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941.
942.
Mengying Chen Dongrui Yang Shifan Wu Dr. Jiabei Zhou Prof. Dali Zhou Dr. Can Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(38):9866-9875
One-dimensional materials exhibit fascinating properties in electrocatalytic applications but their fabrication faces the challenge of tedious and complicated operations. We have developed a bottom-up strategy to construct a 1D metal carbide catalyst (Mo2C@NC) consisting of ultrafine Mo2C nanoparticles embedded within nitrogen-doped carbon layers by simply calcining a mixture of ammonium molybdate, urea and melamine. Experimental results and thermodynamic calculations demonstrate that the retainable pyrolysis-generated self-supporting atmosphere plays a crucial role in the crystalline phase and morphology of materials. When functioned as an electrocatalyst for the hydrogen evolution reaction (HER), the achieved Mo2C@NC presents an excellent catalytic activity as well as outstanding stability. This work could shed fresh light onto the facile synthesis of effective HER catalysts with 1D nanostructure. 相似文献
943.
A Two‐Component Alkyne Metathesis Catalyst System with an Improved Substrate Scope and Functional Group Tolerance: Development and Applications to Natural Product Synthesis 下载免费PDF全文
Sebastian Schaubach Dr. Konrad Gebauer Felix Ungeheuer Dr. Laura Hoffmeister Marina K. Ilg Conny Wirtz Prof. Alois Fürstner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8494-8507
Although molybdenum alkylidyne complexes such as 1 endowed with triarylsilanolate ligands are excellent catalysts for alkyne metathesis, they can encounter limitations when (multiple) protic sites are present in a given substrate and/or when forcing conditions are necessary. In such cases, a catalyst formed in situ upon mixing of the trisamidomolybenum alkylidyne complex 3 and the readily available trisilanol derivatives 8 or 11 shows significantly better performance. This two‐component system worked well for a series of model compounds comprising primary, secondary or phenolic ‐OH groups, as well as for a set of challenging (bis)propargylic substrates. Its remarkable efficiency is also evident from applications to the total syntheses of manshurolide, a highly strained sesquiterpene lactone with kinase inhibitory activity, and the structurally demanding immunosuppressive cyclodiyne ivorenolide A; in either case, the standard catalyst 1 largely failed to effect the critical macrocyclization, whereas the two‐component system was fully operative. A study directed toward the quinolizidine alkaloid lythrancepine I features yet another instructive example, in that a triyne substrate was metathesized with the help of 3 / 11 such that two of the triple bonds participated in ring closure, while the third one passed uncompromised. As a spin‐off of this project, a much improved ruthenium catalyst for the redox isomerization of propargyl alcohols to the corresponding enones was developed. 相似文献
944.
Pavel A. Dub Natalia V. Belkova Dr. Oleg A. Filippov Dr. Jean‐Claude Daran Dr. Lina M. Epstein Prof. Agustí Lledós Prof. Elena S. Shubina Prof. Rinaldo Poli Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(1):189-201
Low‐temperature (200 K) protonation of [Mo(CO)(Cp*)H(PMe3)2] ( 1 ) by Et2O ? HBF4 gives a different result depending on a subtle solvent change: The dihydrogen complex [Mo(CO)(Cp*)(η2‐H2)(PMe3)2]+ ( 2 ) is obtained in THF, whereas the tautomeric classical dihydride [Mo(CO)(Cp*)(H)2(PMe3)2]+ ( 3 ) is the only observable product in dichloromethane. Both products were fully characterised (νCO IR; 1H, 31P, 13C NMR spectroscopies) at low temperature; they lose H2 upon warming to 230 K at approximately the same rate (ca. 10?3 s?1), with no detection of the non‐classical form in CD2Cl2, to generate [Mo(CO)(Cp*)(FBF3)(PMe3)2] ( 4 ). The latter also slowly decomposes at ambient temperature. One of the decomposition products was crystallised and identified by X‐ray crystallography as [Mo(CO)(Cp*)(FH???FBF3)(PMe3)2] ( 5 ), which features a neutral HF ligand coordinated to the transition metal through the F atom and to the BF4? anion through a hydrogen bond. The reason for the switch in relative stability between 2 and 3 was probed by DFT calculations based on the B3LYP and M05‐2X functionals, with inclusion of anion and solvent effects by the conductor‐like polarisable continuum model and by explicit consideration of the solvent molecules. Calculations at the MP4(SDQ) and CCSD(T) levels were also carried out for calibration. The calculations reveal the key role of non‐covalent anion–solvent interactions, which modulate the anion–cation interaction ultimately altering the energetic balance between the two isomeric forms. 相似文献
945.
