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921.
High-performance liquid chromatography (HPLC) was coupled with ultraviolet absorption spectroscopy (UV) for the simultaneous separation and identification of a series of perchlorinated polycyclic aromatic hydrocarbons, such as perchlorobenzene (C6Cl6), perchloronaphthalene (C10Cl8), perchlorobiphenyl (C12Cl10), perchloroanthracene (C14Cl10), perchlorophenanthrene (C14C10), perchloroacenaphthylene (C12Cl8), perchloropyrene (C16Cl10) and perchlorofluoranthene (C16Cl10). HPLC was performed on an ODS column using methanol-hexane (80:20) as mobile phase at a flow-rate of 1.0 ml/min. UV absorption spectra of the elutes were detected in the region of 210-350 nm. 相似文献
922.
New synthetic polymeric chiral selectors were developed recently as chiral stationary phases. They were tested with supercritical fluid mobile phases made of CO2 plus an alcohol modifier and 0.2% v/v trifluoroacetic acid. The polymeric N,N′-(1S,2S)-1,2-cyclohexanediyl-bis-2-propenamide (P-CAP), the polymeric N,N′-[(1R,2R)]-1,2-diphenyl-1,2-ethanediyl] bis-2-propenamide (P-CAP-DP), the polymeric trans-9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid bis-4-vinylphenylamide (DEABV) and the polymeric N,N′-[(1R,2R)-1,2-diphenyl-1,2-ethanediyl] bis-4-vinylbenzamide (DPEVB) were bonded to 5 μm silica particles and used to prepare four columns that were tested with a set of 88 chiral compounds with a wide variety of chemical functionalities. All 88 test compounds were separated on one or more of these “related” polymeric CSPs. Forty-three enantiomeric pairs were separated in SFC conditions by only one of the CSPs. Twenty pairs were separated by two CSPs and 18 and 7 enantiomeric pairs were separated by 3 and all 4 CSPs, respectively. The three P-CAP, P-CAP-DP and DEABV CSPs have equivalent success being able to separate 49 enantiomeric pairs of the studied set with respectively 12, 14 and 20 at baseline (R s > 1.5). The DPEVB CSP was significantly less efficient separating only 18 chiral compounds with only one at baseline. The great advantage of the SFC mobile phases is the rapid separation, witch most achieved in less than 5 min. 相似文献
923.
Jian‐Hua Zhao Hsuan‐Liang Liu Hsin‐Yi Lin Chih‐Hung Huang Hsu‐Wei Fang Shau‐Wei Tsai 《中国化学会会志》2007,54(4):835-842
In this study, we present the results from the semiempirical molecular orbital calculations for the acylation step in the lipase‐catalyzed ester hydrolysis. The results reveal that the lowest energy path for the formation of the tetrahedral intermediate is for the serine residue of the catalytic triad to attack the substrate, followed by coupling heavy atom movement and proton transfer. The calculations of four active site models show that the cooperation of the aspartate group and the oxyanion hole is capable of lowering the activation energy by about 16 kcalmol?1. Our results further suggest that the lipase‐catalyzed ester hydrolysis adopts the single proton transfer mechanism. 相似文献
924.
使用密度泛函理论B3LYP方法和6-31G(d,p)、6-31+G(d,p)、6-311G(d,p)及6-311+G(d,p)基组,分别对2-C5H10+和1-C5H10+的各种构象进行了几何构型优化,并用B3LYP/6-311G(d,p)进行了频率分析计算.计算预言1-C5H10+具有非平面构型,与以往报导的从头算计算结论相反.在两个自由基阳离子的各种构象的B3LYP几何构型上,进行了B3LYP和UMP2(full)方法的超精细偶合常数计算,得到了比以往更好的结果. 相似文献
925.
