全文获取类型
收费全文 | 1042篇 |
免费 | 36篇 |
国内免费 | 5篇 |
专业分类
化学 | 787篇 |
晶体学 | 24篇 |
力学 | 22篇 |
数学 | 54篇 |
物理学 | 196篇 |
出版年
2023年 | 14篇 |
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 14篇 |
2017年 | 11篇 |
2016年 | 27篇 |
2015年 | 21篇 |
2014年 | 17篇 |
2013年 | 48篇 |
2012年 | 62篇 |
2011年 | 63篇 |
2010年 | 44篇 |
2009年 | 41篇 |
2008年 | 60篇 |
2007年 | 86篇 |
2006年 | 70篇 |
2005年 | 43篇 |
2004年 | 68篇 |
2003年 | 46篇 |
2002年 | 38篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1987年 | 3篇 |
1985年 | 16篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1968年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1083条查询结果,搜索用时 15 毫秒
951.
952.
Look-up table and Gaussian filter-based inverse halftoning method excellent in gray-scale reproducibility of details and flat regions 总被引:1,自引:0,他引:1
Halftoning is a technique in which gray-scale images are converted into binary ones, and has been used widely in many practical
image processing applications. On the other hand, inverse halftoning is a technique of reproducing a grayscale image from
a binary one. One of the sophisticated inverse halftoning methods which can yield a high quality grayscale image is that based
on a look-up table (LUT). In this paper, a new inverse halftoning method based on a combination of this LUT method and a Gaussian
filter is discussed. Here, the output gray-scale image is reproduced by blending the output of the LUT-based inverse halftoning
and that of the Gaussian filtering appropriately in accordance with local statistics of the image. The effectiveness and the
validity of the described method are verified through experiments. 相似文献
953.
Tsuyoshi Michinobu Hiroe Kumazawa Eiji Otsuki Hiroaki Usui Kiyotaka Shigehara 《Journal of polymer science. Part A, Polymer chemistry》2009,47(15):3880-3891
A novel class of carbazole polymers, nitrogen‐linked poly(2,7‐carbazole)s, was synthesized by polycondensation between two bifunctional monomers using the palladium‐catalyzed amination reaction. The polymers were characterized by 1H NMR, Infrared, Gel permeation chromatography, and MALDI‐TOF MS and it was revealed that the combination of the monomer structures is important for producing high molecular weight polymers. Thermal analysis indicated a good thermal stability with high glass transition temperatures, e.g., 138 °C for the higher molecular weight polymer P2 . To pursue the application possibilities of these polymers, their optical properties and energy levels were investigated by UV‐Vis absorption and fluorescence spectra as well as their electrochemical characteristics. Although the blue light emission was indeed observed for all polymers in solution, the quantum yields were very low and the solid films were not fluorescent. On the other hand, the HOMO levels of the polymers estimated from the onset potentials for the first oxidation in the solid thin films were relatively high in the range of ?5.12 to ?5.20 eV. Therefore, light emitting diodes employing these polymers as a hole‐transport layer and iridium(III) complex as a triplet emitter were fabricated. The device of the nitrogen‐linked poly(2,7‐carbazole) P3 with p,p′‐biphenyl spacer, which has a higher HOMO level and a higher molecular weight, showed a much better performance than the device of P2 with m‐phenylene spacer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3880–3891, 2009 相似文献
954.
955.
Kiyoshi Hosono 《Discrete Mathematics》2008,308(20):4696-4709
Let P be a finite point set in general position in the plane. We consider empty convex subsets of P such that the union of the subsets constitute a simple polygon S whose dual graph is a path, and every point in P is on the boundary of S. Denote the minimum number of the subsets in the simple polygons S's formed by P by fp(P), and define the maximum value of fp(P) by Fp(n) over all P with n points. We show that ⌈(4n-17)/15⌉?Fp(n)?⌊n/2⌋. 相似文献
956.
