全文获取类型
收费全文 | 2189篇 |
免费 | 162篇 |
国内免费 | 158篇 |
专业分类
化学 | 269篇 |
晶体学 | 1篇 |
力学 | 165篇 |
综合类 | 15篇 |
数学 | 1357篇 |
物理学 | 702篇 |
出版年
2024年 | 4篇 |
2023年 | 34篇 |
2022年 | 30篇 |
2021年 | 36篇 |
2020年 | 51篇 |
2019年 | 46篇 |
2018年 | 51篇 |
2017年 | 82篇 |
2016年 | 81篇 |
2015年 | 58篇 |
2014年 | 136篇 |
2013年 | 150篇 |
2012年 | 128篇 |
2011年 | 153篇 |
2010年 | 127篇 |
2009年 | 148篇 |
2008年 | 134篇 |
2007年 | 143篇 |
2006年 | 118篇 |
2005年 | 95篇 |
2004年 | 96篇 |
2003年 | 86篇 |
2002年 | 75篇 |
2001年 | 46篇 |
2000年 | 48篇 |
1999年 | 49篇 |
1998年 | 52篇 |
1997年 | 40篇 |
1996年 | 38篇 |
1995年 | 23篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有2509条查询结果,搜索用时 15 毫秒
991.
设计出变焦投影物镜,能满足相同光学引擎、相同屏幕位置下不同屏幕尺寸的需要。考虑到所设计的系统为大相对孔径、中等视场和小变焦比,从变焦理论出发,采用正组补偿的机械补偿法,对变倍组进行合理的倍率选段,求出了高斯解;然后分组元选用合理的初始结构,利用ZEMAX光学设计软件进行优化设计,解决了变焦系统畸变难以控制的问题,并使用调制传递函数对整个系统进行了综合评价。设计结果表明:该变焦投影物镜系统的光学性能和成像质量均满足设计指标要求,能应用于101.6~177.8cm的大屏幕电视。 相似文献
992.
993.
本文研究了凸多胞形的锥体积泛函.利用投影体以及Lutwak、杨和张最近所建立的仿射等周不等式,得到了刻划平行四边形特征的一个崭新不等式和用锥体积泛函以及投影体的体积所表达的关于配极体体积的严格下界. 相似文献
994.
Yuan Xu 《Journal of Approximation Theory》2001,112(2):295
For the weight function (1−x2)μ−1/2 on the unit ball, a closed formula of the reproducing kernel is modified to include the case −1/2<μ<0. The new formula is used to study the orthogonal projection of the weighted L2 space onto the space of polynomials of degree at most n, and it is proved that the uniform norm of the projection operator has the growth rate of n(d−1)/2 for μ<0, which is the smallest possible growth rate among all projections, while the rate for μ0 is nμ+(d−1)/2. 相似文献
995.
In this paper, we consider convergence properties of a class of penalization methods for a general vector optimization problem with cone constraints in infinite dimensional spaces. Under certain assumptions, we show that any efficient point of the cone constrained vector optimization problem can be approached by a sequence of efficient points of the penalty problems. We also show, on the other hand, that any limit point of a sequence of approximate efficient solutions to the penalty problems is a weekly efficient solution of the original cone constrained vector optimization problem. Finally, when the constrained space is of finite dimension, we show that any limit point of a sequence of stationary points of the penalty problems is a KKT stationary point of the original cone constrained vector optimization problem if Mangasarian–Fromovitz constraint qualification holds at the limit point.This work is supported by the Postdoctoral Fellowship of Hong Kong Polytechnic University. 相似文献
996.
The surface defect of a moving spare part is measured by a line-scan system online. The experimental system is combined with a line-scan CCD, a LCD projector, a translation stage, and a personal computer. The deformed fringe patterns of the spare part can be captured and stored in the personal computer. The Fourier transform method is used to extract the fringe deformation. Following the geometric relationship between the fringe deformation and the surface height, the full-field surface 3D information can be obtained. Furthermore, the projection dual-frequency composite grating technique is used to solve 2π phase ambiguity problem because of some bigger surface defect steps. Some experimental results are presented to prove the feasibility of the proposed method and the inspection system. 相似文献
997.
A velocity sensing approach using the fringe projection technique is presented. The moving object is projected with a sinusoidal fringe pattern. A CCD camera located at a different view angle observes the projected fringes on the dynamic object. The long exposure time of the CCD camera makes the fringes blurred by linear motion. The blurred fringes provide additional information to describe the depth displacement, and therefore the velocity vector can be identified. There is no need to take multiple-shot measurements to address the change in 3D positions at a sequence of time. Only one-shot measurement is required. Consequently, there is no need to perform image registration. The full-field approach also makes it possible to simultaneously inspect several objects. 相似文献
998.
Igor Moret 《Journal of Computational and Applied Mathematics》1992,40(3):269-284
A direct method is described for the approximation of nonsimple turning points, corresponding to cusp points, of nonlinear operator equations depending on two parameters. The procedure is based on the application of a special projection method to the computation of simple turning points of a suitable augmented system. Numerical examples illustrate the features of the proposed algorithm. 相似文献
999.
A generalization is given of the canonical map from a discrete group into K
1 of the group C
*-algebra. Our map also generalizes Rieffel's construction of a projection in an irrational rotation C
*-algebra. 相似文献
1000.
The traditional fractional fringe method has been applied to measure 1-dimensional size of a block gauge using multiple wavelengths. Recently, similar methods have been used in pattern interferometry and also in pattern projection profilometry. However, the technique does not seem to be based on a well-established principle. In this paper, the fractional fringe method is formulated on the basis of the least squares method and on its basis effects of errors in fractional fringes and wavelengths are analyzed and the effective selection of wavelengths is considered. 相似文献