全文获取类型
收费全文 | 2204篇 |
免费 | 144篇 |
国内免费 | 50篇 |
专业分类
化学 | 1774篇 |
晶体学 | 8篇 |
力学 | 64篇 |
综合类 | 1篇 |
数学 | 183篇 |
物理学 | 368篇 |
出版年
2023年 | 13篇 |
2022年 | 31篇 |
2021年 | 41篇 |
2020年 | 48篇 |
2019年 | 63篇 |
2018年 | 29篇 |
2017年 | 33篇 |
2016年 | 86篇 |
2015年 | 78篇 |
2014年 | 115篇 |
2013年 | 133篇 |
2012年 | 211篇 |
2011年 | 206篇 |
2010年 | 122篇 |
2009年 | 92篇 |
2008年 | 158篇 |
2007年 | 134篇 |
2006年 | 133篇 |
2005年 | 113篇 |
2004年 | 85篇 |
2003年 | 76篇 |
2002年 | 98篇 |
2001年 | 39篇 |
2000年 | 35篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 11篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2398条查询结果,搜索用时 31 毫秒
101.
Prof. Pil Seok Chae Andrew C. Kruse Dr. Kamil Gotfryd Rohini R. Rana Kyung Ho Cho Prof. Søren G. F. Rasmussen Hyoung Eun Bae Richa Chandra Prof. Ulrik Gether Prof. Lan Guan Prof. Brian K. Kobilka Prof. Claus J. Loland Dr. Bernadette Byrne Prof. Samuel H. Gellman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(46):15645-15651
Integral membrane proteins play central roles in controlling the flow of information and molecules across membranes. Our understanding of membrane protein structures and functions, however, is seriously limited, mainly due to difficulties in handling and analysing these proteins in aqueous solution. The use of a detergent or other amphipathic agents is required to overcome the intrinsic incompatibility between the large lipophilic surfaces displayed by the membrane proteins in their native forms and the polar solvent molecules. Here, we introduce new tripod amphiphiles displaying favourable behaviours toward several membrane protein systems, leading to an enhanced protein solubilisation and stabilisation compared to both conventional detergents and previously described tripod amphiphiles. 相似文献
102.
Prof. Pil Seok Chae Prof. Søren G. F. Rasmussen Rohini R. Rana Kamil Gotfryd Andrew C. Kruse Aashish Manglik Kyung Ho Cho Shailika Nurva Prof. Ulrik Gether Prof. Lan Guan Prof. Claus J. Loland Dr. Bernadette Byrne Prof. Brian K. Kobilka Prof. Samuel H. Gellman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(16):4964-4964
103.
Cotton fabrics with antibacterial properties were prepared by the treatment with 3,3′4,4′-benzophenone tetracarboxylic dianhydride (BPTCD) in a combined process of shaking immersion in dyeing machine and pad-dry-cure. Environmentally-benign choline chloride (ChCl)-based deep eutectic solvents (DESs) were mainly examined as treatment media instead of using organic solvent. The results revealed that cotton fabrics treated with BPTCD in urea-ChCl DES showed a strong ester carbonyl peak in fourier transform infrared (FTIR) analysis, indicating fixation of BPTCD on cotton cellulose. Detailed characterizations of the BPTCD-treated cotton were carried out by FTIR, thermogravimetric analysis, scanning electron microscopy, dye staining, and evaluation of hydrophilicity and strength. The treated fabrics demonstrated a high level of antibacterial characteristics before and after UV irradiation. This indicated that addition of ChCl could enhance antibacterial activity of cotton before UV irradiation. Therefore, use of ChCl-based DES along with BPTCD incorporation provided environmentally-acceptable and economically-feasible treatment process for preparation of novel antibacterial cotton. 相似文献
104.
We show how to reduce the general formulation of the mass–angular momentum–charge inequality, for axisymmetric initial data of the Einstein–Maxwell equations, to the known maximal case whenever a geometrically motivated system of equations admits a solution. It is also shown that the same reduction argument applies to the basic inequality yielding a lower bound for the area of black holes in terms of mass, angular momentum, and charge. This extends previous work by the authors (Cha and Khuri, Ann Henri Poincaré, doi: 10.1007/s00023-014-0332-6, arXiv:1401.3384, 2014), in which the role of charge was omitted. Lastly, we improve upon the hypotheses required for the mass–angular momentum–charge inequality in the maximal case. 相似文献
105.
A general and efficient P(V)–N activation method for the preparation of symmetrical and asymmetrical dinucleoside polyphosphates (NpnN′s, n=2–4) and P2,P3-CX2-dinucleoside tetraphosphates (X=H, F, and Cl) has been established. Twenty-two dinucleoside polyphosphates and their phosphonate analogs were synthesized from nucleoside 5′-phosphoropiperidates with 4,5-dicyanoimidazole as the activator in good to high yields. 相似文献
106.
Nucleophile‐Dependent Regio‐ and Stereoselective Ring Opening of 1‐Azoniabicyclo[3.1.0]hexane Tosylate
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mi‐Kyung Ji Dietmar Hertsen Doo‐Ha Yoon Heesung Eum Hannelore Goossens Prof. Dr. Michel Waroquier Prof. Dr. Veronique Van Speybroeck Prof. Dr. Matthias D'hooghe Prof. Dr. Norbert De Kimpe Prof. Dr. Hyun‐Joon Ha 《化学:亚洲杂志》2014,9(4):1060-1067
1‐[(1R)‐(1‐Phenylethyl)]‐1‐azoniabicyclo[3.1.0]hexane tosylate was generated as a stable bicyclic aziridinium salt from the corresponding 2‐(3‐hydroxypropyl)aziridine upon reaction with p‐toluenesulfonyl anhydride. This bicyclic aziridinium ion was then treated with various nucleophiles including halides, azide, acetate, and cyanide in CH3CN to afford either piperidines or pyrrolidines through regio‐ and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring‐opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways. 相似文献
107.
