全文获取类型
收费全文 | 2090篇 |
免费 | 115篇 |
国内免费 | 1篇 |
专业分类
化学 | 1554篇 |
晶体学 | 7篇 |
力学 | 30篇 |
数学 | 237篇 |
物理学 | 378篇 |
出版年
2024年 | 8篇 |
2023年 | 23篇 |
2022年 | 70篇 |
2021年 | 85篇 |
2020年 | 74篇 |
2019年 | 107篇 |
2018年 | 106篇 |
2017年 | 82篇 |
2016年 | 134篇 |
2015年 | 96篇 |
2014年 | 102篇 |
2013年 | 145篇 |
2012年 | 140篇 |
2011年 | 171篇 |
2010年 | 98篇 |
2009年 | 72篇 |
2008年 | 115篇 |
2007年 | 107篇 |
2006年 | 110篇 |
2005年 | 87篇 |
2004年 | 67篇 |
2003年 | 49篇 |
2002年 | 49篇 |
2001年 | 21篇 |
2000年 | 13篇 |
1999年 | 13篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1967年 | 3篇 |
1966年 | 5篇 |
1962年 | 1篇 |
排序方式: 共有2206条查询结果,搜索用时 15 毫秒
151.
152.
Monika S. K. Fuchs Alexey M. Shor Notker Rsch 《International journal of quantum chemistry》2002,86(5):487-501
The parallel density functional program PARA GAUSS has been extended by a tool for computing solvent effects based on the conductor‐like screening model (COSMO). The molecular cavity in the solvent is constructed as a set of overlapping spheres according to the GEPOL algorithm. The cavity tessellation scheme and the resulting set of point charges on the cavity surface comply with the point group symmetry of the solute. Symmetry is exploited to reduce the computational effort of the solvent model. To allow an automatic geometry optimization including solvent effects, care has been taken to avoid discontinuities due to the discretization (weights of tesserae, number of spheres created by GEPOL). In this context, an alternative definition for the grid points representing the tesserae is introduced. In addition to the COSMO model, short‐range solvent effects are taken into account via a force field. We apply the solvent module to all‐electron scalar‐relativistic density functional calculations on uranyl, UO22+, and its aquo complexes in aqueous solution. Solvent effects on the geometry are very small. Based on the model [UO2(H2O)5]2+, the solvation energy of uranyl is estimated to be about ?400 kcal/mol, in agreement with the range of experimental data. The major part of the solvation energy, about ?250 kcal/mol, is due to a donor–acceptor interaction associated with a coordination shell of five water ligands. One can interpret this large solvation energy also as a compounded effect of an effective reduction of the uranyl moiety plus a solvent polarization. The energetic effect of the structure relaxation in the solution is only about 8 kcal/mol. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
153.
Nargiz B. Asanbaeva Larisa Yu. Gurskaya Yuliya F. Polienko Tatyana V. Rybalova Maxim S. Kazantsev Alexey A. Dmitriev Nina P. Gritsan Nadia Haro-Mares Torsten Gutmann Gerd Buntkowsky Evgeny V. Tretyakov Elena G. Bagryanskaya 《Molecules (Basel, Switzerland)》2022,27(10)
Spiro-substituted nitroxyl biradicals are widely used as reagents for dynamic nuclear polarization (DNP), which is especially important for biopolymer research. The main criterion for their applicability as polarizing agents is the value of the spin–spin exchange interaction parameter (J), which can vary considerably when different couplers are employed that link the radical moieties. This paper describes a study on biradicals, with a ferrocene-1,1′-diyl-substituted 1,3-diazetidine-2,4-diimine coupler, that have never been used before as DNP agents. We observed a substantial difference in the temperature dependence between Electron Paramagnetic Resonance (EPR) spectra of biradicals carrying either methyl or spirocyclohexane substituents and explain the difference using Density Functional Theory (DFT) calculation results. It was shown that the replacement of methyl groups by spirocycles near the N-O group leads to an increase in the contribution of conformers having J ≈ 0. The DNP gain observed for the biradicals with methyl substituents is three times higher than that for the spiro-substituted nitroxyl biradicals and is inversely proportional to the contribution of biradicals manifesting the negligible exchange interaction. The effects of nucleophiles and substituents in the nitroxide biradicals on the ring-opening reaction of 1,3-diazetidine and the influence of the ring opening on the exchange interaction were also investigated. It was found that in contrast to the methyl-substituted nitroxide biradical (where we observed the ring-opening reaction upon the addition of amines), the ring opening does not occur in the spiro-substituted biradical owing to a steric barrier created by the bulky cyclohexyl substituents. 相似文献
154.
