全文获取类型
收费全文 | 3217篇 |
免费 | 824篇 |
国内免费 | 258篇 |
专业分类
化学 | 848篇 |
晶体学 | 27篇 |
力学 | 127篇 |
综合类 | 28篇 |
数学 | 167篇 |
物理学 | 3102篇 |
出版年
2024年 | 9篇 |
2023年 | 41篇 |
2022年 | 97篇 |
2021年 | 98篇 |
2020年 | 115篇 |
2019年 | 92篇 |
2018年 | 83篇 |
2017年 | 137篇 |
2016年 | 130篇 |
2015年 | 119篇 |
2014年 | 237篇 |
2013年 | 255篇 |
2012年 | 230篇 |
2011年 | 221篇 |
2010年 | 188篇 |
2009年 | 200篇 |
2008年 | 230篇 |
2007年 | 217篇 |
2006年 | 228篇 |
2005年 | 171篇 |
2004年 | 161篇 |
2003年 | 146篇 |
2002年 | 108篇 |
2001年 | 111篇 |
2000年 | 117篇 |
1999年 | 87篇 |
1998年 | 89篇 |
1997年 | 67篇 |
1996年 | 58篇 |
1995年 | 46篇 |
1994年 | 33篇 |
1993年 | 36篇 |
1992年 | 35篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 19篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有4299条查询结果,搜索用时 15 毫秒
91.
This work aims at elucidating the mechanism of solvation of a radical ion pair (RIP) in a micro‐heterogeneous binary solvent mixture using magnetically affected reaction yield (MARY) spectroscopy. For the exciplex‐forming 9,10‐dimethylanthracene/N,N‐dimethylaniline system a comparative, composition‐dependent MARY line‐broadening study is undertaken in a heterogeneous (toluene/dimethylsulfoxide) and a quasi‐homogenous (propyl acetate/butyronitrile) solvent mixture. The half‐saturation field extrapolated to zero‐quencher concentration, B1/2, and the self‐exchange rate constants are analyzed in the light of solvent dynamical properties of the mixtures and a dielectric continuum solvation model. The dependence of B1/2 on the solvent composition is explained by cluster formation giving rise to shortened RIP lifetimes. The results are in qualitative agreement with the continuum solvation model suggesting that it could serve as a theoretical basis for quantitative modeling. 相似文献
92.
The lowest-energy state of a macroscopic system in which symmetry is spontaneously broken, is a very stable wavepacket centered around a spontaneously chosen, classical direction in symmetry space. However, for a Heisenberg ferromagnet the quantum groundstate is exactly the classical groundstate, there are no quantum fluctuations. This coincides with seven exceptional properties of the ferromagnet, including spontaneous time-reversal symmetry breaking, a reduced number of Nambu–Goldstone modes and the absence of a thin spectrum (Anderson tower of states). Recent discoveries of other non-relativistic systems with fewer Nambu–Goldstone modes suggest these specialties apply there as well. I establish precise criteria for the absence of quantum fluctuations and all the other features. In particular, it is not sufficient that the order parameter operator commutes with the Hamiltonian. It leads to a measurably larger coherence time of superpositions in small but macroscopic systems. 相似文献
93.
94.
Fen Jin Yan Lian Jishan Li Jing Zheng Yaping Hu Jinhua Liu Jin Huang Ronghua Yang 《Analytica chimica acta》2013
A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively. 相似文献
95.
《Arabian Journal of Chemistry》2014,7(3):261-266
Effect of the micelles of anionic, cationic and non-ionic surfactants on the fluorescence quenching of 1- and 2-naphthols has been studied in the presence of copper ion. The excited state lifetime, dynamic and static quenching constants for these systems have been determined. Fluorescence quenching in water and SDS micelle is due to the collision of the fluorophore with the quencher with a small static component. The negatively charged naphtholate ions in the excited state are quenched with significantly higher rates than the neutral naphthol molecules, which are located further inside the mesophase. CTAB micelle is less effective than the SDS micelle for fluorescence quenching. The effect of CTAB on water-assisted excited-state deprotonation has been investigated in the presence of ZnSO4. For TX-100 micelle there is negligible quenching even at higher concentration of the quencher. 相似文献
96.
Dr. Somnath Dey Dr. Andreas Schönleber Prof. Dr. Sander van Smaalen Dr. Wolfgang Morgenroth Prof. Dr. Finn Krebs Larsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202104151
Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C12H30N8)]3+ ⋅ 3 NO3− is reported to undergo a disorder-order phase transition at Tc1 ≈133 K upon cooling. Temperature-dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below Tc1. The modulation wave vector varies as function of temperature and locks in at Tc3≈98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in Tc1<T<Tc3. Distinctive levels of competitions: trade-off between longer N−H⋅⋅⋅O and shorter C−H⋅⋅⋅O hydrogen bonds; steric constraints to dense C−H⋅⋅⋅O bonds give rise to pronounced modulation of the basic structure. Severely frustrated crystal packing in the incommensurate phase is precursor to optimal balance of intermolecular interactions in the lock-in phase. 相似文献
97.
