全文获取类型
收费全文 | 57135篇 |
免费 | 13832篇 |
国内免费 | 3737篇 |
专业分类
化学 | 48625篇 |
晶体学 | 476篇 |
力学 | 1134篇 |
综合类 | 164篇 |
数学 | 3433篇 |
物理学 | 6684篇 |
无线电 | 14188篇 |
出版年
2024年 | 50篇 |
2023年 | 283篇 |
2022年 | 402篇 |
2021年 | 653篇 |
2020年 | 2203篇 |
2019年 | 3575篇 |
2018年 | 1846篇 |
2017年 | 1453篇 |
2016年 | 4487篇 |
2015年 | 4682篇 |
2014年 | 4803篇 |
2013年 | 5558篇 |
2012年 | 4627篇 |
2011年 | 3939篇 |
2010年 | 4224篇 |
2009年 | 4244篇 |
2008年 | 3877篇 |
2007年 | 3277篇 |
2006年 | 2796篇 |
2005年 | 2772篇 |
2004年 | 2418篇 |
2003年 | 2148篇 |
2002年 | 2940篇 |
2001年 | 2107篇 |
2000年 | 1945篇 |
1999年 | 773篇 |
1998年 | 352篇 |
1997年 | 281篇 |
1996年 | 260篇 |
1995年 | 215篇 |
1994年 | 191篇 |
1993年 | 194篇 |
1992年 | 136篇 |
1991年 | 107篇 |
1990年 | 91篇 |
1989年 | 69篇 |
1988年 | 70篇 |
1987年 | 65篇 |
1986年 | 46篇 |
1985年 | 52篇 |
1984年 | 47篇 |
1983年 | 29篇 |
1982年 | 35篇 |
1981年 | 44篇 |
1980年 | 31篇 |
1979年 | 50篇 |
1978年 | 40篇 |
1977年 | 37篇 |
1976年 | 29篇 |
1974年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
A new topology for a photonic signal processor, which overcomes the basic recursive frequency response problem that limits the passband range, is presented. The structure is based on a new multiple-wavelength offset-cavity structure that is cascaded with a series of unbalanced delay line structures. This not only can synthesize a very narrow notch response with good shape factor but also permits a multifold extension of the free spectral range (FSR) and passband width. Results on the interference mitigation filter demonstrate a stopband of 1% of center frequency and a fourfold increase in the FSR and passband width, while also having a very small shape factor, in excellent agreement with predictions. 相似文献
53.
L. Sheeney‐Haj‐Ichia S. Pogorelova Y. Gofer I. Willner 《Advanced functional materials》2004,14(5):416-424
Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation. 相似文献
54.
M. Ganschow C. Hellriegel E. Kneuper M. Wark C. Thiel G. Schulz‐Ekloff C. Bruchle D. Whrle 《Advanced functional materials》2004,14(3):269-276
Dye‐loaded AlPO4‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative. 相似文献
55.
介绍了非规则LDPC码的发展并给出了其优势及缺点,重点论述用ACE算法来构造非规则LDPC码从而降低其差错平底特性。对降低非规则LDPC码的差错平底特性的其它方法提出了展望。 相似文献
56.
57.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
58.
基于体全息技术的WDM器件 总被引:2,自引:0,他引:2
利用体全息技术制作波分复用器件是一种新方法。本文介绍了此种方法的基本原理和器件的基本性能,并报道了国外对该项技术的研究进展。 相似文献
59.
60.
Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications 总被引:1,自引:0,他引:1
The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly. 相似文献