全文获取类型
收费全文 | 1988篇 |
免费 | 354篇 |
国内免费 | 218篇 |
专业分类
化学 | 1398篇 |
晶体学 | 15篇 |
力学 | 93篇 |
综合类 | 6篇 |
数学 | 276篇 |
物理学 | 772篇 |
出版年
2024年 | 6篇 |
2023年 | 47篇 |
2022年 | 50篇 |
2021年 | 51篇 |
2020年 | 67篇 |
2019年 | 61篇 |
2018年 | 69篇 |
2017年 | 60篇 |
2016年 | 85篇 |
2015年 | 73篇 |
2014年 | 94篇 |
2013年 | 126篇 |
2012年 | 157篇 |
2011年 | 164篇 |
2010年 | 96篇 |
2009年 | 127篇 |
2008年 | 122篇 |
2007年 | 119篇 |
2006年 | 120篇 |
2005年 | 100篇 |
2004年 | 73篇 |
2003年 | 58篇 |
2002年 | 56篇 |
2001年 | 62篇 |
2000年 | 52篇 |
1999年 | 62篇 |
1998年 | 34篇 |
1997年 | 45篇 |
1996年 | 46篇 |
1995年 | 33篇 |
1994年 | 18篇 |
1993年 | 26篇 |
1992年 | 30篇 |
1991年 | 28篇 |
1990年 | 22篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有2560条查询结果,搜索用时 15 毫秒
91.
Efficiency Improvement in Polymer Light‐Emitting Diodes by “Far‐Field” Effect of Gold Nanoparticles 下载免费PDF全文
Xiaoyan Wu Linlin Liu Zhicong Deng Li Nian Wenzhuo Zhang Dehua Hu Zengqi Xie Yueqi Mo Yuguang Ma 《Particle & Particle Systems Characterization》2015,32(6):686-692
The “far‐field” effect of metal nanoparticles (NPs), when chromophores localized nearby metal NPs (typically the distance >λ/10), is an important optical effect to enhance emission in photoluminescence. The far‐field effect originates mainly from the interaction between origin emission and mirror‐reflected emission, resulting in the increased irradiative rate of chromophores on the mirror‐type substrate. Here, the far‐field effect is used to improve emission efficiency of polymer light‐emitting diodes (PLEDs). A universal performance improvement is achieved for the full visible light (red, green, blue) PLEDs, utilizing gold (Au) NPs to modify the indium tin oxide (ITO) substrates; this is shown by experimental and theoretical simulation to mainly come from the far‐field effect. The optimized distance, between the NPs and chromophores with visible light emission ranging from 400 to 700 nm, is 80–120 nm. Thus the scope of the far‐field may overlap the light‐emitting profile very well to enhance the efficiency of optoelectronic devices. The 30–40% enhancement is obtained for different color‐emitting materials through distance optimization. The far‐field effect is demonstrated to enhance device performance for materials in the full‐visible spectral range, which extends the optoelectric applications of Au NPs. 相似文献
92.
采用常见元器件等效实现一个广义忆阻器, 进而制作出一个电路特性可靠的非线性电路, 有助于忆阻混沌电路的非线性现象的实验展示及其所产生的混沌信号的实际工程应用. 基于忆阻二极管桥电路, 构建了一种无接地限制的、易物理实现的一阶有源广义忆阻模拟器; 由该模拟器并联电容后与RC桥式振荡器线性耦合, 实现了一种无电感元件的忆阻混沌电路; 建立了无感忆阻混沌电路的动力学模型, 开展了相应的耗散性、平衡点、稳定性和动力学行为等分析. 结果表明, 无感忆阻混沌电路在相空间中存在分布2个不稳定非零鞍焦的耗散区和包含1个不稳定原点鞍点的非耗散区; 当元件参数改变时, 无感忆阻混沌电路有着共存分岔模式和共存吸引子等非线性行为. 研制了实验电路, 该电路结构简单、易实际制作, 实验测量和数值仿真两者结果一致, 验证了理论分析的有效性. 相似文献
93.
考虑空气柱的水力旋流器内流场的数值模拟 总被引:1,自引:0,他引:1
对水力旋流器内流场进行了数值模拟.旋流器内液相和气相的湍流模拟采用了雷诺应力模型(RSM),边界条件采用速度进口、压力出口.在同一工况下选用三维模型及二维简化模型、分别用VOF模型及刚盖法对空气柱进行处理,就空气柱形成、切向及轴向速度与相同条件下试验测量的结果进行比较.结果表明,三维模型计算结果较二维简化模型与实验值吻合得更好,但二维简化模型在降低精度不大的前提下大大减少了计算时间.对空气柱的处理,选用VOF模型得到的结果更准确,而刚盖法减少了计算用时. 相似文献
94.