Eiji Nakashima Kazuo Neriishi Atsushi Minamoto 《Annals of the Institute of Statistical Mathematics》2008,60(3):465-482
In analyses of bivariate ordered polytomous cataract data from atomic-bomb survivors, we compared two methods, the univariate
worse-eye method, and the bivariate generalized estimating equations (GEE’s) method using global odds ratio by Williamson
et al. (Journal of the American Statistical Association, 90, 1432–1437, 1995). When the association was large and only subject level covariates were used, model selection in the univariate
and bivariate methods resulted in the same mean model and similar risk estimates. We showed that the mean parameter and the
standard error (SE) in the univariate model are emphasized relative to those in the bivariate model, the biases of which are
negligible when the association between both eyes is large. Large sample simulation studies indicated that the univariate
Wald statistics are slightly conservative. The simulations also showed that, in bivariate cases, irrespective of the degree
of association, the independence estimating equations method with robust SE, and the GEE method with model-based and robust
SE are almost fully efficient in parameter estimation when only subject level covariates are included in the mean. 相似文献
957.
Eiji Ihara Naoki Yoshida Jun‐Ichi Ikeda Tomomichi Itoh Kenzo Inoue 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2636-2641
The cationic polymerization of isobutyl vinyl ether was examined with transition‐metal ate complexes with trityl cation as initiators. The initiators were generated by the reaction of triphenylmethyl chloride [trityl chloride (TrCl)] with ate complexes of Nb, Mo, and W with lithium cation, which were obtained in situ by the reaction of the transition‐metal halides with anionic reagents (organolithium or lithium amide). When the polymerization was initiated with a mixture of TrCl and Li+[NbH5(NnBuPh)]?, the resulting poly(isobutyl vinyl ether)s had narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight = 1.13–1.20). Although the polymerization was supposed to be initiated by the electrophilic attack of the trityl cation, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of the resulting poly(isobutyl vinyl ether)s revealed the presence of H at the α‐chain end. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2636–2641, 2006 相似文献
958.
Marek?FilaEmail author Juan?Luis?Vázquez Michael?Winkler Eiji?Yanagida 《Archive for Rational Mechanics and Analysis》2012,204(2):599-625
We study the asymptotic behaviour of positive solutions of the Cauchy problem for the fast diffusion equation as t approaches the extinction time. We find a continuum of rates of convergence to a self-similar profile. These rates depend
explicitly on the spatial decay rates of the initial data. 相似文献
959.
A simple multilevel halftoning method, which is based on the conventional error diffusion method and realizes halftoning excelled in the distribution of dots, is proposed. The proposed method consists of three steps, e.g., the image decomposition, the generation of binary halftone images by the error diffusion, and the synthesis of a multilevel halftone image, and each step does not require a complicated algorithm. The effectiveness of the proposed method is indicated by applying it to three- and four-level halftoning of gray-tone and natural images. 相似文献
960.
Taku Hayashi Ka Hung Lee Hiroki Iida Eiji Yashima Stephan Irle Yuh Hijikata 《Journal of computational chemistry》2019,40(23):2036-2042
Attracted by the numerous regulatory functions of double-helical biopolymers such as DNA, many researchers have synthesized various double-helical systems. A recently synthesized double-stranded helical oligomer covalently bridged by rotary boronate esters (BBDD) was shown to undergo helix-inversion that might serve as platform to design rotor systems. However, the detailed helix-inversion mechanism could not be investigated experimentally. Direct molecular dynamics simulations based on density-functional tight-binding energies and gradients computed on-the-fly reveal that disentanglement to the unraveled form and following exchange of the twisted terminal trimethylsilyl (TMS) groups are prerequisites for the observed helix-inversion. The potential of mean force confirms that the originally assumed “concurrent” rotation of the boronate esters and the helix-inversion involves shorter time scale “step-wise” processes, triggered by the disentanglement and exchange of the TMS groups. These results indicate that inversion dynamics of double-helical molecules such as BBDD may be controllable by chemical fine-tuning of the terminal groups. © 2019 Wiley Periodicals, Inc. 相似文献