全文获取类型
收费全文 | 629篇 |
免费 | 0篇 |
专业分类
化学 | 381篇 |
晶体学 | 1篇 |
力学 | 36篇 |
数学 | 113篇 |
物理学 | 98篇 |
出版年
2023年 | 4篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 21篇 |
2012年 | 33篇 |
2011年 | 33篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 32篇 |
2007年 | 30篇 |
2006年 | 22篇 |
2005年 | 31篇 |
2004年 | 37篇 |
2003年 | 29篇 |
2002年 | 19篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1966年 | 3篇 |
1965年 | 4篇 |
排序方式: 共有629条查询结果,搜索用时 109 毫秒
621.
The oxidation of o-xylene and/or naphthalene to phthalic anhydride is one of the important industrial processes based on catalytic selective oxidation reactions. Vanadia--titania catalysts have been used in the industrial phthalic anyhdride process for the last 50 years. The operation parameters like the temperature range of operation, reactor inlet pressures, contact times, o-xylene loadings, etc. were constantly improved during this period of continuous process optimization so as to optimize catalyst performance and increase its life time. However, a fundamental understanding of the mutual interaction of the rather complex reaction network and the catalyst formulation is still missing. Recently, a detailed study of by-product formation as function of process conditions allowed us to develop a novel, improved reaction scheme for the catalytic oxidation of o-xylene. Based on this understanding, a detailed investigation was conducted for the first time of the by-product formation under varying operation conditions and as a function of the active mass variation exploiting high-throughput, as well as bench scales reactors. This high-throughput testing allowed us to relate reaction kinetics to novel catalyst formulations. 相似文献
622.
When a solvent drop evaporates from a polymer surface, it leaves behind a characteristic structure, typically a crater. We deposited toluene drops with a microsyringe onto planar polystyrene (PS) surfaces and analyzed the surface topography after drying. For low molar mass PS (Mw = 20.9-24.3 kDa) dotlike protrusions with a ridge at the periphery formed on the polymer surface. With increasing molar mass the central region decreased in height. At Mw = 29.6-643 kDa a craterlike structure with a depression in the center and a ridge was observed. At even higher molar mass, irregular structures without rotational symmetry occurred. We explain the observed dependence on the molar mass with a different degree of entanglement, leading to different dissolution rates and different diffusion constants. 相似文献
623.
Ally J Kappl M Butt HJ Amirfazli A 《Langmuir : the ACS journal of surfaces and colloids》2010,26(23):18135-18143
The detachment force required to pull a microparticle from an air-liquid interface is measured using atomic force microscopy (AFM) and the colloidal probe technique. Water, solutions of sodium dodecyl sulfate (SDS), and silicone oils are tested in order to study the effects of surface tension and viscosity. Two different liquid geometries are considered: the air-liquid interface of a bubble and a liquid film on a solid substrate. It was shown that detaching particles from liquid films is fundamentally different than from bubbles or drops due to the restricted flow of the liquid phase. Additional force is required to detach a particle from a film, and the maximum force during detachment is not necessarily at the position where the particle breaks away from the interface (as seen in bubble or drop systems). This is due to the dynamics of meniscus formation and viscous effects, which must be considered if the liquid is constrained in a film. The magnitude of these effects is related to the liquid viscosity, film thickness, and detachment speed. 相似文献
624.
Oksana Ozhoga-Maslovskaja Holm Altenbach Konstantin Naumenko Oleksandr Prygorniev Oleksii Vodka 《PAMM》2011,11(1):419-420
A Unit Cell made of copper is simulated and investigated under creep conditions within the framework of micromechanics. Geometrical 3D model of the copper microstructure is represented as a Unit Cell with grains of random crystallographical orientation and geometry. Such simulation enables algorithm of Voronoi tessellation. The stress-strain behavior of grains in the general case is anisotropic due to the ordered crystalline structure. The anisotropic model for a material with a cubic symmetry is implemented in Abaqus and used to assign behavior of grain interior in elastic and creep regions. Material parameters for elastic model are taken from elastic tests of single crystal copper [1]. Power law material parameters for creep model are taken from creep test performed for single crystal copper [2]. The model parameter ξ is validated numerically. Creep results are presented for the case of proportional loading during the primary and secondary creep. Statistical analysis of creep curves received for 55 different realizations of Unit Cell geometry is carried out. As a result confident interval and mathematical expectation of creep data are calculated. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
625.
