全文获取类型
收费全文 | 270篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 197篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 45篇 |
物理学 | 30篇 |
出版年
2023年 | 2篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2013年 | 7篇 |
2012年 | 12篇 |
2011年 | 14篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 16篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1967年 | 7篇 |
1966年 | 9篇 |
1916年 | 2篇 |
1912年 | 3篇 |
1902年 | 3篇 |
1901年 | 3篇 |
1897年 | 2篇 |
1896年 | 2篇 |
1883年 | 1篇 |
1882年 | 2篇 |
1870年 | 1篇 |
排序方式: 共有278条查询结果,搜索用时 15 毫秒
261.
Emile H. L. Aarts Jan H. M. Korst Peter J. M. van Laarhoven 《Journal of statistical physics》1988,50(1-2):187-206
A quantitative study is presented of the typical behavior of the simulated annealing algorithm based on a cooling schedule presented previously by the authors. The study is based on the analysis of numerical results obtained by systematically applying the algorithm to a 100-city traveling salesman problem. The expectation and the variance of the cost are analyzed as a function of the control parameter of the cooling schedule. A semiempirical average-case performance analysis is presented from which estimates are obtained on the expectation of the average final result obtained by the simulated annealing algorithm as a function of the distance parameter, which determines the decrement of the control parameter. 相似文献
262.
263.
The preparation of meso-substituted tetrafuryl-porphines is described. These new compounds are very soluble either in organic solvent or in water depending upon the furyl groups substitution. Their spectroscopic absorption, nmr characteristics, and some of their electrochemical properties are reported. 相似文献
264.
265.
Emile Frainnet Veronique Martel-Siegfried Eliane Brousse James Dedier 《Journal of organometallic chemistry》1975,85(3):297-310
The preparion of alkoxysilanes and alkenoxysilanes has been achieved by the reaction of enolizable aliphatic or cyclic ketones with triethylsilane in the presence of nickel catalysts. For some catalysts, the reaction can be directed to give exclusively one or the other of these derivatives. The use of certain nickel catalysts gives very high yields of alkenoxysilanes, and this has been closely investigated. 相似文献
266.
Ahamed T Nfor BK Verhaert PD van Dedem GW van der Wielen LA Eppink MH van de Sandt EJ Ottens M 《Journal of chromatography. A》2007,1164(1-2):181-188
This work demonstrates that a highly linear, controllable and wide-ranged pH-gradient can be generated through an ion-exchange chromatography (IEC) column. Such a pH-gradient anion-exchange chromatography was evaluated with 17 model proteins and found that acidic (pI<6) and basic (pI>8) proteins elute roughly at their pI, whereas neutral proteins (pI 6-8) elute at pH 8-9 regardless their pI values. Because of the flat nature of protein titration curves from pH approximately 6 to approximately 9, neutral proteins indeed exhibit nearly zero net charge at pH approximately 9. The elution-pH in pH-gradient IEC or the titration curve, but not the pI, was identified as the key parameter for pH optimization of preparative IEC in a fast and rational way. The pH-gradient IEC was also applied and found to be an excellent analytical tool for the fractionation of crude protein mixtures. 相似文献
267.
Ubbink SW van Dijk P de Kleine E Brienesse P Chenault MN Tan FE Anteunis LJ 《The Journal of the Acoustical Society of America》2011,130(6):3788-3796
An anechoic wind tunnel dedicated to fan self-noise studies has been designed and constructed at the von Karman Institute The multi-chamber, mass flow driven design allows for all fan performance characteristics, aerodynamic quantities (e.g., wake turbulence measurements), and acoustic properties to be assessed in the same facility with the same conditions. The acoustic chamber performance is assessed using the optimum reference method and found to be within the ISO 3745 standards down to 150 Hz for pure tone and broadband source mechanisms. The additional influence of installation effects of an aerodynamic inlet was found to create a scattered sound field only near the source location, while still providing good anechoic results at more distant sound pressure measurement positions. It was found to have inflow properties, span-wise uniformity, and low turbulence intensity, consistent with those desired for fan self-noise studies. 相似文献
268.
Two monoterpenols, perillyl alcohol and nerol, have been converted into their γ,δ-unsaturated ester derivatives following a modified process of microwave-assisted ortho ester Claisen rearrangement. The yields obtained (>90%) are better than those previously obtained. The optimized process needs less reaction time (5 min), smaller amount of reagent, and no solvent. 相似文献
269.
Banu Korbahti Emile Kagambage Thomas Andrianne Norizham Abdul Razak Grigorios Dimitriadis 《Journal of Fluids and Structures》2011,27(3):408-426
Limit Cycle Oscillations (LCOs) involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric or aerodynamic nonlinearity. In this paper, a flexible half-span Delta wing is tested in a low speed wind tunnel in order to investigate its dynamic response. The wing is designed to be more flexible than the models used in previous research on the subject in order to expand the airspeed range in which LCOs occur. The experiments reveal that this wing features a very rich bifurcation behavior. Three types of bifurcation are observed for the first time for such an aeroelastic system: subcritical bifurcations, period-doubling/period-halving and nontypical bifurcations. They give rise to a great variety of LCOs, even at very low angles of attack. The LCOs resulting from the nontypical bifurcation display Hopf-type behavior, i.e. having fundamental frequencies equal to one of the linear modal frequencies. All of the other LCOs have fundamental frequencies that are unrelated to the underlying linear system modes. 相似文献
270.
W. Chadwick Ellis Andreas Fischer Joshua A. Hayden Longzhu Q. Shen Emile L. Bominaar 《Journal of Coordination Chemistry》2018,71(11-13):1822-1836
AbstractThe preparation, characterization, and evaluation of a cobalt(III) complex with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) S = 1 paramagnetic (1H NMR) compound, which becomes an S = 0 diamagnetic octahedral species in excess d5-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest E½ value (0.66 V vs SCE) among all investigated CoIII TAML complexes. The oxidation results in a neutral blue species which is consistent with a CoIII/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other CoIII TAMLs). The oxidized neutral species are unexpectedly EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4-tert-butylpyridine or 4-tert-butyl isonitrile. The EPR spectra are more consistent with the CoIII/radical-cation ligand formulation rather than with a CoIV complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [VVO(OCHMe2)3] were not successful. TAML-free decavanadate was isolated instead. 相似文献