全文获取类型
收费全文 | 5301篇 |
免费 | 997篇 |
国内免费 | 528篇 |
学科分类
数理化 | 6826篇 |
出版年
2024年 | 23篇 |
2023年 | 123篇 |
2022年 | 198篇 |
2021年 | 203篇 |
2020年 | 204篇 |
2019年 | 196篇 |
2018年 | 193篇 |
2017年 | 143篇 |
2016年 | 258篇 |
2015年 | 266篇 |
2014年 | 266篇 |
2013年 | 346篇 |
2012年 | 499篇 |
2011年 | 551篇 |
2010年 | 327篇 |
2009年 | 334篇 |
2008年 | 350篇 |
2007年 | 291篇 |
2006年 | 265篇 |
2005年 | 210篇 |
2004年 | 185篇 |
2003年 | 127篇 |
2002年 | 146篇 |
2001年 | 112篇 |
2000年 | 121篇 |
1999年 | 109篇 |
1998年 | 94篇 |
1997年 | 107篇 |
1996年 | 86篇 |
1995年 | 79篇 |
1994年 | 63篇 |
1993年 | 72篇 |
1992年 | 42篇 |
1991年 | 63篇 |
1990年 | 42篇 |
1989年 | 36篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有6826条查询结果,搜索用时 0 毫秒
991.
992.
Xihong Zu Jian Gong Weiping Tu Yulin Deng 《Macromolecular rapid communications》2011,32(19):1526-1532
We report that the nanostructures of poly(styrene‐block‐4‐vinylpyridine) block copolymer (PS‐b‐P4VP) thin film on a wafer substrate can be re‐assembled by sequential vapor treatment using selected solvents. Metal or other inorganic nanoparticles that were randomly pre‐loaded inside or on the surface of PS‐b‐P4VP thin film could be pulled to the rim of PS and P4VP along with the movements of PS and P4VP blocks during the treatment. As a result, the patterned polymeric or inorganic/polymer composite nanoisland and nanoring arrays were fabricated.
993.
Chao‐Jian Chen Gong‐Yan Liu Ye‐Ting Shi Cong‐Shan Zhu Shao‐Peng Pang Xiang‐Sheng Liu Jian Ji 《Macromolecular rapid communications》2011,32(14):1077-1081
A novel comb‐like derivative CPEG‐g‐DNQ was prepared by incorporating light responsive 2‐diazo‐1,2‐naphthoquinone (DNQ) groups into the structure of comb‐like poly(ethylene glycol) (CPEG). DLS and TEM results showed that CPEG‐g‐DNQ self‐assembled into spherical micelles with an average size of about 135 nm in water. Upon exposure to light, the micelles could be disrupted because of the conversion of hydrophobic DNQ to hydrophilic 3‐indenecarboylic acid. Additionally, hydrophobic coumarin 102 was successfully loaded into the micelles and photo‐induced ON‐OFF release was demonstrated by fluorescence spectroscopy. MTT assay revealed that the micelles are biocompatible. These photo‐responsive micelles might have great potential for controlled release of hydrophobic drugs.
994.
基于BV理论建立基片及其上方回转椭球粒子的复合散射模型,通过矢量球谐函数展开,对散射过程进行了分析,对散射场及微分散射截面详细求解,并给出了数值计算结果,与离散源方法做了比较,同时退化为球粒子与扩展Mie理论做了比较,说明了此方法的有效性。并详细讨论分析了微分散射截面随不同入射角,散射角,回转椭球粒子的尺寸、长短轴比例,距基片的距离,介电常数,粒子取向角的变化关系。结果表明:同一散射角下入射角越大,其微分散射截面越大;粒子尺寸越大,相互作用越大,其微分散射截面越大;长短轴比例越大,其微分散射截面越小;距离基片的距离越大,微分散射截面越大;微分散射截面的变化主要依赖于相对介电常数实部、虚部数值较大的一方,并且随粒子取向角的增大而增大。 相似文献
995.
996.
