全文获取类型
收费全文 | 1728篇 |
免费 | 620篇 |
国内免费 | 261篇 |
专业分类
化学 | 591篇 |
晶体学 | 119篇 |
力学 | 27篇 |
综合类 | 23篇 |
数学 | 114篇 |
物理学 | 1735篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 67篇 |
2021年 | 54篇 |
2020年 | 54篇 |
2019年 | 42篇 |
2018年 | 49篇 |
2017年 | 66篇 |
2016年 | 71篇 |
2015年 | 73篇 |
2014年 | 120篇 |
2013年 | 167篇 |
2012年 | 161篇 |
2011年 | 141篇 |
2010年 | 138篇 |
2009年 | 135篇 |
2008年 | 146篇 |
2007年 | 137篇 |
2006年 | 137篇 |
2005年 | 107篇 |
2004年 | 90篇 |
2003年 | 82篇 |
2002年 | 90篇 |
2001年 | 58篇 |
2000年 | 66篇 |
1999年 | 68篇 |
1998年 | 36篇 |
1997年 | 37篇 |
1996年 | 44篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 18篇 |
1992年 | 26篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2609条查询结果,搜索用时 968 毫秒
91.
Due to their special polar structure, amphiphilic molecules are simple to process, low in cost and excellent in material properties. Thus, they can be widely applied in the preparation of functional film materials and bionics related to cell membranes. Therefore, amphiphilic organic semiconductor materials are receiving increasing attention in research and industrial fields. The structure of organic amphiphilic semiconductor molecules usually consists of three functional parts: a hydrophilic group, a hydrophobic group, and a linking group between them. The adjustment of their correlation to achieve the target performance is particularly important and needs experimental discussion regarding synthetic methodologies. In this work, we focused on the engineering of a substituent alkyl-chain, and an amphiphilic functional molecule (benzo[b]benzo[4, 5] thieno[2, 3-d]thiophene, named CnPA-BTBT, n = 3–11) was proposed and synthesized. This molecule links the hydrophobic semiconductor backbone and hydrophilic polar group through alkyl chains of different lengths. Fundamental properties were investigated by nuclear magnetic resonance (NMR) and ultraviolet-visible spectroscopy (UV-Vis) to conform the structure and the band gap properties of the designed organic semiconductor. Thermodynamic features were investigated by thermogravimetric analysis (TGA) and corresponding differential thermal gravity (DTG), which indicate that the functional molecule CnPA-BTBT (n = 3–11) has a great stability in ambient conditions. Moreover, the results show that the binding ability of the amphiphilic molecule to water molecules was regulated by the odd-even alternating effect of the alkyl chain and the intramolecular coupling with BTBT. Furthermore, differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were used to study the material properties in detail. As the length of the alkyl chain increased, the functional molecule CnPA-BTBT (n = 3–11) gradually changed from "hard" species with no thermodynamic changes to a transition one with a pair of thermodynamic peaks, and eventually to a "soft" one as a typical liquid crystal with clear observation of Maltese-cross spherulites. The cooling and freezing points were further studied, and the values and trends of their enthalpy and corresponding temperature fluctuated and alternated due to the volume effect, odd-even alternating effect, flexibility, and other functions of the alkyl chain. Three molecular models were proposed according to the thermodynamic study results, namely the brick-like model, transition model, and liquid crystal model. This work presents in-depth discussion on material structure and corresponding thermodynamic properties, and it is an experimental basis for the design, synthesis, optimization, and screening of target performance materials. 相似文献
92.
《中国化学快报》2020,31(12):3047-3054
As a class of metal-free two-dimensional (2D) semiconductor materials, polymeric carbon nitrides have attracted wide attention recently due to its facile regulation of the molecular and electronic structures, availability in abundance and high stability. According to the different ratios of C and N atoms in the framework, a series of CxNy materials have been successfully synthesized by virtue of various precursors, which further triggers extensive investigations of broad applications ranging from sustainable photocatalytic reactions and highly sensitive optoelectronic biosensing. In view of topological structures on their electronic structures and material properties, the as-reported CxNy could be generally classified into two main categories with three- or six-bond-extending frameworks. Owing to the effective n→π* transition in most CxNy materials, the relative energy level of the lone-pair electrons on N atoms is high, which thus endows the materials with the capability of visible light absorption. Meanwhile, the different repeating units, bridging groups and defect sites of these two kinds of CxNy allow them to effectively drive a diverse of promising applications that require specific electronic, interfacial and geometric properties. This review paper aims to summarize the recent progress in topological structure design and the relevant electronic band structures and striking properties of CxNy materials. In the final part, we also discuss the existing challenges of CxNy and outlook the prospect possibilities. 相似文献
93.
