全文获取类型
收费全文 | 659篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 456篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 89篇 |
物理学 | 57篇 |
无线电 | 55篇 |
出版年
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2013年 | 16篇 |
2012年 | 7篇 |
2011年 | 19篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 17篇 |
2007年 | 15篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 25篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1991年 | 6篇 |
1944年 | 9篇 |
1943年 | 7篇 |
1928年 | 6篇 |
1919年 | 5篇 |
1916年 | 7篇 |
1915年 | 8篇 |
1913年 | 5篇 |
1911年 | 8篇 |
1910年 | 12篇 |
1909年 | 10篇 |
1908年 | 7篇 |
1907年 | 8篇 |
1905年 | 5篇 |
1904年 | 6篇 |
1902年 | 5篇 |
1901年 | 8篇 |
1900年 | 12篇 |
1899年 | 6篇 |
1898年 | 11篇 |
1897年 | 6篇 |
1895年 | 7篇 |
1894年 | 5篇 |
1892年 | 11篇 |
1891年 | 12篇 |
1890年 | 9篇 |
1889年 | 6篇 |
1888年 | 6篇 |
1883年 | 5篇 |
1882年 | 10篇 |
1870年 | 8篇 |
1869年 | 5篇 |
1866年 | 7篇 |
排序方式: 共有663条查询结果,搜索用时 15 毫秒
1.
This paper describes several combinatorial models for Laguerre, Charlier, and Hermite polynomials, and uses them to prove combinatorially some classical formulas. The so-called “Italian limit formula” (from Laguerre to Hermite), the Appel identity for Hermite polynomials, and the two Sheffer identities for Laguerre and Charlier polynomials are proved. We also give bijective proofs of the three-term recurrences. These three families form the bottom triangle in R. Askey's chart classifying hypergeometric orthogonal polynomials. 相似文献
2.
3.
This paper presents results on symmetries of the spectrum of singularities for random cascades found in the statistical theory of turbulence. It is shown that empirical dimension curves possess a natural symmetry whose presence restricts the class of allowable probability distributions of the cascade generator in a simple manner. In particular, necessary and sufficient conditions on the probability distribution of the generator are obtained for symmetry of the singularity spectrum within a large class of cascade models. 相似文献
4.
5.
Functionalised hydroxylamine derivatives of (S)-prolinol prepared by a Cope elimination have been found to undergo oxidation to the nitrone either in the presence of air or a catalytic quantity of TPAP. These undergo intramolecular cycloaddition to give tricyclic isoxazolidines with high diastereoselectivity. 相似文献
6.
Everette S. GardnerJr. Ed. McKenzie 《The Journal of the Operational Research Society》1988,39(9):863-867
Model identification has traditionally been ignored in forecasting via exponential smoothing. The usual practice is to apply the same model to every time-series in a collection. This paper develops a procedure for model identification in large forecasting applications based on an examination of variances of differences of the time-series. The order of differencing yielding minimum variance suggests an appropriate model for the series. Empirical results show that this procedure selects models that give reasonable ex ante forecast accuracy. 相似文献
7.
Aspen wood substrates with varying degrees of deacetylation, xylan, and lignin removal have been prepared and submitted to
enzymatic hydrolysis with a cellulase/hemicellulase preparation for an extended constant period of hydrolysis. Controlled
deacetylation has been achieved by treating wood with various alkali metal hydroxide solutions, at various alkali/wood ratios.
It has been found that samples with the same extent of deacetylation produce the same sugar yields upon enzymatic hydrolysis.
Increased degree of deacetylation increases the yield of sugars obtained from enzymatic hydrolysis, all other compositional
parameters held constant. The acetyl group removal is proportional to the stoichiometric relation between added base and wood
acetyl content, i.e., the same number of milliequivalents of base/weight of wood remove the same extent of acetyl groups,
regardless of the concentration of the base solution. No cation effects are found among Li, Na, and K alkali hydroxide solutions,
suggesting that swelling is not as important a parameter as is the removal of the acetyl groups from the xylan backbone in
determining the extent of hydrolyzability of the resulting sample. 相似文献
8.
