首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   631篇
  免费   150篇
  国内免费   79篇
化学   406篇
晶体学   6篇
力学   10篇
综合类   2篇
数学   1篇
物理学   435篇
  2024年   2篇
  2023年   2篇
  2022年   10篇
  2021年   13篇
  2020年   23篇
  2019年   14篇
  2018年   16篇
  2017年   21篇
  2016年   30篇
  2015年   45篇
  2014年   48篇
  2013年   61篇
  2012年   49篇
  2011年   69篇
  2010年   51篇
  2009年   60篇
  2008年   61篇
  2007年   55篇
  2006年   56篇
  2005年   29篇
  2004年   34篇
  2003年   27篇
  2002年   21篇
  2001年   13篇
  2000年   18篇
  1999年   4篇
  1998年   6篇
  1997年   4篇
  1996年   2篇
  1995年   3篇
  1994年   2篇
  1993年   3篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1987年   2篇
  1984年   1篇
  1981年   1篇
排序方式: 共有860条查询结果,搜索用时 15 毫秒
51.
首先, 在碱性条件下, 不使用表面活性剂, 采用St?ber小球法以正硅酸四乙酯(TEOS)和正硅酸四丙酯(TPOS)为硅源, 生成初级氧化硅球形颗粒; 然后, 使酚醛树脂(间苯二酚和甲醛)与球形氧化硅的羟基共缩合形成酚醛树脂-氧化硅复合材料; 最后, 经高温碳化和酸蚀获得了空心碳纳米球(HCNSs). 通过调节TEOS/TPOS的摩尔比获得了一系列具有良好的单分散性且粒径、 壁厚可调节的HCNSs, 其粒径和壁厚分别在280~430 nm和15~63 nm的范围内. 仅以TPOS为硅源时合成的HCNS-0/4具有较大的粒径(426 nm)和壁厚(63 nm)、 较高的比表面积(1216 m2/g)和孔容(0.508 cm3/g), 并且具有较大的挥发性有机化合物(VOCs)吸附性能, 其正己烷、 甲苯和油气的静态吸附容量分别为2.02, 1.42和0.926 g/g, 正己烷和甲苯的动态吸附容量分别为2.01 g/g和1.37 g/g, 均远高于商业化活性炭.  相似文献   
52.
表面等离子共振光谱(Surface Plasmon Resonance,SPR)是近年来得到快速发展的一门技术。它是一种无标记的、可用于实时定量检测某些固定于传感芯片上的组分与被结合物种间的绑定亲合度(binding affinity)、且可用于对相对小量物质进行检测的重要手段。由于它可方便地研究不同生物或化学物种的有关反应与动力学问题,因此具有重要的实用意义,受到广泛关注和重视。本文对有关等离子共振现象的形成及其作为敏感检测手段的机制、原理和改进等问题作了简要的介绍。  相似文献   
53.
Monodisperse polymeric nanospheres, which consist of polystyrene cores and poly(ethylene glycol) (PEG) branches on their surfaces, were prepared by the dispersion copolymerization of styrene (St) with PEG macromonomers that had a methacryloyl (MMA-PEG) or p-vinylbenzyl (St-PEG) end group in various organic solvent/water media. Electron spectroscopy for chemical analysis (ESCA) of the nanosphere surfaces indicated that PEG macromonomer chains were favorably located on their surfaces. The morphologies of the nanospheres were observed via a scanning electron micrograph (SEM), and particle sizes were estimated by a submicron particle analyzer. When both the concentration of macromonomers and molecular weight were higher, small nanospheres in diameter were obtained. Larger nanospheres in diameter were obtained using macromonomers with low molecular weight at lower concentration. The functions that correlate the diameter (Dn) on different concentration units were Dn = K[St]0.64[MMA-PEG]−0.53±0.01[I]−0.49 and Dn = K[St]0.80[St-PEG]−0.69±0.01[I]−0.22, where [I], [St], [MMA-PEG], and [St-PEG] are initiator, styrene, MMA-PEG, and St-PEG macromonomer concentration in feed, respectively. When the reaction parameters such as the molecular weight of the macromonomers were properly chosen, the particle size could be controlled in a range from ca. 80 to 3100 nm. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2155–2166, 1999  相似文献   
54.
