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761.
N. A. Gasviani Dzh. I. Dzhaparidze G. N. Kipiani S. G. Gasviani L. M. Abazadze 《Russian Journal of Electrochemistry》2005,41(1):44-48
To establish the effect of the nature of supporting electrolytes KCl; K, Na/Cl; K, Na, Cs/Cl; and K, Na, Ba/Cl on the electrochemical deposition of yttrium from melts, the electroreduction of yttrium fluoride in the said melts is studied by a linear voltammetry method. The discharge of ions Y3+ in all the melts occurs via one stage. The diffusion coefficients, activation energy, product of transfer coefficients and the number of electrons n
, diffusion layer thickness, diffusion constant, and rate constant of charge transfer are determined.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 48–53.Original Russian Text Copyright © 2005 by N. Gasviani, Dzhaparidze, Kipiani, S. Gasviani, Abazadze. 相似文献
762.
运用密度泛函理论(DFT), 研究了吸电子氟基和供电子羟基在取代甲苯的α-H以后, 其邻、间、对各位次进行硝化反应的速控步骤, 在B3LYP/6-311G**水平上, 计算了该速控步骤基元反应各反应驻点(反应物、过渡态和中间体)的优化几何、电子结构和能量性质, 并首次给出了目标硝化反应速控步骤的IR谱学的动态特征及解析, 从微观层面上验证了反应坐标C—N的形成和C—H的断裂是非协同的, 从而无一级动力学同位素效应的实验事实. 通过对目标硝化反应速控步骤的微观动态计算, 验证了氟基对甲基定位的影响. 氟基的电负性大, 吸电子能力强, 取代甲苯的α-H以后对硝酰阳离子的进攻有抑制作用, 活化能较取代前高, 但比较苄基氟各位次硝化活化能的相对大小得知, -CH2F仍为邻、对位定向基团. 而供电子羟基取代甲苯的α-H以后, 则对硝酰阳离子的进攻有促进作用, 因而各反应驻点络合物的稳定化能较α-H取代前甲苯的有所增大, 且邻、对位硝化的活化能较间位低, 故-CH2OH为邻、对位定位基. 但对位因硝化活化能低, 反应放热多, 空间位阻小, 为亲电试剂NO2+最有利的进攻位; 而邻位则因羟基取代甲苯α-H后多了一个氧原子, 增大了邻位进攻的空间位阻, 使得其络合物的能量比相应对位的高. 相似文献
763.
掺杂纳米SiO2的PVDF-g-PSSA质子交换膜 总被引:1,自引:0,他引:1
以聚偏氟乙烯(PVDF)为骨架, 采用溶液接枝苯乙烯磺酸, 合成了掺杂纳米SiO2颗粒的复合质子交换膜(PVDF/xSiO2-g-PSSA). 利用红外光谱、热失重分析方法、扫描电镜, 对膜的结构、热稳定性、表面及断面形态进行了表征. 考察了膜的吸水率、电导率、甲醇渗透性等性质. 结果表明, 纳米SiO2颗粒能提高膜的阻醇性能, 掺杂质量分数10%的适量SiO2颗粒所得的复合膜的甲醇渗透系数达1.0×10-7 cm2/s, 低于聚偏氟乙烯接枝苯乙烯磺酸(PVDF-g-PSSA)膜的1.7×10-7 cm2/s, 仅为Nafion-117的渗透系数的二十分之一. PVDF/10% SiO2-g-PSSA复合膜具有较高的选择性, 在直接甲醇燃料电池中具有良好的应用前景. 相似文献
764.
Hydrogen fluoride analyzer for gases and aerosols 总被引:1,自引:0,他引:1
Many fire suppression agents are currently used, and the replacement candidates for these agents contain fluorine atoms. When these agents are used to extinguish a fire, large quantities of hydrogen fluoride gas can be produced from the thermal degradation of fluorinated organic compounds. A real-time analyzer has been developed to measure exposure levels of hydrogen fluoride gas and aerosols during fire suppression tests. A vacuum pump pulls air through a continuous denuder, where the toxic gas and aerosols are extracted from the air into an aqueous trapping solution. The trapping solution then passes through a flow cell, where a fluoride ion-selective electrode measures the fluoride ion concentration. A solenoid pump moves the trapping solution and calibration standards through the analyzer. Once calibrated, the analyzer can generate a concentration profile of hydrogen fluoride versus time. This hydrogen fluoride analyzer is portable and can be calibrated in about 5 min. It provides rapid response to hydrogen fluoride gas and aerosols, over a detection range from 1 to 5000 mg/m3. 相似文献
765.
