全文获取类型
收费全文 | 4103篇 |
免费 | 738篇 |
国内免费 | 235篇 |
专业分类
化学 | 1179篇 |
晶体学 | 27篇 |
力学 | 264篇 |
综合类 | 28篇 |
数学 | 298篇 |
物理学 | 3280篇 |
出版年
2024年 | 5篇 |
2023年 | 54篇 |
2022年 | 83篇 |
2021年 | 148篇 |
2020年 | 149篇 |
2019年 | 102篇 |
2018年 | 107篇 |
2017年 | 149篇 |
2016年 | 167篇 |
2015年 | 139篇 |
2014年 | 258篇 |
2013年 | 292篇 |
2012年 | 264篇 |
2011年 | 304篇 |
2010年 | 243篇 |
2009年 | 243篇 |
2008年 | 281篇 |
2007年 | 255篇 |
2006年 | 253篇 |
2005年 | 202篇 |
2004年 | 189篇 |
2003年 | 155篇 |
2002年 | 137篇 |
2001年 | 109篇 |
2000年 | 121篇 |
1999年 | 98篇 |
1998年 | 92篇 |
1997年 | 80篇 |
1996年 | 60篇 |
1995年 | 47篇 |
1994年 | 41篇 |
1993年 | 36篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 15篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有5076条查询结果,搜索用时 31 毫秒
121.
122.
Dawei Xu Li Zheng Xinhong Cheng Gang Wang Qian Wang Wenbo Xin Peiyi Ye Lingyan Shen Yuehui Yu 《Physics letters. A》2019,383(25):3134-3137
The efficient passivation of in situ NH3-plasma pre-treatment and its regulation of the band alignment between HfO2 and 4H-SiC have been investigated by XPS. With in situ NH3-plasma passivation by PEALD, a VBO of 0.72 eV and a CBO of 1.54 eV can be obtained across the HfO2/4H-SiC interface. The Si-O bonds components reduction in the passivated interface layers will lead to band bending or band shift at the interface and regulate the band alignments between HfO2 and 4H-SiC. The physical mechanism investigation of band alignments can be a cornerstone for the application of HfO2/4H-SiC heterojunctions in the high-power devices. 相似文献
123.
六方氮化硼(h-BN)晶格结构是一种类六方对称复式超晶格结构。具有h-BN晶格构型的光子晶体以其宽光子带隙特点受到国内外学者的广泛关注。本文利用不同尺度低压气体放电管与Al2O3介质棒周期性排列,构建了新型h-BN型超晶格等离子体光子晶体,实现其空间结构和等离子体参数的动态调控。利用微波透射谱对比研究了h-BN型超晶格与简单三角晶格等离子体光子晶体禁带位置、宽度和数目。分析了放电电流、介质棒阵列数对不同频段光子带隙的影响,以及电磁波入射角度对电磁传输特性的影响。结果表明:等离子体的引入不仅能够形成新的光子带隙,而且可以选择性地使部分禁带位置发生移动;相对于简单三角晶格,h-BN型超晶格等离子体光子晶体呈现出更多光子带隙;Al2O3介质棒阵列数对等离子体光子晶体禁带位置、宽度和数目均具有重要影响。电磁波入射角度变化越大,电磁传输特性差别越显著,透射谱相关性越差。本文所设计的新型h-BN型超晶格等离子体光子晶体为制作可调谐光子晶体提供了新的思路,在微波和太赫兹波控制领域具有潜在应用价值。 相似文献
124.
A. Frommer S. Luryi D. T. Nichols J. Lopata W. S. Hobson 《Fiber and Integrated Optics》2013,32(2):81-88
Abstract A method for modulation of semiconductor lasers is demonstrated. The method is based on the modulation of the optical confinement factor. Using this method an enhanced—3-dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved. This supports the theoretical predictions, showing an intrinsic 1/f decay rate for the optical confinement factor modulation scheme versus an intrinsic 1/f2 decay for direct modulation. 相似文献
125.
Peng Xiang Xiaoping Zheng Hanyi Zhang Yuquan Li Jintian Xiong 《Fiber and Integrated Optics》2013,32(3):222-232
Abstract The generation of ultra-wideband signals in the optical domain is highly desirable for ultra-wideband-over-fiber systems, which has recently become a topic of interest. In this article, a novel and simple approach to achieve all-optical generation of ultra-wideband signals is proposed, which is based on delaying and superimposing optical Gaussian pulses with opposite polarities. The proposed system is capable of generating both ultra-wideband monocycle and doublet pulses, and the polarity of the generated ultra-wideband monocycle pulses can be fast-switched to implement pulse polarity modulation with the required bit pattern. A model to describe the proposed system is developed, and the generation of ultra-wideband signals is demonstrated with simulations and a proof-of-concept experiment. 相似文献
126.
