全文获取类型
收费全文 | 833篇 |
免费 | 47篇 |
国内免费 | 4篇 |
专业分类
化学 | 701篇 |
晶体学 | 8篇 |
力学 | 12篇 |
数学 | 34篇 |
物理学 | 129篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 20篇 |
2020年 | 14篇 |
2019年 | 21篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 29篇 |
2015年 | 31篇 |
2014年 | 22篇 |
2013年 | 48篇 |
2012年 | 57篇 |
2011年 | 73篇 |
2010年 | 50篇 |
2009年 | 37篇 |
2008年 | 65篇 |
2007年 | 52篇 |
2006年 | 47篇 |
2005年 | 33篇 |
2004年 | 45篇 |
2003年 | 31篇 |
2002年 | 33篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有884条查询结果,搜索用时 15 毫秒
851.
Two calix[4]arene tetracarboxylates, [calix[4]arene tetraacetate (K(4)CTA) and calix[4]arene tetrabenzoate (K(4)CTB)] as their potassium salts, have been prepared. Employing these as precursors, two Ag(I) coordination polymers incorporating calix[4]arene units have been successfully prepared and their X-ray crystal structures have been determined. In these, the CTA and CTB derivatives are linearly bound to two and four silver atoms, respectively, to generate unusual tubular nanostructures. A comparative NMR study was undertaken to investigate the nature of the metal ion blocking of the tube as observed in the CTA-derived structure. The thermal properties for both coordination polymers were also examined. 相似文献
852.
Shim D Jung SH Han SY Shin K Lee KH Han JH 《Chemical communications (Cambridge, England)》2011,47(18):5202-5204
To realize transparent conductive films based on single-walled carbon nanotubes (SWCNTs), we applied a spray coating process with transition metal doping to SWCNT networks. Schottky contacts between metallic and semiconducting SWCNTs changed to Ohmic contacts due to the reduction of metals on the SWCNT surfaces via direct conversion from solution. 相似文献
853.
The exchange coupling between quantum dot spin qubits is isotropic, which restricts the types of quantum gates that can be formed. Here, we propose a method for controlling anisotropic interactions between spins arranged in a bus geometry. The symmetry is broken by an external magnetic field, resulting in XXZ-type interactions that can efficiently generate maximally entangled Greenberger-Horne-Zeilinger states or universal gate sets for exchange-only quantum computing. We exploit the XXZ couplings to propose a qubit scheme, based on double dots. 相似文献
854.
In-Ho Park Kwang-Ho Kim Hyun-Kyung Choi Jae-Seung Shim Soo-Young Whang Sang June Hahn Oh-Joo Kwon Il-Hoan Oh 《Experimental & molecular medicine》2013,45(9):e44
With the increasing use of culture-expanded mesenchymal stromal cells (MSCs) for cell therapies, factors that regulate the cellular characteristics of MSCs have been of major interest. Oxygen concentration has been shown to influence the functions of MSCs, as well as other normal and malignant stem cells. However, the underlying mechanisms of hypoxic responses and the precise role of hypoxia-inducible factor-1α (Hif-1α), the master regulatory protein of hypoxia, in MSCs remain unclear, due to the limited span of Hif-1α stabilization and the complex network of hypoxic responses. In this study, to further define the significance of Hif-1α in MSC function during their self-renewal and terminal differentiation, we established adult bone marrow (BM)-derived MSCs that are able to sustain high level expression of ubiquitin-resistant Hif-1α during such long-term biological processes. Using this model, we show that the stabilization of Hif-1α proteins exerts a selective influence on colony-forming mesenchymal progenitors promoting their self-renewal and proliferation, without affecting the proliferation of the MSC mass population. Moreover, Hif-1α stabilization in MSCs led to the induction of pluripotent genes (oct-4 and klf-4) and the inhibition of their terminal differentiation into osteogenic and adipogenic lineages. These results provide insights into the previously unrecognized roles of Hif-1α proteins in maintaining the primitive state of primary MSCs and on the cellular heterogeneities in hypoxic responses among MSC populations. 相似文献
855.
Minkyung Kang Yejin Yang Jun Ho Shim Sang Cheol Lee Youngmi Lee Chongmok Lee 《Electroanalysis》2013,25(12):2691-2699
Metallic palladium (Pd) electrocatalysts for oxygen reduction and hydrogen peroxide (H2O2) oxidation/reduction are prepared via electroplating on a gold metal substrate from dilute (5 to 50 mM) aqueous K2PdCl4 solution. The best Pd catalyst layer possessing dendritic nanostructures is formed on the Au substrate surface from 50 mM Pd precursor solution (denoted as Pd‐50) without any additional salt, acid or Pd templating chemical species. The Pd‐50 consisted of nanostructured dendrites of polycrystalline Pd metal and micropores within the dendrites which provide high catalyst surface area and further facilitate reactant mass transport to the catalyst surface. The electrocatalytic activity of Pd‐50 proved to be better than that of a commercial Pt (Pt/C) in terms of lower overpotential for the onset and half‐wave potentials and a greater number of electrons (n) transferred. Furthermore, amperometric i–t curves of Pd‐50 for H2O2 electrochemical reaction show high sensitivities (822.2 and ?851.9 µA mM?1 cm?2) and low detection limits (1.1 and 7.91 µM) based on H2O2 oxidation H2O2 reduction, respectively, along with a fast response (<1 s). 相似文献
856.
