全文获取类型
收费全文 | 20791篇 |
免费 | 3413篇 |
国内免费 | 2309篇 |
专业分类
化学 | 14781篇 |
晶体学 | 260篇 |
力学 | 1263篇 |
综合类 | 186篇 |
数学 | 2069篇 |
物理学 | 7954篇 |
出版年
2024年 | 75篇 |
2023年 | 468篇 |
2022年 | 675篇 |
2021年 | 754篇 |
2020年 | 820篇 |
2019年 | 793篇 |
2018年 | 664篇 |
2017年 | 633篇 |
2016年 | 983篇 |
2015年 | 984篇 |
2014年 | 1112篇 |
2013年 | 1454篇 |
2012年 | 1871篇 |
2011年 | 1900篇 |
2010年 | 1256篇 |
2009年 | 1113篇 |
2008年 | 1298篇 |
2007年 | 1288篇 |
2006年 | 1132篇 |
2005年 | 1012篇 |
2004年 | 723篇 |
2003年 | 630篇 |
2002年 | 569篇 |
2001年 | 430篇 |
2000年 | 410篇 |
1999年 | 473篇 |
1998年 | 359篇 |
1997年 | 371篇 |
1996年 | 311篇 |
1995年 | 298篇 |
1994年 | 304篇 |
1993年 | 248篇 |
1992年 | 198篇 |
1991年 | 201篇 |
1990年 | 178篇 |
1989年 | 113篇 |
1988年 | 87篇 |
1987年 | 89篇 |
1986年 | 60篇 |
1985年 | 45篇 |
1984年 | 43篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 14篇 |
1975年 | 2篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A Novel UWB Antenna with Small Side-Leakage 总被引:2,自引:0,他引:2
Wang Xianghui Jiang Yangsheng Wan Wenbing 《International Journal of Infrared and Millimeter Waves》2004,25(9):1325-1335
A successful design for a UWB (ultra-wideband antennas) antenna based on NRD-guide (nonradiative dielectric waveguide) with small side-leakage is presented. The rule of the theoretical selection of its parameters, if NRD-guide is used as the UWB antennas, is studied firstly, then the temporal propagation characteristics of the NRD-guide and the radiation characteristics for an tapered open-ended NRD-guide are calculated by FDTD (finite-difference time-domain) method. 相似文献
992.
L. J. Qin X. L. Meng Ch. L. Du L. Zhu B. Ch. Xu H. Zh. Xu F. Y. Jiang Z. Sh. Shao 《Optics & Laser Technology》2004,36(1):47-50
We have demonstrated a passively Q-switched operation of Nd:GdVO4 laser in which a GaAs crystal is used as the saturable absorber for the first time as far as we know. A maximum average output power of 1.64 W was obtained at an incident pump power of 12 W, the corresponding optical conversion efficiency and peak power were 13.7% and 116.8 W, respectively. The maximum peak energy obtained in the experiment by 50% transmission couple was 19 μJ. 相似文献
993.
采用新型贵金属铱的配合物bis(1,2-dipheny1-1H-benzoimida-zole)iridium (acetylacetonate)作为磷光敏化剂,与荧光染料4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-en-yl)-4H-pyran共同掺杂到聚合物主体材料poly(N-vinylcarbazole)中,以N,N'-diphenyl-N,N'-bis(1-naphthyl) (1,1'-biphenyl)-4,4'-diami-ne作为蓝光发光层,制备了白色有机电致发光器件. 通过对掺杂体系的紫外-可见吸收光谱、光致发光光谱以及电致发光光谱的表征,分析了该磷光敏化体系的能量转移机制. 结果表明,在该聚合物磷光荧光双掺杂体系中,由于磷光与荧光材料之间的不完全的F?rster能量传递过程,导致电致发光光谱中同时存在磷光材料三线态到基态与荧光材料单线态到基态的辐射衰减发光. 该掺杂体系成功实现了白光发射,随着偏置电压的升高,器件的CIE色坐标有微小的红移,但都非常接近等能白光点,器件表现出了很好的色纯度. 相似文献
994.
Chengyong Liu Zhongwen LanXiaona Jiang Zhong YuKe Sun Lezhong LiPeiyuan Liu 《Journal of magnetism and magnetic materials》2008
The effects of sintering temperature and Bi2O3 content on the microstructure and magnetic properties of lithium–zinc (LiZn) ferrites prepared by a conventional ceramic method were investigated. The results show that the densification behavior and grain growth rate were greatly improved by the addition of Bi2O3, because a liquid phase sintering occurred during the sintering process at high temperature due to the low-melting point of Bi2O3 (825 °C). X-ray diffraction (XRD) patterns of the slightly doped samples did not reveal the appearance of any phase other than spinel LiZn ferrite. However, the secondary phase of perovskite BiFeO3 was detected for Bi2O3 content of more than 0.25 wt%. The studies further show that Bi oxide was present at grain boundary, and promoted the grain growth as reaction center at lower temperature. A high saturation magnetization, squareness ratio, minimum ferromagnetic resonance linewidth and low coercive force were obtained for the sample with 1.00 wt% Bi2O additive at lower sintering temperature (1100 °C). 相似文献
995.
