全文获取类型
收费全文 | 216篇 |
免费 | 34篇 |
国内免费 | 9篇 |
专业分类
化学 | 24篇 |
晶体学 | 3篇 |
力学 | 6篇 |
综合类 | 5篇 |
数学 | 26篇 |
物理学 | 195篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 19篇 |
2013年 | 2篇 |
2012年 | 10篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 18篇 |
2008年 | 15篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1982年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有259条查询结果,搜索用时 15 毫秒
11.
Yi‐Fei Pu Patrick Siarry Ji‐Liu Zhou Ni Zhang 《Mathematical Methods in the Applied Sciences》2014,37(12):1784-1806
Traditional integer‐order partial differential equation based image denoising approach can easily lead edge and complex texture detail blur, thus its denoising effect for texture image is always not well. To solve the problem, we propose to implement a fractional partial differential equation (FPDE) based denoising model for texture image by applying a novel mathematical method—fractional calculus to image processing from the view of system evolution. Previous studies show that fractional calculus has some unique properties that it can nonlinearly enhance complex texture detail in digital image processing, which is obvious different with integer‐order differential calculus. The goal of the modeling is to overcome the problems of the existed denoising approaches by utilizing the aforementioned properties of fractional differential calculus. Using classic definition and property of fractional differential calculus, we extend integer‐order steepest descent approach to fractional field to implement fractional steepest descent approach. Then, based on the earlier fractional formulas, a FPDE based multiscale denoising model for texture image is proposed and further analyze optimal parameters value for FPDE based denoising model. The experimental results prove that the ability for preserving high‐frequency edge and complex texture information of the proposed fractional denoising model are obviously superior to traditional integral based algorithms, as for texture detail rich images. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
12.
Using only one diffractive element, the Talbot interferometer provides a robust and inherently stable method for reproducing fiber Bragg gratings with variable wavelengths, and reduces the complexity of the fiber grating fabrication system. However, the usable length of the grating is limited by the practical length of the mirrors. This paper presents a phase mask with two fixed prisms and two rotational prisms to inscribe fiber Bragg gratings with variable Bragg wavelengths. In this system, the fiber Bragg grating is inscribed by UV interference stripes of 193 nm derived from two rotational prisms and two fixed prisms, where phase mask is used as a beam splitter of ±1 order diffraction light. It is noteworthy that the tunable phase mask interferometer decreases the demand of the length of prism evidently. 相似文献
13.
C. -H. Chien Y. -C. Chen C. -C. Hsieh Y. -T. Chiou Y. -D. Wu T. -P. Chen 《Experimental Mechanics》2004,44(2):214-220
With the increasing application of flip-chip technology in the microelectronics industry, the adhesion strength of interfaces
in flip-chip microelectronic structures has become an important issue for manufacturing and operation. In this paper we present
an experimental investigation of the adhesive strength of underfill material to solder mask coated FR-4 substrate under thermal
cycling. The effects of the number of thermal cycles on interfacial strength were investigated by using the button shear test.
The relationship between interfacial strength and the thickness of solder mask was also examined. Furthermore, the morphologies
of fracture surfaces of the test specimens were analyzed by scanning electron microscopy. The results of this study show that
the interfacial strength of the underfill/solder mask/substrate joint was significantly reduced by thermal fatigue. Finally,
the degradation behavior and possible mechanisms were then determined on the basis of these observations. 相似文献
14.
In this paper, digital mask technique is presented, and a high-quality projecting reduction lithography system has been set up successfully. The core device of digital mask technique is digital micromirror device (DMD) which belongs to one of the electrically addressed spatial light modulators. The output image of DMD can be equivalent to a gray-scale mask of high precision, which can control the exposure precisely. If it is combined with a high-quality projecting reduction system, the fabrication of submicron diffractive optical elements can be realized successfully. The overall design of the system is described in detail, and some diffractive optical element masks are fabricated. Experimental results verify that the system is feasible. In the end, system characteristics and system error are summarized. 相似文献
15.
CHEN Genxiang JIAN Shuisheng GE Huang YANG Ling LI Xun WANG Wei 《Chinese Journal of Lasers》1997,6(2):185-188
l.IntroductionFibergratingshaveattractedanincreasingamountofattentionsineeG.Meltz[1Jandhisco-workersfirstdemonstratedinl989thatPermanentgratingscouldbewrittenbyex-peinganoPticalfiberfromthesidetotwointerferingbeamsofultraviolet(UV)light.Inrecentyears,avastresearchefforthasbeendevotedtoopticalfiberBragggratingsallovertheworld.Theirsimplicity,usefu1nesscoupledtotheiruniqueproPertiesandnu-merousadvantagesmakethemidealforawiderangeofimPOrtantapplicationsinopticalfibertelecommunications,lasersa… 相似文献
16.
二元光学元件及其应用 总被引:3,自引:0,他引:3
叙述一种新型衍射光学元件──—二元光学元件的设计原理及其制造方法。分析二元光学元件的衍射效率和色差,讨论光刻法对其最小特征线宽的限制因素,阐明二无光学元件的特点及应用。 相似文献
17.
LI Song & ZHOU Xinlong Department of Mathematics Zhejiang University Hangzhou China Instititute of Mathematics University of Duisburg-Essen D- Duisburg Germany 《中国科学A辑(英文版)》2006,49(4):439-450
This paper is concerned with multivariate refinement equations of the type where (?) is the unknown function defined on the s-dimensional Euclidean space Rs, a is a finitely supported nonnegative sequence on Zs, and M is an s×s dilation matrix with m := |detM|. We characterize the existence of L2-solution of refinement equation in terms of spectral radius of a certain finite matrix or transition operator associated with refinement mask a and dilation matrix M. For s = 1 and M = 2, the sufficient and necessary conditions are obtained to characterize the existence of continuous solution of this refinement equation. 相似文献
18.
The concept of a two-direction multiscaling functions is introduced. We investigate the existence of solutions of the two-direction
matrix refinable equation
where r × r matrices {P
k
+
} and {P
k
−
} are called the positive-direction and negative-direction masks, respectively. Necessary and sufficient conditions that the
above two-direction matrix refinable equation has a compactly supported distributional solution are established. The definition
of orthogonal two-direction multiscaling function is presented, and the orthogonality criteria for two-direction multiscaling
function is established. An algorithm for constructing a class of two-direction multiscaling functions is obtained. In addition,
the relation of both orthogonal two-direction multiscaling function and orthogonal multiscaling function is discussed. Finally,
construction examples are given. 相似文献
19.
建立了QuEChERS/高效液相色谱-串联质谱法测定面膜中10种荧光增白剂的分析方法。样品经水溶解后,以乙腈提取目标化合物,加入NaCl和无水MgSO_4,再通过C_(18)填料和正丙基乙二胺(PSA)净化,离心氮吹浓缩,乙腈定容后上机检测。C_(18)色谱柱分离,以10 mmol/L乙酸铵-乙腈梯度洗脱,多反应监测(MRM)正负离子模式交替扫描,外标法定量。结果显示,10种荧光增白剂在一定浓度范围内呈良好的线性,相关系数(r~2)均大于0.99,正离子模式的6种目标化合物检出限(S/N=3)为0.05~1.0μg/kg,定量下限为0.2~3.0μg/kg,负离子模式的4种目标化合物检出限(S/N=3)为0.1~1.0 mg/kg,定量下限为0.3~2.0 mg/kg;方法平均回收率为64.4%~106%,相对标准偏差(n=6)为2.6%~8.5%,该方法操作简单,回收率高,适用于面膜中10种荧光增白剂的测定。 相似文献
20.