全文获取类型
收费全文 | 1725篇 |
免费 | 567篇 |
国内免费 | 118篇 |
专业分类
化学 | 286篇 |
晶体学 | 29篇 |
力学 | 158篇 |
综合类 | 63篇 |
数学 | 478篇 |
物理学 | 1396篇 |
出版年
2024年 | 3篇 |
2023年 | 20篇 |
2022年 | 42篇 |
2021年 | 48篇 |
2020年 | 51篇 |
2019年 | 46篇 |
2018年 | 56篇 |
2017年 | 92篇 |
2016年 | 100篇 |
2015年 | 88篇 |
2014年 | 137篇 |
2013年 | 138篇 |
2012年 | 120篇 |
2011年 | 105篇 |
2010年 | 103篇 |
2009年 | 106篇 |
2008年 | 125篇 |
2007年 | 139篇 |
2006年 | 109篇 |
2005年 | 110篇 |
2004年 | 78篇 |
2003年 | 72篇 |
2002年 | 79篇 |
2001年 | 48篇 |
2000年 | 55篇 |
1999年 | 49篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 28篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2410条查询结果,搜索用时 15 毫秒
991.
谢海 《数学的实践与认识》2016,(13):148-153
由属性值贴近度和阈值λ可构建λ-容差关系,利用此λ-容差关系可定义直觉模糊决策信息系统属性约简的λ-可辨识矩阵,进一步可定义λ-辨识公式,最后通过λ-辨识公式的极小析取范式可以唯一确定直觉模糊决策信息系统所有的相对约简,从而可成功地解决求解直觉模糊决策信解息系统属性约简问题. 相似文献
992.
针对ECG信号的非线性和非平稳性,利用不同经验模态分解的小波软阈值方法对其进行降噪处理.根据希尔伯特-黄(Hilbert-Huang)变换提出的一系列的EMD算法,有EMD、EEMD、CEEMD等.首先,将含高斯白噪声的ECG信号分别进行EMD、EEMD、CEEMD分解,所得到的固有模态函数(IMF)分量是从高频到低频排列的,分别舍去前几层含噪IMF'进行重构去噪.由于舍去的IMF分量中含有少部分信号的细节信息,然后利用小波软阈值对前几层含噪IMF提取细节信息得到新的分量,再将剩余分量和新的分量重构去噪后的ECG信号.利用去噪信号图和不同性能指标验证了不同方法的有效性,得出了基于CEEMD的小波软阈值ECG降噪效果最佳.最后,用上述方法对MIT-BIH心电噪声库信号进行去噪处理,其结果与仿真实验相吻合. 相似文献
993.
Log Canonical Thresholds of Del Pezzo Surfaces 总被引:1,自引:0,他引:1
Ivan Cheltsov 《Geometric And Functional Analysis》2008,18(4):1118-1144
We study global log canonical thresholds of del Pezzo surfaces.
All varieties are assumed to be defined over .
Received: May 2007 Revision: October 2007 Accepted: April 2008 相似文献
994.
995.
We prove that if A is a finite set, and if
is an downwards-closed family of subsets of A, and if fx is the proportion of x-element subsets of A in
, then fa · fb fa + b – r, if r <
. We connect this result with the Weak Threshold Theorem. 相似文献
996.
A 3.5m fiber laser with low threshold power using a 12 cm long, 1 mol-% Er3+-doped ZBLAN fiber with core radiusa=5m and numerical aperture of 0.4 has been developed. The fiber laser was pumped at 650 nm with an Ar-laser-pumped dye-laser. The measured threshold power of 76 mW is 13 times lower than our previously reported value of 996 mW. The improvement is in good agreement with the theory developed in this paper. On the basis of this theory we show how the threshold power can be further reduced by optimizing the fiber design. The theory may be generally applied to mid-infrared fiber lasers pumped at short wavelengths. 相似文献
997.
本文讨论按生命周期方法开发大型软件的SA/SD自动转换技术,将知识引入转换工具,重点介绍三维十字链表的数据模型和转换过程中专家知识的组织和引用原则。 相似文献
998.
999.
Low thresholds for a nonconventional polymer blend—Amplified spontaneous emission and lasing in F81−x:SYx system
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haider Butt Kamran ul Hasan Jui‐Fen Chang Ayooye Abigael Olawoyin Richard Henry Friend 《Journal of Polymer Science.Polymer Physics》2016,54(1):15-21
A mixture of two polymer materials, poly (9,9‐dioctylfluorene) (F8), and one of the poly(para‐phenylenevinylene) derivatives, superyellow (SY) have been used to make F81?x:SYx polymer blend system. Under a 3–5 ns pulsed‐laser excitation, this system showed excellent optical properties with low threshold values of ≈14 µJ/cm2 and ≈8 µJ/cm2 for amplified spontaneous emission and optically pumped lasing, respectively. The proposed system was also electroluminescent and an interesting candidate for future research on polymer injection lasers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 15–21 相似文献
1000.
Organic single crystals of 4-methyl-3-nitrobenzoic acid (4M3N) have been grown by slow evaporation solution growth technique at room temperature. The single crystal X-ray diffraction study reveals that 4M3N crystallizes in monoclinic system with space group P21/n. The crystalline perfection of the crystal was analyzed by high resolution X-ray diffraction (HRXRD) measurements. The functional groups present in 4M3N have been identified from FT-IR and FT-Raman spectra. The lower cut-off wavelength of 4M3N is found to be 404 nm and the optical band gap is calculated as 2.91 eV. The refractive index shows normal behavior with wavelength. The physio chemical changes, decomposition and stability of the 4M3N compound were established by TG-DTA studies. Vickers microhardness measurement concludes that 4M3N belongs to soft material (n=2.5) category. The LDT value is found to be higher than that of KDP and some of the important organic NLO materials. The third order nonlinear refractive index and nonlinear absorption coefficient of the 4M3N have been measured by Z-scan studies. The imaginary and real parts of the third-order susceptibility values were determined as Im χ3=9.129×10−11 esu and Re χ3=1.4034×10−9 esu respectively. The dislocation density was calculated to be 3.0448×106 cm−2 which indicates the quality of the crystal. 相似文献