Controlled growth and field emission of vertically aligned AlN nanostructures with different morphologies 下载免费PDF全文
The controllable growth of three different morphologies of AlN
nanostructures (nanorod, nanotip and nanocrater) arrays are
successfully realized by using chemical vapour deposition (CVD)
technology. All three nanostructures are of single crystal h-AlN
with a growth orientation of [001]. Their growth is attributed to
the vapour-liquid-solid (VLS) mechanism. To investigate the factors
affecting field emission (FE) properties of AlN nanostructures, we
compare their FE behaviours in several aspects. Experimental results
show that AlN nanocrater arrays possess the best FE properties, such
as a threshold field of 7.2~V/μm and an emission current
fluctuation lower than 4%. Moreover, the three AlN nanostructures
all have good field emission properties compared with a number of
other excellent cathode nanomaterials, which suggests that they are
future promising FE nanomaterials. 相似文献
95.
96.
The intent of this study is to examine nonequilibrium heat transfer in a copper-argon nanofluid by molecular dynamics simulation. Two different methods, the physical definition method and the curve fitting method, are introduced to calculate the coupling factor between nanoparticles and base fluid. The results show that the coupling factors obtained by these two methods are consistent. The coupling factor is proportional to the volume fraction of the nanoparticle and inversely proportional to nanoparticle diameter. In the temperature range of 90-200 K, the coupling factor is not affected by temperature. The nanoparticle aggregation results in a decrease of the coupling factor. 相似文献
97.
B.??ywicka P.?Mo?ejkoEmail author 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(2):54
Total cross section for single electron-impact ionization of cisplatin
(H6N2Cl2Pt) molecule has been calculated with the
binary-encounter-Bethe (BEB) model from the ionization threshold up to 5 keV. To obtain
input data for the BEB calculations, geometric and electronic structures of the cisplatin
have been studied with quantum chemical methods. Elastic cross section for electron
collisions with cisplatin have also been evaluated using independent atom method with
static-polarization model potential for incident energies ranging from 50 to 3000 eV. The
obtained geometric structure of cisplatin is compared with available experimental and
theoretical data. Calculated cross sections have been compared with related cross sections
for selected purine and pirimidine bases. 相似文献
98.
The utilization of a simple focused optical cell to bring to light the competition between wideband stimulated Brillouin scattering (WSBS) and forward stimulated Raman scattering (FSRS) is investigated experimentally. A pulsed, wide bandwidth second-harmonic Nd:YAG laser is used as the pump source. We found that, the competition between WSBS and FSRS is an alternate process, which one dominated depends on the linewidth and energy of the pump laser, focal length, and optical breakdown. 相似文献
99.
100.
Quadrature demodulation-based phase rotation beamforming (QD-PRBF) is commonly used to support dynamic receive focusing in medical ultrasound systems. However, it is computationally demanding since it requires two demodulation filters for each receive channel. To reduce the computational requirements of QD-PRBF, we have previously developed two-stage demodulation (TSD), which reduces the number of lowpass filters by performing demodulation filtering on summation signals. However, it suffers from image quality degradation due to aliasing at lower beamforming frequencies. To improve the performance of TSD-PRBF with reduced number of beamforming points, we propose a new adaptive field-of-view (AFOV) imaging method. In AFOV imaging, the beamforming frequency is adjusted depending on displayed FOV size and the center frequency of received signals. To study its impact on image quality, simulation was conducted using Field II, phantom data were acquired from a commercial ultrasound machine, and the image quality was quantified using spatial (i.e., axial and lateral) and contrast resolution. The developed beamformer (i.e., TSD-AFOV-PRBF) with 1024 beamforming points provided comparable image resolution to QD-PRBF for typical FOV sizes (e.g., 4.6% and 1.3% degradation in contrast resolution for 160 mm and 112 mm, respectively for a 3.5 MHz transducer). Furthermore, it reduced the number of operations by 86.8% compared to QD-PRBF. These results indicate that the developed TSD-AFOV-PRBF can lower the computational requirement for receive beamforming without significant image quality degradation. 相似文献