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101.
Mangles SP Thomas AG Kaluza MC Lundh O Lindau F Persson A Tsung FS Najmudin Z Mori WB Wahlström CG Krushelnick K 《Physical review letters》2006,96(21):215001
Beam profile measurements of laser-wakefield accelerated electron bunches reveal that in the monoenergetic regime the electrons are injected and accelerated at the back of the first period of the plasma wave. With pulse durations ctau >or= lambda(p), we observe an elliptical beam profile with the axis of the ellipse parallel to the axis of the laser polarization. This increase in divergence in the laser polarization direction indicates that the electrons are accelerated within the laser pulse. Reducing the plasma density (decreasing ctau/lambda(p)) leads to a beam profile with less ellipticity, implying that the self-injection occurs at the rear of the first period of the plasma wave. This also demonstrates that the electron bunches are less than a plasma wavelength long, i.e., have a duration <25 fs. This interpretation is supported by 3D particle-in-cell simulations. 相似文献
102.
Growth of gold nanorods and bipyramids using CTEAB surfactant 总被引:1,自引:0,他引:1
Kou X Zhang S Tsung CK Yeung MH Shi Q Stucky GD Sun L Wang J Yan C 《The journal of physical chemistry. B》2006,110(33):16377-16383
Gold nanorods and bipyramids have been synthesized using the seed-mediated approach in aqueous cetyltriethylammonium bromide (CTEAB) solutions in the presence of silver nitrate. Gold nanoparticle seeds that are stabilized with either CTEAB or sodium citrate have been used. The use of the CTEAB-stabilized seeds gives gold nanorods in high yield in one step with the longitudinal plasmon wavelength ranging from 750 to 1030 nm, depending on the amount of the seeds. The longitudinal plasmon wavelength can be extended to 1100 nm by the use of a two-step growth method. The growth of gold nanorods in CTEAB solutions takes 5-10 h, more than 5 times slower than that in cetyltrimethylammonium bromide solutions at the same concentration of surfactants. The use of the citrate-stabilized seeds gives both gold bipyramids and a small percentage of gold nanorods. The longitudinal plasmon wavelength of the bipyramids is tunable from 700 to 1100 nm by varying the amount of the citrate-stabilized seeds. The growth of gold bipyramids takes more than 1 day. Transmission electron microscopy characterizations reveal that the gold nanorods grown from both types of gold nanoparticle seeds are single-crystalline and that the gold bipyramids are penta-twinned. 相似文献
103.
Grace Shiahuy Chen Rahul Subhash Talekar Ken‐Tsung Wong Liang‐Chen Chi Ji‐Wang Chern 《中国化学会会志》2007,54(6):1387-1394
Derivatives of 5,7‐dichloro‐2‐styrylquinoline ( 1 ), modified at position 8 of quinoline moiety with a methyl ether ( 4 , DCSQM) or acetate ( 5 , DCSQA), were synthesized and investigated. Both compounds exhibited high thermal stability (Td > 320 °C). The UV‐vis absorption of DCSQM and DCSQA varied only slightly in different solvents, whereas the emission spectra showed pronounced red shifts with increasing solvent polarity, suggesting the intramolecular charge transfer character of the emission state. Compounds 4 and 5 can emit lights from blue to green color in different solvents. The solvent polarity dependent electronic transitions are attributed to efficient intramolecular charge transfer (ICT) processes, in which the HOMOs and LUMOs are localized on the styrene‐based ring and the quinoline‐based moiety, respectively. The quinoline‐based LUMO provides compelling evidence that the first reduction site occurs on the electron‐deficient quinoline moiety. 相似文献
104.
In recent years, excellent surface passivation has been achieved on both p‐type and n‐type surfaces of silicon wafers and solar cells using aluminum oxide deposited by plasma‐assisted atomic layer deposition. However, alternative deposition methods may offer practical advantages for large‐scale manufacturing of solar cells. In this letter we show that radio‐frequency magnetron sputtering is capable of depositing negatively‐charged aluminum oxide and achieving good surface passivation both on p‐type and n‐type silicon wafers. We thus establish that sputtered aluminum oxide is a very promising method for the surface passivation of high efficiency solar cells. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
105.
Chieh‐Tsung Lo Francis C. Laabs Balaji Narasimhan 《Journal of Polymer Science.Polymer Physics》2004,42(14):2667-2679
The mechanism of adhesion at semicrystalline polymer interfaces between isotactic polypropylene (iPP) and linear low‐density polyethylene (PE) was studied with transmission electron microscopy (TEM) and an asymmetric‐double‐cantilever‐beam test. From the TEM images, both the interfacial width and the lamellar thickness of the polymers were extracted. During annealing, the interfacial width increased with the annealing temperature, and this indicated the accumulation of amorphous polymers at the interface. The interfacial strength, determined from the critical fracture energy (Gc), also increased with the annealing temperature and reached a maximum above the melting temperatures of iPP and PE, whereas the smallest Gc value was obtained below the melting temperatures of the two materials. A mechanism of interfacial strengthening was proposed accounting for the competition between the interdiffusion of PE and crystallization of iPP. As the annealing temperature increased, the rates of PE diffusion and iPP crystallization increased. Although the crystallization of iPP hindered the interdiffusion of PE, both the interfacial width and the fracture energy increased with the temperature, and this indicated that PE interdiffusion dominated iPP crystallization. Below the critical temperature, the fracture surfaces of both iPP and PE were smooth, and chain pullout dominated the fracture mechanism. Above the critical temperature, iPP crystallization still hindered the interdiffusion, and crazes could be seen on the iPP side. Above the melting temperatures of the two materials, ruptured surfaces could also be seen on the PE side, and crazing was the fracture mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2667–2679, 2004 相似文献
106.
