全文获取类型
收费全文 | 3906篇 |
免费 | 75篇 |
国内免费 | 9篇 |
专业分类
化学 | 2688篇 |
晶体学 | 40篇 |
力学 | 52篇 |
数学 | 711篇 |
物理学 | 499篇 |
出版年
2020年 | 32篇 |
2019年 | 33篇 |
2017年 | 28篇 |
2016年 | 76篇 |
2015年 | 56篇 |
2014年 | 69篇 |
2013年 | 150篇 |
2012年 | 135篇 |
2011年 | 131篇 |
2010年 | 91篇 |
2009年 | 92篇 |
2008年 | 136篇 |
2007年 | 125篇 |
2006年 | 135篇 |
2005年 | 116篇 |
2004年 | 130篇 |
2003年 | 105篇 |
2002年 | 85篇 |
2001年 | 60篇 |
2000年 | 62篇 |
1999年 | 83篇 |
1998年 | 58篇 |
1997年 | 56篇 |
1996年 | 68篇 |
1995年 | 51篇 |
1994年 | 54篇 |
1993年 | 54篇 |
1992年 | 51篇 |
1991年 | 61篇 |
1990年 | 62篇 |
1989年 | 62篇 |
1988年 | 68篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 70篇 |
1984年 | 78篇 |
1983年 | 70篇 |
1982年 | 78篇 |
1981年 | 67篇 |
1980年 | 58篇 |
1979年 | 58篇 |
1978年 | 73篇 |
1977年 | 58篇 |
1976年 | 50篇 |
1975年 | 62篇 |
1974年 | 49篇 |
1973年 | 28篇 |
1972年 | 43篇 |
1971年 | 31篇 |
1970年 | 37篇 |
排序方式: 共有3990条查询结果,搜索用时 0 毫秒
941.
Matthias Hlderle Matthias Bruch Holger Lüchow Wolfram Gronski Rolf Mülhaupt 《Journal of polymer science. Part A, Polymer chemistry》1998,36(11):1821-1827
Oxazoline-functionalized, crosslinked PMMA-particles, prepared by free radical nonaqueous dispersion polymerization, were grafted with n-decanoic acid and carboxylic acid-terminated polystyrene. Oxazoline groups, separated by an alkylspacer from the PMMA backbone, showed enhanced mobility with respect to the backbone, as evaluated by solid-state NMR spectroscopy using a dipolar filter. As a function of molecular mass of the carboxylic acid, the oxazoline conversion varied from 70 mol % for n-decanoic acid to 1% for monocarboxylate-terminated polystyrene CT-PS with Mn: 15,900 g/mol. Morphological studies, performed by TEM, showed that reaction with acid terminated polystyrene results exclusively in interfacial grafting at the particle surface. At low grafting levels a raspberry-like morphology was obtained, whereas grafting levels exceeding 14 wt % CT-PS resulted in core-shell morphology. Core-shell morphology was also verified by static light scattering using toluene solvent, which is isorefractive to the PMMA core. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1821–1827, 1998 相似文献
942.
The oxidation of 1‐(3,8‐dimethylazulen‐1‐yl)alkan‐1‐ones 1 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (=4,5‐dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,2‐dicarbonitrile; DDQ) in acetone/H2O mixtures at room temperature does not only lead to the corresponding azulene‐1‐carboxaldehydes 2 but also, in small amounts, to three further products (Tables 1 and 2). The structures of the additional products 3 – 5 were solved spectroscopically, and that of 3a also by an X‐ray crystal‐structure analysis (Fig. 1). It is demonstrated that the bis(azulenylmethyl)‐substituted DDQ derivatives 5 yield on methanolysis or hydrolysis precursors, which in a cascade of reactions rearrange under loss of HCl into the pentacyclic compounds 3 (Schemes 4 and 7). The found 1,1′‐[carbonylbis(8‐methylazulene‐3,1‐diyl)]bis[ethanones] 4 are the result of further oxidation of the azulene‐1‐carboxaldehydes 2 to the corresponding azulene‐1‐carboxylic acids (Schemes 9 and 10). 相似文献
943.
Lightweight structures become more and more important and one great class within these structures are parts produced by injection moulding. To improve the mechanical properties of these parts short fibers are injected within the molten plastics. Now a way to describe these properties without knowing the fibre orientation exactly is needed. We show an intuitive way, how mechanical properties of short fibre reinforced composites for linear thermoelasticity can be described and show the relation to other approaches. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
944.
