全文获取类型
收费全文 | 1363篇 |
免费 | 29篇 |
国内免费 | 4篇 |
专业分类
化学 | 906篇 |
晶体学 | 5篇 |
力学 | 21篇 |
数学 | 218篇 |
物理学 | 246篇 |
出版年
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 8篇 |
2016年 | 24篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 48篇 |
2012年 | 63篇 |
2011年 | 49篇 |
2010年 | 36篇 |
2009年 | 37篇 |
2008年 | 64篇 |
2007年 | 63篇 |
2006年 | 74篇 |
2005年 | 56篇 |
2004年 | 67篇 |
2003年 | 62篇 |
2002年 | 40篇 |
2001年 | 21篇 |
2000年 | 26篇 |
1999年 | 26篇 |
1998年 | 22篇 |
1997年 | 23篇 |
1996年 | 26篇 |
1995年 | 39篇 |
1994年 | 15篇 |
1993年 | 21篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1988年 | 11篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1974年 | 9篇 |
1973年 | 20篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1931年 | 7篇 |
排序方式: 共有1396条查询结果,搜索用时 31 毫秒
71.
Julia Rebholz Peter Bonanati Udo Weimar Nicolae Barsan 《Analytical and bioanalytical chemistry》2014,406(16):3977-3983
A model for sensing with semiconducting metal oxide (SMOX)-based gas sensors was developed which takes the effect of the shape of the grains in the sensing layers into account. Its validity is limited to materials in which the grains of the SMOX sensing layer are large enough to have an undepleted bulk region (large grains). This means that in all experimental conditions, the SMOX properties ensure that the influence of surface phenomena is not extended to the whole grain. The model takes the surface chemistry and its impact on the electrical properties of the sensing material into consideration. In this way, it relates the sensor signal—defined as the relative change of the sensor’s conductance—directly to the concentration of the target gas and also exhibits meaningful chemical parameters, such as the type of reactive oxygen species, the reaction constants, and the concentration of adsorption sites. The validity of the model is confirmed experimentally by applying it to data gathered by measuring homemade sensors in relevant conditions. 相似文献
72.
73.
Mingming Huang Dr. Jiefeng Hu Shasha Shi Dr. Alexandra Friedrich Johannes Krebs Prof. Dr. Stephen A. Westcott Prof. Dr. Udo Radius Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(24):e202200480
Defunctionalization of readily available feedstocks to provide alkenes for the synthesis of multifunctional molecules represents an extremely useful process in organic synthesis. Herein, we describe a transition metal-free, simple and efficient strategy to access alkyl 1,2-bis(boronate esters) via regio- and diastereoselective diboration of secondary and tertiary alkyl halides (Br, Cl, I), tosylates, and alcohols. Control experiments demonstrated that the key to this high reactivity and selectivity is the addition of a combination of potassium iodide and N,N-dimethylacetamide (DMA). The practicality and industrial potential of this transformation are demonstrated by its operational simplicity, wide functional group tolerance, and the late-stage modification of complex molecules. From a drug discovery perspective, this synthetic method offers control of the position of diversification and diastereoselectivity in complex ring scaffolds, which would be especially useful in a lead optimization program. 相似文献
74.
Ban G Bodek K Daum M Henneck R Heule S Kasprzak M Khomutov N Kirch K Kistryn S Knecht A Knowles P Kuźniak M Lefort T Mtchedlishvili A Naviliat-Cuncic O Plonka C Quéméner G Rebetez M Rebreyend D Roccia S Rogel G Tur M Weis A Zejma J Zsigmond G 《Physical review letters》2007,99(16):161603
In case a mirror world with a copy of our ordinary particle spectrum would exist, the neutron n and its degenerate partner, the mirror neutron n', could potentially mix and undergo nn' oscillations. The interaction of an ordinary magnetic field with the ordinary neutron would lift the degeneracy between the mirror partners, diminish the n' amplitude in the n wave function and, thus, suppress its observability. We report an experimental comparison of ultracold neutron storage in a trap with and without superimposed magnetic field. No influence of the magnetic field is found and, assuming negligible mirror magnetic fields, a limit on the oscillation time taunn' > 103 s (95% C.L.) is derived. 相似文献
75.