Marie-Pierre Gelin 《Journal of fluorine chemistry》2005,126(4):575-583
The radical copolymerisation in solution of vinylidene fluoride (or 1,1-difluoroethylene (VDF)) with hexafluoropropylene (HFP) initiated by di-tert-butyl peroxide is presented. A series of eight copolymerisation reactions was investigated with initial [VDF]o/[HFP]o molar ratios ranging from 5.0/95.0 to 85.2/14.8. Both co-monomers copolymerised in this range of copolymerisation. Moreover, only VDF homopolymerised in these conditions. The copolymer compositions of these random-type copolymers were calculated by means of 19F NMR spectroscopy which allowed the respective amount of each monomeric unit in the copolymer to be quantified. The Tidwell and Mortimer method led to the assessment of the reactivity ratios, ri, of both co-monomers showing a higher incorporation of VDF in the copolymer (rHFP = 0.12 ± 0.05 and rVDF = 2.9 ± 0.6 at 393 K). Alfrey-Price's Q and e values of HFP were calculated to be 0.002 (from QVDF = 0.008) or 0.009 (from QVDF = 0.015) and +1.44 (versus eVDF = 0.40) or +1.54 (versus eVDF = 0.50), respectively, indicating that HFP is an electron-accepting monomer. The thermal properties of these fluorinated copolymers were also determined. Except for those containing a high amount of VDF, they were amorphous. Each showed one glass transition temperature (Tg) only, and from known laws of Tg, that of the homopolymer of HFP was assessed. It was compared with that obtained from the literature after extrapolation and is discussed. 相似文献
766.
Hisatoshi Konishi Kazunari Tanaka Yuki Teshima Takayuki Mita Osamu Morikawa Kazuhiro Kobayashi 《Tetrahedron letters》2006,47(24):4041-4044
The nucleophilic aromatic substitution of 1,5-difluoro-2,4-dinitrobenzene with 2-propylresorcinol in Et3N/CH3CN produces a mixture of syn and anti conformers of the cyclic tetramer and the cyclic hexamer with a kinetically controlled product distribution. Moreover, the reaction in DMF was catalyzed by CsF to also produce a mixture of these cyclic oligomers. In this case, however, the C-O bond is cleaved by the fluoride ion and the cyclization reaction is reversible; therefore, in the presence of excess CsF, the thermodynamically favored product (syn-isomer of cyclic tetramer) is obtained as the major product. The structures of the two conformational isomers of cyclic tetramers were determined by X-ray crystallography. 相似文献
767.
The standard gaseous enthalpy of formation for methyl fluoride is estimated by five methods, all of which are in remarkable agreement with each other and which deviate significantly from the available experimental values. The suggested derived value is 225.4±3.2 kJ/mol. 相似文献
768.
769.
Reactions between carbon dioxide and fluorine were examined at temperatures of 303-523 K under various pressure and mixture ratios of both gases. Reactions were carried out similarly under the existence of NaF, CsF and EuF3.After the reaction, fluorine was removed and the reaction products were analyzed using FT-IR, GC/FT-IR and GC/MS. The major products were CF3OF, COF2, CF4 and CF2(OF)2.The best yield of COF2 was 11.1% under the reaction condition of CO2/F2 = 76 kPa/76 kPa with temperature of 498 K for 72 h in a direct reaction. The formation rate of COF2 in the direct reaction was estimated as 0.232 dm3 mol−1 h−1 under the reaction conditions of CO2/F2 = 76 kPa/76 kPa, at 498 K. In the presence of CsF, it was estimated as 1.88 dm3 mol−1 h−1 at CO2/F2 = 76 kPa/76 kPa at 498 K.The activation energy of the COF2 formation in the direct reaction was estimated as 45.7 kJ mol−1 at CO2/F2 = 76 kPa/76 kPa at 498 K. In addition, 24.2 and 38.9 kJ mol−1 were evaluated at CO2/F2 = 76 kPa/76 kPa at 498 K, respectively, in the presence of CsF and EuF3. 相似文献
770.
E. Wynne Evans William O. George James A. Platts 《Journal of Molecular Structure》2005,730(1-3):185-197
Theoretical calculations (DFT, MP2) are reported for up to four sets of reaction products of trimethylphosphine, (CH3)3P, each with H2O, HCl and HF together with DFT calculations on up to three sets of reaction products of substituted phosphonium cations, (CH3)3P–R+. These products comprise (a) P(III) normal complexes (CH3)3PHY, (b) P(IV) ‘reverse’ complexes Y(H–CH2)3P–R, (c) P(IV) ylidic complexes YHCH2(CH3)2P–R and (d) P(V) covalent compounds Y–P(CH3)3–R for Y=HO, Cl and F and R=H, CH3, C2H5, C2H4OH and C2H4OC:OCH3. Calculations are carried out at the B3LYP/6-31+G(d,p) level in all cases and also at the MP2/6-31+G(d,p) level for systems in which R=H. Minimum energy structures are determined for predicted complexes or structures and geometrical properties, harmonic vibrations and BSSE corrected binding energies are reported and compared with the limited experimental information available. Potential energy scans predict equilibria between covalent trigonal bipyramidal P(V) forms and reverse complexes comprising hydrogen bonded or ion pair, tetrahedral P(IV) forms separated by low potential energy barriers. Similar scans are also reported for equilibria between reverse complexes and ylidic complexes for Y=OH and R=CH3, C2H5, C2H4OH and C2H4OC:OCH3. Corrected binding energies, structures and values of harmonic modes are discussed in relation to bonding The names ‘pholine’ and ‘acetylpholine’ are suggested for phosphorus analogues to choline and acetylcholine. 相似文献