全文获取类型
收费全文 | 454篇 |
免费 | 35篇 |
国内免费 | 1篇 |
专业分类
化学 | 361篇 |
晶体学 | 4篇 |
力学 | 9篇 |
数学 | 21篇 |
物理学 | 95篇 |
出版年
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 22篇 |
2013年 | 21篇 |
2012年 | 30篇 |
2011年 | 39篇 |
2010年 | 37篇 |
2009年 | 30篇 |
2008年 | 34篇 |
2007年 | 29篇 |
2006年 | 27篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1968年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有490条查询结果,搜索用时 31 毫秒
51.
We report on an interdisciplinary approach to the study of finds of unfired clay lumps and unfired broken vessels from two workshops in the Leche Valley, north coast of Peru. The material is used as a reference in the study of pottery making at both workshops. 相似文献
52.
Ryosuke Sakae Dr. Koji Hirano Prof. Dr. Tetsuya Satoh Prof. Dr. Masahiro Miura 《Angewandte Chemie (International ed. in English)》2015,54(2):613-617
A copper‐catalyzed aminoboration of bicyclic alkenes, including oxa‐ and azabenzonorbornadienes, has been developed. With this method, amine and boron moieties are simultaneously introduced at an olefin with exo selectivity. Subsequent stereospecific transformations of the boryl group can provide oxygen‐ and nitrogen‐rich cyclic molecules with motifs that may be found in natural products or pharmaceutically active compounds. Moreover, a catalytic asymmetric variant of this transformation was realized by using a copper complex with a chiral bisphosphine ligand, namely (R,R)‐Ph‐BPE. 相似文献
53.
Hydroxylation of lysine, one of posttranslational modifications of proteins, generates 5‐hydroxylysine (Koh) and plays a crucial role in regulating protein functions in cellular activity. We have developed a chemical labeling method of Koh. The 1,2‐aminoalcohol moiety of Koh in synthetic peptide sequences was trapped by an alkyne‐containing benzimidate to form a 2‐oxazoline ring. An additional ammonia treatment process removed the undesirable amidine residue formed between benzimidate and lysine. During the ammonia treatment, the oxazoline residue formed at Koh mainly remained intact, and the ring opening to the amide form was observed for only part of oxazoline, indicating that the chemical labeling is amino acid selective. Azide‐substituted biotin or fluorescent dye was attached to the peptide through Huisgen cycloaddition at Koh and converted into an alkyne‐labeled oxazoline form. The Koh‐labeling assay could provide a platform to enhance proteomic research of lysine hydroxylation. 相似文献
54.
Iron–Oxalato Framework with One‐Dimensional Open Channels for Electrochemical Sodium‐Ion Intercalation
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Xianfen Wang Ryosuke Kurono Dr. Shin‐ichi Nishimura Dr. Masashi Okubo Prof. Atsuo Yamada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(3):1096-1101
Discovery of a new class of ion intercalation compounds is highly desirable due to its relevance to various electrochemical devices, such as batteries. Herein, we present a new iron–oxalato open framework, which showed reversible Na+ intercalation/extraction. The hydrothermally synthesized K4Na2[Fe(C2O4)2]3 ? 2 H2O possesses one‐dimensional open channels in the oxalato‐bridged network, providing ion accessibility up to two Na+ per the formula unit. The detailed studies on the structural and electronic states revealed that the framework exhibited a solid solution state almost entirely during Na+ intercalation/extraction associated with the reversible redox of Fe. The present work demonstrates possibilities of the oxalato frameworks as tunable and robust ion intercalation electrode materials for various device applications. 相似文献
55.
Dr. Kensei Hayashida 《Rheologica Acta》1962,2(4):261-273
Zusammenfassung In der vorliegenden Arbeit wurde der Versuch unternommen, eine einheitliche Theorie aller Strömungsvorgänge im Extruder zu entwickeln, wobei von einer strukturviskosen bzw. pseudoplastischen Schmelze ausgegangen und daher die rheologischen Zustandsgleichungen vonRabinowitsch undOstwald-de Waele der Analyse der aus einer Schlepp- und einer Druckströmung überlagerten Strömungsform zugrunde gelegt wurden. Die Ergebnisse der Analyse wurden in zwei dimensionslosen Diagrammen zusammengefaßt. Die weitere Untersuchung ergab, daß nicht nur die Strömung in Richtung des Schneckenkanals, sondern auch die Leck- und die Querströmung mit den dimensionslosen Diagrammen erfaßt werden können. Als Anwendungsbeispiele der genannten Diagramme wurde der Druckgradientenverlauf, der Druckverlauf sowie die Schneckenkennlinie für eine beliebig variierbare Schneckenabmessung und einen beliebig gewählten Temperaturverlauf berechnet und mit den Versuchsergebnissen verglichen. Es wurde eine befriedigende Übereinstimmung gefunden.Es ist mir eine angenehme Pflicht, Herrn Prof. Dr.Mori für seinen wertvollen Rat bei der Durchführung dieser Untersuchungen meinen verbindlichen Dank auszusprechen. 相似文献
56.
