全文获取类型
收费全文 | 1315篇 |
免费 | 206篇 |
国内免费 | 123篇 |
专业分类
化学 | 734篇 |
晶体学 | 19篇 |
力学 | 58篇 |
综合类 | 21篇 |
数学 | 183篇 |
物理学 | 629篇 |
出版年
2024年 | 7篇 |
2023年 | 46篇 |
2022年 | 58篇 |
2021年 | 59篇 |
2020年 | 53篇 |
2019年 | 34篇 |
2018年 | 38篇 |
2017年 | 38篇 |
2016年 | 50篇 |
2015年 | 42篇 |
2014年 | 60篇 |
2013年 | 71篇 |
2012年 | 87篇 |
2011年 | 106篇 |
2010年 | 76篇 |
2009年 | 77篇 |
2008年 | 79篇 |
2007年 | 55篇 |
2006年 | 49篇 |
2005年 | 54篇 |
2004年 | 45篇 |
2003年 | 50篇 |
2002年 | 38篇 |
2001年 | 35篇 |
2000年 | 24篇 |
1999年 | 43篇 |
1998年 | 47篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1644条查询结果,搜索用时 31 毫秒
911.
利用偏振时间分辨光谱和时间分辨Kerr旋转谱,研究了GaAs中的InAs单层和亚单层的电子自旋动力学.实验发现,在非共振激发条件下,厚度为1/3单层的InAs亚单层中电子自旋弛豫寿命长达3.4ns,而1个单层厚的InAs层的电子自旋寿命只有0.48ns;而在共振激发条件下,亚单层结构中的电子自旋寿命大大减少,只有70ps,单层InAs中电子自旋寿命没有显著变化.分析表明,低温下InAs单层和亚单层结构中,Bir-Aronov-Pikus(BAP)自旋弛豫机理占主导地位.通过改变材料结构特性和激发条件来改变电子空穴的空间相关性,从而达到控制自旋弛豫的目的.
关键词:
InAs亚单层
自旋弛豫
BAP机理 相似文献
912.
用化学镀的方法制备了NiFeCoP/CuBe复合结构丝,研究了其巨磁阻抗特性.结果表明复合结构丝在较低频率的驱动电流下就有明显的磁阻抗效应,当驱动电流频率在20kHz时的磁阻抗效应为40%,最大磁阻抗效应出现的频率在180kHz,为97%.利用复数磁导率和等效电路探讨了该复合丝铁磁层磁化过程的频率特性,复合结构丝的特征弛豫频率在1MHz左右.外加直流磁场抑制畴壁移动,在等效电路中与抵消部分并联电路相关.
关键词:
巨磁阻抗效应
磁导率
弛豫频率
等效电路 相似文献
913.
Microwave-assisted synthesis and magnetic property of magnetite and hematite nanoparticles 总被引:1,自引:0,他引:1
Nanoparticles of magnetite (Fe3O4) and hematite (α-Fe2O3) have been prepared by a simple microwave heating method using FeCl3, polyethylene glycol and N2H4·H2O. The amount of N2H4·H2O has an effect on the final phase of Fe3O4. The morphology of α-Fe2O3 was affected by the heating method. Crystalline α-Fe2O3 agglomerates were formed immediately at room temperature and most of these nanoparticles within agglomerates show the same
orientation along [110] direction. After microwave heating, ellipsoidal α-Fe2O3 nanoparticles were formed following an oriented attachment mechanism. Both Fe3O4 and α-Fe2O3 nanoparticles exhibit a small hysteresis loop at room temperature. 相似文献
914.
Zheng Sun Z.Y. Xu X.Z. Ruan Yang Ji B.Q. Sun M. Wang H.Q. Ni 《Solid State Communications》2007,143(3):158-160
Using time-resolved photoluminescence and time-resolved Kerr rotation spectroscopy, we explore the unique electron spin behavior in an InAs submonolayer sandwiched in a GaAs matrix, which shows very different spin characteristics under resonant and non-resonant excitations. While a very long spin relaxation lifetime of a few nanoseconds at low temperature is observed under non-resonant excitation, it decreases dramatically under resonant excitation. These interesting results are attributed to the difference in electron-hole interactions caused by non-geminate or geminate capture of photo-generated electron-hole pairs in the two excitation cases, and provide a direct verification of the electron-hole spatial correlation effect on electron spin relaxation. 相似文献
915.