Thermally Activated Delayed Fluorescence in a Y3N@C80 Endohedral Fullerene: Time‐Resolved Luminescence and EPR Studies 下载免费PDF全文
Dr. Michal Zalibera Denis S. Krylov Dimitrios Karagiannis Paul‐Anton Will Frank Ziegs Sandra Schiemenz Prof. Dr. Wolfgang Lubitz Prof. Dr. Sebastian Reineke Dr. Anton Savitsky Dr. Alexey A. Popov 《Angewandte Chemie (International ed. in English)》2018,57(1):277-281
The endohedral fullerene Y3N@C80 exhibits luminescence with reasonable quantum yield and extraordinary long lifetime. By variable‐temperature steady‐state and time‐resolved luminescence spectroscopy, it is demonstrated that above 60 K the Y3N@C80 exhibits thermally activated delayed fluorescence with maximum emission at 120 K and a negligible prompt fluorescence. Below 60 K, a phosphorescence with a lifetime of 192±1 ms is observed. Spin distribution and dynamics in the triplet excited state is investigated with X‐ and W‐band EPR and ENDOR spectroscopies and DFT computations. Finally, electroluminescence of the Y3N@C80/PFO film is demonstrated opening the possibility for red‐emitting fullerene‐based organic light‐emitting diodes (OLEDs). 相似文献
155.
156.
Egor I. Nagaev Ilya V. Baimler Alexey S. Baryshev Maxim E. Astashev Sergey V. Gudkov 《Molecules (Basel, Switzerland)》2022,27(19)
The influence of laser radiation of a typical surgical laser on the physicochemical properties of the Bovine Serum Albumin (BSA) protein was studied. It was established that the physicochemical characteristics of optical breakdown weakly depend on the concentration of protein molecules. At the same time, the patterns observed for an aqueous solution of BSA irradiated with a laser for different time periods were extremely similar to the classical ones. It was established that after exposure to laser radiation, the optical density of protein solutions increases. At the same time, the intensity of BSA fluorescence due to aromatic amino acid residues decreases insignificantly after exposure to laser radiation. In this case, the position of the excitation and emission maximum does not change, and the shape of the fluorescence spot on 3D maps also does not change significantly. On the Raman spectrum after exposure to laser radiation, a significant decrease in 1570 cm−1 was observed, which indicates the degradation of α-helices and, as a result, partial denaturation of BSA molecules. Partial denaturation did not significantly change the total area of protein molecules, since the refractive index of solutions did not change significantly. However, in BSA solutions, after exposure to laser radiation, the viscosity increased, and the pseudoplasticity of aqueous solutions decreased. In this case, there was no massive damage to the polypeptide chain; on the contrary, when exposed to optical breakdown, intense aggregation was observed, while aggregates with a size of 400 nm or more appeared in the solution. Thus, under the action of optical breakdown induced by laser radiation in a BSA solution, the processes of partial denaturation and aggregation prevail, aromatic amino acid residues are damaged to a lesser extent, and fragmentation of protein molecules is not observed. 相似文献
157.
