全文获取类型
收费全文 | 2474篇 |
免费 | 107篇 |
国内免费 | 23篇 |
专业分类
化学 | 1688篇 |
晶体学 | 15篇 |
力学 | 66篇 |
数学 | 349篇 |
物理学 | 486篇 |
出版年
2023年 | 27篇 |
2022年 | 51篇 |
2021年 | 54篇 |
2020年 | 65篇 |
2019年 | 78篇 |
2018年 | 54篇 |
2017年 | 57篇 |
2016年 | 96篇 |
2015年 | 54篇 |
2014年 | 69篇 |
2013年 | 132篇 |
2012年 | 162篇 |
2011年 | 190篇 |
2010年 | 107篇 |
2009年 | 68篇 |
2008年 | 134篇 |
2007年 | 177篇 |
2006年 | 157篇 |
2005年 | 121篇 |
2004年 | 104篇 |
2003年 | 78篇 |
2002年 | 53篇 |
2001年 | 29篇 |
2000年 | 28篇 |
1999年 | 39篇 |
1998年 | 20篇 |
1997年 | 27篇 |
1996年 | 25篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 7篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1887年 | 6篇 |
排序方式: 共有2604条查询结果,搜索用时 15 毫秒
991.
Ran Su H. Alex Hsain Ming Wu Dawei Zhang Xinghao Hu Zhipeng Wang Xiaojing Wang Fa‐tang Li Xuemin Chen Lina Zhu Yong Yang Yaodong Yang Xiaojie Lou Stephen J. Pennycook 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(42):15220-15225
Piezocatalysis, converting mechanical vibration into chemical energy, has emerged as a promising candidate for water‐splitting technology. However, the efficiency of the hydrogen production is quite limited. We herein report well‐defined 10 nm BaTiO3 nanoparticles (NPs) characterized by a large electro‐mechanical coefficient which induces a high piezoelectric effect. Atomic‐resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) and scanning probe microscopy (SPM) suggests that piezoelectric BaTiO3 NPs display a coexistence of multiple phases with low energy barriers and polarization anisotropy which results in a high electro‐mechanical coefficient. Landau free energy modeling also confirms that the greatly reduced polarization anisotropy facilitates polarization rotation. Employing the high piezoelectric properties of BaTiO3 NPs, we demonstrate an overall water‐splitting process with the highest hydrogen production efficiency hitherto reported, with a H2 production rate of 655 μmol g?1 h?1, which could rival excellent photocatalysis system. This study highlights the potential of piezoelectric catalysis for overall water splitting. 相似文献
992.
Stefano Sainas Agnese C. Pippione Alessandro Giraudo Katia Martina Federica Bosca Barbara Rolando Alessandro Barge Alex Ducime Antonella Federico Stuart J. Grossert Robert L. White Donatella Boschi Marco L. Lolli 《Journal of heterocyclic chemistry》2019,56(2):501-519
Acidic 4‐hydroxy‐1,2,3‐triazole is a proven bioisostere of acidic functions that has recently been used to replace the acidic moieties of biologically active leads. Straightforward chemical strategies for the synthesis of the three possible N‐alkylated 4‐hydroxy‐1,2,3‐triazole regioisomers have been designed and reported herein, by identifying the optimal conditions under which the alkylation of ethyl 4‐benzyloxy‐1,2,3‐triazolecarboxylate (compound 19 ) can be regiodirected to the triazole N(b) position and thus produce the only isomer that cannot be obtained via the cycloaddition reaction. Furthermore, an innovative platform for parallel synthesis, called Arachno and which has been patented by the authors' group, has been used to speed up the process, and an NMR study has been carried out to better understand the reactivity of compound 19 towards the N(b) position. A library of benzyloxy protected 4‐hydroxy‐1,2,3‐triazoles has been prepared using the two strategies: regiodirection for the N(b) and N(c) isomers and cycloaddition for the N(a) isomers; the processes are described herein. The three N‐alkylated regioisomer series have been characterized spectroscopically (NMR and MS). The subsequent catalytic hydrogenation of the 4‐benzyloxy protective group on the N‐alkylated‐4‐benzyloxy‐5‐ethoxycarbonyl‐1,2,3‐triazoles provided the corresponding substituted 4‐hydroxy‐1,2,3‐triazoles. 相似文献
993.
Alex J. Plajer Edmundo G. Percstegui Marco Santella Felix J. Rizzuto Quan Gan Bo W. Laursen Jonathan R. Nitschke 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(13):4244-4248
The design of aqueous probes and binders for complex, biologically relevant anions presents a key challenge in supramolecular chemistry. Herein, a tetrahedral assembly with cationic faces and corners is reported that is capable of discriminating between anionic and neutral guests in water. Electrostatic repulsion between subcomponents can be overcome by the addition of an anionic template, or generating a robust covalent framework by incorporating tris(2‐aminoethyl)amine (TREN). The resultant TREN‐capped, water‐soluble, fluorescent cage binds mono‐ and poly‐phosphoric esters, including nucleotides. Its covalent skeleton renders it stable at micromolar concentrations in water, enabling the fluorometric detection of biologically relevant guests in an aqueous environment. Selective supramolecular encapsulants, such as 1 , could enable new sensing applications, such as recognition of toxins and drugs, under biological conditions. 相似文献
994.
