全文获取类型
收费全文 | 4246篇 |
免费 | 840篇 |
国内免费 | 401篇 |
专业分类
化学 | 2939篇 |
晶体学 | 39篇 |
力学 | 275篇 |
综合类 | 55篇 |
数学 | 496篇 |
物理学 | 1683篇 |
出版年
2024年 | 10篇 |
2023年 | 93篇 |
2022年 | 171篇 |
2021年 | 185篇 |
2020年 | 207篇 |
2019年 | 185篇 |
2018年 | 169篇 |
2017年 | 134篇 |
2016年 | 224篇 |
2015年 | 216篇 |
2014年 | 271篇 |
2013年 | 358篇 |
2012年 | 389篇 |
2011年 | 362篇 |
2010年 | 279篇 |
2009年 | 208篇 |
2008年 | 258篇 |
2007年 | 244篇 |
2006年 | 203篇 |
2005年 | 169篇 |
2004年 | 114篇 |
2003年 | 114篇 |
2002年 | 105篇 |
2001年 | 95篇 |
2000年 | 86篇 |
1999年 | 121篇 |
1998年 | 74篇 |
1997年 | 87篇 |
1996年 | 68篇 |
1995年 | 65篇 |
1994年 | 49篇 |
1993年 | 47篇 |
1992年 | 27篇 |
1991年 | 27篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有5487条查询结果,搜索用时 234 毫秒
991.
992.
考虑自重载荷作用的连续体结构拓扑优化 总被引:2,自引:0,他引:2
针对自重载荷作用下连续体结构拓扑优化中常遇到的柔顺度随单元密度变化的非单调性、非有效的材料体积约束和材料低密度区出现的``附属'效应等主要困难,提出了RAMP材料插值模型和平均敏度过滤技术相结合的求解策略,并采用MMA方法进行了优化求解. 研究了惩罚因子的选择对最优拓扑以及材料体积约束的影响. 结果表明,合理增大RAMP材料模型中惩罚因子(例如取值达到20.0), 可使材料体积约束达到有效约束. 此外,通过与Sigmund提出的敏度过滤技术比较表明,当引入平均敏度过滤技术时,结果0/1化程度较Sigmund的敏度技术高,可获得清晰的黑白拓扑. 相似文献
993.
Jianyong Huang Tao Zhu Lei Qin Xiaoling Peng Chunyang Xiong Jing Fang 《Acta Mechanica Solida Sinica》2009,22(6):563-570
Quantitative investigation on mechanical characteristics of cardiac myocytes has important physiological significance. Based on elastic substrate technique, this paper develops a set of algorithms for high-efficiency cellular traction recovery. By applying a gradient-based digital image correlation method to track randomly distributed fluorescence microbeads on the deformed substrate induced by single cardiac myocyte, high-resolution substrate displacement field can readily be obtained. By using a numerical algorithm based on the integral Boussinesq solution, cell-substrate tractions are reconstructed in a stable and reliable manner. Finally, spatiotemporal dynamics of a single cardiac myocyte is investigated as it adheres to a polyacrylamide elastic substrate. 相似文献
994.
995.
Bubble generation and transport in a micro-device composed of a micro-T-junction and a following serpentine micro-channel was experimentally investigated. It has a rectangular cross-sectional with an aspect ratio of 7.425. Air and water were used as gas and liquid, respectively. Mixtures of water–glycerol and water–Tween-20 were used to study the effects of liquid viscosity and surface tension. Compared with previous T-junction bubble generation, the liquid and gas inlets orientation was switched in this work. The continuous flow was driven from the perpendicular channel and the dispersion flow was from the main channel. It shows that the break-up process has three periodic steps under certain operating conditions. The dimensionless bubble length L/w in the micro-channel with high aspect ratio is much larger than that in square microchannels. A correlation is proposed to correlate L/w with liquid flow rate JL, gas flow rate JG, and liquid viscosity μL. Surface tension σ can change the bubble shape but almost does not affect the bubble length in this fast break-up process. Additionally, a long bubble may be broken up at the corners at the same time because the locations of gas and liquid are exchanged relative to the concave and convex portions of an elbow after a turn which may result in the change of fluid velocities and gas–liquid pressure drop. 相似文献
996.
