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121.
采用密度泛函理论(DFT)和ONIOM方法, 研究了H-ZSM-5分子筛上二甲苯异构化机理. 描述了中间体物种和过渡态的结构. 反应物吸附和产物脱附对二甲苯异构化的反应趋势有重要影响. 反应活化能的计算结果表明, 在H-ZSM-5分子筛延伸的孔道结构中, 异构化反应沿着生成间二甲苯的方向进行. 但是较高的脱附能使生成的间二甲苯滞留在分子筛孔道中,其进一步异构化生成对二甲苯具有动力学优势. 对二甲苯产物在分子筛孔道的酸中心上可选择性生成. 在H-ZSM-5分子筛外表面, 不受延伸孔道结构的静电限制时, 二甲苯异构化生成间二甲苯产物, 其可以很容易从活性位上脱附. 非选择性异构化降低了对二甲苯的选择性. 因此, 对H-ZSM-5分子筛外表面改性能够抑制二甲苯的非选择性异构化, 因此限制了反应在分子筛孔道中进行, 提高了对二甲苯的选择性. 二甲苯异构化相对反应速率常数的计算结果也表明, 在分子筛外表面上, 生成间二甲苯的异构化反应速率较快. 升高反应温度会降低对二甲苯的选择性. 相似文献
122.
A divergent isomerization of 5-hydroxyl-2,3-dienoate 1 catalyzed by Lewis base has been developed, the phosphine catalyst leads to 5-oxohex-2(3)-enoates 2 while DABCO catalyst affords 3-ethoxy α,β-unsaturated lactone 3. 相似文献
123.
124.
Kui Lu Guang-Zhong Tu Xiang-Feng Guo Xiao-Bin Sun Yan Liu Yu-Ping Feng Yu-Fen Zhao 《Journal of Molecular Structure》2002,610(1-3):65-72
A stable penta-coordinated serine-carboxylic-phosphoric anhydride may be synthesized at temperatures below −18 °C. Above that temperature, the product was shown to isomerize to another penta-coordinated phosphorus compound, which was proven by the change in the magnitude of observed P–C coupling constants. The mechanism for the anhydride to ester isomerization might provide a clue to the proposal of high-energy supply for biochemistry. Organic bases were shown to exert little influence on the rate of isomerization. 相似文献
125.
B.M. Choudary K.V.S. Ranganath Jagajit Yadav M. Lakshmi Kantam 《Tetrahedron letters》2005,46(8):1369-1371
The design and development of a truly nano heterogeneous catalyst for the Claisen-Schmidt condensation (CSC) of benzaldehydes with 2-hydroxyacetophenone to yield substituted chalcones followed by isomerization to afford flavanones with excellent yields and selectivity is described. 相似文献
126.
Akella Sivaramakrishna Paul Mushonga Ian L. Rogers Feng Zheng Raymond J. Haines Ebbe Nordlander John R. Moss 《Polyhedron》2008,27(7):1911-1916
An efficient and selective isomerization of 1-alkenes to their corresponding 2-alkenes is achieved by using binary metal carbonyls such as Ru3(CO)12 as catalysts. Possible mechanisms are discussed. Substituents on the 1-alkene have a significant effect on the isomerization. 相似文献
127.
N3H5异构化及构象分析 总被引:1,自引:0,他引:1
采用量子化学的方法, 对氮氢化合物N3H5所有可能的二面角变化进行松散势能面扫描, 获得了相应的能量和构象之间的关系, 研究了N3H5的异构化机理和构象的变化. 分子中的原子(AIM))理论计算得到的键临界点电荷密度的增大和减小,及其拉普拉斯值的正负变化, 可以清楚地反映构象转化过程中键的增长、断裂和新键生成的相关信息. 自然键轨道(NBO)理论分析表明, 立体排斥作用使分子能量升高, 而超共轭作用使分子能量降低, 它们对分子构象的相对稳定性起了重要作用. 相似文献
128.
Daniel Hugenbusch Marc Lehr Jan-Simon von Glasenapp Prof. Dr. Anna J. McConnell Prof. Dr. Rainer Herges 《Angewandte Chemie (International ed. in English)》2023,62(1):e202212571
We report on two regioisomeric, diazocine ligands 1 and 2 that can both be photoswitched between the E- and Z-configurations with violet and green light. The self-assembly of the four species ( 1 -Z, 1 -E, 2 -Z, 2 -E) with CoII ions was investigated upon changing the coordination vectors as a function of the ligand configuration (E vs Z) and regioisomer ( 1 vs 2 ). With 1 -Z, Co2( 1 -Z)3 was self-assembled, while a mixture of ill-defined species (oligomers) was observed with 2 -Z. Upon photoswitching with 385 nm to the E configurations, the opposite was observed with 1 -E forming oligomers and 2 -E forming Co2( 2 -E)3. Light-controlled dis/assembly was demonstrated in a ligand competition experiment with sub-stoichiometric amounts of CoII ions; alternating irradiation with violet and green light resulted in the reversible transformation between Co2( 1 -Z)3 and Co2( 2 -E)3 over multiple cycles without significant fatigue by photoswitching. 相似文献
129.
Willi Desens Marleen Winterberg Dirk Michalik Peter Langer 《Helvetica chimica acta》2016,99(5):361-372
The reaction of perfluorinated 3,5‐dioxoesters with 1,2‐diaminobenzenes or 2,3‐diaminonaphthalenes afforded two types of 1H‐benzo‐1,5‐diazepine derivatives containing a perfluorinated side chain. 2,5‐Dihydro‐1H‐benzo‐1,5‐diazepin‐2‐ones were formed by cyclocondensation via the central keto and the ester group, whereas 1H‐benzo‐1,5‐diazepines resulted from cyclocondensation via the two keto groups. The tautomerism and isomerization of these compounds have been investigated by 1H‐, 13C‐, and 19F‐NMR spectroscopy. The 1,5‐diazepines appear in CDCl3 solution as mixtures of two tautomeric forms, the enaminoimine I and diaminodiene II . In DMSO solution, besides I and II , two further species, III and IV , are formed by (E/Z) isomerization on the exocyclic C=C bond. 相似文献
130.
Túlio F. Gallatti Gustavo Von Poelhsitz Eduardo E. Castellano Márcio P. de Araujo 《Journal of organometallic chemistry》2007,692(24):5447-5452
The synthesis and characterization of trans/cis-[RuCl2(dppf)(diimines)], dppf = 1,1′-bis(diphenylphosphino)ferrocene; diimines = 2,2′-bipyridine (trans/cis-(1)), the new complexes with 4,4′-dimethyl-2,2′-bipyridine (trans/cis-(2)) and 1,10-phenanthroline (cis-(3)) are presented. The complexes were synthesized using two routes and the trans/cis-isomer formation is dependent upon conditions and the precursor applied. The trans-isomer (kinetic) readily isomerizes to the cis-isomer (thermodynamic) when exposed to light (fluorescent) and this process was followed by cyclic voltammetry and UV-vis. The electrochemical studies on these complexes reveal that Fe(III)/Fe(II) couples are insensitive to the isomer (trans/cis) formed, but the Ru(III)/Ru(II) couples are dependent on the isomer. Transfer-hydrogenation reactions for reduction of acetophenone were conducted using complexes cis-(1) and cis-(2) and the results are compared with that obtained for similar complexes. X-ray structure for cis-(3) are presented and discussed. 相似文献