及对称和反对称于赤道的耦合扰动特征 相似文献
40.
Analytical expressions are derived for the Poisson's ratios associated with a three-dimensional network of regular, corner-sharing
tetrahedra in which: (1) the tetrahedra are assumed to be rigid and free to rotate relative to each other; (2) the tetrahedra
are assumed to maintain shape and orientation but are free to change size (dilate); (3) tetrahedral rotation and dilation
are assumed to act concurrently. The structure has a primitive unit cell containing four tetrahedra and is analogous to the
molecular structure of α-cristobalite. Strain-dependent variations in Poisson's ratio are also predicted by the models. For
deformation due to tetrahedral rotation the network is found to exhibit negative Poisson's ratios in each of the three principal
directions, with the magnitude of the Poisson's ratio being dependent on the angle of rotation of the tetrahedra. The behaviour
of the Poisson's ratio is isotropic in the transverse plane, but anisotropic elsewhere. In the dilation model negative Poisson's
ratios equal to −1 are observed for uniaxial loading in any of the principal directions, with the value being constant irrespective
of tetrahedral size. The model for concurrent tetrahedral rotation and dilation allows positive as well as negative Poisson's
ratios, with the values determined by the framework geometry and relative strengths of the two mechanisms. The concurrent
model also offers a design route to materials and structures having ultrahigh Young's moduli.
Received: 15 February 2000 / Accepted: 1 October 2000 相似文献