Surface‐enhanced Raman scattering (SERS) spectroscopy on semiconductors has attracted increasing attention due to its high spectral reproducibility and unique selectively to target molecules. Recently, endeavors have been made in fabricating novel SERS‐active semiconductor substrates and exploring new enhancement mechanisms to improve the sensitivity of semiconductor substrates. This Minireview explains the enhancement mechanism of the semiconductor SERS effect in a brief tutorial and summarize recent developments of novel semiconductor substrates, in particular with regard to the remarkable SERS activity of amorphous semiconductor nanomaterials. Potential applications of semiconductor SERS are also a key issue of concern. We discuss a variety of promising applications of semiconductor SERS in the fields of in situ analytical chemistry, spectroelectrochemical analysis, biological sensing, and trace detection. 相似文献
94.
室温下我们研究了稀磁半导体(Ga,Mn)As的光调制反射(PR)光谱,观测到来自样品的Franz-Keldysh振荡(FKO)信号。随着Mn原子浓度的增加,PR线形展宽,但是临界点E0和E0+Δ0没有明显的移动。根据FKO振荡数据,计算得到样品表面电场强度随Mn原子掺杂浓度的增加而增强。测量到与Mn原子掺杂相关的杂质带,其能量位置离GaAs价带边~100 meV。根据样品的表面电场强度和表面耗尽层模型,估算样品的空穴浓度为~1017cm-3,较低的空穴浓度可能与样品具有较低的居里温度有关,或测量的PR信号来自于样品中外延层的部分耗尽区域。 相似文献
95.
96.
高功率半导体激光器(LD)是广泛应用于固体激光泵浦、材料加工等方面的重要器件。数值模拟了一种自行设计的光栅输出镜结构的高功率半导体激光器的输出特性,分析了具有光栅输出镜的LD波长随温度的变化情况,以及光栅输出镜对输出功率的影响。 相似文献
97.
98.
GaAs与InP半导体光导开关特性实验研究 总被引:1,自引:0,他引:1
利用Ⅲ-Ⅴ族化合物半导体材料砷化镓(GaAs)和磷化铟(InP)及其掺杂材料制作的光导开关具有很好的时间响应及高功率输出特性.比较了这两种材料制作的不同电极间隙类型的光导开关的开关时间响应速度、导通光能与饱和触发激光能量、线性与非线性工作模式及触发稳定性等特性.结果表明,利用InP和GaAs两种材料制作的光导开关都具有达到皮秒级的超快时间响应,其对时间最佳响应与偏置电场有关.两种开关的多次触发时间抖动在几个皮秒范围,输出电压峰峰值抖动优于10%.GaAs开关的非线性工作电场阈值比InP开关低,更容易实现非线性输出. 相似文献
99.
分子张力作为空间设计的重要组成部分正成为调控有机半导体的重要手段。由于分子内产生的拉伸张力、扭曲/弯曲张力以及空间张力而导致p轨道排布重组和构型构象结构发生变化,最近各种几何与拓扑结构的高张力有机半导体材料相继被报道,这使得高张力有机半导体材料成为有机电子领域研究的焦点。为了进一步梳理分子张力在有机半导体材料中扮演的角色与价值,该综述从分子张力的类型、实验与理论量化以及可视化出发,总结了高张力共轭芳烃的分子设计策略、与其光电性能分子张力之间的关系,以及这类新兴材料在光电领域的应用。最后,对高张力共轭芳烃的研究前景进行了展望,阐述了该类材料所面临的机遇与挑战。 相似文献
100.