A low cost spin coating route of fabricating CuInS2 polycrystalline thin films by reactive sin-tering method was put forward. The ink for spin coating was optimized by pre-reducing the precursor powders in hydrogen, which turned the nanoparticle precursor powders from mixed sulfides into a mixture of CuInS2 and Cu-In metal alloys. The results of scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Raman spectra showed that this optimization could highly improve the performance of CuInS2 polycrystalline thin films, including higher packing density, less impurity phases, and better quality. The en-ergy gap of optimized CuInS2 thin film was determined to be about 1.45 eV by absorption spectroscopy measurement. 相似文献
997.
Influence of local environment on the intensity of the localized surface plasmon polariton of Ag nanoparticles 下载免费PDF全文
A combined Ag nanoparticle with an insulating or conductive
layer structure has been designed for molecular detection using
surface enhanced Raman scattering microscopy. Optical absorption
studies revealed localized surface plasmon resonance, which shows
regular red shift with increasing environmental dielectric
constant. With the combined structure of surface enhanced Raman
scattering substrates and rhodamine 6G as a test molecule, the
results in this paper show that the absorption has a linear
relationship with the local electromagnetic field for insulating
substrates, and the electrical property of the substrate has a
non-negligible effect on the intensity of the local electromagnetic
field and hence the Raman enhancement. 相似文献
998.
Yi-Zhen Wang Guan-Hai Wang Xiao-Min Xiong Biao Wang Li-Ming Zhang Jin-Xiu Zhang 《Rheologica Acta》2010,49(11-12):1117-1126
Traditional torsional resonators, often obtaining the viscoelastic moduli of complex fluids only at one or several given discrete frequencies, lack the continuously varying frequency capability. This is an obvious disadvantage of the traditional torsional resonator technique. This paper presents an improved strategy, based on our previous discrete-frequency-measuring method (Wang et al., J Rheol 52:999–1011, 2008), to overcome such restriction and thus accomplish the continuously varying frequency capability of the traditional torsional resonator for measuring the viscoelastic properties of complex fluids. The feasibility of this strategy is demonstrated with the Newtonian fluids (several water–glycerol solutions) of viscosities varying from 10 to 1,400 cp by using our homemade torsion resonator apparatus in the 10 ~ 2,500 rad/s frequency range (continuous frequencies). Some results for typical viscoelastic polymers (two polyethylene oxide (PEO) aqueous solutions) are also given. Additionally, a comparison of the PEO results is made with the common rheometer technique. It is demonstrated that this improved strategy could enable the traditional torsional resonators, with one oscillating resonance mode, to work as the microrheological technique and the common rheometer technique in the continuous frequency range. 相似文献
999.
The influence of the ultra-short pulse wavelength on the populations in the three electronic states of CsI molecule is investigated using the time-dependent wave packet method. The calculated results show that the populations in the two excited states approach to the maxima at the wavelengths of 369 nm and 297 nm, respectively. The photodissociation reaction channels of the CsI molecule can be chosen by controlling the pump pulse wavelength. 相似文献
1000.
飞秒物理、飞秒化学和飞秒生物学 总被引:7,自引:0,他引:7
飞秒激光技术因其极高的时间分辨特性而被广泛应用于研究多种材料的超快过程,文章从几个侧面就飞秒技术在物理学,化学及生物学等方面的应用作了介绍,在飞秒物理方面,介绍了飞秒技术在研究半导体量子阱材料,纳米材料的性质及高次谐波产生等方面的研究进展,飞秒化学则主要介绍了飞秒技术在研究光化学反应,光解离过程、键的断裂及结合以及相关的动力学过程的应用;在生物方面,则介绍利用飞秒技术研究光合作用中的能量传递过程,视觉系统中的光致异构化过程以及DNA中的电荷传递及质子传递等过程的研究现状。 相似文献