全文获取类型
收费全文 | 2172篇 |
免费 | 81篇 |
国内免费 | 5篇 |
专业分类
化学 | 1358篇 |
晶体学 | 5篇 |
力学 | 63篇 |
数学 | 458篇 |
物理学 | 374篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 53篇 |
2021年 | 60篇 |
2020年 | 55篇 |
2019年 | 63篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 97篇 |
2015年 | 74篇 |
2014年 | 80篇 |
2013年 | 118篇 |
2012年 | 181篇 |
2011年 | 155篇 |
2010年 | 90篇 |
2009年 | 100篇 |
2008年 | 132篇 |
2007年 | 130篇 |
2006年 | 117篇 |
2005年 | 95篇 |
2004年 | 104篇 |
2003年 | 77篇 |
2002年 | 87篇 |
2001年 | 29篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 22篇 |
1995年 | 14篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1966年 | 2篇 |
1939年 | 1篇 |
1910年 | 1篇 |
排序方式: 共有2258条查询结果,搜索用时 15 毫秒
51.
Marco Lopez Fabio Sacconi Matthias Auf der Maur Alessandro Pecchia Aldo Di Carlo 《Optical and Quantum Electronics》2012,44(3-5):89-94
In this work electronic and optoelectronic properties of InGaN/GaN nanocolumn quantum disk LEDs have been studied with the multiscale simulation tool tiberCAD. Calculations have been performed with an atomistic tight-binding model. Results shows that emission energies have a minor dependence on the nanocolumn dimension while In concentration in the active region is a critical parameter. 相似文献
52.
53.
Carlos Raimundo Andrade Lima Jefferson da Silva Martins Caroline Pinheiro Luis Fernando de Avila Roberto Rosas Pinho Maria Luiza Miranda Rocco Wilson de Souza Melo Fabio Zappa 《Journal of Polymer Science.Polymer Physics》2019,57(15):967-972
Photopolymerization is a phenomenon that is the basis of much of today's microfabrication technology and intense research is conducted to improve its control and the characteristics of end products for a variety of applications. The design of microscopic structures often relies on the accurate knowledge and modeling of photopolymer's behavior upon exposure, i.e. the Dill parameters, for each radiation species of interest and therefore the development of flexible characterization techniques is of great importance. SU‐8 is a popular compound that is representative of a whole class that relies on cationic polymerization, where an acid is obtained via photolysis of an onium salt during exposure. Here we report on the observation of SbF6? via laser desorption mass spectrometry on SU‐8 exposed to UV light at the wavelength of 365 nm and demonstrate that the yield of this counter‐anion as a function of exposure is consistent with the Dill C parameter value available in the literature. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 967–972 相似文献
54.
Meccanica - The advancement of manufacturing techniques has led to a rapid increase in the design and fabrication of periodic and architectured materials for a variety of dynamics and wave... 相似文献
55.
Polyamide 12 (PA12) is used in a variety of applications when low moisture absorption, good dimensional stability, and toughness are required. Polyamide 12 is one of the polymers most frequently employed to fabricate angioplasty balloon catheters; however, its high hydrophobicity and chemical inertness require the application of coatings to make its surface more hydrophilic and biocompatible. In this work, an alternative method, based on the photochemical reaction of PA12 with a hydrophilic aromatic azide, was developed. Static and dynamic contact angle measurements evidenced that the surface modification process was able to improve PA12 wettability and that the effects were retained even after 12 months from surface treatment. Polyamide 12 modification resulted in an increase of its surface free energy, as evaluated by the van Oss, Good, and Chaudhury method. X‐ray photoelectron spectroscopy confirmed the presence of the aromatic azide on PA12 surface. Finally, compliance tests showed that the modification process did not reduce the mechanical performance of balloons. 相似文献
56.