Oksana Ozhoga-Maslovskaja Holm Altenbach Konstantin Naumenko Oleksandr Prygorniev 《PAMM》2012,12(1):145-146
A polycrystalline material is investigated under creep conditions within the framework of continuum micromechanics. Geometrical 3D model of a polycrystalline microstructure is represented as a unit cell with grains of random crystallographical orientation and shape. Thickness of the plains, separating neighboring grains in the unit cell, can have non-zero value. Obtained geometry assigns a special zone in the vicinity of grain boundaries, possessing unordered crystalline structure. A mechanical behavior of this zone should allow sliding of the adjacent grains. Within the grain interior crystalline structure is ordered, what prescribes cubic symmetry of a material. The anisotropic material model with the orthotropic symmetry is implemented in ABAQUS and used to assign elastic and creep behavior of both the grain interior and grain boundary material. Appropriate parameters set allows transition from the orthotropy to the cubic symmetry for the grain interior. Material parameters for the grain interior are identified from creep tests for single crystal copper. Model parameters for the grain boundary are set from the physical considerations and numerical model validation according to the experimental data of the grain boundary sliding in a polycrystalline copper [2]. As the result of analysis representative number of grains and grain boundary thickness in the unit cell are recommended. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
626.
D Lehr K Dietrich C Helgert T Käsebier HJ Fuchs A Tünnermann EB Kley 《Optics letters》2012,37(2):157-159
In this Letter we evaluate a technique for the efficient and flexible generation of aluminum nanorings based on double patterning and variable shaped electron beam lithography. The process is demonstrated by realizing nanorings with diameters down to 90 nm and feature sizes of 30 nm utilizing a writing speed of one ring per microsecond. Because of redepositions caused by involved etching processes, the material of the rings and, therefore, the impact on the plasmonic properties, are unknown. This issue, which is commonly encountered when metals are nanostructured, is solved by adapting a realistic simulation model that accounts for geometry details and effective material properties. Based on this model, the redepositions are quantified, the plasmonic properties are investigated, and a design tool for the very general class of nanofabrication techniques involving the etching of metals is provided. 相似文献
627.
Dirk Kuckling Thomas Schmidt Genovéva Filipcsei Hans-Jürgen P. Adler Karl-Friedrich Arndt 《Macromolecular Symposia》2004,210(1):369-376
Temperature-sensitive filled poly(N-isopropylacrylamide) (PNIPAAm) gel beads with diameters in the range of millimeters were prepared using the alginate technique. The polymerization and cross-linking reaction of NIPAAm in the presence of inorganic filling particles was performed in spherical networks of Ca-alginate forming interpenetrating networks (IPN). Thermo-sensitive gel beads could be obtained by washing these IPN with EDTA solution. The PNIPAAm gel beads were analyzed by optical methods to observe there swollen diameter in dependence on the temperature. The diameters of the swollen gel beads were in the range of 0.1 - 2 mm. The influence of the monomer to cross-linker ratio (MCR) and the filling materials (ferrofluid, BaTiO3, TiO2, and Ni,) were studied. The phase transition temperature (Tpt) was only weakly influenced by the MCR and the filling material remaining at around 34°C. 相似文献
628.
Stanislav Nešpůrek Geng Wang Stanislav Böhm Marek Kořínek Hans-J. Adler 《Macromolecular Symposia》2004,210(1):513-521
The charge carrier transport in poly[methyl(phenyl)silylene] (PMPSi) proceeds predominantly along the σ-delocalized Si backbone with participation of interchain hopping and polaron formation. The charge carrier mobility increases with increasing electron affinity of acceptor dopands having zero dipole moments. On the other band, the hole drift mobility is influenced by the dipole moment of the dopand. The electrostatic charge-dipole interactions cause a broadening of the energy distribution of transport states, which results in a decrease in the charge carrier mobility. An addition of organic salts leads, under the conditions of increased humidity, to an increase in electrical conductivity and capacitance. This is demonstrated on the layers PMPSi/1,5-dimorpholino-1,5-diphenylpentamethinium perchlorate. 相似文献
629.
Meifang Zhu Qiang Xing Houkang He Yu Zhang Yanmo Chen Petra Pötschke Hans-Jürgen Adler 《Macromolecular Symposia》2004,210(1):251-261
In this work, surface modification technique with coupling agents and anchoring polymerization was adopted to tailor the surface properties of nanoscaled titanium dioxide (TiO2). Ethyl glycol sols with TiO2 were prepared in order to simulate the dispersibility of differently modified TiO2 in a molten polyamide 6 (PA6) matrix. The modified TiO2 were melt compounded with PA6 and composites and fibers were prepared. The average filler diameter of 47 nm (in composites) and 44 nm (in fibers) indicated homogeneous dispersion of TiO2 in the matrix, whereas unmodified TiO2 showed agglomerated structures in the PA6 matrix. The mechanical properties of the composite fibers were improved as compared to pure PA6 fibers and composite fibers with unmodified TiO2. 相似文献