W. Haerdi et Ed. Mérat 《Fresenius' Journal of Analytical Chemistry》1973,264(5):376-377
A method for the rapid separation of copper(II) traces on metallic mercury is proposed. The separation is rendered possible by the reduction of Cu(II) to Cu(I) on mercury in the presence of iodide ions followed by the adsorption of the uncharged complex, Cu(I), on Hg0. After a minute of agitation, this adsorption is quantitative (90–100%) for initial concentrations of Cu(II) between 10–4 to 10–6 M and iodide cone, of 10–2 to 10–3 M at pH 3. The volumes of the aqueous solutions are of the order of 3–10 ml and those of the drops of mercury between 0.5–1 ml. The tests were made using the isotope 64Cu (T
1/2 = 12.8 h).
Trennung von Metallspuren am Quecksilbertropfen; Anwendung auf die Anreicherung von Cu(II) und Cu(I)
Zusammenfassung Die Arbeit beschreibt eine Methode zur Schnelltrennung von Kupfer(II)-Spuren auf metallischem Quecksilber. Diese Vorkonzentration ist durch die Reduktion des Cu(II) zu Cu(I) durch Hg0 in Jodidmedium und anschließende Adsorption des ungeladenen Kupferjodidkomplexes, CuJ, an diesem Metall möglich. Die Adsorption ist nach 1 min Rühren quantitativ (90–100%) für Ausgangswerte von Cu(II) zwischen 10–6 und 10–4M, im Jodidmedium von 10–3 bis 10–2 M bei pH 3. Die Volumina der wäßrigen Lösung liegen in der Größenordnung von 3–10 ml, die der Hg-Tropfen von 0,5–1 ml. Die Versuche wurden mit Hilfe von 64Cu (T 1/2 = 12,8 h) durchgeführt.
Exposé présenté à la conférence Euroanalysis I, août 28 à septembre 1, 1972, à Heidelberg, Allemagne. 相似文献
9.
Kuiry SC Megen E Patil SD Deshpande SA Seal S 《The journal of physical chemistry. B》2005,109(9):3868-3872
This article reports an easy chemical method of synthesizing boehmite nanofibers by a modified sol-gel process involving aluminum isopropoxide precursor. Nanorods of gamma-alumina have been successfully prepared after dehydration of the viscous sol at 600 degrees C for 4 h in air. The boehmite nanofibers and gamma-alumina nanorods were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy for surface chemistry and functional groups, scanning electron microscopy, high-resolution transmission electron microscopy with selected area electron diffraction, and energy-dispersed spectroscopy for morphology and structure identification. The length of the boehmite nanofibers was found to be more than 10 mum with a crystalline lattice structure. The mechanism of formation of the boehmite nanofibers included the preferential growth along the longitudinal axis due to interaction between the solvent molecules and the surface OH- groups of hydrogen bonds. It is also suggested that the boehmite nanofibers may have formed due to the inherent instability of the planar structure of the boehmite lattice. The diameter of the gamma-alumina nanorods was found to be less than 10 nm with a varying length in the range of 50-200 nm. Boehmite to gamma-Al2O3 transformation was attributed to the loss of water molecules by internal condensation of protons and hydroxyl ions. 相似文献
10.
It is shown that several recursive least squares (RLS) type equalization algorithms such as, e.g., decisiondirected schemes and orthogonalized constant modulus algorithms, possess a common algorithmic structure and are therefore rather straightforwardly implemented on an triangular array (filter structure) for RLS estimation with inverse updating. While the computational complexity for such algorithms isO(N
2), whereN is the problem size, the throughput rate for the array implementation isO(1), i.e., independent of the problem size. Such a throughput rate cannot be achieved with standard (Gentleman-Kung-type) RLS/QR-updating arrays because of feedback loops in the computational schemes. 相似文献