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991.
Let X, Y be two Banach spaces. We say that Y is a quasi-quotient of X if there is a continuous operator R: X → Y such that its range, R(X), is dense in Y. 相似文献
992.
Steiner P Gnecco E Krok F Budzioch J Walczak L Konior J Szymonski M Meyer E 《Physical review letters》2011,106(18):186104
We report on high-resolution friction force microscopy on a stepped NaCl(001) surface in ultrahigh vacuum. The measurements were performed on single cleavage step edges. When blunt tips are used, friction is found to increase while scanning both up and down a step edge. With atomically sharp tips, friction still increases upwards, but it decreases and even changes sign downwards. Our observations extend previous results obtained without resolving atomic features and are associated with the competition between the Schw?bel barrier and the asymmetric potential well accompanying the step edges. 相似文献
993.
Melnychuk Khrystyna Marchuk Oleg Daszkiewicz Marek Gulay Lubomir 《Structural chemistry》2020,31(5):1945-1957
Structural Chemistry - The crystal structures of quaternary R3Fe0.5SnS7, R3Co0.5SnS7 and R3Ni0.5SnS7 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Ho) compounds of La3Mn0.5SiS7 structure type (space... 相似文献
994.
Dr. Olga A. Stasyuk Prof. Dr. Miquel Solà Prof. Dr. Marcel Swart Prof. Dr. Célia Fonseca Guerra Prof. Dr. Tadeusz Marek Krygowski Prof. Dr. Halina Szatylowicz 《Chemphyschem》2020,21(18):2112-2126
For many years, non-covalently bonded complexes of nucleobases have attracted considerable interest. However, there is a lack of information about the nature of hydrogen bonding between nucleobases when the bonding is affected by metal coordination to one of the nucleobases, and how the individual hydrogen bonds and aromaticity of nucleobases respond to the presence of the metal cation. Here we report a DFT computational study of nucleobase pairs interacting with alkali metal cations. The metal cations contribute to the stabilization of the base pairs to varying degrees depending on their position. The energy decomposition analysis revealed that the nature of bonding between nucleobases does not change much upon metal coordination. The effect of the cations on individual hydrogen bonds were described by changes in VDD charges on frontier atoms, H-bond length, bond energy from NBO analysis, and the delocalization index from QTAIM calculations. The aromaticity changes were determined by a HOMA index. 相似文献
995.
Aleš Marek František Tureček 《Journal of the American Society for Mass Spectrometry》2014,25(5):778-789
Gas-phase dissociations were investigated for several peptide ions containing the Gly-Leu* N-terminal motif where Leu* was a modified norleucine residue containing the photolabile diazirine ring. Collisional activation of gas-phase peptide cations resulted in facile N2 elimination that competed with backbone dissociations. A free lysine ammonium group can act as a Brønsted acid to facilitate N2 elimination. This dissociation was accompanied by insertion of a lysine proton in the side chain of the photoleucine residue, as established by deuterium labeling and gas-phase sequencing of the products. Electron structure calculations were used to provide structures and energies of reactants, intermediates, and transition states for Gly-Leu*-Gly-Gly-Lys amide ions that were combined with RRKM calculations of unimolecular rate constants. The calculations indicated that Brønsted acid-catalyzed eliminations were kinetically preferred over direct loss of N2 from the diazirine ring. Mechanisms are proposed to explain the proton-initiated reactions and discuss the reaction products. The non-catalyzed diazirine ring cleavage and N2 loss is proposed as a thermometer dissociation for peptide ion dissociations. Fig. a
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996.
Mária Chromčíková Marek Liška Tadeáš Gavenda Jan Macháček 《Journal of Thermal Analysis and Calorimetry》2014,118(2):835-840
The present contribution deals with the Raman spectra and structure of Na2O–MgO–CaO–SiO2 glasses. Six glasses with the trisilicate overall composition 15Na2O·xMgO·(10–x)CaO·75SiO2 (x = 0, 2, 4, 6, 8, 10) were studied. The structure of studied glasses was described by the thermodynamic model of Shakhmatkin and Vedishcheva. From the 27 components with the stoichiometry given by the composition of stable crystalline phases, only eight were found in significant abundance in the studied glasses—namely: SiO2, 2MgO·SiO2 (M2S), MgO·SiO2 (MS), Na2O·3CaO·6SiO2 (NC3S6), Na2O·CaO·5SiO2 (NCS5), Na2O·MgO·4SiO2 (NMS4), Na2O·SiO2 (NS), and Na2O·2SiO2 (NS2). The correlation analysis points out that the strong positive correlations between the equilibrium molar amounts of: {M2S–MS–SiO2}, {NC3S6–NCS5}, and {NMS4–NS–NS2}. From the components of significant abundance, only the content of MS and NC3S6 change significantly within the studied compositional series. These two components were identified with the result of the principal component analysis of Raman spectra that indicated the presence of two independent spectral components. Using the method of Malfait the partial Raman spectra of MS and NC3S6 components were found. The obtained results very well reproduce the experimental Raman spectra and confirmed in such way the thermodynamic model. 相似文献
997.
