全文获取类型
收费全文 | 498篇 |
免费 | 16篇 |
国内免费 | 4篇 |
专业分类
化学 | 321篇 |
晶体学 | 3篇 |
力学 | 21篇 |
数学 | 83篇 |
物理学 | 90篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 49篇 |
2011年 | 55篇 |
2010年 | 24篇 |
2009年 | 20篇 |
2008年 | 41篇 |
2007年 | 25篇 |
2006年 | 23篇 |
2005年 | 31篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 20篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有518条查询结果,搜索用时 265 毫秒
141.
Conditional statistics concerning evaporation and combustion of a spray are investigated in homogeneous, isotropic, and decaying two-dimensional (2D) turbulence. Randomly distributed, polydisperse droplets of n-heptane go through single-step combustion chemistry. Attention is focused on parametric effects of initial Sauter mean radius (SMR), turbulence level and droplet velocity in both reacting and nonreacting cases. A simple linear model for the conditional evaporation rate is proposed and validated against DNS data. A conventional β-probability density function (pdf) is shown to be valid with no peak occurring on the fuel side. The amplitude mapping closure (AMC) model works well for the conditional scalar dissipation rate with evaporating and reacting sprays. Parametric study shows that initial SMR and droplet velocity are major factors affecting conditional flame structures, whereas the effect of reaction is not significant except during autoignition. 相似文献
142.
The influence of phosphate glass electrode in the configuration of resistive plate chamber has been studied using GEANT3.21
Monte Carlo code. Bakelite electrodes were replaced by phosphate glass electrodes, as these glass materials have low bulk
resistivity, are portable and easy to handle. These types of RPCs in their compact form of all materials are suitable for
high rate background environment. We find that these new types of RPCs give little higher response to γ-rays and e+/e− particles, both for single-and double gap RPCs. The results of simulation are discussed.
相似文献
143.
144.
Pojman JA Masere J Petretto E Rustici M Huh DS Kim MS Volpert V 《Chaos (Woodbury, N.Y.)》2002,12(1):56-65
Using reactors of different sizes and geometries the dynamics of the frontal polymerization of 1,6-hexanediol diacrylate (HDDA) and pentaerythritol tetraacrylate (PETAC), with ammonium persulfate as the initiator were studied. For this system, the frontal polymerization exhibits complex behavior that depends on the ratio of the monomers. For a particular range of monomers concentration, the polymerization front becomes nonplanar, and spin modes appear. By varying the reactor diameter, we experimentally confirmed the expected shift of the system to a greater number of "hot spots" for larger diameters. For square test tubes a "zig-zag" mode was observed for the first time in frontal polymerization. We confirmed the viscosity-dependence of the spin mode instabilities. We also observed novel modes in cylinder-inside-cylinder reactors. Lastly, using a conical reactor with a continuously varying diameter, we observed what may be evidence for bistability depending on the direction of propagation. We discuss these finding in terms of the standard linear stability analysis for propagating fronts. (c) 2002 American Institute of Physics. 相似文献
145.
Dong‐Wan Kim Du‐Hee Lee Byung‐Kook Kim Hae‐June Je Jae‐Gwan Park 《Macromolecular rapid communications》2006,27(21):1821-1825
Summary: This study examines the use of a PMMA‐mediated assembly of BaTiO3 nanoparticles directly onto Cu electrodes under an electric field. The compatibility of the interface between BaTiO3 nanoparticles and PMMA in a mixed organic solvent system enables the homogeneous dispersion of nanoparticles in a solid polymer matrix. This results in the effective packing of particles, which is desirable from the point of view of achieving a high dielectric constant in the composite. In this study, three‐phase Al/BaTiO3/PMMA nanocomposite films from stable colloidal suspensions containing aluminium nitrate salts were also designed using an electrodeposition process. The simultaneous formation of Al metallic inclusions in the BaTiO3 nanoparticles in the PMMA matrix significantly improved the dielectric constant of nanocomposite films.
146.
