全文获取类型
收费全文 | 175973篇 |
免费 | 1838篇 |
国内免费 | 478篇 |
专业分类
化学 | 84497篇 |
晶体学 | 2053篇 |
力学 | 6704篇 |
综合类 | 7篇 |
数学 | 15938篇 |
物理学 | 48961篇 |
无线电 | 20129篇 |
出版年
2020年 | 1232篇 |
2019年 | 1296篇 |
2018年 | 1605篇 |
2017年 | 1610篇 |
2016年 | 2714篇 |
2015年 | 1694篇 |
2014年 | 2701篇 |
2013年 | 6863篇 |
2012年 | 5354篇 |
2011年 | 6783篇 |
2010年 | 4722篇 |
2009年 | 4980篇 |
2008年 | 6693篇 |
2007年 | 6958篇 |
2006年 | 6563篇 |
2005年 | 6151篇 |
2004年 | 5516篇 |
2003年 | 4784篇 |
2002年 | 4785篇 |
2001年 | 5200篇 |
2000年 | 4139篇 |
1999年 | 3357篇 |
1998年 | 2994篇 |
1997年 | 2941篇 |
1996年 | 2670篇 |
1995年 | 2546篇 |
1994年 | 2519篇 |
1993年 | 2286篇 |
1992年 | 2534篇 |
1991年 | 2636篇 |
1990年 | 2405篇 |
1989年 | 2378篇 |
1988年 | 2298篇 |
1987年 | 1975篇 |
1986年 | 1948篇 |
1985年 | 2443篇 |
1984年 | 2554篇 |
1983年 | 2133篇 |
1982年 | 2278篇 |
1981年 | 2177篇 |
1980年 | 2101篇 |
1979年 | 2183篇 |
1978年 | 2350篇 |
1977年 | 2216篇 |
1976年 | 2256篇 |
1975年 | 2144篇 |
1974年 | 2181篇 |
1973年 | 2188篇 |
1972年 | 1446篇 |
1971年 | 1295篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
23.
24.
25.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
26.
27.
Stievano I.S. Maio I.A. Canavero F.G. Siviero C. 《Advanced Packaging, IEEE Transactions on》2006,29(1):31-38
This paper addresses the impact of device macromodels on the accuracy of signal integrity and performance predictions for critical digital interconnecting systems. It exploits nonlinear parametric models for both single-ended and differential devices, including the effects of power supply fluctuations and receiver bit detection. The analysis demonstrates that the use of well-designed macromodels dramatically speeds up the simulation as well it preserves timing accuracy even for long bit sequences. 相似文献
28.
de Oliveira J.C. Hosseini M. Shirmohammadi S. Malric F. Nourian S. El Saddik A. Georganas N.D. 《Multimedia, IEEE》2003,10(3):18-29
Using Java-based tools in multimedia collaborative environments accessed over the Internet can increase an application's client base. Most operating systems support Java, and its "compile once-run everywhere" architecture is easy to maintain and update. The Java-based tools presented here let users share Internet resources, including resources originally designed for single use. 相似文献
29.
Experimental and numerical assessment of gate-lag phenomena in AlGaAs-GaAs heterostructure field-effect transistors (FETs) 总被引:1,自引:0,他引:1
Verzellesi G. Mazzanti A. Basile A.F. Boni A. Zanoni E. Canali C. 《Electron Devices, IEEE Transactions on》2003,50(8):1733-1740
Gate-lag effects are characterized in AlGaAs-GaAs heterostructure field-effect transistors (HFETs) by means of measurements and numerical device simulations. Gate lag increasingly affects device switching at increasing ungated recess extension, suggesting that responsible deep levels be located at the ungated, recess surface of the HFET. Gate lag diminishes by making the off-state gate-source voltage less negative and by increasing the drain bias. Increasing the temperature makes the turn-on transient faster at low drain bias, while slightly delaying it at high drain bias. Numerical device simulations accounting for acceptor-like traps at the ungated surface predict gate-lag phenomena in good agreement with experiments, reproducing correctly the observed bias and temperature dependences. Simulations show that surface states behave, during the turn-on transient, as hole traps capturing holes attracted at the ungated surface by the negative trapped charge. 相似文献
30.
Piedade M. Sousa L. A. de Almeida T. M. Germano J. da Costa B. A. Lemos J. M. Freitas P. P. Ferreira H. A. Cardoso F. A. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(11):2384-2395
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays 相似文献