提出了一种曲折双脊波导慢波结构,理论分析了慢波结构的高频特性,并在此基础上设计了工作在Ka波段的曲折双脊波导行波管.利用三维粒子模拟软件MAGIC 3D建立了曲折双脊波导行波管模型,并对行波管中的注-波互作用进行了模拟分析.在相同工作条件下,分析比较了曲折双脊波导行波管和曲折波导行波管的各种性能参量,从中发现:在行波管增益峰值相近的情况下,曲折双脊波导行波管具有更好的带宽性能,其3 dB增益带宽为22%;同时具有更高的电子效率,其峰值接近9%. 相似文献
997.
<正>We presented a novel orthogonally linearly polarized Nd:YVO4 laser.Two pieces of a-cut grown-together composite YVO4/Nd:YVO4 crystals were placed in the resonant cavity with the c-axis of the two crystals orthogonally.The polarization and power performance of the orthogonally polarized laser were investigated.A 26.2-W orthogonally linearly polarized laser was obtained.The power ratio between the two orthogonally polarized lasers was varied with the pump power caused by the polarized mode coupling.The longitudinal modes competition and the corresponding variable optical beats were also observed from the orthogonally polarized laser.We also adjusted the crystals with their c-axis parallele to each other,and a 40.7-W linearly polarized TEMoo laser was obtained,and the beam quality factors were Mx2=1.37 and My2 =1.25. 相似文献
998.
Linghong Yi Liya Zhou Zhengliang Wang Jianhua Sun Fuzhong Gong Weiping Wan Wei Wang 《Current Applied Physics》2010,10(1):208-213
A red phosphor KGd(MoO4)2:Eu3+ was prepared by solid-state reaction technique at high temperature. Its photoluminescent property was investigated and the optimum concentration of Eu3+ doped in the KGd(MoO4)2 is 25 mol%. Compared with Y2O2S:0.05Eu3+, the obtained KGd(MoO4)2:Eu3+ shows wider excitation band around 400 nm, higher intensity of Eu3+ 5D0–7F2 emission upon excitation 393 nm, and the CIE chromaticity coordinates (x = 0.655, y = 0.345) are closer to the standard of National Television Standard Committee (NTSC). The optical properties of KGd(MoO4)2:Eu3+ suggest that it is an efficient red-emitting phosphor for light-emitting diode applications. 相似文献
999.
This article presents both theoretical and experimental studies on the superharmonic generation and its imaging in biological tissues. A superharmonic component is defined as a summation of the third-, fourth-, and fifth-order harmonics. A superharmonic signal is produced using an 8-mm-diam, 2.5-MHz planar piston source that is excited by eight-cycle, 2.5-MHz tone bursts. Axial and lateral field distributions of the superharmonic component and the second harmonic are first calculated based on the nonlinear KZK model and then compared with those experimentally determined at two different source pressures of 0.5 and 1 MPa. Results indicate that the amplitude of the superharmonic component can exceed that of the second harmonic, depending on the axial distance and the fundamental pressure amplitude. Also, the 3-dB beamwidth of the superharmonic component is about 23% narrower than that of the second harmonic. Additional experiments are performed in vitro using liver and fatty tissues in transmission mode and produced two-dimensional images using the fundamental, the second harmonic, and the superharmonic signals. Although the clinical applicability of this work still needs to be assessed, these results indicate that the superharmonic image quality is better than that of the other two images. 相似文献
1000.
An efficient solid-phase methodology has been developed for the synthesis of 2-aminobenzoxazole derivatives. The key step in this procedure involves preparation of polymer-bound 2-mercaptobenzoxazole resins 3 by reaction of the Merrifield resin with 2-aminophenols and CS(2) in the presence of DIC in MeCN. Oxidation of the resulting resins followed by treatment with amines gives the desired 2-aminobenzoxazole products 5. Further diversification can be introduced to the key resin 11, derived from the nitro group containing resin 3c. This process produces the corresponding amine, which upon reaction with acid chlorides and isocyanates can be used to generate various 6-functionalized 2-aminobenzoxazole analogues 13 and 15. 相似文献