Toward a Consistent Interpretation of the QTAIM: Tortuous Link between Chemical Bonds,Interactions, and Bond/Line Paths 下载免费PDF全文
Dr. Cina Foroutan‐Nejad Prof. Dr. Shant Shahbazian Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):10140-10152
Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, “misinterpretations” of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM’s topological analysis of the one‐electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the “interaction” to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed “line paths” in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some “problematic” molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new “interpretation” of data is performed. 相似文献
998.
Tomasz Chmielniak Marek Sciazko Grzegorz Tomaszewicz Martyna Tomaszewicz 《Journal of Thermal Analysis and Calorimetry》2014,117(3):1479-1488
Carbon dioxide was considered as a co-gasifying agent in a coal gasification reactor. The work presented herein describes the simulation results for the process and the experimental data on coal char gasification with CO2 addition as the rate-controlling step for the entire process. To study the potentially beneficial effect of the introduction of CO2 into the gasification system, several simulations were conducted using the commercial process simulation software ChemCAD 6.3®. The results of a Gibbs equilibrium reactor were evaluated. The Boudouard reaction is a critical path for the development of this process, and the kinetics were studied experimentally. Four chars derived from the pyrolysis of Polish coals of different origins were selected for the experiments. The kinetic characteristics of this system were examined using a custom-designed pressurized fixed-bed reactor. To determine the effect of pressure on the gasification rate, several preliminary studies on the gasification of coal chars were performed isothermally at the temperature of 950 °C and pressures of 1, 10, and 20 bars. In contrast to the thermodynamic calculations, the experimental data revealed that increasing the CO2 pressure leads to a higher reaction rate for medium-rank coal chars and low-rank lignite coal char, resulting in higher efficiency for carbon monoxide production. The pressure influences the reactivity more strongly when varied from 1 to 10 bars; a further increase in pressure affects the rate almost insignificantly. The observed behavior representing the changes in carbon conversion degree during gasification is satisfactorily described by the grain model. 相似文献
999.
Patrik Pařík Josef Jansa Sylva Holešová Aleš Marek Věra Klimešová 《Journal of heterocyclic chemistry》2013,50(4):903-910
Reactivity of 2‐(4‐hydroxyphenyl)‐1H‐imidazoline and 2‐(4‐hydroxyphenyl)‐1H‐imidazole toward substituted phenyl isocyanates was studied. When mentioned imidazoline was treated with 2.5 equiv of substituted phenyl isocyanate, three N,O‐dicarboxamides were prepared (substituents are H, 4‐NO2, and 4‐CH3). Subsequently, N,O‐diacetylated 2‐(4‐hydroxyphenyl)‐1H‐imidazoline was prepared and selective deprotection method was developed for preparation of 1‐acetyl‐2‐(4‐hydroxyphenyl)‐1H‐imidazoline using diethylamine in acetone. Six carbamates derived from this imidazoline were then prepared using 1.1 equiv of substituted phenyl isocyanates (substituents are H, 4‐CH3, 4‐OCH3, 4‐NO2, 4‐CN, and 3‐CF3). Finally, two carbamates were prepared from 2‐(4‐hydroxyphenyl)‐1H‐imidazole (substituents are 4‐NO2 and 4‐CN). No reactivity to imidazole ring was observed in this case. Eight derivatives were subjected to antimycobacterial screening. Concurrently, reactivity of 2‐(2‐aminophenyl)‐ and 2‐(2‐hydroxyphenyl)‐1H‐imidazole toward aliphatic and aromatic isocyanates was studied. Eight ureas were prepared using equivalent mixture of 2‐(2‐aminophenyl)‐1H‐imidazole and isocyanate (Et, Pr, isoPr, terc‐Bu, Cy, Ph, 4‐CH3C6H4, 4‐CNC6H4). Similar attempts to obtain related carbamates from 2‐(2‐hydroxyphenyl)‐1H‐imidazole lead only to three substituted phenyl carbamates (substituents are 4‐CH3, 4‐NO2, and 4‐CN). In both cases, no reactivity to imidazole ring was observed again. 相似文献
1000.
Kristyna Pospiskova Ivo Safarik Marek Sebela Gabriela Kuncova 《Mikrochimica acta》2013,180(3-4):311-318
We have developed a fibre optic biosensor with incorporated magnetic microparticles for the determination of biogenic amines. The enzyme diamine oxidase from Pisum sativum was immobilized either on chitosan-coated magnetic microparticles or on commercial microbeads modified with a ferrofluid. Both the immobilized enzyme and the ruthenium complex were incorporated into a UV-cured inorganic–organic polymer composite and deposited on a lens that was connected, by optical fibres, to an electro-optical detector. The enzyme catalyzes the oxidation of amines under consumption of oxygen. The latter was determined by measuring the quenched fluorescence lifetime of the ruthenium complex. The limits of detection for the biogenic amines putrescine and cadaverine are 25–30 μmol?L?1, and responses are linear up to a concentration of 1 mmol L?1. Figure
Response (fluorescence lifetime) of a novel optical biosensor for biogenic amines (putrescine, cadaverine) determination based on Pisum sativum diamine oxidase immobilized on magnetically responsive chitosan microparticles with entrapped magnetite encapsulated in inorganic–organic polymer ORMOCER® together with ruthenium complex. 相似文献