全文获取类型
收费全文 | 68139篇 |
免费 | 2728篇 |
国内免费 | 1526篇 |
专业分类
化学 | 34357篇 |
晶体学 | 983篇 |
力学 | 3809篇 |
综合类 | 85篇 |
数学 | 5679篇 |
物理学 | 27480篇 |
出版年
2022年 | 648篇 |
2021年 | 817篇 |
2020年 | 919篇 |
2019年 | 831篇 |
2018年 | 901篇 |
2017年 | 783篇 |
2016年 | 1371篇 |
2015年 | 1063篇 |
2014年 | 1502篇 |
2013年 | 3244篇 |
2012年 | 3249篇 |
2011年 | 3948篇 |
2010年 | 2741篇 |
2009年 | 2777篇 |
2008年 | 3420篇 |
2007年 | 3183篇 |
2006年 | 2978篇 |
2005年 | 2632篇 |
2004年 | 2333篇 |
2003年 | 2061篇 |
2002年 | 1907篇 |
2001年 | 3185篇 |
2000年 | 2345篇 |
1999年 | 1794篇 |
1998年 | 1279篇 |
1997年 | 1178篇 |
1996年 | 1001篇 |
1995年 | 938篇 |
1994年 | 836篇 |
1993年 | 721篇 |
1992年 | 1035篇 |
1991年 | 998篇 |
1990年 | 913篇 |
1989年 | 785篇 |
1988年 | 771篇 |
1987年 | 829篇 |
1986年 | 674篇 |
1985年 | 898篇 |
1984年 | 832篇 |
1983年 | 569篇 |
1982年 | 570篇 |
1981年 | 539篇 |
1980年 | 498篇 |
1979年 | 619篇 |
1978年 | 644篇 |
1977年 | 658篇 |
1976年 | 573篇 |
1975年 | 481篇 |
1974年 | 521篇 |
1973年 | 448篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We proposed an electro-optic modulator with two-bus one-ring (TBOR) structure to improve the extinction ratio and reduce insert loss. It has a dual output compared with one-bus one-ring structure. In addition, double-layer graphene makes it possible for the modulation in the visible to mid-infrared wavelength range. It shows that this new electro-optic modulator can present two switching states well with low insertion loss, high absorption and high extinction ratio. At , when the switching states are based on the chemical potential, and , the insertion losses of both output ports are less than 2 dB, the absorption of the output port coupled via a micro-ring reaches 45 dB and the extinction ratio reaches 14 dB. When the refractive index of the dielectric material is 4.2, the applied voltage will be less than 1.2 V, thus can be used in low-voltage CMOS technology. 相似文献
32.
33.
In this Letter,a novel system for adaptively correcting the phase of a dynamic multimode beam is proposed.While using merely one spatial light modulator,the phase measurement of the first-order diffraction pattern and the correction of the zeroth diffraction order are simultaneously realized.The real-time experimental result is obtained at a control rate of 10 Hz.The power-in-the-bucket value is improved from 38.5%to 61.8%,even with fundamental mode content that is consistently below 30%.To the best of our knowledge,this is the first implementation of real-time adaptive correction of the entire multimode beam. 相似文献
34.
Zhang Kailun Wu Hongjuan Wang Tian Yao Meng Xie Jixing Jiao Yunhong 《Journal of Thermal Analysis and Calorimetry》2021,145(6):3067-3075
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy... 相似文献
35.
36.
Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices.... 相似文献
37.
Dongping Wang Jie Dong Wenjing Fan Prof. Dr. Xiang-Ai Yuan Prof. Dr. Jian Han Prof. Dr. Jin Xie 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(22):8508-8512
An unprecedented Mn(I)-catalyzed selective hydroarylation and hydroalkenylation of unsaturated amides with commercially available organic boronic acids is reported. Alkenyl boronic acids have been successfully employed for the first time in Mn(I)-catalyzed carbon–carbon bond formation. A wide array of β-alkenylated amide products can be obtained in moderate to good yields, which offers practical access to five- and six-membered lactams. This protocol has predictable regio- and chemoselectivity, excellent functional group compatibility and ease of operation in air, representing a significant step-forward towards manganese-catalyzed C−C coupling. 相似文献
38.
39.