Kuang Q Jiang ZY Xie ZX Lin SC Lin ZW Xie SY Huang RB Zheng LS 《Journal of the American Chemical Society》2005,127(33):11777-11784
Epitaxial growth, as a best strategy to attain a heterostructure with a well-defined and clean interface, usually takes place on a planar substrate. In this paper, using a ZnO/SnO2 core-shell heterostructure as an example, we demonstrate the possibility of establishing a three-dimensional epitaxial interface between two materials with different crystal systems for the first time and show possible tailoring optical properties by building the heteroepitaxial crystal interface. The characterization results of element mapping, high-resolution transmission electron microscopy, and selected area electric diffraction reveal that the as-prepared ZnO/SnO2 heterostructure has a tetrapod-like ZnO core and a SnO2 shell with 15-30 nm, and their special epitaxial relation is (010)SnO2//(010)ZnO and [100]SnO2//[0001]ZnO. Such three-dimensional epitaxy between the ZnO core and SnO2 shell is quite different from the usual planar epitaxy or three-dimensional epitaxy between materials having the same crystal structure. A rational model of such complicated epitaxy has been proposed through investigating the certain structural comparability between the wurtzite ZnO and rutile SnO2 crystals. The as-prepared T-ZnO/SnO2 epitaxial heterostructure exhibits unique luminescence properties in contrast with individual tetrapod ZnO and SnO2 nanostructures, in which the epitaxial interface induces new luminescence properties. This result may inspire great interest in exploring other complicated epitaxy systems and their potential applications in laser, gas sensor, solar energy conversion, photo catalysis, and nanodevices in the future. 相似文献
926.
Palladium-benzimidazolium salt catalyst systems have been studied for the Suzuki coupling. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium-imidazolium salt analogs. A practical and highly active palladium catalyst system, PdCl2/N,N′-dibenzylbenzimidazolium chloride 2, has been identified for the Suzuki coupling of aromatic halides with arylboronic acids. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl2-2 catalyst system gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01-0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs2CO3 as base with a 2 mol% palladium loading. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl2-2 system while the electronic effect from the arylboronic counterparts is negligible. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the PdCl2-2 catalyst system. 相似文献
927.
Hedstrom JA Toney MF Huang E Kim HC Volksen W Magbitang T Miller RD 《Langmuir : the ACS journal of surfaces and colloids》2004,20(5):1535-1538
Materials with nanometer size heterogeneities are commonplace in the chemical and biological sciences (e.g, polymer blends, microemulsions, gels) and often exhibit complex morphologies. Although this morphology has a dramatic effect on the materials' properties, it is often difficult to accurately characterize. We describe a method, using small-angle X-ray scattering data, of generating representative three-dimensional morphologies of isotropic two-phase materials where the morphology is disordered, and we apply this to thin films containing nanometer sized pores with a range of porosities (4-44%). These representations provide a visualization of the pore morphology, give the pore size scale and extent of interconnection, and permit the determination of the transitions from closed pore to interconnected pores to bicontinuous morphology. 相似文献
928.
Bivalent germanium was polarographically studied in sodium hydroxide solution at various concentrations. A well-defined reduction wave with half-wave potential varying from ?0.90 to ?0.98 volt vs. S.C.E. was observed for 1×10?4 M Ge(II) in concentration range of 0.2 to 2.0 F with respect to NaOH, and from ?0.70 to ?0.88 volt vs. S.C.E. in the pH range 9.0–12.1 at 25°. The value of id/C is 5.43 μα/mM and that of id/C mfor t1/8 is 5.21. Dependence of E1/2 upon pH is expressed by —E1/2 =0.18+0.058 pH. Experimental result suggests that the reaction proceeds in two-steps involving an irreversible two-electron reduction: Ge(OH)2+OH?→HGeO2?+H2O and HGeO2?+H2O+2e→Ge0+3OH?. 相似文献
929.
环状芴基张力半导体由于其特殊的分子结构,发射状排布的p轨道和纳米级空腔等诸多特点,引起了科学家广泛的关注.相对于直链型芴基半导体,环状芴基张力半导体展现出独特的光电性质.然而,迄今为止其振动性质没有被报道.对四元环芴的晶体与直链四聚芴粉末样品进行拉曼光谱表征和归一化处理,并结合理论计算.结果表明,与直链寡聚芴相比,环芴类似于碳纳米管的G峰发生了偏移,并且低频区域拉曼频移峰的峰强增加.其原因是由于张力的引入,改变了芴基主链的骨架和电子结构,加强芴骨架上π电子离域,同时使环芴中每个芴单元都参与到振动中.该研究结果为芴基张力半导体材料拉曼光谱的研究提供了一定的工作基础. 相似文献
930.
J. P. Huang 《Chemical physics letters》2004,390(4-6):380-383
Under the application of electric fields, the structure of electrorheological (ER) solids can be changed from the body-centered tetragonal lattice to other lattices. We have derived the dipole factor for the lattice by taking into account the local-field effect through the Ewald–Kornfeld formulation, and expressed it in the spectral representation exactly. It is found that when the ER solid is subject to a nonuniform ac electric field, the force acting on the microparticle can be affected by the structure transformation, and local-field effect as well as field frequency. Our results are very well understood in the spectral representation theory. 相似文献