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991.
晶化时间对ZSM-5分子筛物化性质及催化性能的影响   总被引:4,自引:1,他引:4  
 考察了ZSM-5分子筛在晶化过程中的变化规律及其在苯与乙烯气相烷基化制乙苯反应中的催化性能.结果表明,当晶化时间为70h时,分子筛晶体开始出现;晶化90h时无定形物相基本消失.晶化时间从90h再延长至150h,ZSM-5分子筛晶粒的大小、形貌和体相硅铝比都基本不变,但分子筛表面的硅铝比逐渐降低.以晶化时间为90h的ZSM-5分子筛原粉为活性组元制备的催化剂,对苯与乙烯气相烷基化制乙苯反应表现出最佳的催化性能.  相似文献   
992.
激光促进甲醇在杂多化合物上的表面反应   总被引:1,自引:0,他引:1  
利用红外光谱 (IR)、程序升温脱附 (TPD)和激光促进表面反应 (L SSR)技术 ,研究了甲醇吸附于杂多化合物 H3PMo1 2 O40 · x H2 O、H3PW1 2 O40 · x H2 O、H6 PMo6 W6 O40 · x H2 O表面上所形成体系的振动结构、化学吸附形态和光促表面反应规律 .实验结果表明 ,在各固体材料表面上甲醇同时发生分子吸附和解离吸附 ,且在室温条件下体系即发生显著的光促表面反应 ;与甲醇吸附强度和吸附量相比 ,反应体系的振动结构对 L SSR效率起着更重要的作用 .根据表征和反应结果 ,分析了体系中活性物种的产生途径 ,并给出了反应机理的模型  相似文献   
993.
利用角分辨紫外光电子能谱对低温下(160 K)乙炔(C2H2)气体在Ru()表面的吸附 进行了研究.实验结果表明:乙炔的C-C轴并不平行于衬底表面, C-C轴在<0001>晶向和表 面法线组成的平面内有一定的倾斜.与气相乙炔分子不同,在Ru()表面吸附的乙炔分子的C-H 轴不是沿C-C轴向.  相似文献   
994.
改性ZSM-5分子筛催化甲苯、甲醇苯环烷基化反应的研究进展   总被引:14,自引:0,他引:14  
综述了近三十年来国内外有关在改性ZSM-5沸石催化剂上,甲苯、甲醇苯环烷基化制备对二甲苯反应的研究状况。经过改性的XSM-5型沸石具有合适的孔径和适当强度及数量的表面酸中心,有利于反应活性及选择性的提高。参考文献145篇。  相似文献   
995.
The structure of the conformationally flexible 2-fluoroethanal molecule (CH2FCHO, FE) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was investigated by ab initio quantum-chemical methods. The FE molecule in the S0 state was found to exist as two conformers, viz., as cis (the F—C—C—O angle is 0°) and trans (the F—C—C—O angle is 180°) conformers. On going both to the T1 and S1 states, the FE molecule undergoes substantial structural changes, in particular, the CH2F top is rotated with respect to the core and the carbonyl CCHO fragment becomes nonplanar. The potential energy surfaces for the T1 and S1 states are qualitatively similar, viz., six minima in each of the excited states of FE correspond to three pairs of mirror-symmetrical conformers. Based on the potential energy surfaces calculated for the FE molecule in the T1 and S1 states, the one-dimensional problems on the torsion and inversion nuclear motions as well as the two-dimensional torsion-inversion problems were solved.  相似文献   
996.