Yasuda M Nakajima H Takeda R Yoshioka S Yamasaki S Chiba K Baba A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):3856-3867
Boron complexes that contain new tridentate ligands, tris(o‐oxyaryl)methanes and ‐silanes, were prepared. These complexes had a cage‐shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open‐shaped boron compounds. The cage‐shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L?B(OC6H4)3CH, L?B(OC6H4)3SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage‐shaped borates had a large dihedral angle (Cipso‐O‐B‐O) compared with open‐shaped borates. The geometric effect due to the dihedral angle means that compared with open‐shaped, the cage‐shaped borates have a greater Lewis acidity. The introduction of electron‐withdrawing groups on the aryl moieties in the cage‐shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of Cipso‐O‐B‐O. The ligand‐exchange rates of the para‐fluoro‐substituted compound B(OC6H3F)3CH and the ortho‐phenyl‐substituted compound B(OC6H3Ph)3CH were less than that of the unsubstituted borate B(OC6H4)3CH. The ligand‐exchange rate of B(OC6H4)3SiMe was much faster than that of B(OC6H4)3CH. A hetero Diels–Alder reaction and Mukaiyama‐type aldol reactions were more effectively catalyzed by cage‐shaped borates than by the open‐shaped borate B(OPh)3 or by the strong Lewis acid BF3?OEt2. The cage‐shaped borates with the bulky substituents at the ortho‐positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity. 相似文献
57.
Yamaguchi K Ueki R Nonaka H Sugihara F Matsuda T Sando S 《Journal of the American Chemical Society》2011,133(36):14208-14211
Monoamine oxidase (MAO) A is a flavoenzyme that catalyzes the oxidation of biologically important monoamines and is thought to be associated with psychiatric disorders. Here, we report a strategy for rationally designing a (19)F magnetic resonance imaging probe for the specific detection of human MAO-A (hMAO-A) activity. Our designed (19)F probe was oxidized expeditiously by hMAO-A to produce 2-fluoro-4-nitrophenol via a spontaneous β-elimination mechanism. Concomitant with the structural change of the probe to the product, the (19)F chemical shift changed by 4.2 ppm, which was enough to visualize the probe and enzymatic product separately. Importantly, our probe achieved excellent discrimination of hMAO-A from its isoform hMAO-B. 相似文献
58.
Iwasaki Y Matsui R Suzuki T Nakazaki A Kobayashi S 《Chemical & pharmaceutical bulletin》2011,59(4):522-524
We have developed a high-yielding and stereoselective vinylogous Mukaiyama aldol reaction (VMAR) of α-haloenals. Contrary to the simple α,β-unsaturated aldehyde, α-haloenals were found to be reactive affording the corresponding VMAR adducts in excellent yields. Some transformations of VMAR adducts by Pd-mediated cross-coupling were also examined in order to demonstrate the synthetic utility of VMAR of α-haloenals. 相似文献
59.
Keller A Fritzsche M Ogaki R Bald I Facsko S Dong M Kingshott P Besenbacher F 《The Journal of chemical physics》2011,134(10):104705
The hydrophobicity of surfaces has a strong influence on their interactions with biomolecules such as proteins. Therefore, for in vitro studies of bio-surface interactions model surfaces with tailored hydrophobicity are of utmost importance. Here, we present a method for tuning the hydrophobicity of atomically flat mica surfaces by hyperthermal Ar ion irradiation. Due to the sub-100 eV energies, only negligible roughening of the surface is observed at low ion fluences and also the chemical composition of the mica crystal remains almost undisturbed. However, the ion irradiation induces the preferential removal of the outermost layer of K(+) ions from the surface, leading to the exposure of the underlying aluminosilicate sheets which feature a large number of centers for C adsorption. The irradiated surface thus exhibits an enhanced chemical reactivity toward hydrocarbons, resulting in the adsorption of a thin hydrocarbon film from the environment. Aging these surfaces under ambient conditions leads to a continuous increase of their contact angle until a fully hydrophobic surface with a contact angle >80° is obtained after a period of about 3 months. This method thus enables the fabrication of ultrasmooth biological model surfaces with precisely tailored hydrophobicity. 相似文献
60.
Jinnouchi R Kodama K Hatanaka T Morimoto Y 《Physical chemistry chemical physics : PCCP》2011,13(47):21070-21083
A first principles-based mean field model was developed for the oxygen reduction reaction (ORR) taking account of the coverage- and material-dependent reversible potentials of the elementary steps. This model was applied to the simulation of single crystal surfaces of Pt, Pt alloy and Pt core-shell catalysts under Ar and O(2) atmospheres. The results are consistent with those shown by past experimental and theoretical studies on surface coverages under Ar atmosphere, the shape of the current-voltage curve for the ORR on Pt(111) and the material-dependence of the ORR activity. This model suggests that the oxygen associative pathway including HO(2)(ads) formation is the main pathway on Pt(111), and that the rate determining step (RDS) is the removal step of O(ads) on Pt(111). This RDS is accelerated on several highly active Pt alloys and core-shell surfaces, and this acceleration decreases the reaction intermediate O(ads). The increase in the partial pressure of O(2)(g) increases the surface coverage with O(ads) and OH(ads), and this coverage increase reduces the apparent reaction order with respect to the partial pressure to less than unity. This model shows details on how the reaction pathway, RDS, surface coverages, Tafel slope, reaction order and material-dependent activity are interrelated. 相似文献