Alkyne Metathesis with Silica‐Supported and Molecular Catalysts at Parts‐per‐Million Loadings 下载免费PDF全文
Deven P. Estes Martin Casey Alexey Fedorov Matthias Tamm Christophe Copéret 《Angewandte Chemie (International ed. in English)》2016,55(45):13960-13964
Improvement of the activity, stability, and chemoselectivity of alkyne‐metathesis catalysts is necessary before this promising methodology can become a routine method to construct C≡C triple bonds. Herein, we show that grafting of the known molecular catalyst [MesC≡Mo(OtBuF6)3] ( 1 , Mes=2,4,6‐trimethylphenyl, OtBuF6=hexafluoro‐tert‐butoxy) onto partially dehydroxylated silica gave a well‐defined silica‐supported active alkyne‐metathesis catalyst [(≡SiO)Mo(≡CMes)(OtBuF6)2] ( 1 /SiO2‐700). Both 1 and 1 /SiO2‐700 showed very high activity, selectivity, and stability in the self‐metathesis of a variety of carefully purified alkynes, even at parts‐per‐million catalyst loadings. Remarkably, the lower turnover frequencies observed for 1 /SiO2‐700 by comparison to 1 do not prevent the achievement of high turnover numbers. We attribute the lower reactivity of 1 /SiO2‐700 to the rigidity of the surface Mo species owing to the strong interaction of the metal site with the silica surface. 相似文献
158.
Michael Bodensteiner Ulf Vogel Dr. Alexey Y. Timoshkin Dr. Manfred Scheer Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(25):4629-4633
PAls should stick together : The cyclo‐trimer 2 is obtained by H2 elimination of Lewis acid/base‐stabilized parent compound of the phosphanylalanes 1 . The elimination is controlled by fine tuning the temperature and solvent conditions. A subsequent H2 elimination produces the ladder compound 3 . Compounds 2 and 3 are the first of a new class of Group 13/15 compounds which show no additionally donor–acceptor bonds within the framework.
159.
Al(III)- and Zr(IV)-salophens of novel structures were tested as anion-selective ionophores. It was shown that these compounds are highly selective to fluoride and give selectivity greatly deviating from classical Hofmeister pattern, when doped into the polymeric membrane of ion-selective electrode (ISE). The following selectivity sequence has been recorded for both ionophores: F− > ClO4− > SCN− > NO3− ≈ Br− ≈ Cl−. The results of potentiometric and spectrophotometric measurements allow to conclude that the nature and structure of salophen ligands influence stability of ISE working parameters. An increase in salophen ligands lipophilicity results in prolongation of the ISE lifetime, most likely due to slower ionophore decomposition caused by the hydrolysis of imine bonds in salophen structure. Ion-selective electrodes (ISEs) with the most successful Al(III)-salophen exhibited a stable, fast and near-Nernstian fluoride response and a functional lifetime near 3 weeks and selectivity coefficients with as follows: −2.8 (Y− = Br−), −2.7 (Cl−), −2.8 (NO3−), −1.5 (SCN−), −1.3 (ClO4−), which is better than for other ones based on Zr(IV)- and Al(III)-salophens and salens described to date. 相似文献
160.
Dr. Michael Bodensteiner Prof. Dr. Alexey Y. Timoshkin Dr. Eugenia V. Peresypkina Dr. Ulf Vogel Prof. Dr. Manfred Scheer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):957-963
The reaction of [{(CO)5W}PRH2] (R=H, Ph) with H3Al ? NR3 (R=Et, Me) leads to the formation of four‐membered heterocyclic compounds [({(CO)5W}P(H)AlH ? NEt3)2] and [({(CO)5W}PhPAlH ? NMe3)2]. Upon dissolving the solid compounds, fast equilibria between the isomers are observed on the NMR timescale. Further insight into the stability and reactivity of the isomers was gained by applying theoretical methods. DFT calculations predict that hydrogen elimination in the case of [({(CO)5W}PhPAlH ? NMe3)2] may be reversible. 相似文献