The effect of swirling intensity on the structure and heat transfer of a turbulent gas–droplet flow after a sudden pipe expansion has been numerically simulated. Air is used as the carrier phase, and water, ethanol, and acetone are used as the dispersed phase. The Eulerian approach is applied to simulate the dynamics and heat transfer in the dispersed phase. The gas phase is described by a system of Reynolds-averaged Navier-Stokes (RANS) equations, taking into account the effect of droplets on mean transport and turbulent characteristics in the carrier phase. Gas phase turbulence is predicted using the second-moment closure. A swirling droplet-laden flow is characterized by an increase in the number of small particles on the pipe axis due to their accumulation in the zone of flow recirculation and the action of the turbulent migration (turbophoresis) force. A rapid dispersion of fine droplets over the pipe cross-section is observed without swirling. With an increase in swirling intensity, a significant reduction in the length of the separation region occurs. The swirling of a two-phase flow with liquid droplets leads to an increase in the level of turbulence for all three types of liquid droplets investigated in this work due to their intensive evaporation. It is shown that the addition of droplets leads to a significant increase in heat transfer in comparison with a single-phase swirling flow. The greatest effect of flow swirling on heat transfer intensification in a two-phase gas-droplet flow is obtained for the droplets of ethanol and water and smallest effect is for the acetone droplets. 相似文献
127.
We study stable blow-up dynamics in the generalized Hartree equation with radial symmetry, which is a Schrödinger-type equation with a nonlocal, convolution-type nonlinearity: First, we consider the -critical case in dimensions and obtain that a generic blow-up has a self-similar structure and exhibits not only the square root blowup rate , but also the log-log correction (via asymptotic analysis and functional fitting), thus, behaving similarly to the stable blow-up regime in the -critical nonlinear Schrödinger equation. In this setting, we also study blow-up profiles and show that generic blow-up solutions converge to the rescaled , a ground state solution of the elliptic equation . We also consider the -supercritical case in dimensions . We derive the profile equation for the self-similar blow-up and establish the existence and local uniqueness of its solutions. As in the NLS -supercritical regime, the profile equation exhibits branches of nonoscillating, polynomially decaying (multi-bump) solutions. A numerical scheme of putting constraints into solving the corresponding ordinary differential equation is applied during the process of finding the multi-bump solutions. Direct numerical simulation of solutions to the generalized Hartree equation by the dynamic rescaling method indicates that the is the profile for the stable blow-up. In this supercritical case, we obtain the blow-up rate without any correction. This blow-up happens at the focusing level , and thus, numerically observable (unlike the -critical case). In summary, we find that the results are similar to the behavior of stable self-similar blowup solutions in the corresponding settings for the nonlinear Schrödinger equation. Consequently, one may expect that the form of the nonlinearity in the Schrödinger-type equations is not essential in the stable formation of singularities. 相似文献
128.
In this work, we performed first principles calculations based on self-consistent charge density functional tight-binding to investigate different mechanisms of band gap tuning of silicene. We optimized structures of silicene sheet, functionalized silicene with H, CH3 and F groups and nanoribbons with the edge of zigzag and armchair. Then we calculated electronic properties of silicene, functionalized silicene under uniaxial elastic strain, silicene nanoribbons and silicene under external electrical fields. It is found that the bond length and buckling value for relaxed silicene is agreeable with experimental and other theoretical values. Our results show that the band gap opens by functionalization of silicene. Also, we found that the direct band gap at K point for silicene changed to the direct band gap at the gamma point. Also, the functionalized silicene band gap decrease with increasing of the strain. For all sizes of the zigzag silicene nanoribbons, the band gap is near zero, while an oscillating decay occurs for the band gap of the armchair nanoribbons with increasing the nanoribbons width. At finally, it can be seen that the external electric field can open the band gap of silicene. We found that by increasing the electric field magnitude the band gap increases. 相似文献
129.
Biotransformation and metabolic profile of Xian‐Ling‐Gu‐Bao capsule,a traditional Chinese medicine prescription,with rat intestinal microflora by ultra‐performance liquid chromatography coupled with quadrupole time‐of‐flight tandem mass spectrometry analysis 下载免费PDF全文
《Biomedical chromatography : BMC》2018,32(4)
130.
A simple model is proposed to take into account secondary X-ray fluorescence and absorption effects near the interface. This model is based on the investigation of the shape change of the first derivative equation that can fit the sigmoidal EDS profile obtained when a high vacuum electron beam passes through the interface of two adjacent materials. The contribution of the photoelectric absorption of primary X-rays (characteristic and Bremsstrahlung) and the secondary fluorescence on the degradation of the X-ray spatial resolution can be easily quantified. The close agreement between the simulated (Monte Carlo simulation using the Casino software) and the experimental data serves to assess the reliability of this developed model. 相似文献