Pierre Thureau Simone Sturniolo Miri Zilka Fabio Ziarelli Stéphane Viel Jonathan R. Yates Giulia Mollica 《Magnetic resonance in chemistry : MRC》2019,57(5):256-264
Structure determination of functional organic compounds remains a formidable challenge when the sample exists as a powder. Nuclear magnetic resonance crystallography approaches based on the comparison of experimental and Density Functional Theory (DFT)-computed 1H chemical shifts have already demonstrated great potential for structure determination of organic powders, but limitations still persist. In this study, we discuss the possibility of using 13C-13C dipolar couplings quantified on powdered theophylline at natural isotopic abundance with the help of dynamic nuclear polarization, to realize a DFT-free, rapid screening of a pool of structures predicted by ab initio random structure search. We show that although 13C-13C dipolar couplings can identify structures possessing long range structural motifs and unit cell parameters close to those of the true structure, it must be complemented with other data to recover information about the presence and the chemical nature of the supramolecular interactions. 相似文献
57.
The rate constants for the reaction between chlorine atoms and either 5-methyl-2-hexanol, 2,2-dimethyl-3-hexanol, or 2,4,4-trimethyl-1-pentanol at 298 K were determined using the relative method with 2-butanol and 1-pentanol as reference compounds. The values obtained for 5-methyl-2-hexanol, 2,2-dimethyl-3-hexanol, and 2,4,4-trimethyl-1-pentanol (k × 1010 cm3 molec−1 s−1) were, respectively, (2.64 ± 0.5), (2.72 ± 0.5), and (2.50 ± 0.4), in agreement with the values of the rate constants reported in bibliography for similar alcohols and the values estimated by structure activity relationship methods. The photooxidation products of 2,4,4-trimethyl-1-pentanol initiated by chlorine atoms were identified (formaldehyde, 2-propanone, 2,2-dimethyl propanal, 4,4,-dimethyl-2-pentanone, and 3,3-dimethylbutanal), and the reaction mechanism was determined. 相似文献
58.
Dr. Joohyun Lim Ghoncheh Kasiri Dr. Rajib Sahu Kevin Schweinar Dr. Katharina Hengge Prof. Dr. Dierk Raabe Prof. Dr. Fabio La Mantia Prof. Dr. Christina Scheu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):4917-4922
The structural changes of copper hexacyanoferrate (CuHCF), a Prussian blue analogue, which occur when used as a cathode in an aqueous Zn-ion battery, are investigated using electron microscopy techniques. The evolution of ZnxCu1−xHCF phases possessing wire and cubic morphologies from initial CuHCF nanoparticles are monitored after hundreds of cycles. Irreversible introduction of Zn ions to CuHCF is revealed locally using scanning transmission electron microscopy. A substitution mechanism is proposed to explain the increasing Zn content within the cathode material while simultaneously the Cu content is lowered during Zn-ion battery cycling. The present study demonstrates that the irreversible introduction of Zn ions is responsible for the decreasing Zn ion capacity of the CuHCF cathode in high electrolyte concentration. 相似文献
59.
Fabio Cameli Prof. Dr. Joop H. ter Horst Dr. René R. E. Steendam Dr. Ir. Christos Xiouras Prof. Dr. Georgios D. Stefanidis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1344-1354
Herein, the pivotal role of secondary nucleation in a crystallization-enhanced deracemization process is reported. During this process, complete and rapid deracemization of chiral conglomerate crystals of an isoindolinone is attained through fast microwave-assisted temperature cycling. A parametric study of the main factors that affect the occurrence of secondary nucleation in this process, namely agitation rate, suspension density, and solute supersaturation, confirms that an enhanced stereoselective secondary nucleation rate maximizes the deracemization rate. Analysis of the system during a single temperature cycle showed that, although stereoselective particle production during the crystallization stage leads to enantiomeric enrichment, undesired kinetic dissolution of smaller particles of the preferred enantiomer occurs during the dissolution step. Therefore, secondary nucleation is crucial for the enhancement of deracemization through temperature cycles and as such should be considered in further design and optimization of this process, as well as in other temperature cycling processes commonly applied in particle engineering. 相似文献
60.
A tunable microwave-assisted protocol for the synthesis of two biologically relevant families of heterocycles has been designed. Via a simple switch of reaction conditions, the same starting materials can be engaged in either an improved synthesis of the dihydrotriazine scaffold or a novel, first-in-class MCR to render the challenging 5-aminoimidazole nucleus in a single step. An additional first-in-class MCR is also reported utilizing guanidines to afford 2,5-aminoimidazoles. 相似文献