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排序方式: 共有595条查询结果,搜索用时 640 毫秒
91.
Yueqiang Cao Hao Zhang Shufang Ji Zhijun Sui Zheng Jiang Dingsheng Wang Francisco Zaera Xinggui Zhou Xuezhi Duan Yadong Li 《Angewandte Chemie (International ed. in English)》2020,59(28):11647-11652
Atomic regulation of metal catalysts has emerged as an intriguing yet challenging strategy to boost product selectivity. Here, we report a density functional theory‐guided atomic design strategy for the fabrication of a NiGa intermetallic catalyst with completely isolated Ni sites to optimize acetylene semi‐hydrogenation processes. Such Ni sites show not only preferential acetylene π‐adsorption, but also enhanced ethylene desorption. The characteristics of the Ni sites are confirmed by multiple characterization techniques, including aberration‐corrected high‐resolution scanning transmission electron microscopy and X‐ray absorption spectrometry measurements. The superior performance is also confirmed experimentally against a Ni5Ga3 intermetallic catalyst with partially isolated Ni sites and against a Ni catalyst with multi‐atomic ensemble Ni sites. Accordingly, the NiGa intermetallic catalyst with the completely isolated Ni sites shows significantly enhanced selectivity to ethylene and suppressed coke formation. 相似文献
92.
This paper describes the method of assessing the composition of the intermetallic compounds in nanoscale electrolytic deposits. The formula was developed for calculating the deflection potential in the case of selective electrooxidation electronegative component of the alloy composition. The processes of electro binary electrolytic precipitation in mercury-rhodium chloride electrolyte by anodic stripping voltammetry were studied. It was established that an electrolytic precipitate contains rhodium, mercury and rhodium IC with mercury composition Hg5Rh. 相似文献
93.
《Acta Crystallographica. Section C, Structural Chemistry》2018,74(3):295-299
A new Cu3Au‐type ternary phase (τ phase) is found in the AuPd‐rich part of the Au–In–Pd system. It has a broad homogeneity range based on extensive (Pd,Au) and (In,Au) replacement, with the composition varying between Au17.7In25.3Pd57.0 and Au50.8In16.2Pd33.0. The occupancies of the crystallographic positions were studied by single‐crystal X‐ray diffraction for three samples of different composition. The sites with mm symmetry are occupied by atoms with a smaller scattering power than the atoms located on 4/mmm sites. Two extreme structure models were refined. Within the first, the occupation type changes from (Au,In,Pd)3(Pd,In) to (Au,Pd)3(In,Pd,Au) with an increase in the Au gross content. For the second model, the occupation type (Au,In,Pd)3(Pd,Au) remains essentially unchanged for all Au concentrations. Although the diffraction data do not allow the choice of one of these models, the latter model, where Au substitutes In on 4/mmm sites, seems to be preferable, since it agrees with the fact that the homogeneity range of the τ phase is inclined to the Au corner and provides the same occupation type for all the studied samples of different compositions. 相似文献
94.
Berger RF Lee S Johnson J Nebgen B So AC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(22):6627-6639
Of the most common cubic intermetallic structure types, several (MgCu(2), Cu(5)Zn(8), Ti(2)Ni, and alpha-Mn) have superstructures with unusual symmetry properties. These superstructures (Be(5)Au, Li(21)Si(5), Sm(11)Cd(45), and Mg(44)Ir(7)) have the unusual property of pairs of perpendicular pseudo fivefold axes, most apparent in their X-ray diffraction patterns. The current work shows that an 8D to 3D projection method cleanly describes most (and in one case, all) of the atomic positions in the four superstructures mentioned above. This type of projection, which maps the E(8) lattice (a mathematically simple 8D crystal) into 3D space, combines the desired higher dimensional point group's perpendicular fivefold rotations with 3D translational symmetry-exactly what we see in the experimental crystal structures. The projection method successfully accounts for all heavy atom positions in the four superstructures, and at least 60-70 % of the light atom positions. The results suggest that all of these structures, previously known to be connected only by qualitative similarities in their atomic "clusters", are approximants of a single, as-yet unknown, class of quasicrystal. 相似文献
95.
Christoph Ziegler Stefan Klosz Lars Borchardt Stefan Kaskel Alexander Eychmüller 《Advanced functional materials》2016,26(7):1014-1020
Many different aerogel materials are known to be accessible via the controlled destabilization of the respective nanoparticle suspensions. Especially for applications in heterogeneous catalysis such materials with high specific surface areas are highly desirable. Here, a facile method to obtain a mixed ZnPd/ZnO aerogel via a reductive treatment of a preformed Pd/ZnO aerogel is presented. Different morphologies of the Pd/ZnO aerogels could be achieved by controlling the destabilization of the ZnO sol. All aerogels show a high CO2 selectivity of up to 96% and a very good activity in methanol steam reforming that delivers hydrogen, which is one of the most important fuels for future energy concepts. The method presented is promising for different transition metal/metal oxide systems and hence opens a path to a huge variety of materials. 相似文献
96.
