全文获取类型
收费全文 | 5062篇 |
免费 | 982篇 |
国内免费 | 530篇 |
专业分类
化学 | 3507篇 |
晶体学 | 49篇 |
力学 | 194篇 |
综合类 | 72篇 |
数学 | 450篇 |
物理学 | 2302篇 |
出版年
2024年 | 14篇 |
2023年 | 113篇 |
2022年 | 126篇 |
2021年 | 160篇 |
2020年 | 172篇 |
2019年 | 183篇 |
2018年 | 173篇 |
2017年 | 135篇 |
2016年 | 243篇 |
2015年 | 245篇 |
2014年 | 250篇 |
2013年 | 339篇 |
2012年 | 479篇 |
2011年 | 553篇 |
2010年 | 329篇 |
2009年 | 327篇 |
2008年 | 354篇 |
2007年 | 294篇 |
2006年 | 266篇 |
2005年 | 218篇 |
2004年 | 185篇 |
2003年 | 129篇 |
2002年 | 149篇 |
2001年 | 113篇 |
2000年 | 119篇 |
1999年 | 109篇 |
1998年 | 98篇 |
1997年 | 111篇 |
1996年 | 92篇 |
1995年 | 80篇 |
1994年 | 63篇 |
1993年 | 72篇 |
1992年 | 43篇 |
1991年 | 63篇 |
1990年 | 44篇 |
1989年 | 35篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有6574条查询结果,搜索用时 781 毫秒
991.
A master oscillator power amplifier (MOPA) system in which the output from an end-pumped Nd:YAG oscillator cavity dumped at
500 kHz is scaled up by a four-stage Nd:YVO4 amplifier is reported. Decrease in extraction efficiency of the amplifier chain with crystals different from that in the
oscillator was analyzed. With the 5.4 W seed output, 118 W of power was extracted from the amplifier chain at the pump power
of 345 W, with an extraction efficiency of 34.2% and an overall optical–optical efficiency of 30.9% for the MOPA system. The
beam quality factors were measured as M
x
2=1.45 and M
y
2=1.59 in two orthogonal directions, respectively. 相似文献
992.
W. J. Guo Y. F. Lin X. H. Gong Y. J. Chen Z. D. Luo Y. D. Huang 《Applied physics. B, Lasers and optics》2009,94(1):155-163
A Pr3+:NaGd(MoO4)2 single crystal has been grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra,
and fluorescence decay curves of the crystal were measured at room temperature. The Judd–Ofelt intensity parameters Ω
t,q
(t=2,4,6) and the spectroscopic parameters related to the 3
P
0 and 1
D
2 multiplets were obtained and analyzed. The decay mechanisms for the 3
P
0 and 1
D
2 multiplets were also discussed. 相似文献
993.
采用第一性原理在B3LYP\6-311G水平上对MnPm(n=1~2, m=1~10)(M=Be 、Mg 、Ca)团簇进行几何构型优化和频率分析,得到团簇各个尺寸的基态结构,结果表明,在m+n=5~6时锥体结构居多,相应的稳定性要高于同尺寸其他构型,m+n>6时,基态结构中出现四元环和五元环。裂化能和二阶能量差分计算结果表明,MPm(m=1~10)团簇在m=2时同时获得局域的最大值, Be2Pm(m=1~10)团簇幻数结构呈现规则的奇偶振荡。Be掺杂P团簇稳定性高于同尺寸的Mg 、Ca掺杂,与Mg 、Ca相比Be原子更易于与P原子结合。稳定结构团簇红外和拉曼光谱显示,高频段MP2团簇红外和拉曼活性较强,Mg2P2, Ca2P2团簇红外谱主峰在高频段出现,与拉曼活性谱主峰相反。 相似文献
994.
Using the finite-difference time-domain (FDTD) method, we simulate the coupling between a gold nanorod and gold nanoparticles
with different plasmonic resonant frequencies/volumes as well as that between the nanorod and a dielectric nanosphere. The
influences of coupling with different nanoparticles on the excitation of a forbidden longitudinal surface plasmon mode of
the nanorod under normal incidence are investigated. It is found that the cause of this excitation is the broken symmetry
of the local electric field experienced by the nanorod resulting from the charge pileup on the other nanoparticle. This result
is valuable for understanding the near-field optical characterization of plasmonic metal nanoparticles.
Supported by the National Natural Science Foundation of China (Grant Nos. 10821062 and 10804004), the National Basic Research
Program of China (Grant No. 2007CB307001), and the Specialized Research Fund for the Doctoral Program of Higher Education
(Grant No. 200800011023)
Contributed by GONG QiHuang 相似文献
995.
996.
Structure, ferroelectric and dielectric properties of Bi2WO6 with different bismuth content
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper reports that the Bi 2 WO 6 ferroelectric ceramics with excess Bi 2 O 3 of 0.0, 2.0, 3.5 and 5.0 wt.% of the stoichiometric composition are prepared by the conventional solid-state reaction method. Their microstructure, ferroelectric properties, the concentration and mobility of the defects have been analysed systematically. With increasing Bi content, the remnant polarization decreases, and the broken-down voltage increases. The optimum Bi excess, 3.5, lowers the oxygen vacancy concentration, while further Bi-addition brings about more defects. The activation energies fitted from cole-cole plots are 0.97 eV, 1.07 eV, 1.18 eV, and 1.33 eV, respectively. This suggests that the mobility of the defects is weakened by Bi-addition, which may be due to the increase of the ratio of the number of Bi 2 O 2 layers to that of the perovskite blocks. 相似文献
997.
TiC/PVDF nanocomposite is prepared via simple blending and hot pressing route. Percolation theory was employed to explain the dielectric behavior of the TiC/PVDF composites. The dependence of the dielectric properties of the composite on both volume fraction of the filler and frequency is investigated. High dielectric constant (? = 540) and low loss (tan δ = 0.48) of the composites at 100 Hz have been observed near the percolation threshold (0.12). The composites show a weak frequency dependence towards the high frequency range (10–100 kHz), regardless of the TiC content. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
998.
Protuberance cutting and recoverable damage of olfactory ensheathing cells (OECs) using femto-second laser surgery are reported. The damages of OECs protuberance are induced by using femtosecond laser surgery with different laser powers and scanning velocities. Through optimizing the parameters, steady cutting of OEC protuberance is achieved. After femtosecond laser surgery with 150 μ W and 10 μm/s is conducted, we found that the cell recovers its viability, such as growth, spread, and motility 1.5 h after the damage, which prove cell’s recovery and regeneration. Current work offers a novel method for establishing cell damage model and studying on cytokinetics. 相似文献
999.
1000.
P. B. Li Y. Gu Q. H. Gong G. C. Guo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(1):205-209
We propose a scheme for realizing the Ising spin-spin
interaction and atomic cluster states utilizing the trapped
two-level atoms inside a one-dimensional coupled resonator
waveguide. In the strong driving and large detuning conditions, an
effective Ising spin-spin interaction can be generated through
suitably tuning the parameters. Then atomic cluster states are
produced by using this Ising interaction. This scheme need not
initially prepare the superposition states of atoms, and is
insensitive to cavity decay. 相似文献