Aleix Comas‐Vives Dr. Agustí Lledós Prof. Rinaldo Poli Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(7):2147-2158
A DFT analysis of the epoxidation of C2H4 by H2O2 and MeOOH (as models of tert‐butylhydroperoxide, TBHP) catalyzed by [Cp*MoO2Cl] ( 1 ) in CHCl3 and by [Cp*MoO2(H2O)]+ in water is presented (Cp*=pentamethylcyclopentadienyl). The calculations were performed both in the gas phase and in solution with the use of the conductor‐like polarizable continuum model (CPCM). A low‐energy pathway has been identified, which starts with the activation of ROOH (R=H or Me) to form a hydro/alkylperoxido derivative, [Cp*MoO(OH)(OOR)Cl] or [Cp*MoO(OH)(OOR)]+ with barriers of 24.9 (26.5) and 28.7 (29.2) kcal mol?1 for H2O2 (MeOOH), respectively, in solution. The latter barrier, however, is reduced to only 1.0 (1.6) kcal mol?1 when one additional water molecule is explicitly included in the calculations. The hydro/alkylperoxido ligand in these intermediates is η2‐coordinated, with a significant interaction between the Mo center and the Oβ atom. The subsequent step is a nucleophilic attack of the ethylene molecule on the activated Oα atom, requiring 13.9 (17.8) and 16.1 (17.7) kcal mol?1 in solution, respectively. The corresponding transformation, catalyzed by the peroxido complex [Cp*MoO(O2)Cl] in CHCl3, requires higher barriers for both steps (ROOH activation: 34.3 (35.2) kcal mol?1; O atom transfer: 28.5 (30.3) kcal mol?1), which is attributed to both greater steric crowding and to the greater electron density on the metal atom. 相似文献
946.
A new 1D compound [(H2bpe)Mo4O13](1) (bpe=trans-1,2-Di-(4-pyridyl)-ethylen) was hydrothermally synthesized and characterized. Compound 1 comprises 3D supramolecular network constructed from 1D [Mo4O13]2- anion chains and protonated bpe layers via hydrogen bonds and π-π stacking interactions. The crystal data are the following: C12H12Mo4N2O13, Monoclinic, space group P21/n, a=0.968 64(13) nm, b=1.349 68(18) nm, c=1.514 9(2) nm, β=99.766(2)°, Z=4. The inorganic chain built up from only molybdenum oxide building blocks is interesting. The luminescent property of 1 was studied. CCDC: 739954. 相似文献
947.
948.
A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (λmax = 530 nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20 ng mL−1 with sample throughput of 15 h−1. The limit of detection was 0.5 ng mL−1 and a relative standard deviation for 10 ng mL−1 molybdenum(VI) (n = 10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs. 相似文献
949.
The title compound has been prepared as polycrystalline powder by thermal treatments of mixtures of Pr6O11 and MoO2 in air. In the literature, an oxide with a composition Pr2MoO6 has been formerly described to present interesting catalytic properties, but its true stoichiometry and crystal structure are reported here for the first time. It is cubic, isostructural with CdTm4Mo3O16 (space group Pn-3n, Z=8), with a=11.0897(1) Å. The structure contains MoO4 tetrahedral units, with Mo-O distances of 1.788(2) Å, fully long-range ordered with PrO8 polyhedra; in fact it can be considered as a superstructure of fluorite (M8O16), containing 32 MO2 fluorite formulae per unit cell, with a lattice parameter related to that of cubic fluorite (af=5.5 Å) as a≈2af. A bond valence study indicates that Mo exhibits a mixed oxidation state between 5+ and 6+ (perhaps accounting for the excellent catalytic properties). One kind of Pr atoms is trivalent whereas the second presents a mixed Pr3+-Pr4+ oxidation state. The similarity of the XRD pattern with that published for Ce2MoO6 suggests that this compound also belongs to the same structural type, with an actual stoichiometry Ce5Mo3O16. 相似文献
950.
We present theoretical study of morphology of Fe islands grown at Mo(110) surface in submonolayer MBE mode. We utilize atomistic
SOS model with bond counting, and interactions of Fe adatom up to third nearest neighbors. We performed KMC simulations for
different values of adatom interactions and varying temperatures. We have found that, while for the low temperature islands
are fat fractals, for the temperature 500 K islands have faceted rhombic-like shape. For the higher temperature, islands acquire
a rounded shape. In order to evaluate qualitatively morphological changes, we measured average aspect ratio of islands. We
calculated dependence of the average aspect ratio on the temperature, and on the strength of interactions of an adatom with
neighbors.
相似文献