Inverse gas chromatography (IGC) was applied to characterize the surface energy of organically modified silicates (ormosils) by measuring the interaction of molecular organic probes with the ormosil surface. Ormosils were prepared by the sol-gel method by the reaction of TEOS (tetraethoxysilane), PDMS (polydimethylsiloxane) and different types of silica (Aerosil 130, Aerosil 200 and Aerosil 380). The isosteric heat of adsorption, q st, and the dispersive component of the surface energy, s D, were estimated by using the retention volume of different nonpolar and polar probes at infinite dilution. The dispersive component shows an increase as the specific surface area of the silica is increased from 29.6 mJ/m2 to 51.4 mJ/m2 at 60°C. Such values are lower than that obtained for aerosil particles meaning that PDMS chains impede the interaction with silanol groups located on the silica surface. The specific interaction parameter, ISP, and the enthalpy of specific adsorption, H a SP, of polar probes on the ormosil surface were also measured in order to obtain the acid-base character of ormosil surface. The H a SP, was correlated with the donor, DN, and the acceptor, AN, numbers of the probes to quantify the acidic, K A, and the basic, K B, parameters of the substrate surface. The obtained results suggest that the silica particles were covered by PDMS chains in a different way depending on the type of silica used. The values of K A and K B suggest that the ormosil surface is amphoteric, with predominantly acceptor electron sites.  相似文献   
997.
A prepared transparent HA solution was coated on Ti6Al4V substrates by a spin-coating technique. The crystallization of the sol-gel-derived HA coated on the metallic substrates could be done at relatively low firing temperatures (as low as 600°C). The characteristics of the HA-coated layer were dependent on the surface roughness of substrates and heating conditions such as firing temperature, holding time, heating rate, and atmosphere. The heat treatment at a slow heating rate (<2°C/min.) and a long heating time (>10 hrs) at 600°C in air produced the uniform surface and improved the crystallinity. The HA layer coated on 20 m grit-blasted substates was more uniform and had fever cracks after firing, compared with that coated on 100 m grit-blasted rougher substrates.  相似文献   
998.
SiO2–Al2O3 aerogels and xerogels with a Si to Al molar ratio r Si/Al varying from 0.25 to 20, were made by sol-gel process in acidic conditions at pH 2 and respectively dried by the CO2 supercritical method and by solvent evaporation. The Al precursor was also chelated with ethylacetoacetate, which made it possible to study the structure and texture of such gels in conditions favorable to the formation of mixed Al–O–Si bonds. Nitrogen adsorption isotherms according to the Brunauer, Emmett and Teller method (BET), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR), Fourier Transformed Infrared Spectroscopy (FTIR) and Infrared absorbance spectra after Temperature Programmed Desorption (TPD) of pyridine, showed that the Si–O infrared asymmetric stretching vibration and the Bronsted acidity relative to the Lewis acidity, depended on the ratio of AlIV to Si atoms.  相似文献   
999.
A procedure for pH-metric determination of the limiting adsorption of OH groups (A OH) by FeIII, ZrIV, CrIII, and InIII oxyhydroxide hydrogels from 0.1 and 1.0 M solutions of NaCl is described. Data on the molecular area occupied by a single OH group on the hydrogel surface (S OH) and the S spec values, which were calculated from A OH and S OH, are presented. The S spec value does not depend on the pH of hydrogel precipitation; the true S spec value can be determined only from sorption of the OH groups at the actual point of zero charge of the hydrogel. The A OH values for hydrogels were found to change only slightly during aging of hydrogels in electrolyte solutions.  相似文献   
1000.
Fragments of the potential energy surfaces (PES) of the systems [C3H8 + CBr3 +] and [C3H8 + Br2CBr+·Br2AlBr2 ] were simulated by the MNDO/PM3 method. Energy minima corresponding to weakly bound adducts of propane molecule with the CBr3 + cation or neutral complex CBr3 +·AlBr4 were found on the PES's of both systems. These are adducts with the coordination of a H atom of the methylene group of the propane molecule to the electrophile at the Br atom carrying the largest positive charge. As the fragments of the adducts are brought close together, the coordinated H atom migrates to the C atom of the CBr3 + fragment. The potential barriers of these migrations were found to be low for both systems. The reactions proceed without formation of cyclic intermediates or transition states typical of the Olah mechanism.  相似文献   
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