916.
PIV measurements for gas flow under gradient magnetic fields 总被引:1,自引:0,他引:1
Particle Image Velocimetry (PIV) techniques were developed to measure the convective N2-air flow under gradient magnetic fields. The velocity fields were calculated by the Minimum Quadratic Difference (MQD) algorithm and spurious vectors were eliminated by Delaunay Tessellation.The N2-air flow was measured as the magnetic flux density varying from 0~1.5T. A strengthened vortex flow of air was observed under the condition that the magnetic field was applied, and the velocity of N2 jet rose with the increase of the magnetic density. The experimental results show that the magnetic force will induce a vortex flow and cause a convection flow of the air mixture when both gradients of the O2 concentration and the magnetic field intensity exist. 相似文献
917.
918.
阻转异构体是一类特殊的手性化合物. 利用轴手性配体制得的具有阻转异构行为的配合物在不对称催化等领域有广泛的应用. 相比之下, 通过原位反应由非手性底物制备这类手性配合物的报道较少, 而利用非轴手性化合物原位组装得到非轴手性阻转异构体的报道则更加罕见. 乙腈是一种廉价易得的基本化工原料, 在金属离子存在下活化乙腈分子是向有机分子中引入氰甲基的一种有效手段. 本文利用乙腈分子进攻2-二吡啶基酮获得了一例含有氰甲基官能团的配体dpkMeCN-H[dpkMeCN=cyanomethyl-di(pyridin-2-yl)methanol]. 在NiII和KI的配位作用下, 该体系发生原位组装生成了一对阻转异构体. 磁性拟合结果表明镍离子之间主要为铁磁耦合, 且它们由于八面体畸变产生一定的零场分裂, 使手性镍配合物产生磁各向异性. 相似文献
919.
Qi Xin Li Wang Haiyan Ruan Ling Liu Si Sun Jing Zhang Menglin Wu Xiaoyu Mu Hao Wang Shaofang Zhang Xiao-Dong Zhang 《Particle & Particle Systems Characterization》2023,40(7):2200203
Redox-active nanozymes offer low-cost controlled synthesis, high stability, and tunable catalytic properties over natural enzymes, which have attracted wide attention in the field of disease diagnosis and treatment. However, the improvement of catalytic activity remains an important challenge for nanozymes. Herein, the Au/CeO2 nanozymes is developed to achieve enhanced multiple enzyme-mimetic activity. The Au/CeO2 nanozymes at 5% doping possess best peroxidase-like activity with threefold higher catalytic rate than CeO2. For catalase-mimic catalysis, the Au/CeO2 nanozymes at 5% doping also exhibited a 1.5-fold enhanced reaction rate higher than pure CeO2. The superoxide dismutase (SOD)-like capacity of Au/CeO2 nanozymes is proportional to Au content. The Au/CeO2 nanozymes at 10% doping show optimal SOD-like capacity of 60.2 U mg−1. In vitro experiments validate the regulation ability of intracellular oxidative stress and inflammation. Au/CeO2 nanozymes can reduce lipopolysaccharide- or H2O2-induced oxidative damage by scavenging excess ROS in nerve cell. Therefore, Au/CeO2 can be used as a promising antioxidant in disease treatment, and the study offers general guidelines for achieving enhanced biocatalytic property through atomic doping. 相似文献
920.
The vibrational spectra of cyclo[18]carbon and its analogues, cyclo[2n]carbon (n=3 to 15), were carefully simulated and characterized. The in-plane C−C stretching vibrations shows strong rigidity, while out-of-plane motions seem to be extremely flexible. The solvation effect can enhance signal strengths of the vibrational spectra, but does not evidently change the shape of the spectral curves. The infrared and Raman spectra of cyclo[2n]carbons are quite sensitive to ring size in the range of n=3 to 7, while the size only modestly affects peak positions and strengths for larger rings. Molecular dynamic trajectories show that the fluctuation period of the skeleton of cyclo[18]carbon is basically constant at different temperatures, and they are all about 300 fs. With increase of simulation temperature, the ring distortion due to thermal motion is notable and becomes much stronger. However, neither ring breaking nor isomerization in cyclo[18]carbon is observed during the simulations untill 298.15 K. 相似文献