全文获取类型
收费全文 | 175篇 |
免费 | 7篇 |
专业分类
化学 | 101篇 |
晶体学 | 1篇 |
数学 | 32篇 |
物理学 | 48篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2000年 | 1篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1989年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有182条查询结果,搜索用时 0 毫秒
41.
Adrian Crisan Pavlo Mikheenko Asis Sarkar Van Son Dang Mohammed M. Awang Kechik John S. Abell Petriina Paturi Hannu Huhtinen 《Physica C: Superconductivity and its Applications》2010,470(19):840-843
We have introduced artificial pinning centres in thick (>1 μm) YBCO films grown by Pulsed Laser Deposition using substrate decoration, quasi-multilayers, and target doping approaches. We have found that the frequency dependence of critical current density is consistent with a logarithmic dependence of pinning potential on current density. For most of materials used as nano-dots, artificially-induced pinning centres have a larger potential than natural ones. From angle-dependent in-field transport measurements and from Transmission Electron Microscopy we have found evidence of c-axis correlated pinning centres. 相似文献
42.
Marko Ahlmark Tomi Järvinen Hannu Taipale Riku Niemi Jouko Vepsäläinen 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract Clodronate (1) belongs to family of bisphosphonates which are used to inhibit mineralization of soft tissues as well as bone formation and resorption disorders.[I] The clinical use of bisphosphonates is limited due to their poor bióvailability which is mostly attributed to their hydrophilic structure. More lipophilic molecules are obtained if some or all of the anionic sites are converted to covalent bonds. We herein report a new prodrug serie for clodronate: the anhydrides 2 and 3. Previously we have reported that the simple alkyl esters 4 do not release clodronate via chemical or enzymatic hydrolysis.[2] The prepared new derivatives are stable in water (pH 5–7.5) but clodronate isrelased rapidly with enzymatic hydrolysis. 相似文献
43.
Template‐Free Supracolloidal Self‐Assembly of Atomically Precise Gold Nanoclusters: From 2D Colloidal Crystals to Spherical Capsids
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Nonappa Dr. Tanja Lahtinen M. Sc. Johannes. S. Haataja Dr. Tiia‐Riikka Tero Prof. Hannu Häkkinen Prof. Olli Ikkala 《Angewandte Chemie (International ed. in English)》2016,55(52):16035-16038
We report supracolloidal self‐assembly of atomically precise and strictly monodisperse gold nanoclusters involving p‐mercaptobenzoic acid ligands (Au102‐pMBA44) under aqueous conditions into hexagonally packed monolayer‐thick two‐dimensional facetted colloidal crystals (thickness 2.7 nm) and their bending to closed shells leading to spherical capsids (d ca. 200 nm), as controlled by solvent conditions. The 2D colloidal assembly is driven in template‐free manner by the spontaneous patchiness of the pMBA ligands around the Au102‐pMBA44 nanoclusters preferably towards equatorial plane, thus promoting inter‐nanocluster hydrogen bonds and high packing to planar sheets. More generally, the findings encourage to explore atomically precise nanoclusters towards highly controlled colloidal self‐assemblies. 相似文献
44.
Site Preference in Multimetallic Nanoclusters: Incorporation of Alkali Metal Ions or Copper Atoms into the Alkynyl‐Protected Body‐Centered Cubic Cluster [Au7Ag8(C≡CtBu)12]+
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yu Wang Dr. Haifeng Su Liting Ren Dr. Sami Malola Dr. Shuichao Lin Prof. Boon K. Teo Prof. Hannu Häkkinen Prof. Nanfeng Zheng 《Angewandte Chemie (International ed. in English)》2016,55(48):15152-15156
The synthesis, structure, substitution chemistry, and optical properties of the gold‐centered cubic monocationic cluster [Au@Ag8@Au6(C≡CtBu)12]+ are reported. The metal framework of this cluster can be described as a fragment of a body‐centered cubic (bcc) lattice with the silver and gold atoms occupying the vertices and the body center of the cube, respectively. The incorporation of alkali metal atoms gave rise to [MnAg8?nAu7(C≡CtBu)12]+ clusters (n=1 for M=Na, K, Rb, Cs and n=2 for M=K, Rb), with the alkali metal ion(s) presumably occupying the vertex site(s), whereas the incorporation of copper atoms produced [CunAg8Au7?n(C≡CtBu)12]+ clusters (n=1–6), with the Cu atom(s) presumably occupying the capping site(s). The parent cluster exhibited strong emission in the near‐IR region (λmax=818 nm) with a quantum yield of 2 % upon excitation at λ=482 nm. Its photoluminescence was quenched upon substitution with a Na+ ion. DFT calculations confirmed the superatom characteristics of the title compound and the sodium‐substituted derivatives. 相似文献
45.