Kyung Joong Kim 《Surface and interface analysis : SIA》2022,54(4):405-416
Mutual calibration was suggested as a method to determine the absolute thickness of ultrathin oxide films. It was motivated from the large offset values in the reported thicknesses in the Consultative Committee for Amount of Substance (CCQM) pilot study P-38 for the thickness measurement of SiO2 films on Si(100) and Si(111) substrates in 2004. Large offset values from 0.5 to 1.0 nm were reported in the thicknesses by ellipsometry, X-ray reflectometry (XRR), medium-energy ion scattering spectrometry (MEIS), Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), and transmission electron microscopy (TEM). However, the offset value for the thicknesses by X-ray photoelectron spectroscopy (XPS) was close to zero (−0.013 nm). From these results, the mutual calibration method was reported for the thickness measurement of SiO2 films on Si(100) by combination of TEM and XPS. The mutual calibration method has been applied for the thickness measurements of hetero oxide films such as Al2O3 and HfO2. Recently, the effect of surface contamination was reported to be critical to the thickness measurement of HfO2 films by XPS. On the other hand, MEIS was proved to be a powerful zero offset method which is not affected by the surface contamination. As a result, the reference thicknesses in the CCQM pilot study P-190 for the thickness measurement of HfO2 films on Si(100) substrate were determined by mutual calibration method from the average XRR data and MEIS analysis. Conclusively, the thicknesses of ultrathin oxide films can be traceably certified by mutual calibration method and most thickness measurement methods can be calibrated from the certified thicknesses. 相似文献
108.
Growing concerns related to antibiotic residues in environmental water have encouraged the development of rapid, sensitive, and accurate analytical methods. Single-drop microextraction has been recognized as an efficient approach for the isolation and preconcentration of several analytes from a complex sample matrix. Thus, single-drop microextraction techniques are cost-effective and less harmful to the environment, subscribing to green analytical chemistry principles. Herein, an overview and the current advances in single-drop microextraction for the determination of antibiotics in environmental water are presented were included. In particular, two main approaches used to perform single-drop microextraction (direct immersion-single-drop microextraction and headspace-single-drop microextraction) are reviewed. Furthermore, the impressive analytical features and future perspectives of single-drop microextraction are discussed in this review. 相似文献
109.
Marija R. Zoric Usha Pandey Kadel Kirill A. Korvinson Hoi Ling Luk Arunpatcha Nimthong‐Roldan Matthias Zeller Ksenija D. Glusac 《Journal of Physical Organic Chemistry》2016,29(10):505-513
The conformational flexibility of three covalently linked dimers consisting of two xanthene‐based moieties connected by a diphenyl ether linker was studied using NMR spectroscopy, X‐ray crystallography, and density functional theory (DFT) calculations. The three dimers interconvert as a function of pH: the doubly cationic dimer (Xan+)2 exists in acidic solutions (pH < 0.5), the mono‐alcohol monocation Xan+–Xan‐OH at intermediate pH values (pH = 1–3), and the neutral diol at the highest pH‐values (pH > 3). Each dimer exhibits conformational degrees of freedom associated with rotations of either the xanthene moiety or of the diphenyl ether (DPE) linker. The barriers for rotation of the xanthylium moiety were evaluated using DFT calculations, yielding values of 23 kcal/mol for (Xan+)2 and 11 kcal/mol for (Xan‐OH)2, respectively. The rotational barrier for the diphenyl ether linker in Xan+–Xan‐OH (15 kcal/mol) was experimentally determined using variable temperature NMR measurements. The relative orientation of the two –OH groups in (Xan‐OH)2 diol was investigated in solution and the solid state using NMR spectroscopy and X‐ray crystallography. The conformer observed in the solid state was found to be the In–Out conformer, while free rotation of the xanthenol units is thought to occur on the NMR timescale at room temperature. These studies are relevant for the design of linkers for efficient water oxidation catalysts. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
110.
Pourbaix diagrams in weakly coupled systems: a case study involving acridinol and phenanthridinol pseudobases
下载免费PDF全文
![点击此处可从《Journal of Physical Organic Chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Renat Khatmullin Hoi Ling Luk Christopher M. Hadad Ksenija D. Glusac 《Journal of Physical Organic Chemistry》2016,29(4):204-208
The thermodynamics of proton‐coupled electron transfer (PCET) in weakly coupled organic pseudobases was investigated using 2,7‐dimethyl‐9‐hydroxy‐9‐phenyl‐10‐tolyl‐9,10‐dihydroacridine (AcrOH) and 6‐phenylphenanthridinol (PheOH) as model compounds. Pourbaix diagrams for two model compounds were constructed using the oxidation potentials and the pKa values obtained, respectively, from cyclic voltammetry and photometric titrations. Our comparative study reveals the importance of having the redox active –N center closer to –OH functionality on the thermodynamics of PCET process: PheOH exhibits a wider range of pH values (pH = 2.8 to 13.3) in which both the alcohol and the corresponding alkoxy radical are expected to coexist in solution. This result indicates that a concerted mechanism is more likely to be discovered in pseudobases analogous to PheOH. The thermochemical data also indicate that the concerted PCET mechanism cannot be achieved if water is used as the proton acceptor: assuming the pKa of hydronium ions as ?1.7, the PCET involving PheOH or AcrOH as proton/electron donors and water as the proton acceptor is expected to follow the stepwise ET/PT mechanism. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献