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991.
《Electroanalysis》2004,16(24):2082-2086
Effect of in situ complexation of some ions with variable valencies, like Co(II), Ni(II), Mn(II), Cu(II) and Pb(II) on the the electrooxidation of Vitamin C (L ‐ascorbic acid) was studied by cyclic voltammetry using carbon paste electrodes modified with p‐tert‐butylcalix[4]arene and p‐tert‐butylcalix[6]arene in perchloric acid, acetic acid and ammonium acetate media. Pb(II) was found to bind strongly with p‐tert‐butylcalix[4]arene in acetate medium, resulting in its being retained at the electrode surface and catalyzing the oxidation of ascorbic acid. The overpotential was reduced by about 200 mV with an increase in the peak currents. Linearity was observed over the range of 0.07–400 ppm with a detection limit of 30 ppb by differential pulse voltammetry. Interferences of some common substances like sugars and amino acids were studied and the modified electrode was used for the determination of vitamin C in commercial samples. 相似文献
992.
The isolation and identification of eleven crystalline components from the aerial part of Cynanchum taiwanianum Yamazaki (Asclepiadaceae) are described. Their structures were determined on the basis of spectral evidence and chemical transformation. Besides caffeic acid, β-amyrin, and methyl phaeophorbide a, the isolated flavonoid components are classified into two groups, i.e. kaempferol derivatives (kaempferol, astragalin, afzelin, trifolin) and quercetin derivatives (quercetin, isoquercitrin, quercitrin, hyperin). 相似文献
993.
3-Arylsydnone-4-carbonitrile oxides may undergo 1,3-dipolar cycloadditions with alkenes to produce the corresponding 3-aryl-4-(5-substituted-isoxazolin-3-yl)sydnones. The direct reaction of 3-arylsydone-4-carbohydroximic acid chlorides with alkenes may also give the same products, and with higher yield. 相似文献
994.
995.
Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol
(“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional
C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid. 相似文献
996.
The cloud point extraction behaviors of lanthanoids(III) (Ln(III) = La(III), Eu(III) and Lu(III)) with and without di(2-ethylhexyl)phosphoric acid (HDEHP) using Triton X-100 were investigated. It was suggested that the extraction of Ln(III) into the surfactant-rich phase without added chelating agent was caused by the impurities contained in Triton X-100. The extraction percentage more than 91% for all Ln(III) metals was obtained using 3.0 × 10−5 mol dm−3 HDEHP and 2.0% (v/v) Triton X-100. From the equilibrium analysis, it was clarified that Ln(III) was extracted as Ln(DEHP)3 into the surfactant-rich phase. The extraction constant of Ln(III) with HDEHP and 2.0% (v/v) Triton X-100 were also obtained. 相似文献
997.
The crystal of [Co(H2O)6]·(Hnip)2·(H2nip)2·(OMA)2·(H2O)8 has been cultured using direct method and characterized by X-ray single crystal diffractometry, elemental analysis and FTIR spectroscopy. It crystallizes in triclinic system, P-1 space group with the cell parameters of a=0.7012(1) nm, b=1.1378(2) nm, c=1.6612(3) nm, α= 84.92(3)°, β=85.19(3)°, γ=85.91(3)°, V= 1.3128(5) nm^3, Z=1, Dc= 1.573 g·cm^-3. Final R indices [1〉2σ(I)] are: R1 =0.0279, wR2=0.0765 while R indices for all data are: R1 =0.0327, wR2=0.0806. The Co coordination octahadra are each surrounded by two Hnip, two H2nip, two DMA and eight water molecules that are linked by hydrogen bonds and π-π stacking interactions. Thermal analyses of DSC and TG-DTG have been performed on the complex to predict its thermal decomposition mechanism and determine the most probable kinetic model function using Kissinger, Ozawa, integral and differential methods. 相似文献
998.
Ali Souldozi 《Tetrahedron letters》2007,48(9):1549-1551
The reactions of benzoic acid derivatives with (N-isocyanimino)triphenylphosphorane proceed smoothly at room temperature to afford 2-aryl-1,3,4-oxadiazoles in high yields. 相似文献
999.
B. Michalkiewicz 《Chemical Papers》2006,60(5):371-374
The reactions taking place during methane esterification in oleum were investigated. It was found that the primary products
were methyl bisulphate and formaldehyde, which was subsequently oxidized to carbon dioxide. The catalyst, Pd or PtCl4, was needed to activate methane and for its oxidation to the primary products. The formation of CO2 was not a catalytic process. It was found that the addition of either carbon dioxide or ester into the reaction mixture did
not slow down the reactions. Methane oxidation in oleum is an irreversible process, during which water is produced and subsequently
consumed to give sulphuric acid by the reaction with sulphur trioxide.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献
1000.
The hydrogenation of benzene and toluene was investigated over US-SSY, -Al2O3, and Ha1-MCM-41 supported platinum catalysts. The acidity of catalyst supports was measured by IR spectra of pyridine adsorption. On the Brönsted acid supported catalyst, both the hexacyclic saturation product and the pentacyclic one, the hydroisomerization product, were observed, and these two products were revealed to be primary reaction products. The two products were proposed to be formed competitively on Brönsted acid sites with carbonium ions as the reaction intermediate. By contrast, no hydroisomerization product was found on Lewis acid supported catalysts. It was inferred that the electron-deficient reaction intermediate formed on Lewis acids could not undertake any skeletal isomerization process to give a pentacyclic saturation product. 相似文献