Milla M H?nninen Joonas Haapasalo Hannu Haapasalo Robert E Fleming Robert S Britton Bruce R Bacon Seppo Parkkila 《BMC neuroscience》2009,10(1):36
Background
Defective iron homeostasis may be involved in the development of some diseases within the central nervous system. Although the expression of genes involved in normal iron balance has been intensively studied in other tissues, little is known about their expression in the brain. We investigated the mRNA levels of hepcidin (HAMP), HFE, neogenin (NEO1), transferrin receptor 1 (TFRC), transferrin receptor 2 (TFR2), and hemojuvelin (HFE2) in normal human brain, brain tumors, and astrocytoma cell lines. The specimens included 5 normal brain tissue samples, 4 meningiomas, one medulloblastoma, 3 oligodendrocytic gliomas, 2 oligoastrocytic gliomas, 8 astrocytic gliomas, and 3 astrocytoma cell lines. 相似文献46.
47.
Joni Virta Bing Li Klaus Nordhausen Hannu Oja 《Journal of computational and graphical statistics》2018,27(3):628-637
Independent component analysis is a standard tool in modern data analysis and numerous different techniques for applying it exist. The standard methods however quickly lose their effectiveness when the data are made up of structures of higher order than vectors, namely, matrices or tensors (e.g., images or videos), being unable to handle the high amounts of noise. Recently, an extension of the classic fourth-order blind identification (FOBI) specially suited for tensor-valued observations was proposed and showed to outperform its vector version for tensor data. In this article, we extend another popular independent component analysis method, the joint approximate diagonalization of eigen-matrices (JADE), for tensor observations. In addition to the theoretical background, we also provide the asymptotic properties of the proposed estimator and use both simulations and real data to show its usefulness and superiority over its competitors. Supplementary material including the proofs of the theorems and the codes for running the simulations and the real data example are available online. 相似文献
48.
49.
The first study on the mass spectroscopy of various bis(amidinohydrazones) is reported. The compounds studied included the investigational antileukemic drugs methylglyoxal bis(amidino-hydrazone) [‘methylglyoxal bis(guanylhydrazone)’, MGBG] and glyoxal bis(amidinohydrazone), as well as seven mono- and dialkylglyoxal analogs thereof. The results indicate that the free bases of these high-melting compounds are volatilized well enough to allow a facile detection of the molecular ions and to make mass spectroscopy of the underivatized compounds a suitable method for the verification of the identity of the substances. This result is of importance considering the development of novel analogs and derivatives. A compilation of electron-impact mass spectra is reported and possible fragmentation routes are outlined. The fragmentation of the various congeners appears to occur essentially similarly, the main paths involving breakage of the carbon-carbon single bond in the glyoxal moiety or breakage of either one of the nitrogen-nitrogen single bonds. 相似文献
50.
Usama Abo Ramadan Antti T Markkola Juha Halavaara Jukka Tanttu Anna-Maija Häkkinen Hannu J Aronen 《Magnetic resonance imaging》1998,16(10):1191-1199
The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T1ρ) and off-resonance spin lock relaxation parameters (T1ρoff, Me/Mo), MT parameters (T1sat, Ms/Mo), and T1, T2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T1ρ for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 μT to 250 μT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 μT, T1ρoff for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (Beff) and the z-axis (θ) ranging from 60° to 15°, respectively. The T1ρ of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T1ρoff decreased significantly with increasing θ (p < 0.001). T1ρ and T1ρoff with θ ≥ 30° were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and θ of the locking pulse provide additional parameters to optimize contrast in brain SL imaging. 相似文献