Yue Ma Fengchao Cui Huazhen Rong Jian Song Xiaofei Jing Yuyang Tian Guangshan Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202113682
Continuous microporous membranes are widely studied for gas separation, due to their low energy premium and strong molecular specificity. Porous aromatic frameworks (PAFs) with their exceptional stability and structural flexibility are suited to a wide range of separations. Main-stream PAF-based membranes are usually prepared with polymeric matrices, but their discrete entities and boundary defects weaken their selectivity and permeability. The synthesis of continuous PAF membranes is still a major challenge because PAFs are insoluble. Herein, we successfully synthesized a continuous PAF membrane for gas separation. Both pore size and chemistry of the PAF membrane were modified by ion-exchange, resulting in good selectivity and permeance for the gas mixtures H2/N2 and CO2/N2. The membrane with Br? as a counter ion in the framework exhibited a H2/N2 selectivity of 72.7 with a H2 permeance of 51844 gas permeation units (GPU). When the counter ions were replaced by BF4?, the membrane showed a CO2 permeance of 23058 GPU, and an optimized CO2/N2 selectivity of 60.0. Our results show that continuous PAF membranes with modifiable pores are promising for various gas separation situations. 相似文献
98.
To date, luminescent materials have been preferably used for non-contact optical thermometers. In this manner, novel red-emitting Ba2Y0.8Eu0.2NbO6:Mn4+ (BYEN:Mn4+) phosphors were designed for multi-type non-contact luminescent thermometers based on the dual-emission states and temperature-dependent lifetime (TDL) models. In the temperature range of 303–483 K, the sensing sensitivities based on the dual-emission states of (5D0→7F2, 2Eg→4A2g) and (5D0→7F1, 2Eg→4A2g) were estimated. Especially, the maximum absolute sensing sensitivity (Sa) was found to be about 0.1558 K-1 for the BYEN:0.007Mn4+ phosphor based on the 5D0→7F1 and 2Eg→4A2g positions. This phosphor also exhibited good relative sensing sensitivity (Sr) (0.0186 K-1) based on the 5D0→7F2 and 2Eg→4A2g states. Besides, the relative sensing sensitivities (SR) at 5D0→7F1 and 2Eg→4A2g transitions were estimated to be 0.0034 and 0.0194 K-1, respectively with the help of the TDL technique. In the light of these results, novel red-emitting Ba2Y0.8Eu0.2NbO6:Mn4+ phosphors are expected to be a potentially attractive candidate for applications in multi-type luminescent thermometers. Finally, a novel unique polydimethylsiloxane film exhibiting tricolor-luminescent emissions was introduced and further suggested for high-security anti-counterfeiting. 相似文献
99.
Enhanced Static Modulated Fourier Transform Spectrometer for Fast Approximation in Field Application
We discuss the data sampling frequency, the spectral resolution, and the limit for non-aliasing in the static modulated Fourier transform spectrometer based on a modified Sagnac interferometer. The measurement was performed in a very short 4 ms, which is applicable for real time field operation. The improved spectrometer characteristics were used to investigate the spectral properties of an InGaAs light emitting diode. In addition, The measured spectral peak was shifted from 6420 cm−1 to 6365 cm−1, as the temperature increased from 25 °C to 40 °C, when the operating current is fixed to be 0.55 A. As the applied current increased from 0.30 A to 0.55 A at room temperature, the spectral width was broadened from 316 cm−1 to 384 cm−1. Compared to the conventional Fourier transform spectrometer, the measured spectral width by the static modulated Fourier transform spectrometer showed a deviation less than 10%, and the spectral peak shift according to the temperature rise showed a difference within 2%. 相似文献
100.
Jakub Jakowiecki Renata Abel Urszula Orze Pawe Pasznik Robert Preissner Sawomir Filipek 《Molecules (Basel, Switzerland)》2021,26(9)
The CB1 cannabinoid receptor (CB1R) contains one of the longest N termini among class A G protein-coupled receptors. Mutagenesis studies suggest that the allosteric binding site of cannabidiol (CBD) involves residues from the N terminal domain. In order to study the allosteric binding of CBD to CB1R we modeled the whole N-terminus of this receptor using the replica exchange molecular dynamics with solute tempering (REST2) approach. Then, the obtained structures of CB1R with the N terminus were used for ligand docking. A natural cannabinoid receptor agonist, Δ9-THC, was docked to the orthosteric site and a negative allosteric modulator, CBD, to the allosteric site positioned between extracellular ends of helices TM1 and TM2. The molecular dynamics simulations were then performed for CB1R with ligands: (i) CBD together with THC, and (ii) THC-only. Analyses of the differences in the residue-residue interaction patterns between those two cases allowed us to elucidate the allosteric network responsible for the modulation of the CB1R by CBD. In addition, we identified the changes in the orthosteric binding mode of Δ9-THC, as well as the changes in its binding energy, caused by the CBD allosteric binding. We have also found that the presence of a complete N-terminal domain is essential for a stable binding of CBD in the allosteric site of CB1R as well as for the allosteric-orthosteric coupling mechanism. 相似文献