全文获取类型
收费全文 | 1296篇 |
免费 | 192篇 |
国内免费 | 245篇 |
专业分类
化学 | 1094篇 |
晶体学 | 22篇 |
力学 | 28篇 |
综合类 | 14篇 |
数学 | 256篇 |
物理学 | 319篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 25篇 |
2021年 | 32篇 |
2020年 | 44篇 |
2019年 | 56篇 |
2018年 | 36篇 |
2017年 | 28篇 |
2016年 | 59篇 |
2015年 | 54篇 |
2014年 | 67篇 |
2013年 | 83篇 |
2012年 | 79篇 |
2011年 | 90篇 |
2010年 | 96篇 |
2009年 | 79篇 |
2008年 | 90篇 |
2007年 | 94篇 |
2006年 | 64篇 |
2005年 | 51篇 |
2004年 | 62篇 |
2003年 | 70篇 |
2002年 | 141篇 |
2001年 | 118篇 |
2000年 | 70篇 |
1999年 | 33篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有1733条查询结果,搜索用时 15 毫秒
11.
Hai‐Long Qian Fan‐Lin Meng Cheng‐Xiong Yang Xiu‐Ping Yan 《Angewandte Chemie (International ed. in English)》2020,59(40):17607-17613
Design of stable adsorbents for selective gold recovery with large capacity and fast adsorption kinetics is of great challenge, but significant for the economy and the environment. Herein, we show the design and preparation of an irreversible amide‐linked covalent organic framework (COF) JNU‐1 via a building block exchange strategy for efficient recovery of gold. JNU‐1 was synthesized through the exchange of 4,4′‐biphenyldicarboxaldehyde (BA) in mother COF TzBA consisting of 4,4′,4′′‐(1,3,5‐triazine‐2,4,6‐triyl)trianiline (Tz) and BA with terephthaloyl chloride. The irreversible amide linked JNU‐1 gave good stability, unprecedented fast kinetics, excellent selectivity and outstanding adsorption capacity for gold recovery. X‐ray photoelectron spectroscopy along with thermodynamic study and quantum mechanics calculation reveals that the excellent performance of JNU‐1 for gold recovery results from the formation of hydrogen bonds C(N)?H???Cl and coordinate interaction of O and Au. The rational design of irreversible bonds as both inherent linkage and functional groups in COFs is a promising way to prepare stable COFs for diverse applications. 相似文献
12.
13.
Yuguo Li Ruiqin Peng Xianwu Xiu Xuelei Zheng Xiaosen Zhang Guannan Zhai 《Superlattices and Microstructures》2011,50(5):511-516
Tin oxide (SnO2) nanoparticles were fabricated by evaporation of Sn powers at 1000 °C in air pressure. The as-deposited SnO2 particles were single crystal structure, which were mostly spherical shape, the diameter of particles was ranging from 200 to 600 nm. The photoluminescence (PL) spectrum showed that a sharp emission peak at around 393 nm with the excitation wavelength at 325 nm, which suggested possible applications in nanoscaled optoelectronic devices. It was also found that the holding time affects the morphology of the products. The formation mechanism of SnO2 particles was discussed. 相似文献
14.
Wide spectral white light emitting diodes have been designed and grown on a sapphire substrate by using a metal-organic chemical vapor deposition system. Three quantum wells with blue-light-emitting, green-light-emitting and red-light-emitting structures were grown according to the design. The surface morphology of the film was observed by using atomic force microscopy. The films were characterized by their photoluminescence measurements. X-ray diffraction θ/2θ scan spectroscopy was carried out on the multi-quantum wells. The secondary fringes of the symmetric ω/2θ X-ray diffraction scan peaks indicate that the thicknesses and the alloy compositions of the individual quantum wells are repeatable throughout the active region. The room temperature photoluminescence spectra of the structures indicate that the white light emission of the multi-quantum wells is obtained. The light spectrum covers 400-700 nm, which is almost the whole visible light spectrum. 相似文献
15.
Electronic band structure of a type-II ’W’ quantum well calculated by an eight-band k·p model 下载免费PDF全文
In this paper, we present an investigation of type-II 'W' quantum wells for the InAs/Ga1-xInxSb/AlSb family, where 'W' denotes the conduction profile of the material. We focus our attention on using the eight-band k?p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period---AlSb/InAs/Ga1-xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1-xInxSb layer and the alloy composition in Ga1-xInxSb separately. In the last part, in order to compare the eight-band k?p model, we recalculate the conduction bands of the 'W' structure using the one-band k?p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained. 相似文献
16.
A controlled quantum teleportation scheme of an N-particle unknown state via three-particle W1 states 下载免费PDF全文
In this paper a controlled quantum teleportation scheme of an N-particle unknown state is proposed when N groups of three-particle W1 states are utilized as quantum channels. The quantum information of N-particle unknown state is transmitted from the sender to the recipient under the control of all supervisors. It can be realized with a certain probability. After the sender makes Bell-state measurements and the supervisors perform the computational basis measurements, the recipient will introduce auxiliary particles and carry out unitary transformations depending on classical information from the sender and the supervisors. Finally, the computational basis measurement will be performed by the recipient to confirm whether the teleportation succeeds or not. The successful completion of the scheme relies on all supervisors' cooperation. In addition, the fidelity and security of the scheme are discussed. 相似文献
17.
镉污染水稻高光谱诊断分析与建模 总被引:4,自引:0,他引:4
为了快速、准确地探测自然环境下水稻镉污染胁迫状况,提出了一种基于可见光-近红外光谱小波分析技术的快速识别和估算水稻镉污染的方法。根据野外实测水稻高光谱数据、水稻叶片主要生化参数及重金属含量等数据,利用Daubechies小波系的db5小波函数对350~1300nm水稻高光谱反射率进行9层分解,并提取小波能量系数进行镉含量回归建模。结果显示:第5层小波分解(d5)的奇异范围为550~810nm,奇异幅度为0.04,模极大值的中心位于700nm处,对识别水稻镉污染效果最佳;以第3层小波能量系数作为自变量的回归模型对水稻镉含量估算精度最高,其决定系数R2高达0.958,均方根误差RMSE为0.122。小波奇异性分析可以较准确的诊断水稻镉污染胁迫状况,基于小波能量系数的建模能有效估算水稻镉污染胁迫水平。 相似文献
18.
19.
V型原子与光场拉曼相互作用传送未知原子态 总被引:10,自引:0,他引:10
未知量子态从一个地方到另一个地方的隐形传送在量子信息领域中有非常重要的作用,提出了一种利用简并V型三能级原子与振幅很大的单模相干态腔场的拉曼相互作用来传送未知原子态的方案。 相似文献
20.
为了获得1064nm,1319nm,589nm及660nm 4波长激光同时输出,设计了双激光晶体同步声光调Q“T”型复合谐振腔。通过软件模拟与计算,筛选出理想的谐振腔参数,使2波长基频光在大泵浦电流范围内能稳定运转。以KTP晶体和LBO晶体为和频晶体和倍频晶体,在泵浦电流为17A,重复频率为10kHz时,获得了1064nm,1319nm,589nm和660nm 4波长激光输出,最高平均功率分别为150mW,80mW,2.3W和1.7W,同时测得589nm激光和660nm激光的脉冲宽度分别为110ns和130ns。结果表明:使用热稳“T”型复合腔,可以获得4波长激光同时稳定输出。 相似文献