SmCoxTi0.4 (x=6.6, 7.1, 7.6, 8.1) ribbons have been prepared by melt spinning at a wheel speed of 42 m/s, followed by annealing at 750 °C for 2 h. Both as-spun and as-annealed ribbons possess the disordered TbCu7-type (1:7) phase even when the Sm/(Co,Ti) atomic ratio deviates from 1/7. The c/a ratio increases with increasing Co concentration x, but the unit cell volume decreases. The Curie temperatures show above 700 °C, increasing from 707 °C for x=6.6 to 782 °C for x=8.1. The saturation magnetizations increase almost linearly with increasing Co content. The observed magnetic hardening is believed to arise from the high magnetocrystalline anisotropy of the 1:7 phase and the fine nanograin structure. The intrinsic coercivity of 9797 Oe has been obtained in the melt-spun SmCo7.1Ti0.4 ribbons. 相似文献
996.
Polyaniline/Zn0.5Cu0.5Fe2O4 nanocomposite was synthesized by a simple, general and inexpensive in-situ polymerization method in w/o microemulsion. The
effects of polyaniline coating on the magnetic properties of Zn0.5Cu0.5Fe2O4 nanoparticles were investigated. The structural, morphological and magnetic properties of as-prepared samples were characterized
by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, scanning electron microscopy (SEM) and magnetic measurements.
The morphology analysis confirmed that polyaniline was deposited on the porous surface of magnetic Zn0.5Cu0.5Fe2O4. It was shown that the saturation magnetization and coercivity of Zn0.5Cu0.5Fe2O4 decreased after polyaniline coating, which can be interpreted by the interparticle dipole–dipole interactions that contributed
to magnetic anisotropy and changed the magnetic properties of the nanoparticles.
PACS 74.25.Ha; 81.05.-t; 81.05.Lg 相似文献
997.
In this paper, we propose a physical scheme to realize quantum SWAP
gate by using a large-detuned single-mode cavity field and two
identical Rydberg atoms. It is shown that the scheme can also be used
to create multi-atom cluster state. During the interaction between
atom and cavity, the cavity is only virtually excited and thus the
scheme is insensitive to the cavity field states and cavity decay.
With the help of our scheme it is very simple to prepare the $N$-atom
cluster state with perfect fidelity and probability. The practical
feasibility of this method is also discussed. 相似文献
998.
Triangular, truncated triangular, quadrangular, hexagonal, and net-structured silver nanoplates as well as decahedral silver nanoparticles were manipulatively prepared starting from silver nitrate and silver seeds in the presence of poly(ethylene glycol) (PEG), poly(N-vinyl pyrrolidone) (PVP), and Tween 80 at room temperature, respectively. UV-vis spectroscopy, XRD, HRTEM, SAED, and FTIR were used to illustrate the crystal growth process and to characterize the resultant silver nanoparticles. It was found that the silver seeds and organic modifiers synergistically affected the morphology evolution of the silver nanoparticles. The co-presence of silver seeds and PEG was beneficial to the formation of triangular and truncated triangular silver nanoplates; the silver seeds and PVP favored the formation of polygonal silver nanoplates; the silver seeds and Tween 80 preferred to the formation of net-structured silver plates. The morphology evolution of the resultant silver nanoparticles was correlated with the crystallinity of the silver seeds and the adsorption ability of the organic modifiers on the crystal surfaces. 相似文献
999.
Perfect epitaxial growth of La0.67Ca0.33MnO3 (LCMO) thin film has been achieved on (1 0 0) LaAlO3 (LAO) single crystal substrate by radio frequency sputtering method. X-ray diffraction (XRD) and electron diffraction analysis indicates that La0.67Ca0.33MnO3 film grows epitaxially on LaAlO3 along [1 0 0] direction of the substrate. The resistivity variation with temperature of the film shows a sharp metal to semiconductor transition peak around 253 K, which is close to that of the target. The magnetoresistance (MR) also reveals high quality epitaxy film characteristic at low temperatures and near the metal to semiconductor transition temperature. 相似文献
1000.
Wenmeng Duan Xianwu Jing Jiang Tan Minmin Tao Lu Wang 《Journal of Dispersion Science and Technology》2018,39(9):1309-1315
A series of amphiphilic triblock polymers based on poly(ethylene glycol) (PEG) and two symmetrical poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) blocks was synthesized via the Atom Transfer Radical Polymerization (ATRP) method. Conductivity, pH, and viscosity tests demonstrated the CO2-switchability jointly; Cryogenic transmission electron microscopy (Cryo-TEM), Dynamic light scattering (DLS) revealed the self-assembly morphology transformation from unilamellar vesicle to network structure when bubbling CO2. These changes were all attributed to the protonation of tertiary amine groups in PDMAEMA blocks and the mechanism was proved by ?H NMR. The vesicles have a relatively low release rate of drug; once stimulated by CO2, the release rate will be accelerated. The polymeric vesicle has the possibility to find potential applications in drug delivery and release domains. 相似文献