Haotian Sun Farihah M. Haque Yi Zhang Alex Commisso Mohamed Alaa Mohamed Marina Tsianou Honggang Cui Scott M. Grayson Chong Cheng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(31):10682-10686
Herein, the design, synthesis, and characterization of an unprecedented copolymer consisting of alternating linear and dendritic segments is described. First, a 4th‐generation Hawker‐type dendron with two azide groups was synthesized, followed by a step‐growth azide‐alkyne “click” reaction between the 4th‐generation diazido dendron and poly(ethylene glycol) diacetylene to create the target polymers. Unequal reactivity of the functional groups was observed in the step‐growth polymerization. The resulting copolymers, with alternating hydrophilic linear and hydrophobic dendritic segments, can spontaneously associate into a unique type of microphase‐segregated nanorods in water. 相似文献
995.
Alex Akwasi Opoku Kwame Owusu Edusei Richard Kwame Ansah 《Journal of statistical physics》2018,171(1):106-126
This paper proposes a conditional Curie–Weiss model as a model for decision making in a stylized society made up of binary decision makers that face a particular dichotomous choice between two options. Following Brock and Durlauf (Discrete choice with social interaction I: theory, 1955), we set-up both socio-economic and statistical mechanical models for the choice problem. We point out when both the socio-economic and statistical mechanical models give rise to the same self-consistent equilibrium mean choice level(s). Phase diagram of the associated statistical mechanical model and its socio-economic implications are discussed. 相似文献
996.
Jack O. Law Alex G. Wong Halim Kusumaatmaja Mark A. Miller 《Molecular physics》2018,116(21-22):3008-3019
ABSTRACTBy combining Monte Carlo simulations and analytical models, we demonstrate and explain how the gas-to-liquid phase transition of colloidal systems confined to a spherical surface depends on the curvature and size of the surface, and on the choice of thermodynamic ensemble. We find that the geometry of the surface affects the shape of the free energy profile and the size of the critical nucleus by altering the perimeter–area ratio of isotropic clusters. Confinement to a smaller spherical surface results in both a lower nucleation barrier and a smaller critical nucleus size. Furthermore, the liquid domain does not grow indefinitely on a sphere. Saturation of the liquid density in the grand canonical ensemble and the depletion of the gas phase in the canonical ensemble lead to a minimum in the free energy profile, with a sharp increase in free energy for additional growth beyond this minimum. 相似文献
997.
All‐Inorganic Hetero‐Structured Cesium Tin Halide Perovskite Light‐Emitting Diodes With Current Density Over 900 A cm−2 and Its Amplified Spontaneous Emission Behaviors 下载免费PDF全文
998.
Ahmed Farouk J. Batle M. Elhoseny Mosayeb Naseri Muzaffar Lone Alex Fedorov Majid Alkhambashi Syed Hassan Ahmed M. Abdel-Aty 《Frontiers of Physics》2018,13(2):130306
Quantum communication provides an enormous advantage over its classical counterpart: security of communications based on the very principles of quantum mechanics. Researchers have proposed several approaches for user identity authentication via entanglement. Unfortunately, these protocols fail because an attacker can capture some of the particles in a transmitted sequence and send what is left to the receiver through a quantum channel. Subsequently, the attacker can restore some of the confidential messages, giving rise to the possibility of information leakage. Here we present a new robust General Nuser authentication protocol based on N-particle Greenberger–Horne–Zeilinger (GHZ) states, which makes eavesdropping detection more effective and secure, as compared to some current authentication protocols. The security analysis of our protocol for various kinds of attacks verifies that it is unconditionally secure, and that an attacker will not obtain any information about the transmitted key. Moreover, as the number of transferred key bits N becomes larger, while the number of users for transmitting the information is increased, the probability of effectively obtaining the transmitted authentication keys is reduced to zero. 相似文献
999.
Longqing Qiu Yi Zhang Hans-Joachim Krause Alex I. Braginski Andreas Offenhusser 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,196(2):101-104
In reported low-field nuclear magnetic resonance (NMR) measurements using Superconducting Quantum Interference Device (SQUID) detection, the pre-polarizing magnetic field has been usually oriented orthogonal to the measuring field, Bp Bm. Melton et al. systematically analyzed the consequences of Bp decay in time after turnoff and showed that this decay should be nonadiabatic. We evaluated our measuring procedure in the light of that analysis, and found good quantitative agreement. It was showed that, when the decay time constant is comparable to the precession period of the magnetization of the sample, M, the optimum procedure is to orient Bp parallel to Bm and to apply a π/2 pulse to flip M, similar as in the case of conventional NMR. 相似文献
1000.
Pereira Bruna Á. de Bastos Alcione V. Teixeira Wystan K. O. e Silva Sidnei Moura Flores Alex F. C. Flores Darlene C. 《Molecular diversity》2017,21(4):1021-1026
Molecular Diversity - An elegant, efficient, and highly regioselective approach for the synthesis of novel methyl 5-amino-3-(methylthio)-1-differently substituted-1H-pyrazole-4-carboxylates is... 相似文献