全文获取类型
收费全文 | 1949篇 |
免费 | 43篇 |
国内免费 | 16篇 |
专业分类
化学 | 1505篇 |
晶体学 | 14篇 |
力学 | 11篇 |
数学 | 238篇 |
物理学 | 240篇 |
出版年
2023年 | 12篇 |
2021年 | 14篇 |
2020年 | 24篇 |
2019年 | 19篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 19篇 |
2015年 | 36篇 |
2014年 | 49篇 |
2013年 | 124篇 |
2012年 | 76篇 |
2011年 | 111篇 |
2010年 | 62篇 |
2009年 | 65篇 |
2008年 | 106篇 |
2007年 | 108篇 |
2006年 | 109篇 |
2005年 | 109篇 |
2004年 | 108篇 |
2003年 | 107篇 |
2002年 | 103篇 |
2001年 | 42篇 |
2000年 | 45篇 |
1999年 | 43篇 |
1998年 | 34篇 |
1997年 | 26篇 |
1996年 | 33篇 |
1995年 | 10篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 15篇 |
1980年 | 28篇 |
1979年 | 22篇 |
1978年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 24篇 |
1973年 | 14篇 |
1972年 | 12篇 |
排序方式: 共有2008条查询结果,搜索用时 15 毫秒
1.
Masaaki Sugihara 《Numerische Mathematik》1997,75(3):379-395
Summary. In the light of the functional analysis theory we establish the optimality of the double exponential formula. The argument
consists of the following three ingredients: (1) introduction of a number of spaces of functions analytic in a strip region
about the real axis, each space being characterized by the decay rate of their elements (functions) in the neighborhood of
the infinity; (2) proof of the (near-) optimality of the trapezoidal formula in each space introduced in (1) by showing the
(near-) equality between an upper estimate for the error norm of the trapezoidal formula and a lower estimate for the minimum
error norm of quadratures; (3) nonexistence theorem for the spaces, the characterizing decay rate of which is more rapid than
the double exponential.
Received September 15, 1995 / Accepted December 14, 1995 相似文献
2.
3.
4.
In this paper, we provide numerical means to compute the quasi-stationary (QS) distributions inM/GI/1/K queues with state-dependent arrivals andGI/M/1/K queues with state-dependent services. These queues are described as finite quasi-birth-death processes by approximating the general distributions in terms of phase-type distributions. Then, we reduce the problem of obtaining the QS distribution to determining the Perron-Frobenius eigenvalue of some Hessenberg matrix. Based on these arguments, we develop a numerical algorithm to compute the QS distributions. The doubly-limiting conditional distribution is also obtained by following this approach. Since the results obtained are free of phase-type representations, they are applicable for general distributions. Finally, numerical examples are given to demonstrate the power of our method. 相似文献
5.
Recently extremal double circulant self-dual codes have been classified for lengths n ≤ 62. In this paper, a complete classification
of extremal double circulant self-dual codes of lengths 64 to 72 is presented. Almost all of the extremal double circulant
singly-even codes given have weight enumerators for which extremal codes were not previously known to exist. 相似文献
6.
7.
Frequency dependence of ac conductivity from 1 to 105 Hz and time series of the conductivity at 2 kHz were measured along c-axis of thulium nitrate crystal, Tm(NO3)36H2O at temperatures from 203.15 to 293.15 K. The meta-stability was observed. The frequency spectra of the conductivity were similar to those in disorder system. Aging effect was observed. Non-periodic instability (burst) was found. Non-linear dynamical property was characterized by 1/f noise spectrum, limit cycle in return map and dependence of correlation exponent on embedding dimension. 相似文献
8.
Md. Nur Alam Per B. Zetterlund Masayoshi Okubo 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4995-5004
Bimolecular termination in nitroxide‐mediated radical polymerization in miniemulsion has been investigated through the heating of a polystyrene–2,2,6,6‐tetramethylpiperidinyl‐1‐oxy macroinitiator and its 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy analogue in an aqueous toluene dispersion with sodium dodecyl benzenesulfonate as a surfactant at 125 °C. The level of bimolecular termination by combination, evaluated from the high‐molecular‐weight shoulder, was higher in miniemulsion than in solution and increased with decreasing particle size. Quantitative analysis revealed that these results cannot be rationalized solely by nitroxide partitioning to the aqueous phase. The results are explained by an interface effect, by which nitroxide is adsorbed or located at the aqueous–organic interface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4995–5004, 2007 相似文献
9.
The potential of the internal rotation of the methyl group was determined for o-, m-, and p-fluorotoluene cations by pulsed field ionization spectroscopy. The potential of the internal rotational motion was also surveyed for other toluene derivative cations. It was found that the barrier height generally increases by ionization. The increase in the barrier height has been discussed in connection with the reduction of the internal rotational constant B by ionization. The geometrical distortion of the methyl group during the internal rotation has been suggested. 相似文献
10.
Shigeru Tasaka Norihiro Inagaki Masaaki Igawa 《Journal of Polymer Science.Polymer Physics》1991,29(6):691-694
The permeability of annealed poly (l-(trimethylsilyl)-l-propyne) was studied from the viewpoint of structural information obtained from x-ray diffraction and density. The sample cast from benzene solution had low density (0.82 g/cm3) and high permeability, whereas the annealed sample had a higher density (0.88 g/cm3) and permeability lower by two orders of magnitude. The smaller-angle x-ray diffraction peak for each sample, which was likely to reflect the distance between intermolecular chains, increased in intensity and shifted toward higher angle, corresponding to the change of the density with annealing. The logarithmic oxygen permeability was proportional to the density, namely the free volume fraction correlated with the diffusion coefficient and controlled by annealing and swelling by alcohols. 相似文献