全文获取类型
收费全文 | 11943篇 |
免费 | 2170篇 |
国内免费 | 1418篇 |
专业分类
化学 | 8331篇 |
晶体学 | 167篇 |
力学 | 816篇 |
综合类 | 115篇 |
数学 | 1285篇 |
物理学 | 4817篇 |
出版年
2024年 | 24篇 |
2023年 | 297篇 |
2022年 | 388篇 |
2021年 | 504篇 |
2020年 | 553篇 |
2019年 | 542篇 |
2018年 | 439篇 |
2017年 | 403篇 |
2016年 | 635篇 |
2015年 | 593篇 |
2014年 | 707篇 |
2013年 | 845篇 |
2012年 | 1103篇 |
2011年 | 1074篇 |
2010年 | 815篇 |
2009年 | 754篇 |
2008年 | 737篇 |
2007年 | 647篇 |
2006年 | 660篇 |
2005年 | 568篇 |
2004年 | 371篇 |
2003年 | 315篇 |
2002年 | 312篇 |
2001年 | 236篇 |
2000年 | 212篇 |
1999年 | 213篇 |
1998年 | 178篇 |
1997年 | 202篇 |
1996年 | 184篇 |
1995年 | 168篇 |
1994年 | 138篇 |
1993年 | 99篇 |
1992年 | 90篇 |
1991年 | 81篇 |
1990年 | 82篇 |
1989年 | 69篇 |
1988年 | 56篇 |
1987年 | 29篇 |
1986年 | 45篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
The band gap of a photonic crystal (PhC) cavity intrinsically avoids HOM problems. In this paper, we present a new PBG structure based on the possible advantage of using hybrid structures and aperiodic lattices. This novel hybrid and aperiodically ordered cavity was designed for apparently higher Q-factor (more than 10300) and achieving large accelerating field gradient. The HOMs in the cavity are able to be absorbed efficiently. 相似文献
992.
J. -L. Guo C. Fan Z. -H. Guo 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(3):341-344
In order to describe the phenomenon that people’s interest in doing something always keep high in the beginning while gradually
decreases until reaching the balance, a model which describes the attenuation of interest is proposed to reflect the fact
that people’s interest becomes more stable after a long time. We give a rigorous analysis on this model by non-homogeneous
Poisson processes. Our analysis indicates that the interval distribution of arrival-time is a mixed distribution with exponential
and power-law feature, which is a power law with an exponential cutoff. After that, we collect blogs in ScienceNet.cn and
carry on empirical study on the interarrival time distribution. The empirical results agree well with the theoretical analysis,
obeying a special power law with the exponential cutoff, that is, a special kind of Gamma distribution. These empirical results
verify the model by providing an evidence for a new class of phenomena in human dynamics. It can be concluded that besides
power-law distributions, there are other distributions in human dynamics. These findings demonstrate the variety of human
behavior dynamics. 相似文献
993.
We propose a novel terahertz-wave source through the four-wave mixing effect in a conventional single-mode optical fiber pumped by a dual-wavelength laser whose difference frequency lies in the terahertz range. Surface-emitted geometry is employed to decrease absorption loss. A detailed derivation of the terahertz-wave power expression is presented using the coupled-wave theory. This is a promising way for realizing a reasonable narrow-band terahertz-wave source. 相似文献
994.
一种短程无衍射激光图像定中算法 总被引:1,自引:1,他引:0
针对短程无衍射激光图像特点,提出了一种由亮度梯度确定图像中心的方法。利用光斑图像边缘的亮度梯度,设定图像二值化阂值范围,根据二值化结果确定光斑图像边缘点,对于各边缘点,利用圆上两点直径最长的原理,通过直径的中点确定圆心,求出均值,作为光斑图像的中心。本方法速度快、精度高,适合于实时性要求较强的应用场合,已经在实际应用中... 相似文献
995.
By considering the relative velocity distribution function and multipole expansion interaction Hamiltonian, a three-state model for calculating the cross section of laser-induced quadrupole-quadrupole collisional energy transfer is presented. Calculated results in Xe-Kr system show that in the present system, the laser-induced collision process occurs for ~4 ps, which is much shorter than the dipole-dipole laser-induced collisional energy transfer (LICET) process. The spectrum of laser-induced quadrupole-quadrupole collisional energy transfer in Xe-Kr system has wider tunable range in an order of magnitude than the dipole-dipole LICET spectra. The peak cross section decreases and moves to the quasi-static wing with increasing temperature and the full width at half peak of the profile becomes larger as the system temperature increases. 相似文献
996.
