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991.
992.
Simple square pulses for implementing spike‐timing‐dependent plasticity in phase‐change memory
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Phase‐change memory (PCM) is a promising candidate as an artificial synapse. A compact operation method to implement synaptic functions with low power consumption is critical for constructing large‐scale neuromorphic system. Here we propose a square spike strategy for implementing spike‐timing‐dependent plasticity (STDP) in PCM. Based on the heat accumulation effect in PCM, modulating the time intervals of pre‐ and post‐spikes results in different heat generation and dissipation conditions, which lead to various crystalline/ amorphous ratios in the phase change material layer in devices with diverse synaptic weights. Four forms of STDP learning rule are experimentally demonstrated. This study will further promote the development of PCM technology involved in neuromorphic systems. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
993.
Durgesh Nandini Mrityunjaya Asthana Kalpana Mishra R.P. Singh Radhey M. Singh 《Tetrahedron letters》2014
Base promoted and temperature dependent reactions of 3-(2,2-dibromovinyl)quinolin-2(1H)-ones have been described. At 50 °C, the cyclization reactions afforded 2-bromofuro[2,3-b]quinolines in good yields. However, at elevated temperature (80 °C) the domino reaction proceeded affording 2-alkoxyfuro[2,3-b]quinolines via cyclization and nucleophilic substitution reactions. 相似文献
994.
Marta E. Alberto Gloria Mazzone Angelo D. Quartarolo Flavio Fortes Ramos Sousa Emilia Sicilia Nino Russo 《Journal of computational chemistry》2014,35(29):2107-2113
The main photophysical properties of a series of recently synthetized 1,2‐ and 1,3‐squaraines, including absorption electronic spectra, singlet‐triplet energy gaps, and spin‐orbit matrix elements, have been investigated by means of density functional theory (DFT) and time‐dependent DFT approaches. A benchmark of three exchange‐correlation functionals has been performed in six different solvent environments. The investigated 1,2 squaraines have been found to possess two excited triplet states (T1 and T2) that lie below the energy of the excited singlet one (S1). The radiationless intersystem spin crossing efficiency is thus enhanced in both the studied systems and both the transitions could contribute to the excited singlet oxygen production. Moreover, they have a singlet‐triplet energy gap higher than that required to generate the cytotoxic singlet oxygen species. According to our data, these compounds could be used in photodynamic therapy applications that do not require high tissue penetration. © 2014 Wiley Periodicals, Inc. 相似文献
995.
[C12mim]Br: A Temperature‐dependent Phase Transfer Catalyst and Its Application for Aerobic Oxidative Synthesis of 2‐Aryl Benzimidazoles,Benzoxazoles or Benzothiozoles Catalyzed by TEMPO Based Ionic Liquid
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The application of [C12mim]Br ionic liquid/o‐xylene temperature‐dependent biphasic system into the [Imim‐TEMPO][Cl]/O2‐promoted condensation between o‐phenylenediamines, o‐aminophenol or o‐aminothiophenol with aldehydes for preparing benzimidazoles, benzoxazoles or benzothiozoles is described. Several aldehydes and o‐phenylenediamines, o‐aminophenol or o‐aminothiophenol were reacted efficiently to form corresponding products in excellent yields. Both the [Imim‐TEMPO][Cl] and [C12mim]Br could be reused at least eight times without significantly decreasing the catalytic activity. 相似文献
996.
Shoubao Gao Wei Wei Bin Zheng Yuzhi Song Qingtian Meng 《International journal of quantum chemistry》2014,114(11):748-754
The time‐dependent wavepacket method is used to study the reaction dynamics of S(3P) + HD (v = 0, 1, 2) on the adiabatic 13A″ potential energy surface constructed by Han and coworkers [J. Chem. Phys. 2012, 136, 094308]. The reaction probabilities and integral cross sections as a function of collision energy are obtained and discussed. The results calculated by using the CC and the CS approximation have been compared, which suggests that for this direct abstraction reaction, the cheaper CS approximation calculation is valid enough in the quantum calculation. The investigation also shows that the reaction probabilities and integral cross sections tend to increase with collision energy. By analyzing the v‐dependent behavior of the integral cross sections, the significant effect of the vibrational excitation of HD is found. Also found in the calculation is a significant resonance feature in the reaction probabilities versus collision energy. © 2014 Wiley Periodicals, Inc. 相似文献
997.
