全文获取类型
收费全文 | 5955篇 |
免费 | 210篇 |
国内免费 | 43篇 |
专业分类
化学 | 4113篇 |
晶体学 | 37篇 |
力学 | 140篇 |
数学 | 1094篇 |
物理学 | 824篇 |
出版年
2024年 | 10篇 |
2023年 | 45篇 |
2022年 | 134篇 |
2021年 | 169篇 |
2020年 | 106篇 |
2019年 | 132篇 |
2018年 | 110篇 |
2017年 | 89篇 |
2016年 | 198篇 |
2015年 | 178篇 |
2014年 | 217篇 |
2013年 | 356篇 |
2012年 | 400篇 |
2011年 | 456篇 |
2010年 | 292篇 |
2009年 | 290篇 |
2008年 | 362篇 |
2007年 | 378篇 |
2006年 | 346篇 |
2005年 | 333篇 |
2004年 | 246篇 |
2003年 | 180篇 |
2002年 | 188篇 |
2001年 | 79篇 |
2000年 | 62篇 |
1999年 | 60篇 |
1998年 | 44篇 |
1997年 | 51篇 |
1996年 | 76篇 |
1995年 | 43篇 |
1994年 | 42篇 |
1993年 | 43篇 |
1992年 | 53篇 |
1991年 | 38篇 |
1990年 | 28篇 |
1989年 | 35篇 |
1988年 | 26篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 35篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1974年 | 7篇 |
排序方式: 共有6208条查询结果,搜索用时 0 毫秒
191.
Double‐Wall Carbon Nanotube–Porphyrin Supramolecular Hybrid: Synthesis and Photophysical Studies 下载免费PDF全文
Dr. María Vizuete Dr. María J. Gómez‐Escalonilla Prof. José Luis G. Fierro Dr. Pedro Atienzar Prof. Hermenegildo García Prof. Fernando Langa 《Chemphyschem》2014,15(1):100-108
Double‐wall carbon nanotubes (DWCNTs) with pyridyl units covalently attached to the external wall through isoxazolino linkers and carboxylic groups that have been esterified by pentyl chains are synthesized. The properties of these modified DWCNTs are then compared with an analogous sample based on single‐wall carbon nanotubes (SWCNTs). Raman spectroscopy shows the presence of characteristic radial breathing mode vibrations, confirming that the samples partly retain the integrity of the nanotubes in the case of DWCNTs, including the internal and external nanotubes. Quantification of the pyridyl content for both samples (DWCNT and SWCNT derivatives) is based on X‐ray photoelectron spectroscopy and thermogravimetric profiles, showing very similar substituent load. Both pyridyl‐containing nanotubes (DWCNTs and SWCNTs) form a complex with zinc porphyrin (ZnP), as evidenced by the presence of two isosbestic points in the absorption spectra of the porphyrin upon addition of the pyridyl‐functionalized nanotubes. Supramolecular complexes based on pyridyl‐substituted DWCNTs and SWCNTs quench the emission and the triplet excited state identically, through an energy‐transfer mechanism based on pre‐assembly of the ground state. Thus, the presence of the intact inner wall in DWCNTs does not influence the quenching behavior, with respect to SWCNTs, for energy‐transfer quenching with excited ZnP. These results sharply contrast with previous ones referring to electron‐transfer quenching, in which the double‐wall morphology of the nanotubes has been shown to considerably reduce the lifetime of charge separation, owing to faster electron mobility in DWCNTs compared to SWCNTs. 相似文献
192.
