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511.
The precipitation magnesium oxalate dihydrate, calcium oxalate monohydrate, strontium oxalate monohydrate and barium oxalate hemihydrate was studied from equivalent solutions of concentrations from 0.001 M to 0.5 M, at pHs from 7 to 6, by optical microscopy and other methods. Crystal growth started after induction periods: the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The crystal form and numbers of the final precipitates depended on the type and number of the nuclei (and crystallites) formed during the induction periods. Crystal numbers at medium to high supersaturation, increased with increasing initial mean metal oxalate concentrations according to the relation, N = N1c; β was 5 for calcium oxalate precipitations and β was 6 for the other metal oxalate precipitations. The N1 values increased in the order MgC2O4 · 2 H2O < BaC2O4 · 1/2 H2O < SrC2O4 · H2O < CaC2O4 · H2O. The final crystal lengths, in this supersaturation range, then decreased (from maximum values) with increasing initial concentrations according to the relation, lfin = l1/CMOxβ, where γ was 1.3 to 1.6. For precipitations from solution of any concentration at any pH, smaller crystals were obtained in the precipitates of the metal oxalate of lower solubility. 相似文献
512.
Gunjan Chauhan Suvarcha Chauhan Surbhi Soni Anand Kumar Devendra Singh Negi Indra Bahadur 《中国化学会会志》2023,70(4):879-893
CoS@MorphcdtH NPs and CoS@4-MPipzcdtH NPs were synthesized by precipitation method involving three mechanisms: inclusion, occlusion, and adsorption. The synthesized NPs were characterized with the help of UV-Vis spectroscopy, FESEM-EDAX, powder x-ray diffraction, TEM, ESIMS, TG/DSC analysis. The morphology of the CoS@MorphcdtH NPs and CoS@4-MPipzcdtH NPs were hexagonal and rectangular, and the particles were in the range 7–12 nm. UV–visible spectral measurements showed surface plasmon resonance at 320 nm–340 nm with band gap of 3.65 eV–3.86 eV. The catalytically active CoSNPs called were investigated for the reduction of 4-nitrophenol (4-NP) via hydrogenation using sodium borohydride (NaBH4) as a reducing agent. Both the CoS NPs successfully reduced 4-NP to 4- aminophenol (4-AP) in a short time, catalytic performances are almost unchanged for the first five cycles. Herein, we report the preparation and characterizations of efficient active CoS NPs consisting carbodithioic acid framework as a support/capping material, along with catalytic property. 相似文献
513.
Namrata Gohain Abhik Bordoloi Amlan J. Kalita Dr. Ankur K. Guha 《Chemphyschem》2023,24(18):e202300581
We report a global planar star-like cluster B3Li3 featuring three planar tetracoordinate boron centres with a rare spin avoided σ-σ diradical character. The cluster was found to be stable towards dissociation into different fragments. The spin density was found to be localized solely on the three boron atoms in the molecular plane. This spin avoided σ-σ diradical character leads to the extension of the coordination number to yield a neutral B3Li3H3 and a cationic B3Li3H3+ cluster with three planar pentacoordinate boron centres in their global minimum structures. The planar geometry of the aninonic B3Li3H3− cluster is slightly higher in energy. The planar global clusters were found to maintain planarity in their ligand protected benzene bound complexes, B3Li3(Bz)3, B3Li3H3(Bz)3 and B3Li3H3(Bz)3+ with high ligand dissociation energies offering candidature for experimental detection. 相似文献
514.
The coprecipitations of magnesium (and barium) iron(II) and nickel oxalate dihydrates were studied from excess magnesium and barium oxalate solutions. Nucleation rates were estimated from the induction periods for the coprecipitations. The nucleation rates in excess magnesium oxalate solutions first decreased with increasing excess oxalate anion concentration to minimum values and then increased with increasing magnesium cation concentration. At low to intermediate Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were FeOx (and NiOx); at intermediate Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were probably MgOx FeOx (and MgOx NiOx) mixtures and/or solid solutions of compositions MgαFe1 αOx (and MgαNi1 αOx); at high Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were MgOx. The nucleation rates in excess barium oxalate solutions were similar to those for the precipitation of barium oxalate from supersaturated equivalent solutions. The main nuclei in most systems were BaOx. 相似文献
515.
A. Packter A. Alleem P. Chauhan S. C. Uppaladini 《Crystal Research and Technology》1981,16(12):1419-1424
The precipitation of series of alkaline-earth metal and transition hydroxides, sulphates, chromates and molybdates, hydrogen phosphate carbonates, oxalates and ‘oxinates’ were studied in aqueous solution of low to intermediate supersaturation. Heterogeneous nucleation probably occurred onto micro-crystalline particles of some siliceous mineral (of the trigonal, hexagonal or cubic system), dispersed in the solution. The heterogeneous nucleus numbers for these precipitations then depended on the rates of the heterogeneous nucleation onto these substrates and the rates of the mononuclear growth of nuclei to crystallites (during the induction periods). Generally, Nhet values in polypropylene and glass beakers, at low supersaturation, varied from 104 to 1013 dm−3: the Nhet values then increased slightly with concentration and supersaturation according to the relation Nhet = KNβ, where KN is a function of the metal salt surface energy and an ‘epitaxy’ factor; β = 0.4–0.5. In turn, at any supersaturation, log Nhet = log N + Fσ, where N and F were constants for any precipitation: Nhet values then increased from 104 to 108 times for increase in σ from 50 to 150 mJ m−2. At any supersaturation and surface energy, Nhet values increased in the order monoclinic < orthohombic < tetragonal < trigonal crystals. 相似文献