Ordered PdCu‐Based Nanoparticles as Bifunctional Oxygen‐Reduction and Ethanol‐Oxidation Electrocatalysts
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Kezhu Jiang Pengtang Wang Prof. Shaojun Guo Dr. Xu Zhang Dr. Xuan Shen Prof. Gang Lu Dr. Dong Su Prof. Xiaoqing Huang 《Angewandte Chemie (International ed. in English)》2016,55(31):9030-9035
The development of superior non‐platinum electrocatalysts for enhancing the electrocatalytic activity and stability for the oxygen‐reduction reaction (ORR) and liquid fuel oxidation reaction is very important for the commercialization of fuel cells, but still a great challenge. Herein, we demonstrate a new colloidal chemistry technique for making structurally ordered PdCu‐based nanoparticles (NPs) with composition control from PdCu to PdCuNi and PtCuCo. Under the dual tuning on the composition and intermetallic phase, the ordered PdCuCo NPs exhibit better activity and much enhanced stability for ORR and ethanol‐oxidation reaction (EOR) than those of disordered PdCuM NPs, the commercial Pt/C and Pd/C catalysts. The density functional theory (DFT) calculations reveal that the improved ORR activity on the PdCuM NPs stems from the catalytically active hollow sites arising from the ligand effect and the compressive strain on the Pd surface owing to the smaller atomic size of Cu, Co, and Ni. 相似文献
97.
A comparative study of alloy formation processes that occur during the electrochemical intercalation of lithium from lithium chloride solutions in dimethylformamide into intermetallic compounds of magnesium with zinc (MgZn2, Mg2Zn3) and the corresponding individual metals is studied by chronopotentiometric and voltammetric methods. Lithium-containing phases are formed in all samples studied; moreover, for MgZn2 and Mg2Zn3 electrodes, the phases formed are preferentially in the Li-Zn system. The largest number of lithium-containing phases is formed in zinc. It is shown that the electrochemical behavior of intermetallic electrodes is associated with their nature, where a single alloy component plays the key role, namely, zinc for MgZn2 and magnesium for Mg2Zn3. The cathodic intercalation of lithium into MgZn2 is characterized by anomalously low polarizability as compared with the other electrodes. The lithium extraction coefficient K ex Li increases from the first to the tenth cycle for all electrode studied. The highest K ex Li are typical of Zn and the lowest are typical of Mg2Zn3. 相似文献
98.
Fokwa BP Lueken H Dronskowski R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(21):6040-6046
Single crystals of the complex boride series Sc(2)FeRu(5-n)Rh(n)B(2) (n=1, 3, 4) were synthesized by arc-melting the elements in water-cooled copper crucibles under argon atmospheres and were chemically characterized by single-crystal XRD and EDX analyses. The new compounds are isotypic and crystallize in the tetragonal space group P4/mbm with Z=2, adopting a substitutional variant of the Ti(3)Co(5)B(2)-type structure. The magnetically active iron atoms are arranged in chains with intra- and interchain distances of about 3.02 and 6.60 A, respectively. Strong ferromagnetic interactions are observed for both Sc(2)FeRuRh(4)B(2) (64 valence electrons (VE), TC approximately 350 K, mu(a)=3.1 mu(B)) and Sc(2)FeRu(2)Rh(3)B(2) (63 VE, T(C) approximately 300 K, mu(a)=3.0 mu(B)), whereas antiferromagnetic interactions are found in the case of Sc(2)FeRu(4)RhB(2) (61 VE, T(N) approximately 10 K, mu(eff)=3.2): The magnetism of the entire Sc(2)FeRu(5-n)Rh(n)B(2) (0相似文献
99.
An improved numerical method for predicting intermetallic layer thickness developed during the formation of solder joints on Cu substrates 总被引:1,自引:0,他引:1
S. Chada W. Laub R. A. Fournelle D. Shangguan 《Journal of Electronic Materials》1999,28(11):1194-1202
An improved numerical method has been developed for calculating the thickness of intermetallic layers formed between Cu substrates
and solders during the soldering process. The improved method takes into account intermetallic dissolution during heating
and intermetallic precipitation during cooling and requires as input (1) the temperature-time profile for the soldering process,
(2) the experimentally determined isothermal growth parameters for the growth of the intermetallic layer into Cu saturated
molten solder, (3) the experimentally determined Nernst-Brunner parameters for the dissolution of Cu into molten solder, (4)
the experimentally determined solubility of Cu in molten solder and (5) assumptions about the thickness of the boundary layer
in the liquid ahead of the growing intermetallic. Calculations show that the improved method predicts intermetallic growth
between Cu substrates and 96.5Sn-3.5Ag solder during reflow soldering better than a previously developed method, which did
not take into account dissolution during heating and precipitation during cooling. Calculations further show that dissolution
has a significant effect on growth, while precipitation does not. 相似文献
100.
The interaction of hydrogen with LaNi2.5Co2.4Mn0.1 was studied in a wide temperature range (308–393 K) using the technique of “calorimetric titration.” The shape of thep-C-T diagrams changes with temperature change. The values of enthalpy and entropy of hydrogenation of LaNi2.5Co2.4Mn0.1 were obtained for the first time by direct calorimetric investigations andp-C-T measurements. The volume effects of the hydrogen absorption reaction are considered, and the LaNi2.4Co2.4Mn0.1H4.9 hydride is shown to retain the CaCu5-type hexagonal structure.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 21–24, January, 1999. 相似文献