全文获取类型
收费全文 | 21147篇 |
免费 | 3939篇 |
国内免费 | 3189篇 |
专业分类
化学 | 15871篇 |
晶体学 | 411篇 |
力学 | 1133篇 |
综合类 | 209篇 |
数学 | 2383篇 |
物理学 | 8268篇 |
出版年
2024年 | 55篇 |
2023年 | 440篇 |
2022年 | 770篇 |
2021年 | 901篇 |
2020年 | 998篇 |
2019年 | 983篇 |
2018年 | 821篇 |
2017年 | 841篇 |
2016年 | 1157篇 |
2015年 | 1188篇 |
2014年 | 1507篇 |
2013年 | 1801篇 |
2012年 | 2128篇 |
2011年 | 2180篇 |
2010年 | 1536篇 |
2009年 | 1390篇 |
2008年 | 1574篇 |
2007年 | 1234篇 |
2006年 | 1132篇 |
2005年 | 932篇 |
2004年 | 780篇 |
2003年 | 565篇 |
2002年 | 495篇 |
2001年 | 405篇 |
2000年 | 316篇 |
1999年 | 362篇 |
1998年 | 246篇 |
1997年 | 182篇 |
1996年 | 223篇 |
1995年 | 184篇 |
1994年 | 165篇 |
1993年 | 123篇 |
1992年 | 106篇 |
1991年 | 109篇 |
1990年 | 98篇 |
1989年 | 77篇 |
1988年 | 47篇 |
1987年 | 36篇 |
1986年 | 56篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Lei Liu 《Journal of Mathematical Analysis and Applications》2007,328(2):1484-1486
In this note, we generalize the inequality about the trace of positive semidefinite matrix trk(AB)?k(trA)k(trB) to Hilbert space, and obtain a relevant inequality about positive trace class operator. 相似文献
92.
93.
Zhitian Liu Lei Wang Junwu Chen Feng Wang Xiaoying Ouyang Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):756-767
2,5‐Bis(2‐bromofluorene‐7‐yl)silole was prepared by a modified one‐pot synthesis with a reverse addition procedure, from which novel silole‐containing polyfluorenes with binary random and alternating structures (silole contents between 4.5 and 25% and high Mw up to 509 kDa were successfully synthesized. The well‐defined repeating unit of the alternating copolymer comprises a terfluorene and a silole ring. Optoelectronic properties including UV absorption, electrochemistry, photoluminescence (PL), and electroluminescence (EL) of the copolymers were examined. The different excitation energy transfers from fluorene to silole of the copolymers in solution and in the solid state were compared. The films of the copolymers showed silole‐dominant green emissions with high absolute PL quantum yields up to 83%. EL devices of the copolymers with a configuration of ITO/PEDOT/copolymer/Ba/Al displayed exclusive silole emissions peaked at around 543 nm and the highest EL efficiency was achieved with the alternating copolymer. Using the alternating copolymer and poly(9,9‐dioctylfluorene) as the blend‐type emissive layer, a maximum external quantum efficiency of 1.99% (four times to that of the neat film) was realized, which was a high efficiency so far reported for silole‐containing polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 756–767, 2007 相似文献
94.
A Generalized Optical Logic Element or GOLE is device that performs any of the 16 Boolean logic operations on signals in an optical beam with very fast switching among functions. The advantages of a generalized or universal gate in manufacturing are obvious. Extremely flexible functioning becomes possible if the GOLE functionality is switched in response to earlier computations. Likewise Field Programmable Gate Arrays or FPGAs can be used to fix the GOLE functions, making one of the most powerful and flexible processor units ever designed - called a Field GOLE. Such systems can be made in bulk optics to utilize Spatial Light Modulator or SLM capabilities, but integrated optics on silicon will be the choice for most applications. GOLEs can be generalized in several ways to become Fredkin gates and generalized Fredkin gates. They can also be cascaded similarly to electronic gates. 相似文献
95.
96.
Hong-Ming Yin 《NoDEA : Nonlinear Differential Equations and Applications》2007,13(5-6):735-757
In this paper we study a phase-change problem arising from induction heating. The mathematical model consists of time-harmonic
Maxwell’s system in a quasi-stationary field coupled with nonlinear heat conduction. The enthalpy form is used to characterize
the phase-change in the material. It is shown that the problem has a global solution. Moreover, it is shown that the solution
is unique and regular in one-space dimension even with an unbounded resistivity.
This work is supported in part by a NSF grant: DMS-0102261 相似文献
97.
98.
99.
针对磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的特点,对常规单沟道HEMT的小信号物理模型进行了修正,提出了一种新的用于复合沟道HEMT的小信号物理模型,用商用器件模拟软件ISE(integrated systems engineering)对其进行了仿真验证,对比了实测和仿真的I-V特性及转移特性曲线,重点研究了在InGaAs/InP双层沟道中考虑量子效应后的电场和电流密度随着不同栅电压的变化趋势,研究结果表明,由于在沟道中存在量子效应,在栅下靠源端低电场区域,电流主要分布在InGaAs沟道
关键词:
高电子迁移率晶体管
复合沟道
物理模型
磷化铟 相似文献
100.