Pentavalent organo-vanadates have been put forth as transition state analogues for a variety of phosphoryl transfer reactions. In particular, uridine 2',3'-cyclic vanadate (U>v) has been proposed to resemble the transition state during catalysis by ribonuclease A (RNase A). Here, this hypothesis is tested. Lys41 of RNase A is known to donate a hydrogen bond to a nonbridging phosphoryl oxygen in the transition state during catalysis. Site-directed mutagenesis and semisynthesis were used to create enzymes with natural and nonnatural amino acid residues at position 41. These variants differ by 10(5)-fold in their k(cat)/K(m) values for catalysis, but <40-fold in their K(i) values for inhibition of catalysis by U>v. Plots of logK(i) vs log(K(m)/k(cat)) for three distinct substrates [poly(cytidylic acid), uridine 3'-(p-nitrophenyl phosphate), and cytidine 2',3'-cyclic phosphate] have slopes that range from 0.25 and 0.36. These plots would have a slope of unity if U>v were a perfect transition state analogue. Values of K(i) for U>v correlate weakly with the equilibrium dissociation constant for the enzymic complexes with substrate or product, indicating that U>v bears some resemblance to the substrate and product as well as the transition state. Thus, U>v is a transition state analogue for RNase A, but only a marginal one. This finding indicates that a pentavalent organo-vanadate cannot necessarily be the basis for a rigorous analysis of the transition state for a phosphoryl transfer reaction. 相似文献
147.
We develop a method to determine the topology of a network that interconnects a number of token rings using source routing bridges. The purpose is to compute a topology that provides low response delays for network users at a minimal cost of bridge installations. We formulate this network design problem as a mixed binary integer linear program. We develop effective heuristic algorithms. The algorithms exploit the topology and routing solutions of the linear programming relaxation in a sophisticated manner which we believe is new in the literature. The model incorporates performance issues, such as network stability, bridge overflow, back pressure effect and broadcast storm, that are specific to the underlying communication technology. By formally incorporating these performance issues, we tighten the model formulation and improve the quality of the LP bound considerably. Computational results are reported for problems with up to 20 token rings and 190 potential bridge locations. 相似文献
148.
Moon Yul Huh 《Journal of computational and graphical statistics》2013,22(4):335-343
Abstract This article introduces a new form of empirical distribution function (EDF) called the flipped empirical distribution function (FEDF), to represent univariate data graphically. Because the plot shows the location of individual points, it may be useful when we need to manipulate specific data points as with dynamic graphics. The article introduces several methods to explore multidimensional data using the FEDF. They are called a parallel FEDF, an FEDF scatterplot matrix, and an FEDF starplot. Usefulness of these plots in exploring multidimensional data becomes more prominent when they are implemented with the methods of dynamic graphics such as selecting, deleting, linking, locating, and identifying a group of data points. 相似文献
149.
Assembly of an Achiral Chromophore into Light‐Responsive Helical Nanostructures in the Absence of Chiral Components 下载免费PDF全文
Prof. Dr. Mina Han Prof. Dr. Sung June Cho Dr. Yasuo Norikane Prof. Dr. Masaki Shimizu Prof. Dr. Takahiro Seki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):3971-3975
The chirality found in living organisms is one of unsolved mysteries on Earth. It is crucial to understand the manner in which small achiral molecules evolve into helical superstructures in the absence of chiral components because this process can provide important insights regarding the origin of chirality in nature. 1) the uncommon helical assembly of an achiral trigonal chromophore into helical nanostructures with aggregation‐induced emission enhancement (AIEE) characteristics and 2) the tunability of the helical pitch and fluorescence intensity in response to light is reported. The Rietveld refinement of X‐ray diffraction (XRD) patterns and the growth process suggest that a striking transformation from an achiral to an asymmetric molecule can occur as a result of specific interactions with certain solvents, presumably leading to the unique helical assembly. More importantly, exposure to UV or visible light promoted not only the formation of irregular helical structures with a wide range of pitch lengths but also an increase in fluorescence intensity. 相似文献
150.
Hye Sun Shin Ik Jun Jang Na Ra Shin Su Hyun Kim Sung June Cho 《Research on Chemical Intermediates》2011,37(9):1239-1246
Dealumination of the small-pore zeolite chabazite (CHA) was performed with ammonium hexafluorosilicate under solid and liquid-state conditions to increase the Si-to-Al ratio from 2.0 to 6.0. In the solid state, the mesopore fraction increased with repeating hydrothermal synthesis at 423 K, which was confirmed by nitrogen adsorption?Cdesorption. In the liquid state, the formation of mesopores decreased substantially and the resulting CHA had an Si-to-Al ratio of ca. 5. The result of desorption of NO?CNO2 from the Cu ion-exchanged dealuminated CHA in the solid state indicated that the presence of mesopores reduced NO?CNO2 adsorption and desorption of NO2 occurred at 383 and 683 K whereas for the high-silica analog SSZ-13 desorption of NO2 occurred mostly at 473 and at 673 K. 相似文献