Fan YeXing-Min Cai Fu-Ping DaiShou-Yong Jing Dong-Ping ZhangPing Fan Li-Jun Liu 《Physica B: Condensed Matter》2011,406(3):516-519
Cu-In-O composite thin films were deposited by reactive DC magnetron sputtering at room temperature. The samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV/vis spectrophotometer, four-probe measurement and Seebeck effect measurement, etc. The samples contain Cu, In and O. The ratios of Cu to In and O to In increase with increase in O2 flow rates. The ratio of Cu to In is over 1 and this suggests that Cu is in excess. The obtained Cu-In-O thin films are very possibly made of rhombohedral In2O3 and monoclinic CuO. Transmittance of the films decreases with increase in O2 flow rate. The decrease in transmittance results from increase in Cu content in the films. The optical band gap of all the samples is estimated to be 4.1-4.4 eV, which is larger than those of In2O3 and CuO. The sheet resistance of the films decreases with increase in O2 flow rate. Conductivity of the films is a little low, due to the addition of Cu and the poor crystalline quality of the film. The conduction behavior of the films is similar to that of In2O3 and the conduction mechanism of Cu-In-O thin films is through O vacancy. 相似文献
997.
Ji-Wei Wang Fang Yang Tou-Wen Fan Bi-Yu Tang Li-Ming Peng Wen-Jiang Ding 《Physica B: Condensed Matter》2011,406(6-7):1330-1335
New ternary magnesium alloys AMgNi4 (A=Y, La, Ce, Pr and Nd) have been studied by First-Principles calculations within the generalized gradient approximation. The optimized structural parameters were in good agreement with the available experimental data. The calculated cohesive energies and formation enthalpies showed that these alloys had strong structural stability. Then the elastic constants Cij of these AMgNi4 alloys were calculated, and the bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν and anisotropy value A of polycrystalline materials were derived from the elastic constants, the related mechanical properties were further discussed. The electronic structures were also calculated to reveal the underlying mechanism for the structural stability and the elastic property. 相似文献
998.
Zhiyun Zhang Chonggao Bao Wenjing YaoShengqiang Ma Lili ZhangShuzeng Hou 《Superlattices and Microstructures》2011
Al-doped ZnO (AZO) transparent conducting films were successfully prepared on glass substrates by RF magnetron sputtering method under different substrate temperatures. The microstructural, electrical and optical properties of AZO films were investigated in a wide temperature range from room temperature up to 350 °C by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), Hall measurement, and UV–visible meter. The nature of AZO films is polycrystalline thin films with hexagonal wurtzite structure and a preferred orientation along c-axis. The crystallinity and surface morphologies of the films are strongly dependent on the growth temperature, which in turn exerts a great effect on microstructural, electrical and optical properties of the AZO films. The atomic arrangement of AZO film having an wurtzite structure was indeed identified by the HRTEM as well as the Selected Area Electron Diffraction (SAED). The defect density of AZO film was investigated by HRTEM. The film deposited at 100 °C exhibited the relatively well crystallinity and the lowest resistivity of 3.6 × 10−4 Ω cm. The average transmission of AZO films in the visible range is all over 85%. More importantly, the low-resistance and high-transmittance AZO film was also prepared at a low temperature of 100 °C. 相似文献
999.
F. Fan Y.M. Lu L.L. Ying Z.Y. Liu C.B. Cai R. Hühne B. Holzapfel 《Physica C: Superconductivity and its Applications》2011,471(15-16):471-475
Biaxially textured Ce2Y2O7 (CYO) films were deposited on Ni–5at.%W (Ni–5W) tapes by a DC reactive sputtering technique in a reel-to-reel system. Subsequent YBa2Cu3O7?δ (YBCO) films were prepared using pulsed laser deposition leading to a simplified coated conductor architecture of YBCO/CYO/Ni–5W. X-ray diffraction measurements revealed an epitaxial growth of the CYO buffer layer with a texture spread down to 2.2° and 4.7° for the out-of-plane and in-plane alignment, respectively. Microstructural investigations showed a dense, smooth and crack-free surface morphology for CYO film up to a thickness of 350 nm, implying an effective suppression of cracks due to the incorporation of Y in CeO2. The superconducting transition temperature Tc of about 90 K with a narrow transition of 0.8 K and the inductively measured critical current density Jc of about 0.7 MA/cm2 indicate the potential of the single CYO buffer layer. 相似文献
1000.
Jian Shen Shiyang Liu Rong Cao Xin Fan Junjie Du Huaiwu Zhang Zhifang Lin Siu-Tat Chui John Q. Xiao 《Applied Physics A: Materials Science & Processing》2011,105(4):789-793
We experimentally studied magnetically controllable photonic band gaps (PBGs) in two-dimensional magnetic photonic crystals
consisting of ferrite rods. Besides the conventional PBG that relates to Bragg scattering, two other types of PBG, resulting
from magnetic surface plasmon (MSP) resonance and spin-wave resonance, respectively, are observed. The PBG due to MSP resonance
is particularly interesting because of its analogy to surface plasmon in metal; furthermore, it is shown to be completely
tunable by an external static magnetic field from both an experimental and a theoretical point of view. 相似文献