全文获取类型
收费全文 | 142529篇 |
免费 | 13042篇 |
国内免费 | 9219篇 |
专业分类
化学 | 48549篇 |
晶体学 | 2025篇 |
力学 | 7970篇 |
综合类 | 1768篇 |
数学 | 44304篇 |
物理学 | 60174篇 |
出版年
2023年 | 655篇 |
2022年 | 2476篇 |
2021年 | 2349篇 |
2020年 | 2017篇 |
2019年 | 2317篇 |
2018年 | 2106篇 |
2017年 | 2231篇 |
2016年 | 2425篇 |
2015年 | 2138篇 |
2014年 | 3776篇 |
2013年 | 6046篇 |
2012年 | 4157篇 |
2011年 | 5103篇 |
2010年 | 5462篇 |
2009年 | 10435篇 |
2008年 | 11717篇 |
2007年 | 10317篇 |
2006年 | 8909篇 |
2005年 | 6545篇 |
2004年 | 6230篇 |
2003年 | 6136篇 |
2002年 | 9064篇 |
2001年 | 5537篇 |
2000年 | 5006篇 |
1999年 | 4673篇 |
1998年 | 4015篇 |
1997年 | 3052篇 |
1996年 | 2811篇 |
1995年 | 3108篇 |
1994年 | 2943篇 |
1993年 | 2395篇 |
1992年 | 1863篇 |
1991年 | 1455篇 |
1990年 | 1174篇 |
1989年 | 1005篇 |
1988年 | 991篇 |
1987年 | 728篇 |
1986年 | 489篇 |
1985年 | 1361篇 |
1984年 | 955篇 |
1983年 | 705篇 |
1982年 | 974篇 |
1981年 | 1138篇 |
1980年 | 1003篇 |
1979年 | 891篇 |
1978年 | 802篇 |
1977年 | 675篇 |
1976年 | 647篇 |
1974年 | 421篇 |
1973年 | 570篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Polymethyl methacrylate (PMMA) is one of the most commonly used optical materials. However, the application of it in the area of optical communication is strongly limited by the intrinsic absorption loss of carbon-hydrogen stretching vibration. In this paper, we present a method to solve the problem by adopting the hollow-core fibers with cobweb cladding structure. The fibers use a single dielectric material and may solve the problem of structural support. Thus the feasibility of the “OmniGuide” fibers is improved, while a series of advantages of the “OmniGuide” hollow-core fiber are retained. It is promising that a fiber with low transmission loss, high bandwidth, large-core, and low costs can be designed and fabricated using PMMA. At the same time, a very broad range of the wavelengths (from visible to near infrared region, for instance, wavelengths at 0.65-1.12 μm, and even 1.30 μm, 1.54 μm and their neighbors) may be adopted for signal wavelength. 相似文献
92.
Well-Posedness by Perturbations of Variational Problems 总被引:3,自引:0,他引:3
Lemaire B. Ould Ahmed Salem C. Revalski J. P. 《Journal of Optimization Theory and Applications》2002,115(2):345-368
In this paper, we consider the extension of the notion of well-posedness by perturbations, introduced by Zolezzi for optimization problems, to other related variational problems like inclusion problems and fixed-point problems. Then, we study the conditions under which there is equivalence of the well-posedness in the above sense between different problems. Relations with the so-called diagonal well-posedness are also given. Finally, an application to staircase iteration methods is presented. 相似文献
93.
WANG Libin 《数学年刊B辑(英文版)》2002,23(4):439-454
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension. 相似文献
94.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
95.
96.
本文定义了二阶微分方程的弱 Carathéodory解 ,在不涉及紧型条件的情形下 ,直接用迭代法证明了 Banach空间二阶非线性常微分方程两点边值问题存在唯一解 ,并给出逼近解迭代序列的误差估计 ,对周期边值问题得到类似的结果 相似文献
97.
Filippo Bracci Roberto Tauraso Fabio Vlacci 《Journal of Mathematical Analysis and Applications》2002,270(2):1131-473
Let f,g be two commuting holomorphic self-maps of the unit disc. If f and g agree at the common Wolff point up to a certain order of derivatives (no more than 3 if the Wolff point is on the unit circle), then f≡g. 相似文献
98.
Recursive algorithms for the computation of standard deviation and average deviation are derived and their applications in data acquisition are discussed. The relative speeds and accuracies of the two algorithms are compared for synthetic data. The performance of recursive estimation under shot and proportional noise limitations is also described. As an example of the utility of these algorithms, absorbance data with constant confidence intervals are collected regardless of incident and transmitted intensities. The desired precision is specified prior to data acquisition and used to control signal-averaging of the data in real time. 相似文献
99.
100.
在长距离无线光通信中,接收点光功率密度与光束发散角平方呈反比关系,为了获得小的发散角和大的功率耦合效率,要求准直系统有较大的数值孔径(NA),但数值孔径过大会增加像差,因此合理设计功率耦合效率与准直系统的数值孔径就非常重要。该文对半导体激光器光束准直系统中功率耦合效率进行了研究,给出了半导体激光器光束功率耦合效率与k(孔径半径与孔径处等效光束半径之比)的关系表达式,并结合激光器光束准直系统,给出了半导体激光器光束功率耦合效率与准直系统数值孔径的关系表达式。该研究结论对于半导体激光器光束准直系统设计具有参考作用。 相似文献