全文获取类型
收费全文 | 516篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
化学 | 420篇 |
晶体学 | 2篇 |
力学 | 10篇 |
数学 | 62篇 |
物理学 | 39篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 11篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 27篇 |
2012年 | 20篇 |
2011年 | 46篇 |
2010年 | 22篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 23篇 |
2006年 | 23篇 |
2005年 | 20篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 18篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1978年 | 2篇 |
1974年 | 4篇 |
1970年 | 5篇 |
1968年 | 2篇 |
1914年 | 1篇 |
1913年 | 3篇 |
1911年 | 1篇 |
1909年 | 1篇 |
排序方式: 共有533条查询结果,搜索用时 20 毫秒
31.
Suwa Y Matsuura S Fujimori M Heike S Onogi T Kajiyama H Hitosugi T Kitazawa K Uda T Hashizume T 《Physical review letters》2003,90(15):156101
Novel atomic structures on a H-terminated Si(100)-(2x1)-H surface were found using scanning tunneling microscopy (STM). The structures are distinguishable only from Si dimers in empty-state STM images. They were observed on arsenic- and phosphorus-doped substrates, but not on boron-doped substrates. Surface density of these structures was found to be proportional to the dopant density in the substrate. First-principles calculations clarify that they are consisting of dopant pairs that are segregated from the bulk material. Hydrogen atoms attached to the dopant pair are found to flip between two positions on the surface due to a quantum effect. 相似文献
32.
33.
34.
35.
Michael Lawrence Hadley Wickham Dianne Cook Heike Hofmann Deborah F. Swayne 《Computational Statistics》2009,24(2):195-205
This paper describes progress towards developing a platform for rapid prototyping of interactive data visualizations, using
R, GGobi, rggobi and RGtk2. GGobi is a software tool for multivariate interactive graphics. At the core of GGobi is a data
pipeline that incrementally transforms data through a series of stages into a plot and maps user interaction with the plot
back to the data. The GGobi pipeline is extensible and mutable at runtime. The rggobi package, an interface from the R language
to GGobi, has been augmented with a low-level interface that supports the customization of interactive data visualizations
through the extension and manipulation of the GGobi pipeline. The large size of the GGobi API has motivated the use of the
RGtk2 code generation system to create the low-level interface between R and GGobi. The software is demonstrated through an
application to interactive network visualization. 相似文献
36.
Heike Mildenberger 《Archive for Mathematical Logic》2001,40(2):93-112
We show that the Filter Dichotomy Principle implies that there are exactly four classes of ideals in the set of increasing
functions from the natural numbers. We thus answer two open questions on consequences of ? < ?. We show that ? < ? implies
that ? = ?, and that Filter Dichotomy together with ? < ? implies ? < ?. The technical means is the investigation of groupwise
dense sets, ideals, filters and ultrafilters. With related techniques we prove the new inequality ?≤ cf(?).
Received: 9 October 1998 / Revised version: 18 August 1999 / Published online: 21 December 2000 相似文献
37.
A pH‐sensitive detector for flow‐through potentiometry based on a graphite/quinhydrone/silicone composite electrode was applied to determine calcium and magnesium in aqueous solutions. The determinations are performed by FIA titrations with EDTA as the carrier solution. The method was applied to the analysis of mineral water, drinking water, and river water. The results were compared with those obtained by batch complexometric titration. The proposed new method is suitable for the simple, rapid and automated determination of water hardness in small sample volumes of aqueous solutions. The detection limit for both ions is about 1×10?5 mol L?1, the standard deviation is less than 2%. The sampling frequency is 60 determinations per hour. 相似文献
38.
Sayed M. Saleh Rainer Müller Heike S. Mader Axel Duerkop Otto S. Wolfbeis 《Analytical and bioanalytical chemistry》2010,398(4):1615-1623
Fluorescent silica nanoparticles (SiNPs) were prepared by covalent attachment of fluorophores to the amino-modified surface
of SiNPs with a typical diameter of 15 nm. The SiNPs are intended for use in novel kinds of fluorescence resonance energy
transfer (FRET)-based affinity assays at the interface between nanoparticle and sample solution. Various labels were employed
to obtain a complete set of colored SiNPs, with excitation maxima ranging from 337 to 659 nm and emission maxima ranging from
436 nm to the near infrared (710 nm). The nanoparticles were characterized in terms of size and composition using transmission
electron microscopy, thermogravimetry, elemental analysis, and dynamic light scattering. The surface of the fluorescent SiNPs
was biotinylated, and binding of labeled avidin to the surface was studied via FRET in two model cases. In the first, FRET
occurs from the biotinylated fluorescent SiNP (the donor) to the labeled avidin (the acceptor). In the second, FRET occurs
in the other direction. Aside from its use in the biotin–avidin system, such SiNPs also are believed to be generally useful
fluorescent markers in various kinds of FRET assays, not the least because the fluorophore is located on the surface of the
SiNPs (and thus always much closer to the second fluorophore) rather than being doped deep in its interior. 相似文献
39.
Juliana Ivanova Ivayla N. Pantcheva Mariana Mitewa Svetlana Simova Heike Mayer-Figge William S. Sheldrick 《Central European Journal of Chemistry》2010,8(4):852-860
The single crystal X-ray structures and the spectroscopic properties of complexes of monensic acid (C36H62O11·H2O) with toxic metal ions of Cd(II) and Hg(II) are discussed. The cadmium(II) complex (1) is of composition [Cd(C36H61O11)2(H2O)2] and crystallizes in the monoclinic system (space group P2(1), Z = 2) with a = 12.4090(8), b = 24.7688(16), c = 14.4358(11) Å, β = 91.979(7)°. Two ligand monoanions are bound in a bidentate coordination mode to Cd(II) via the carboxylate and the primary hydroxyl oxygens occupying the equatorial plane of the complex. The axial positions of the inner coordination sphere of Cd(II) are filled by two water molecules additionally engaged in intramolecular hydrogen bonds. The Hg(II) complex (2), [Hg(C36H60O11)(H2O)], crystallizes in the orthorhombic system (space group P2(1)2(1)2(1), Z = 4) with a = 12.7316(2), b = 16.4379(3), c = 18.7184(4) Å. The monensic acid reacts with Hg(II) in a tetradentate coordination manner via both oxygen atoms of the carboxylate function and oxygens of two hydroxyl groups. The twofold negative charge of the ligand is achieved by deprotonation of carboxylic and secondary hydroxyl groups located at the opposite ends of the molecule. Hg(II) is surrounded by five oxygen atoms in a distorted square pyramidal molecular geometry.
相似文献
40.
Bhandary S Ghosh S Herper H Wende H Eriksson O Sanyal B 《Physical review letters》2011,107(25):257202
One of the primary objectives in molecular nanospintronics is to manipulate the spin states of organic molecules with a d-electron center, by suitable external means. In this Letter, we demonstrate by first principles density functional calculations, as well as second order perturbation theory, that a strain induced change of the spin state, from S=1→S=2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in the sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation. The effect is brought about by a change in Fe-N bond length in FeP, which influences the molecular level diagram as well as the interaction between the C atoms of the graphene layer and the molecular orbitals of FeP. 相似文献