Jing Zhang Xiang Sheng QianQian Hou Yongjun Liu 《International journal of quantum chemistry》2014,114(6):375-382
Benzaldehyde lyase (BAL) is a versatile thiamin diphosphate (THDP)‐dependent enzyme with widespread synthetic applications in industry. Besides lyase activity, BAL also performs the functions as carboligase and decarboxylase. Unlike many other THDP‐dependent enzymes, the active center of BAL is devoid of any acid‐base amino acid residues except Glu50 and His29, and therefore, the catalytic mechanism of BAL is unusual. In this article, the dissociation mechanism of (R)‐benzoin to benzaldehyde catalyzed by BAL has been studied by using density functional theory method. The calculation results indicate that the whole reaction consists of four elementary steps, and at least two steps contribute to rate‐limiting. A big difference with other THDP‐dependent enzymes is that, in the first stage of the reaction, the ligation of substrate and THDP ylide is not companied by proton transfer, and in the subsequent transition states and intermediates, the carbonyl oxygen always exists in the form of anion. Gln113, His29, and 4′‐amino group of THDP are found to have the function to stabilize the transition states and intermediates. His29 acts as the proton acceptor in step 2 and proton donor in step 3 using one water molecule as mediator. © 2013 Wiley Periodicals, Inc. 相似文献
998.
Kazuhide Ichikawa Masahiro Fukuda Akitomo Tachibana 《International journal of quantum chemistry》2014,114(23):1567-1580
We discuss a method to follow step‐by‐step time evolution of atomic and molecular systems based on quantum electrodynamics. Our strategy includes expanding the electron field operator by localized wavepackets to define creation and annihilation operators and following the time evolution using the equations of motion of the field operator in the Heisenberg picture. We first derive a time evolution equation for the excitation operator, the product of two creation or annihilation operators, which is necessary for constructing operators of physical quantities such as the electronic charge density operator. We, then, describe our approximation methods to obtain time differential equations of the electronic density matrix, which is defined as the expectation value of the excitation operator. By solving the equations numerically, we show “electron‐positron oscillations,” the fluctuations originated from virtual electron‐positron pair creations and annihilations, appear in the charge density of a hydrogen atom and molecule. We also show that the period of the electron‐positron oscillations becomes shorter by including the self‐energy process, in which the electron emits a photon and then absorbs it again, and it can be interpreted as the increase in the electron mass due to the self‐energy. © 2014 Wiley Periodicals, Inc. 相似文献
999.
Xiqi Zhang Zhiyong Ma Yang Yang Xiaoyong Zhang Zhenguo Chi Siwei Liu Jiarui Xu Xinru Jia Yen Wei 《Tetrahedron》2014
Three 9,10-bis[(N-alkylphenothiazin-3-yl)vinyl]anthracene derivatives with different propyl, hexyl, and dodecyl side chains (AnPh3, AnPh6, and AnPh12) were synthesized and confirmed by standard spectroscopic methods. All of the compounds exhibited obvious aggregation induced emission (AIE) and piezofluorochromic (PFC) properties. The PFC behaviors were investigated and showed that proportional alkyl-length dependent relationship existed not only in the ground states of the compounds, but also in the melted states compared with the fumed states of the compounds. The PFC mechanism was explored and ascribed to the crystalline–amorphous phase transformation. More importantly, these derivatives showed reversible significant PFC properties and reproducibility in various states including fumed, ground, annealed, and melted states, making them promising stimuli-responsive and smart luminescent materials for pressure-sensors, information-recording, and light-emitting device applications. 相似文献
1000.
Properties of Sizeable [n]Cycloparaphenylenes as Molecular Models of Single‐Wall Carbon Nanotubes Elucidated by Raman Spectroscopy: Structural and Electron‐Transfer Responses under Mechanical Stress
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Miriam Peña Alvarez Paula Mayorga Burrezo Prof. Miklos Kertesz Dr. Takahiro Iwamoto Prof. Shigeru Yamago Jianlong Xia Prof. Ramesh Jasti Prof. Juan T. López Navarrete Prof. Mercedes Taravillo Prof. Valentín G. Baonza Prof. Juan Casado 《Angewandte Chemie (International ed. in English)》2014,53(27):7033-7037
[n]Cycloparaphenylenes behave as molecular templates of “perfectly chemically defined” single‐wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge‐transfer salts, or complexes with fullerene, by one‐electron concave–convex electron transfer. 相似文献