Tsung‐Min Hwang Wen‐Wei Lin Jinn‐Liang Liu Weichung Wang 《Numerical Linear Algebra with Applications》2005,12(7):605-624
Several Jacobi–Davidson type methods are proposed for computing interior eigenpairs of large‐scale cubic eigenvalue problems. To successively compute the eigenpairs, a novel explicit non‐equivalence deflation method with low‐rank updates is developed and analysed. Various techniques such as locking, search direction transformation, restarting, and preconditioning are incorporated into the methods to improve stability and efficiency. A semiconductor quantum dot model is given as an example to illustrate the cubic nature of the eigenvalue system resulting from the finite difference approximation. Numerical results of this model are given to demonstrate the convergence and effectiveness of the methods. Comparison results are also provided to indicate advantages and disadvantages among the various methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
107.
Chang Min Chih‐Tsung Lin Prof. Dr. Daniel Seidel 《Angewandte Chemie (International ed. in English)》2015,54(22):6608-6612
A readily available chiral Brønsted acid was identified as an efficient catalyst for intramolecular Povarov reactions. Polycyclic amines containing three contiguous stereogenic centers were obtained with excellent stereocontrol in a single step from secondary anilines and aldehydes possessing a pendent dienophile. These transformations constitute the first examples of catalytic enantioselective intramolecular aza‐Diels–Alder reactions. 相似文献
108.
Synthesis and Characterization of Poly(ethylene terephthalate)/Modified Lithium‐Aluminum‐Layered Double Hydroxide Nanocomposites Prepared Using In‐situ Polymerization 下载免费PDF全文
Layered double hydroxides are a type of layered stacked compound, which can be intercalated with organic‐molecule modifiers. An ion‐exchange process for layered double hydroxide (LDH) was used to intercalate water‐soluble sulfanilic acid salt (SAS) and dimethyl 5‐sulfoisopthalate (DMSI) into lithium aluminum layered double hydroxides (LiAl LDHs). In this work, a hydrothermal process was used to modify LiAl LDHs, and the modified LiAl LDHs were treated with either SAS or DMSI through an ion‐exchange process and were then intercalated using bis‐hydroxyethylene terephthalate (BHET). The results indicate that the modified LiAl LDHs improved the interlayer compatibility between the PET and LiAl LDH layers; thus, enabling the oligomer molecules to more easily enter the gallery of the LiAl LDH layers so that polymer chains could be included between the LDH layers during polymerization of the matrix. The better barrier, mechanical properties, and thermal stability of these new types of PET nanocomposites are discussed. 相似文献
109.
Chih‐Ching Huang Prof. Yu‐Lun Hung Yen‐Chun Shiang Tai‐Yuan Lin Prof. Yu‐Shen Lin Chao‐Tsen Chen Prof. Huan‐Tsung Chang Prof. 《化学:亚洲杂志》2010,5(2):334-341
We have employed mannose‐modified gold nanodots (Man–Au NDs) as a luminescence sensor for the detection of the thyroid‐cancer marker thyroglobulin (Tg) in homogeneous solutions. The luminescent Man–Au NDs are prepared through the reaction of 2.9 nm‐diameter gold nanoparticles (Au NPs) with 11‐mercapto‐3,6,9‐trioxaundecyl‐α‐D ‐mannopyranoside (Man‐RSH) under the irradiation of a light‐emitting diode (LED). We have found that the irradiation enhances the quantum yield (~11 %), alters the emission wavelength and lifetimes, and shortens the preparation time. A luminescence assay has been developed for Tg based on the competition between Tg and Man–Au NDs for the interaction with the concanavalin A (Con A). Because luminescence quenching of the Man–Au NDs by Con A is inhibited by Tg selectivity, we have obtained a highly sensitive and selective assay for Tg. 相似文献
110.
Analyzing and visualizing a discretized semilinear elliptic problem with Neumann boundary conditions
Tsung‐Min Hwang Weichung Wang 《Numerical Methods for Partial Differential Equations》2002,18(3):261-279
A semilinear elliptic equation dΔu ? u + up =0 over the unit ball in ?2 with positive solution and the homogeneous Neumann boundary condition is considered. This equation models applications like chemotactic aggregation and biological pattern formation. Recent theoretical analyses on the equation suggest little continuous solution properties. Focusing on solving the discretized version of the equation, this work proposes an efficient algorithm that combines a newly developed discretization scheme on polar coordinates with a fast Fourier solver. An analysis of the induced matrix structures proves the algorithm converges to positive solutions; the analysis also establishes the q‐axial symmetry and monotonicity behavior of the solutions. Based on the q‐axial symmetry property, Numerical experiments were conducted to visualize various solution forms that are new to the best of our knowledge. The experiments also illustrated sensitivity behavior of the solutions. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 261–279, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/num.10006 相似文献