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71.
Dr. Anna Pakhomova Birgit Fuchs Prof. Dr. Leonid S. Dubrovinsky Prof. Dr. Natalia Dubrovinskaia Prof. Dr. Hubert Huppertz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(19):6007-6014
Based on the results from previous high-pressure experiments on the gadolinite-type mineral datolite, CaBSiO4(OH), the behavior of the isostructural borates β-HfB2O5 and β-ZrB2O5 have been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction experiments. On compression to 120 GPa, both borate layer-structures are preserved. Additionally, at ≈114 GPa, the formation of a second phase can be observed in both compounds. The new high-pressure modification γ-ZrB2O5 features a rearrangement of the corner-sharing BO4 tetrahedra, while still maintaining the four- and eight-membered rings. The new phase γ-HfB2O5 contains ten-membered rings including the rare structural motif of edge-sharing BO4 tetrahedra with exceptionally short B−O and B⋅⋅⋅B distances. For both structures, unusually high coordination numbers are found for the transition metal cations, with ninefold coordinated Hf4+, and tenfold coordinated Zr4+, respectively. These findings remarkably show the potential of cold compression as a low-energy pathway to discover metastable structures that exhibit new coordinations and structural motifs. 相似文献
72.
Olga Kirichenko Gennadiy Kapustin Vera Nissenbaum Igor Mishin Leonid Kustov 《Journal of Thermal Analysis and Calorimetry》2014,118(2):749-758
The applications of zerovalent iron nanoparticles (nZVI) exploit their high reactivity which decreases due to oxidation in aerobic conditions during manufacture, application, and storage. In this study, we present the new procedure for estimation of the nZVI stability to oxidation in air. The procedure is suitable for characterization of the novel materials based on the supported nZVI. Nanoscale particles were synthesized inside porous silica supports by incipient wetness impregnation with the metal precursor solutions followed by thermal treatment. The TG–DTA studies revealed the decomposition temperature of the supported precursors, as well as the interaction of Fe and precious metal precursors, which resulted in the formation of alloy nanoparticles. Characterization of the samples by XRD confirmed the formation of the nanoparticles of the metallic Pd, Pt, and Fe phases supported on SiO2 carriers, as well as the formation of solid solutions based on the structure of precious metals. The new procedure for estimation of the nZVI stability included (1) TPR with hydrogen up to 400–425 °C followed by isothermal reduction at these temperatures; (2) in situ reoxidation with oxygen at room temperature. The samples were reduced “as obtained” and after in situ reoxidation. The results of the TPR studies exhibited that introduction of both Pd and Pt protected the Fe nanoparticles from oxidation with oxygen and air at ambient conditions. 相似文献
73.
Vasyl Hreb Vira Shved Oleh Buryy Olga Pekinchak Leonid Vasylechko 《无机化学与普通化学杂志》2020,646(14):1138-1143
Crystal structure parameters of the mixed cobaltite–chromite SmCo0.5Cr0.5O3 in the temperature range of 298–1173 K were derived from in situ high-resolution X-ray synchrotron powder diffraction data. Similar to the parent SmCoO3 compound, SmCo0.5Cr0.5O3 reveals anomalous thermal expansion reflected in abnormal temperature dependence of the unit cell dimensions and the selected interatomic distances and angles. These anomalies are associated with temperature induced changes of spin state of Co3+ ions and coupled insulator-metal transition. Observed decreasing behavior of the bandwidth W points on the increasing population of the exited spin states of Co3+ ions in SmCo0.5Cr0.5O3 with increasing temperature. First principle calculations revealed antiferromagnetic ground state of SmCo0.5Cr0.5O3 as the most stable. 相似文献
74.