This work presents the derivation of the effective shear modulus for a heterogeneous material composed of multi-layered composite spheres embedded in a linear elastic matrix. It is based on the composite spheres model known from the literature. In contrast to previous publications the effective shear modulus is obtained by equating the results of two models: In the first model, a heterogeneous sphere is embedded in an equivalent homogeneous material, whereas in the second model, the heterogeneous sphere is replaced by an equivalent homogeneous sphere. In the context of both, a shear stress approach and a shear deformation approach, this results into an overdetermined system of equations which is solved with the least squares method. In a numerical study our results are compared to effective moduli and bounds from the literature. Furthermore, a convincing agreement with experimental data for glass microspheres embedded in a polyester matrix is demonstrated. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
945.
A technique for implementing Dijkstra's shortest paths algorithm is proposed. This method runs in O(mlog logD) time in the worst case, where m is the number of edges and D the length of the longest edge in the graph. 相似文献
946.
Schaefer C Gleiter R Rominger F 《Dalton transactions (Cambridge, England : 2003)》2004,(24):4146-4151
Sterically hindered CpCo stabilized cyclobutadiene complexes 4 were oxidized by ceric ammonium nitrate to yield the dinitratocobalt complexes 5. The thermolysis of 5a and the reaction of 5a with tert-butyl isocyanide as well as NaBH4 is reported. 相似文献
947.
Oxidative Fluorination of (CF3)(R) (R = CF3, Cl) and the Crystal Structure of (CF3)(Cl) F+ AsF6? Oxidative fluorination of (CF3)(R) (R = CF3, Cl) with XeF+MF6? (M = As, Sb) in anhydrous HF results in formation of monofluorsulfonium hexafluorometalates. The salts are characterized by vibrational, NMR, and mass spectra. (CF3)(Cl)F+ AsF6? crystallizes in the monoclinic space group P21/c with a = 9.955(10) Å, b = 11.050(5) Å, c = 12.733(15) Å, β = 97.77(5)°, and Z = 4. 相似文献
948.
Hermes S Schröder F Chelmowski R Wöll C Fischer RA 《Journal of the American Chemical Society》2005,127(40):13744-13745
Metal-Organic open Framework coordination polymers (MOFs) are a fascinating class of materials. We demonstrate the selective growth of patterned thin films of MOF-5 and the subsequent loading with a palladium organic compound, which acts as a precursor for the deposition of palladium nanoclusters inside the cavities of the MOF-5 material. 相似文献
949.
Hartmut Rettig Eberhard Krause Hans G. Brner 《Macromolecular rapid communications》2004,25(13):1251-1256
Summary: A novel two‐step polymerization strategy allowing the integration of sequence‐defined oligopeptides into synthetic polymers has been demonstrated by the successful synthesis of an oligopeptide‐block‐poly(n‐butyl acrylate) copolymer. The approach utilizes a solid‐phase supported synthesis of an oligopeptide macroinitiator (SPPS) followed by solution‐phase atom transfer radical polymerization (ATRP) initiated by the oligopeptide macroinitiator. The resulting block copolymer exhibited a low (1.19) and a controllable .
950.
Rolf Krause Benjamin Müller Gerhard Starke 《Numerical Methods for Partial Differential Equations》2017,33(1):276-289
We present and analyze a least squares formulation for contact problems in linear elasticity which employs both, displacements and stresses, as independent variables. As a consequence, we obtain stability and high accuracy of our discretization also in the incompressible limit. Moreover, our formulation gives rise to a reliable and efficient a posteriori error estimator. To incorporate the contact constraints, the first‐order system least squares functional is augmented by a contact boundary functional which implements the associated complementarity condition. The bilinear form related to the augmented functional is shown to be coercive and therefore constitutes an upper bound, up to a constant, for the error in displacements and stresses in . This implies the reliability of the functional to be used as an a posteriori error estimator in an adaptive framework. The efficiency of the use of the functional as an a posteriori error estimator is monitored by the local proportion of the boundary functional term with respect to the overall functional. Computational results using standard conforming linear finite elements for the displacement approximation combined with lowest‐order Raviart‐Thomas elements for the stress tensor show the effectiveness of our approach in an adaptive framework for two‐dimensional and three‐dimensional Hertzian contact problems. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 276–289, 2017 相似文献