全文获取类型
收费全文 | 1278篇 |
免费 | 55篇 |
国内免费 | 90篇 |
专业分类
化学 | 711篇 |
晶体学 | 5篇 |
力学 | 31篇 |
综合类 | 2篇 |
数学 | 66篇 |
物理学 | 608篇 |
出版年
2023年 | 71篇 |
2022年 | 34篇 |
2021年 | 38篇 |
2020年 | 35篇 |
2019年 | 34篇 |
2018年 | 31篇 |
2017年 | 49篇 |
2016年 | 60篇 |
2015年 | 43篇 |
2014年 | 67篇 |
2013年 | 97篇 |
2012年 | 94篇 |
2011年 | 89篇 |
2010年 | 61篇 |
2009年 | 82篇 |
2008年 | 76篇 |
2007年 | 69篇 |
2006年 | 56篇 |
2005年 | 39篇 |
2004年 | 56篇 |
2003年 | 31篇 |
2002年 | 19篇 |
2001年 | 21篇 |
2000年 | 9篇 |
1999年 | 16篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 10篇 |
1977年 | 1篇 |
1974年 | 3篇 |
排序方式: 共有1423条查询结果,搜索用时 17 毫秒
71.
72.
《中国化学快报》2020,31(6):1640-1643
The physicochemical properties of surfaces have a great effect on the micro-morphologies of the crystal structures which are in contact with them.Understanding the interaction mechanism between the internal driving forces of the crystal and external inducing forces of the surfaces is the prerequisite of controlling and obtaining the desirable morphologies.In this work,the dynamic density functional theory was applied to construct the free energy functional expression of polyethylene(PE) lattice,and the micro-dynamic evolution processes of PE lattice morphology near the surfaces with different properties were observed to reveal the interaction mechanism at atomic scale.The results showed that the physical and chemical properties of the external surfaces synergistically affect the morphologies in both the defect shapes and the distribution of the defect regions.In the absence of the contact surfaces,driven by the oriented interactions among different CH2 groups,PE lattices gradually grow and form a defect-free structure.Conversely,the presence of contact surfaces leads to lattice defects in the interfacial regions,and PE lattice shows different self-healing abilities around different surfaces. 相似文献
73.
74.
Min Cheng 《辐射效应与固体损伤》2013,168(11-12):1083-1089
ABSTRACTThe EPR g factors g// and g⊥ for the tetragonal (CrO4)3? impurity center in ZrSiO4: Cr5+ crystal are studied from the high-order perturbation formulas based on the two-mechanism (the crystal field and charge-transfer mechanisms) model. The studies indicate that differing from the tetragonally-elongated host (SiO4)4- tetrahedron, the dominant defect structure of the substitutional (CrO4)3? tetrahedron is tetragonally- compressed with the ground state |dz2 due to the Jahn-Teller distortion. Furthermore, the agreement of g factors between calculation and experiment requires a small admixture of the first excited state |dx2?y2 to the ground state |dz2 due to the vibrational motion of ligands, which leads a compressed (CrO4)3? tetrahedron to become a twinkling elongated one, These results are discussed. 相似文献
75.
This article illustrates the developments of effective preconcentration techniques and highly sensitive detection methods for accurate measurements of Tl species at extremely low concentration in aqueous solutions. The literature on this topic was taken from the Analytical Abstracts in the period 1990-2005. 相似文献
76.
A detailed investigation of the defect structure of the Co doped BIMEVOX solid electrolyte, Bi2V1 − xCoxO5.5 − 3x/2 (x = 0.1 and x = 0.2), quenched from high temperature, has been carried out using X-ray and neutron powder diffraction data measured at room temperature. The structure is built up from alternating layers of [Bi2O2]n2n+ and [V1 − xCoxO3.5 − 3x/2]n2n− with disorder limited to the vanadate layer. The ideal V/Co co-ordination is octahedral with corner sharing of equatorial oxygens. The refinements show that the true structure is distorted, with disorder in both apical and equatorial oxygens and oxygen vacancies concentrated in the equatorial positions. Detailed analysis of the oxygen site occupancies reveals two main types of V/Co co-ordination viz. distorted octahedral and distorted tetrahedral. The majority of the sites in both compositions are tetrahedral. 相似文献
77.
An algorithm is presented for the design of optimal detection filters in radar and communications systems, subject to inequality constraints on the maximum output sidelobe levels. This problem was reduced in an earlier paper (Ref. 1) to an unconstrained one in the dual space of regular Borel measures, with a nondifferentiable cost functional. Here, the dual problem is solved via steepest descent, using the directional Gateaux differential. The algorithm is shown to be convergent, and numerical results are presented.This research was supported by the Australian Research Grants Committee. 相似文献
78.
79.
Bucur V 《Ultrasonics》2005,43(4):237-239
The aim of this study is to assess wood quality of standing trees with ultrasonic velocity methods. The ultrasonic techniques currently used are: scattering based techniques that use travel time and other wave parameters for measuring the elastic constants of wood, and ultrasonic tomographic imaging techniques which seek to provide a high resolution picture of the defect. Scattering based techniques were firstly used as nondestructive techniques with increment cores of 5 mm diameter. On these specimens measurements with bulk waves--longitudinal and shear were used to detect the influence of sylvicultural treatment (pruning) on wood quality and also to detect defects (slope of grain, wavy figures). High resolution imaging techniques were developed for imaging abnormalities induced by biological attacks of fungi or insects in standing trees. In this case, ultrasonic tomography refers to cross-sectional imaging of trees from data collected by illuminating the tree from different directions. Ultrasonic images were reconstructed from the time of flight. The images were reconstructed from 120 measurements in situ and through the bark with direct transmission technique, using 1 MHz transducers. The resolution is 5 cm. 相似文献
80.
Fabio Fazio 《Tetrahedron letters》2004,45(12):2689-2692
The work presented herein is a new noncovalent glycoarray assembly method for microplates created by simply mixing together an isocyanate-containing C14-hydrocarbon and an amine-containing carbohydrate. 2-Aminoethyl-β-d-galactopyranoside (1) was utilized in model studies and product formation was detected by both ESI-MS and lectin binding. The method has been further extended to array complex carbohydrates. 相似文献