Alexander A. Larin Dmitry M. Bystrov Leonid L. Fershtat Alexey A. Konnov Nina N. Makhova Konstantin A. Monogarov Dmitry B. Meerov Igor N. Melnikov Alla N. Pivkina Vitaly G. Kiselev Nikita V. Muravyev 《Molecules (Basel, Switzerland)》2020,25(24)
In the present work, we studied in detail the thermochemistry, thermal stability, mechanical sensitivity, and detonation performance for 20 nitro-, cyano-, and methyl derivatives of 1,2,5-oxadiazole-2-oxide (furoxan), along with their bis-derivatives. For all species studied, we also determined the reliable values of the gas-phase formation enthalpies using highly accurate multilevel procedures W2-F12 and/or W1-F12 in conjunction with the atomization energy approach and isodesmic reactions with the domain-based local pair natural orbital (DLPNO) modifications of the coupled-cluster techniques. Apart from this, we proposed reliable benchmark values of the formation enthalpies of furoxan and a number of its (azo)bis-derivatives. Additionally, we reported the previously unknown crystal structure of 3-cyano-4-nitrofuroxan. Among the monocyclic compounds, 3-nitro-4-cyclopropyl and dicyano derivatives of furoxan outperformed trinitrotoluene, a benchmark melt-cast explosive, exhibited decent thermal stability (decomposition temperature >200 °C) and insensitivity to mechanical stimuli while having notable volatility and low melting points. In turn, 4,4′-azobis-dicarbamoyl furoxan is proposed as a substitute of pentaerythritol tetranitrate, a benchmark brisant high explosive. Finally, the application prospects of 3,3′-azobis-dinitro furoxan, one of the most powerful energetic materials synthesized up to date, are limited due to the tremendously high mechanical sensitivity of this compound. Overall, the investigated derivatives of furoxan comprise multipurpose green energetic materials, including primary, secondary, melt-cast, low-sensitive explosives, and an energetic liquid. 相似文献
75.
Sebastian Vogel Maxim Bykov Elena Bykova Sebastian Wendl Simon D. Kloß Anna Pakhomova Natalia Dubrovinskaia Leonid Dubrovinsky Wolfgang Schnick 《Angewandte Chemie (International ed. in English)》2020,59(7):2730-2734
Owing to its outstanding elastic properties, the nitride spinel γ‐Si3N4 is of considered interest for materials scientists and chemists. DFT calculations suggest that Si3N4‐analog beryllium phosphorus nitride BeP2N4 adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP2N4 by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP2N4 was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP2N4 a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP2N4 is an ultraincompressible material. 相似文献
76.
Johannes Ihli Leonid Bloch Frank Krumeich Klaus Wakonig Mirko Holler Manuel Guizar‐Sicairos Thomas Weber Julio Cesar da Silva Jeroen Anton van Bokhoven 《Angewandte Chemie (International ed. in English)》2020,59(39):17266-17271
Hydrodesulphurization, the removal of sulphur from crude oils, is an essential catalytic process in the petroleum industry safeguarding the production of clean hydrocarbons. Sulphur removal is critical for the functionality of downstream processes and vital to the elimination of environmental pollutants. The effectiveness of such an endeavour is among other factors determined by the structural arrangement of the heterogeneous catalyst. Namely, the accessibility of the catalytically active molybdenum disulphide (MoS2) slabs located on the surfaces of a porous alumina carrier. Here, we examined a series of pristine sulfided Mo and NiMo hydrodesulphurization catalysts of increasing metal loading prepared on commercial alumina carriers using ptychographic X‐ray computed nanotomography. Structural analysis revealed a build consisting of two interwoven support matrix elements differing in nanoporosity. With increasing metal loading, approaching that of industrial catalysts, these matrix elements exhibit a progressively dissimilar MoS2 surface coverage as well as MoS2 cluster formation at the matrix element boundaries. This is suggestive of metal deposition limitations and/ or catalyst activation and following prohibitive of optimal catalytic utilization. These results will allow for diffusivity calculations, a better rationale of current generation catalyst performance as well as a better distribution of the active phase in next‐generation hydrodesulphurization catalysts. 相似文献
77.
Nonlinear Dynamics - The absolute nodal coordinate formulation (ANCF) is a nonlinear finite element approach proposed for the large deformation dynamics analysis of beam- and plate/shell-type... 相似文献
78.
79.
80.
Leonid Kikot Alexander Lyapunov Tatiana Bogaschenko Sergey Smola Catherine Kulygina 《合成通讯》2013,43(4):478-484
A new facile synthetic route to benzils containing fragments of 12-crown-4, 15-crown-5, and 18-crown-6 by oxidation of corresponding stilbenes was developed. The first representative of a new family of fluorescent sensors was obtained by reaction of bis(15-crown-5)benzil with o-phenylenediamine. The latter exhibits great fluorescence enhancement upon association with K+ and Rb+ compared to Na+ and Cs+. 相似文献