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排序方式: 共有476条查询结果,搜索用时 31 毫秒
471.
A new and highly efficient methodology for the construction of synthetically important highly O-functionalized enantiopure 2,3,4-trisubstituted tetrahydrofurans with three contiguous stereocenters is reported. 相似文献
472.
Ma Q Chakraborty D Faglioni F Muller RP Goddard WA Harris T Campbell C Tang Y 《The journal of physical chemistry. A》2006,110(6):2246-2252
The current work utilizes the ab initio density functional theory (DFT) to develop a molecular level of the mechanistic understanding on the phenol alkylation in the presence of a cation-exchange resin catalyst, Amberlyst-15. The catalyst is modeled with the benzene sulfonic acid, and the effect of this acid on olefins such as isopropene (i-Pr) and tributene (t-Bu) in a phenol solution mimics the experimental condition. A neutral-pathway mechanism is established to account for early-stage high concentration of the phenolic ether observed in experiments. The mechanism involves an exothermic reaction between olefin and the benzene sulfonic acid to form ester followed by three reaction pathways leading to direct O-alkylation, o-C-alkylation, and p-C-alkylation. Our calculations conclude that O-alkylation to form the phenolic ether is the most energetically favorable in the neutral condition. An ionic rearrangement mechanism describes intramolecular migrations of the alkyl group from the phenolic ether to form C-alkylphenols, while the positively charged protonation significantly lowers transition barriers for these migrations. The ionic rearrangement mechanism accounts for high yields of o-C-alkylphenol and p-C-alkylphenol. Competition between the H atom and the alkyl R group at the substitutive site of the protonated ortho configuration is found to be the determining factor to the ortho/para ratio of C-alkylation products. 相似文献
473.
S. Acharya S. Sutradhar J. Mandal K. Mukhopadhyay A.K. Deb P.K. Chakrabarti 《Journal of magnetism and magnetic materials》2012
Nanocrystalline BiFeO3 and rare earth ion doped BiFeO3 (Bi0.9R0.1FeO3, R=Er and Tm) were prepared by sol–gel method. Rietveld analysis of the X-ray diffractograms of the samples revealed that small amount of impurity phase of Bi2Fe4O9 was formed together with the desired phase. In the thermal variation of magnetic mass susceptibility (χm) of the samples, one sharp transition below TM (TM∼100 K, 50 K and 30 K for BiFeO3, Bi0.9Er0.1FeO3 and Bi0.9Tm0.1FeO3, respectively) was observed, which clearly hint the change of the domination of the ferromagnetic exchange interaction over the usual antiferromagnetic exchange interaction. Also, static magnetization (M) and susceptibility of each doped sample have been drastically enhanced compared to that of BiFeO3. The values of χm and M measured at different temperatures confirmed that the magnetic behavior of the doped systems has been dominated by the paramagnetic/ferromagnetic clusters below ∼TM. Another phase transition were observed in the χm vs. T curve of the samples at relatively higher temperature TB (∼260 K for BiFeO3, ∼220 K for Bi0.9Er0.1FeO3 and ∼180 K for Bi0.9Tm0.1FeO3), which may be attributed to the charge ordering transition. Ferroelectric hysteresis loops of the samples observed at 100 Hz confirmed the presence of ferroelectric ordering of the samples. Measured values of dielectric constants at 1 kHz of each sample in presence and absence of magnetic field confirmed a substantial magnetoelectric coupling of all the samples. 相似文献
474.
Katharigatta N. Venugopala Pottathil Shinu Christophe Tratrat Pran Kishore Deb Raquel M. Gleiser Sandeep Chandrashekharappa Deepak Chopra Mahesh Attimarad Anroop B. Nair Nagaraja Sreeharsha Fawzi M. Mahomoodally Michelyne Haroun Mahmoud Kandeel Syed Mohammed Basheeruddin Asdaq Viresh Mohanlall Nizar A. Al-Shari Mohamed A. Morsy 《Molecules (Basel, Switzerland)》2022,27(9)
Alteration of insect growth regulators by the action of inhibitors is becoming an attractive strategy to combat disease-transmitting insects. In the present study, we investigated the larvicidal effect of 1,2,3-triazolyl-pyrimidinone derivatives against the larvae of the mosquito Anopheles arabiensis, a vector of malaria. All compounds demonstrated insecticidal activity against mosquito larvae in a dose-dependent fashion. A preliminary study of the structure–activity relationship indicated that the electron-withdrawing substituent in the para position of the 4-phenyl-pyrimidinone moiety enhanced the molecules’ potency. A docking study of these derivatives revealed favorable binding affinity for the sterol carrier protein-2 receptor, a protein present in the intestine of the mosquito larvae. Being effective insecticides against the malaria-transmitting Anopheles arabiensis, 1,2,3-triazole-based pyrimidinones represent a starting point to develop novel inhibitors of insect growth regulators. 相似文献
475.
Mohammed F. Arshad Aftab Alam Abdullah Ayed Alshammari Mohammed Bader Alhazza Ibrahim Mohammed Alzimam Md Anish Alam Gulam Mustafa Md Salahuddin Ansari Abdulelah M. Alotaibi Abdullah A. Alotaibi Suresh Kumar Syed Mohammed Basheeruddin Asdaq Mohd. Imran Pran Kishore Deb Katharigatta N. Venugopala Shahamah Jomah 《Molecules (Basel, Switzerland)》2022,27(13)
476.
In this work, the anion-responsive conduct of a Ru(II)-bipyridine complex incorporating pyrazolyl-bis (benzimidazole) ligand is thoroughly investigated in acetonitrile and water via absorption and emission spectroscopy as well as by square-wave voltammetry (SWV). Substantial alteration of the photo-redox behavior of the complex is observed in the presence of the selected anions. The free form of the complex exhibits emission indicating the “on-state”, while inclusion of anions leads to quenching of emission and represents the “off-state”. The restoration of the initial state of the complex is feasible in the presence of acid and the process is reversible and can be recycled. In essence, the complex functions as anion- and acid-responsive molecular switches. Additionally, we applied herein neural network based deep learning methodologies, viz. Artificial Neural Networks (ANNs) and Adaptive Neuro-Fuzzy Inference System (ANFIS)} for thorough analysis and fully understand the multi-channel anion sensing behavior of the complex. 相似文献