This work demonstrates the UV nanoimprinting lithography (UV-NIL) of high refractive index and highly transparent polythioethers based on thiol-ene click chemistry. Herein, 9,9-bis(3-mercaptopropylphenylether)fluorene (BMPF) is designed as a new thiol monomer with a high refractive index, high transparency, and good processability for UV-NIL. Colorless polythioethers are synthesized from BMPF and ene monomers under mild thiol-ene click reaction conditions. Excellent transmittance (96%) of 400 nm light is observed in all the polymer films and high refractive index values of 1.5972–1.6382 are attained. UV-NIL using thiol-ene photopolymerization affords polymer nanoimprinting patterns with various features on the order of 100–500 nm without any fractures. To the best of our knowledge, this is the first report on UV-NIL of high refractive index and highly transparent polymers. Through proper monomer and polymer design, novel polythioethers with suitable glass transition temperature (T g) values are developed with high refractive index, high transparency, and good UV-NIL processability. Furthermore, UV-NIL based on thiol-ene click chemistry is accomplished at the nanoscale. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2175–2182  相似文献   
55.
注射用生物可降解胰岛素纳米微球的制备   总被引:10,自引:1,他引:10  
共聚物;药剂释放体系;注射用生物可降解胰岛素纳米微球的制备  相似文献   
56.
Atomic Force Microscopy (AFM) mechanical lithography is a simple but significant method for nanofabrication. In this work, we used this method to construct nanostructures on Pt/Cu bilayer metal electrodes under ambient conditions in air. The influence of various scratch parameters, such as the applied force, scan velocity and circle times, on the lithography patterns was investigated. The Pt-Cu-Cu x O-Cu-Pt nanostructure was constructed by choosing suitable scratch parameters and oxidation at room temperature. The properties of the scratched regions were also investigated by friction force microscopy and conductive AFM (C-AFM). The I–V curves show symmetric and linear properties, and Ohmic contacts were formed. These results indicate that AFM mechanical lithography is a powerful tool for fabricating novel metal-semiconductor nanoelectronic devices. Supported by the National Natural Science Foundation of China (Grant No. 90306010), the Program for New Century Excellent Talents in University of China (Grant No. NCET-04-0653), the National Basic Research Program of China (Grant No. 2007CB616911), and the Science and Technology Department of Henan Province (Grant No. 072300420100)  相似文献   
57.
58.
In this study, after Dill’s model is discussed for transmittance and refractive indices of the non-chemically amplified resists, G- and I-line novolak resists, and the chemically amplified resists, a modification of Dill’s model as a new exposure model is introduced. The simulation results obtained using this new model with the multi-thin film interface method and the Berning theory have shown a good matching to the experimental data. Also, the simulated transmittance change due to the exposure parameters are used to analyze the influence of the coefficients on the transmittance.  相似文献   
59.
气体靶激光等离子体软X-射线源实验研究   总被引:1,自引:0,他引:1  
介绍了一种无碎屑、高亮度、高工作频率的气体靶激光等离子体软X 射线源。其喷气阀门由压电陶瓷驱动 ,工作频率可达到 40 0Hz。与金属靶激光等离子体软X 射线源相比 ,此光源无碎屑。与喷嘴由电磁阀控制的气体靶激光等离子体软X 射线源相比 ,它有较高的工作频率。一工作在模拟模式的通道电子倍增器被用于探测来自光源的软X 射线辐射 ,其输出信号经过一电荷灵敏前置放大器进一步放大变成电压脉冲信号 ,脉冲幅度与输入电荷灵敏前置放大器的电量成正比。实验测得CO2 ,Xe和Kr在 8~ 2 2nm软X 射线投影光刻常用波段的光谱辐射特性。CO2 光谱包括类锂和类铍离子跃迁形成的线谱 ,Xe光谱是多电荷氙离子 4d 5f,4d 4f,4d 6p和 4d 5p跃迁所形成的光谱。Kr气体靶光谱包括类铜离子、类镍离子、类钴离子和类铁离子跃迁形成的线谱和连续谱。  相似文献   
60.
椭圆型激光驻波场作用下Cr原子的汇聚特性研究   总被引:1,自引:0,他引:1       下载免费PDF全文
张文涛  朱保华  熊显名 《物理学报》2009,58(12):8199-8204
利用近共振激光驻波场操纵中性原子实现纳米级条纹沉积技术是一种新型的研制纳米结构长度标准传递的方法.分析了Cr原子在椭圆型激光驻波场作用下的沉积特性,分别对不同椭圆激光驻波场功率下Cr原子的沉积条纹及不同y平面上沉积条纹特性进行了模拟和分析.同时针对椭圆激光驻波场作用下Cr原子发散角对沉积条纹特性的影响进行了模拟计算,比较了不同发散角条件下沉积条纹的对比度和半高宽. 关键词: 原子光刻 椭圆激光驻波场 Cr原子  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号