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391.
Subramanian Sundarrajan Kalathur Sabdham Vangepuram Srinivasan 《Macromolecular rapid communications》2004,25(15):1406-1409
Summary: The effect of structural factors on polymer formation versus cyclization is reported. The reaction of sodium sulfide with either 1,4‐dibromobut‐2‐ene 1 or 1,4‐dibromobutane 2 has been carried out in presence of a phase transfer catalyst and it was observed that the former yields polymer, whereas the latter gives cyclic and linear products. Interestingly, trans/cis isomerization takes place during the polymer formation from 1 and a plausible mechanism has also been discussed.
392.
Using the Picker flow calorimeter, excess molar enthalpies H
E
have been obtained at 25°C for mixtures of 1,2-, 1,3- and 1,4-cis- and trans-dimethylcyclohexane and cis- and trans-decalin with n-hexadecane and the highly branched C16 isomer, 2,2,4,4,6,8,8-heptamethylnonane. Values of H
E
are also obtained for cis- and trans-decalin mixed with C6, C7, and C9 isomers. Anomalously low values of H
E
occur for normal alkanes mixed with cycloalkanes in the di-equatorial configuration, suggesting the presence of a negative contribution in H
E
possibly due to a restriction of n-alkane molecular motion by the flat, plate-like cycloalkane. 相似文献
393.
394.
395.
ZHANG Hui WANG Zhenhui & ZHOU Shuping College of Chemistry Environmental Science Key Laboratory of Environmental Science Engineering Education Commission of Henan Province Henan Normal University Xinxiang China 《中国科学B辑(英文版)》2005,48(3)
One of the challenging areas of electrochemistry and electroanalytical chemistry is the simultaneous determination of isomers at the same electrode. Con- ventional electrode only possesses a single function of electron transfer; therefore, it is difficult… 相似文献
396.
《中国化学会会志》2018,65(4):416-423
In this work, using the MPW1PW91 method, the substituent effect on the stability and on the 14N NQR parameters of linkage isomers of nitriles in a rhodium half‐sandwich metallacycle is illustrated. After determination of the corresponding isomerization transition state (TS), the substituent effect on the barrier energy and on the activation thermodynamic parameters (ΔG‡ and ΔH‡) of isomerization is explored. The electric field gradient tensor, nuclear quadrupole coupling constant, asymmetry parameter, and nuclear quadrupole resonance frequencies of the studied isomers are calculated. Also, linear correlations between these parameters and Hammett constant of the substituent are explored. 相似文献
397.
Adrián Schwarzenberg Héloïse Dossmann Richard B. Cole Xavier Machuron‐Mandard Jean‐Claude Tabet 《Journal of mass spectrometry : JMS》2014,49(12):1330-1337
Explosive detection and identification play an important role in the environmental and forensic sciences. However, accurate identification of isomeric compounds remains a challenging task for current analytical methods. The combination of electrospray multistage mass spectrometry (ESI‐MSn) and high resolution mass spectrometry (HRMS) is a powerful tool for the structure characterization of isomeric compounds. We show herein that resonant ion activation performed in a linear quadrupole ion trap allows the differentiation of dinitrotoluene isomers as well as aminodinitrotoluene isomers. The explosive‐related compounds: 2,4‐dinitrotoluene (2,4‐DNT), 2,6‐dinitrotoluene (2,6‐DNT), 2‐amino‐4,6‐dinitrotoluene (2A‐4,6‐DNT) and 4‐amino‐2,6‐dinitrotoluene (4A‐2,6‐DNT) were analyzed by ESI‐MS in the negative ion mode; they produced mainly deprotonated molecules [M ? H]?. Subsequent low resolution MSn experiments provided support for fragment ion assignments and determination of consecutive dissociation pathways. Resonant activation of deprotonated dinitrotoluene isomers gave different fragment ions according to the position of the nitro and amino groups on the toluene backbone. Fragment ion identification was bolstered by accurate mass measurements performed using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR/MS). Notably, unexpected results were found from accurate mass measurements performed at high resolution for 2,6‐DNT where a 30‐Da loss was observed that corresponds to CH2O departure instead of the expected isobaric NO? loss. Moreover, 2,4‐DNT showed a diagnostic fragment ion at m/z 116, allowing the unambiguous distinction between 2,4‐ and 2,6‐DNT isomers. Here, CH2O loss is hindered by the presence of an amino group in both 2A‐4,6‐DNT and 4A‐2,6‐DNT isomers, but nevertheless, these isomers showed significant differences in their fragmentation sequences, thus allowing their differentiation. DFT calculations were also performed to support experimental observations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
398.
Muhammad Nadeem Md. Shakilur Rahman Muhammad Shahid Guinyun Kim Haladhara Naik Nguyen Thi Hien 《中国物理C(英文版)》2021,45(12):124002-124002-14
The flux-weighted average cross sections of natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV. The activation and off-line γ-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory, Korea. The natCd(γ, xn) reaction cross sections as a function of photon energy were theoretically calculated using the TALYS-1.95 and the EMPIRE-3.2 Malta codes. Then, the flux-weighted average cross sections were obtained from the theoretical values of mono-energetic photons. These values were compared with the flux-weighted values from the present study and were found to be in general agreement. The measured experimental reaction cross-sections and integral yields were described for cadmium and silver isotopes in the natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions. The isomeric yield ratio (IR) of 115g,mCd in the natCd(γ, xn) reaction was determined for the two bremsstrahlung end-point energies. The measured isomeric yield ratios of 115g,mCd in the natCd(γ, xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the 116Cd(γ, n) and 116Cd(n, 2n) reactions. It was found that the IR value increases with increasing projectile energy, which demonstrates the characteristic of excitation energy. However, the higher IR value of 115g,mCd in the 116Cd(n, 2n) reaction compared to that in the 116Cd(γ, n) reaction indicates the role of compound nuclear spin alongside excitation energy. 相似文献
399.
The structures, energetics and stability of the [P, X, Y] (X?=?C, Si; Y?=?O, S) radicals are explored by means of the density functional theory and ab initio levels. Seventeen [P, X, Y] isomers and 14 interconversion transition states are obtained at the B3LYP/6-311G(d) level. At the CCSD(T)/6-311?+?G(2df)//QCISD/6-311G(d)?+?ZPVE level, the lowest-lying isomers are the linear PCO 1a (0.0?kcal/mol), PCS 1b (0.0) and the three-membered ring cPSiO 1c (0.0), cPSiS 1d (0.0) on their respective potential energy surfaces. These four isomers exhibit considerably not only thermodynamic but also kinetic stabilities. Additionally, the cyclic cPCS 2b (32.8) and linear PSiS 2d (18.6) possess also high kinetic stability. All of six isomers 1a, 1b, 2b, 1c, 1d and 2d are considerably stabilized by a barrier of at least 20?kcal/mol, and may be detected in the laboratory or interstellar space. Their valence bond structures and possible formation strategies in the laboratory and space are discussed in detail. Finally, the similarities and discrepancies on structures and stabilities between [P, X, Y] (X?=?C, Si; Y?=?O, S) isomers are compared. These predicted results are highly expected to be informative for the future identification of [P, X, Y] (X?=?C, Si; Y?=?O, S) in the laboratory and space. 相似文献
400.
Abstract Both X-ray diffraction and the Mössbauer effect have been used to study the double rare-earth oxide solid solutions (REu)O3 (R = Pr, Nd, Sm), which were synthesized with a combination of high pressure and high temperature for the first time. It is shown that all products are of the B-type (monoclinic) structures of single phase. The hyperfine interactions depend strongly on the ligand volume of Eu ions. 相似文献