A theoretical study of the conformational profile of two diphosphines, PH2?PH2 and PH2?PHF, is carried using second‐order Møller–Plesset perturbation theory (MP2) computational methods. The chiral minima found are used to build homo‐ and heterochiral dimers. Six minima are found for the (PH2?PH2)2 dimers and 27 for the (PH2?PHF)2 dimers. Pnicogen and hydrogen bonds, the non‐covalent forces that stabilize the complexes, are characterized by Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) methodologies. Those with several pnicogen bonds are more stable than those with hydrogen bonds. The chirodiastaltic energies amount to a total of 1.77 kJ mol?1 for the Ra:Ra versus Ra:Sa (PH2?PH2)2 dimers, 0.81 kJ mol?1 for the RSa:RSa versus RSa:SRa (PH2?PHF)2 dimers, and 2.93 kJ mol?1 for the RRa:RRa versus RRa:SSa (PH2?PHF)2 dimers. In the first and second cases, the heterochiral complex is favored whereas in the third case, the homochiral complex is favored. 相似文献
193.
Inside Cover: Quinone‐Rich Poly(dopamine) Magnetic Nanoparticles for Biosensor Applications (ChemPhysChem 17/2014) 下载免费PDF全文
194.
Susana Araceli Carrizales Álvarez Anna Ilyina Karla Monzerratt Gregorio Jáuregui José Luis Martínez Hernández Brenda Berenice Vazquez Gutiérrez Elda Patricia Segura Ceniceros Alejandro Zugasti Cruz Hened Saade Caballero Raúl Guillermo López Campos 《Applied biochemistry and biotechnology》2014,174(5):1945-1958
Avian influenza viruses preferentially bind to sialic acid alpha-2,3-galactose (N-SA-α-2,3-Gal) receptors on epithelial cells. Herein, we describe a procedure we have developed for isolation of N-SA-α-2,3-Gal receptors from porcine trachea using magnetic nanoparticles (NPs) coated with chitosan (NP-Ch) and functionalized with Maackia amurensis lectin (NP-lectin). Magnetic nanoparticles were coated with chitosan in a one-step co-precipitation, and then M. amurensis lectin was immobilized covalently using glutaraldehyde. Lectin coated nanoparticles were incubated with sialic acid enriched fraction of tracheal homogenate, and N-SA-α-2,3-Gal receptor was extracted under magnetic field in two cycles. The presence of 66.4 kDa protein was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The interaction of immobilized receptor (NP-Ch-R) with M. amurensis lectin (NP-Ch-R-L) was demonstrated by Fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA). 相似文献
195.
Juan A. Gonzlez Francisco J. Martnez Luis F. Sanz Fernando Hevia Isaas Garca de la Fuente Jos C. Cobos 《Journal of solution chemistry》2020,49(3):332-352
Densities, $$\rho$$, and kinematic viscosities, $$\nu$$, have been determined at atmospheric pressure and at 293.15–303.15 K for binary mixtures formed by methanol and one linear polyether of the type CH3–O–(CH2CH2O)n–CH3 (n = 2, 3, 4). Measurements on $$\rho$$ and $$\nu$$ were carried out, respectively, using an Anton Paar DMA 602 vibrating-tube densimeter and an Ubbelohde viscosimeter. The $$\rho$$ values were used to compute excess molar volumes, $$V_{{\text{m}}}^{{\text{E}}}$$, and, together with the $$\nu$$ results, dynamic viscosities ($$\eta$$). Deviations from linear dependence on mole fraction for viscosity, $$\Delta \eta$$, are also provided. Different semi-empirical equations have been employed to correlate viscosity data. Particularly, the equations used are the: Grunberg–Nissan, Hind, Frenkel, Katti–Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The $$V_{{\text{m}}}^{{\text{E}}}$$ values are large and negative and contrast with the positive excess molar enthalpies, $$H_{{\text{m}}}^{{\text{E}}}$$, available in the literature, for these systems. This indicates that structural effects are dominant. The $$\Delta \eta$$ results are positive and correlate well with the difference in volumes of the mixture compounds, confirming the importance of structural effects. The temperature dependences of $$\eta$$ and of the molar volume have been used to calculate enthalpies, entropies and Gibbs energies, $$\Delta G^{*}$$, of viscous flow. It is demonstrated that $$\Delta G^{*}$$ is essentially determined by enthalpic effects. Methanol + CH3–O–(CH2CH2O)n–CH3 mixtures have been treated in the framework of the ERAS model. Results for $$H_{{\text{m}}}^{{\text{E}}}$$ are acceptable, while the composition dependence of the $$V_{{\text{m}}}^{{\text{E}}}$$ curves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions. 相似文献
196.