Woo Young Kim Won-Yong Lee Gwang-Jae Jeon Hyun-Bin Shim In-Ku Kang Jae-Hyun Kim 《Molecular Crystals and Liquid Crystals》2014,599(1):36-42
This study investigates how the fringing field affects the total current flow within a conducting polymer. In order to extract the fringing field component of bar pattern resistors, a solvent-assisted patterning method using subtractive photolithography was successfully established for the conducting polymer poly(3-hexylthiophene). By comparing the current quantities of unpatterned and patterned resistors, a conductance factor for the fringing field was calculated, proving to be almost constant regardless of the resistor length. It is therefore concluded that the length as well as the width of the conducting polymer film need to be suitably patterned for the precise operation of organic electronic devices. In this regard, the patterning method developed will be useful for the fabrication of micro-scale devices. 相似文献
857.
A novel ergosterol conjunction-type alkaloid, hericirine (1), was isolated from the dried fruiting bodies of Hericium erinaceum. The overall framework of 1 was isolated, and combined with hericerin and ergosterol. Its structure was elucidated based on spectroscopic analysis using 1D and 2D NMR, IR and HRESIMS techniques. We found that hericirine significantly inhibited protein expression of iNOS and COX-2 and reduced NO, PGE2, TNF-α, IL-6 and IL-1β production in RAW264.7 cells exposed to LPS. 相似文献
858.
Facile Synthesis of AuPd Nanochain Networks on Carbon Supports and Their Application as Electrocatalysts for Oxygen Reduction Reaction
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The present work reports the facile synthesis and characterization of carbon‐supported porous Pd shell coated Au nanochain networks (AuPdNNs/C). By using Co nanoframes as sacrificial templates, AuPdNNs/C series have been prepared by a two‐step galvanic replacement reaction (GRR) technique. In the first step, the Au metal precursor, HAuCl4, reacts spontaneously with the formed Co nanoframes through the GRR, resulting in Au nanochain networks (AuNNs). The second GRR is performed with various concentrations of Pd precursor (0.1, 1, and 10 mM PdCl2), resulting in AuPdNNs/C. The synthesized AuPdNNs/C series are investigated as electrocatalysts for oxygen reduction reaction (ORR) in alkaline solution. The physical properties of the AuPdNNs/C catalysts are characterized by scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), UV‐vis absorption spectroscopy, and cyclic voltammetry (CV). Rotating disk electrode (RDE) voltammetric studies show that the Au0.8Pd0.2NNs/C (prepared using 1 mM PdCl2) has the highest ORR activity among all the AuPdNNs/C series, which is comparable to commercial Pt catalyst (E‐TEK). The ORR activity of AuPdNNs/C is presumably due to the enhanced Pd surface area and high porosity of Pd nanoshells. 相似文献
859.
Chiral Recognition of Proline Enantiomers by the Catalytic Oxygen Reduction and Formation of Cu(II)‐Polymer Complex Crystals
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dong‐Min Kim Mi‐Sook Won Jang‐Hee Yoon Jung Ho Kim Rajendra N. Goyal Yoon‐Bo Shim 《Electroanalysis》2014,26(10):2110-2117
A Cu(II)‐Poly(terthiophene carboxylic acid) (pTTC)/Nafion modified glassy carbon electrode has been used for the chiral recognition and discrimination of d‐ and l‐prolines by the catalytic oxygen reduction process and the shape of crystals formed on the electrode surface. The cyclic voltammetry with the modified electrode in the presence of oxygen recognized d‐ and l‐form of prolines by exhibiting a difference in the peak potential and the peak current of the oxygen reduction. The effect of pH and proline concentration on the peak current and the peak potential of oxygen have been studied. The SEM studies on the nature of crystals formed on a proline‐Cu(II)pTTC complex. The oxidation state of the copper species present at the electrode surface was characterized by ESCA. 相似文献
860.
In‐Hyeok Park Anjana Chanthapally Dr. Zhenjie Zhang Prof. Dr. Shim Sung Lee Prof. Dr. Michael J. Zaworotko Prof. Dr. Jagadese J. Vittal 《Angewandte Chemie (International ed. in English)》2014,53(2):414-419
Organic polymers are usually amorphous or possess very low crystallinity. The metal complexes of organic polymeric ligands are also difficult to crystallize by traditional methods because of their poor solubilities and their 3D structures can not be determined by single‐crystal X‐ray crystallography owing to a lack of single crystals. Herein, we report the crystal structure of a 1D ZnII coordination polymer fused with an organic polymer ligand made in situ by a [2+2] cycloaddition reaction of a six‐fold interpenetrated metal–organic framework. It is also shown that this organic polymer ligand can be depolymerized in a single‐crystal‐to‐single‐crystal (SCSC) fashion by heating. This strategy could potentially be extended to make a range of monocrystalline metal organopolymeric complexes and metal–organic organopolymeric hybrid materials. Such monocrystalline metal complexes of organic polymers have hitherto been inaccessible for materials researchers. 相似文献