Comparison of Electrochemical Oxidation of Flavonols and Calculated Proton Affinity and Electron Transfer Enthalpy in Water
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Flavonols, a class of flavonoids, are present in flowers, fruits and vegetables. They are jointly responsible for antioxidant activity as free radical acceptors. The redox behaviour of myricetin, quercetin, isorhamnetin, fisetin, morin and kaempferol is investigated using cyclic and differential pulse voltammetry. Quantum chemical calculations of proton affinities and electron transfer enthalpies were performed to identify possible reactive sites and radical species to compare them with measured oxidation potentials of the flavonols. Regarding to their chemical structure, these flavonols showed an oxidation order: myricetin > quercetin > isorhamnetin > fisetin > morin > kaempferol. 相似文献
76.
C,C‐ and N,C‐Coupled Dimers of 2‐Aminotetraphenylporphyrins: Regiocontrolled Synthesis,Spectroscopic Properties,and Quantum‐Chemical Calculations
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Torsten Bruhn Dipl.‐Chem. Franziska Witterauf Dr. Daniel C. G. Götz Carina T. Grimmer Dipl.‐Chem. Max Würtemberger Prof. Dr. Udo Radius Prof. Dr. Gerhard Bringmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3998-4006
β,β′‐Bisporphyrins are intrinsically chiral porphyrin dimers with fascinating properties. The configurational stability at their axes can be directed by variation of the central metal atoms. Herein, we present a regioselective functionalization of the monomeric 2‐amino‐tetraphenyl‐porphyrin as a versatile substrate for dimerization by oxidative coupling. By simple variation of the reaction conditions (solvent and oxidant), the oxidation selectively gave either the axially chiral C,C‐coupled diaminobisporphyrin in high yields or, under Ullmann conditions, the twofold N,C‐linked achiral dimer, also in good yields. A generalized mechanism for the coupling reaction is proposed based on DFT calculations. The axially chiral β,β′‐coupled porphyrin dimers were isolated as racemic mixtures, but can be resolved by HPLC on a chiral phase. TDDFT and coupled‐cluster calculations were used to explain the spectroscopic properties of the aminoporphyrins and their dimers and to elucidate the absolute configurations of the C,C‐coupled bisporphyrins. 相似文献
77.
78.
Miriam R. B. Porzberg Laust Moesgaard Catrine Johansson Udo Oppermann Jacob Kongsted Jasmin Mecinovi 《Molecules (Basel, Switzerland)》2022,27(3)
Epigenetic readout of the combinatorial posttranslational modification comprised of trimethyllysine and asymmetric dimethylarginine (H3K4me3R8me2a) takes place via biomolecular recognition of tandem Tudor-domain-containing protein Spindlin1. Through comparative thermodynamic data and molecular dynamics simulations, we sought to explore the binding scope of asymmetric dimethylarginine mimics by Spindlin1. Herein, we provide evidence that the biomolecular recognition of H3K4me2R8me2a is not significantly affected when R8me2a is replaced by dimethylarginine analogues, implying that the binding of K4me3 provides the major binding contribution. High-energy water molecules inside both aromatic cages of the ligand binding sites contribute to the reader–histone association upon displacement by histone peptide, with the K4me3 hydration site being lower in free energy due to a flip of Trp151. 相似文献
79.
80.
M. Häser R. Ahlrichs H. P. Baron P. Weis H. Horn 《Theoretical chemistry accounts》1992,83(5-6):455-470
Summary The ab initio SCF computation of second-order properties of large molecules (with 50 atoms or more) on workstation computers is demonstrated for static dipole polarizabilities and nuclear magneting shieldings. The magnetic shieldings are calculated on the basis of gauge including atomic orbitals (GIAO). Algorithmic advances (semi-direct algorithms with efficient integral pre-screening, and use of a quadratically convergent functional for the polarizabilities) are presented together with an illustrative application to the fullerenes C60 and C70. 相似文献