197.
Luis K. Ono Shengzhong Liu Yabing Qi 《Angewandte Chemie (International ed. in English)》2020,59(17):6676-6698
In several photovoltaic (PV) technologies, the presence of electronic defects within the semiconductor band gap limit the efficiency, reproducibility, as well as lifetime. Metal halide perovskites (MHPs) have drawn great attention because of their excellent photovoltaic properties that can be achieved even without a very strict film‐growth control processing. Much has been done theoretically in describing the different point defects in MHPs. Herein, we discuss the experimental challenges in thoroughly characterizing the defects in MHPs such as, experimental assignment of the type of defects, defects densities, and the energy positions within the band gap induced by these defects. The second topic of this Review is passivation strategies. Based on a literature survey, the different types of defects that are important to consider and need to be minimized are examined. A complete fundamental understanding of defect nature in MHPs is needed to further improve their optoelectronic functionalities. 相似文献
198.
Uwe Schmidt Luis Werner Merle Arrowsmith Andrea Deissenberger Alexander Hermann Alexander Hofmann Stefan Ullrich James D. Mattock Alfredo Vargas Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2020,59(1):325-329
The reaction of aryl‐ and amino(dihydro)boranes with dibora[2]ferrocenophane 1 leads to the formation 1,3‐trans‐dihydrotriboranes by formal hydrogenation and insertion of a borylene unit into the B=B bond. The aryltriborane derivatives undergo reversible photoisomerization to the cis‐1,2‐μ‐H‐3‐hydrotriboranes, while hydride abstraction affords cationic triboranes, which represent the first doubly base‐stabilized B3H4+ analogues. 相似文献
199.
Luis M. Mateo Qiang Sun Shi‐Xia Liu Jesse J. Bergkamp Kristjan Eimre Carlo A. Pignedoli Pascal Ruffieux Silvio Decurtins Giovanni Bottari Roman Fasel Tomas Torres 《Angewandte Chemie (International ed. in English)》2020,59(3):1334-1339
On‐surface synthesis offers a versatile approach to prepare novel carbon‐based nanostructures that cannot be obtained by conventional solution chemistry. Graphene nanoribbons (GNRs) have potential for a variety of applications. A key issue for their application in molecular electronics is in the fine‐tuning of their electronic properties through structural modifications, such as heteroatom doping or the incorporation of non‐benzenoid rings. In this context, the covalent fusion of GNRs and porphyrins (Pors) is a highly appealing strategy. Herein we present the selective on‐surface synthesis of a Por–GNR hybrid, which consists of two Pors connected by a short GNR segment. The atomically precise structure of the Por–GNR hybrid has been characterized by bond‐resolved scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc‐AFM). The electronic properties have been investigated by scanning tunneling spectroscopy (STS), in combination with DFT calculations, which reveals a low electronic gap of 0.4 eV. 相似文献
200.
Jonathan C. Golec Eve M. Carter John W. Ward William G. Whittingham Luis Simn Robert S. Paton Darren J. Dixon 《Angewandte Chemie (International ed. in English)》2020,59(40):17417-17422
A bifunctional iminophosphorane (BIMP)‐catalysed enantioselective synthesis of α,β‐unsaturated cyclohexenones through a facially selective 1,3‐prototropic shift of β,γ‐unsaturated prochiral isomers, under mild reaction conditions and in short reaction times, on a range of structurally diverse substrates, is reported. α,β‐Unsaturated cyclohexenone products primed for downstream derivatisation were obtained in high yields (up to 99 %) and consistently high enantioselectivity (up to 99 % ee). Computational studies into the reaction mechanism and origins of enantioselectivity, including multivariate linear regression of TS energy, were carried out and the obtained data were found to be in good agreement with experimental findings. 相似文献