全文获取类型
收费全文 | 14014篇 |
免费 | 300篇 |
国内免费 | 77篇 |
专业分类
化学 | 6434篇 |
晶体学 | 270篇 |
力学 | 835篇 |
综合类 | 1篇 |
数学 | 1656篇 |
物理学 | 5195篇 |
出版年
2023年 | 71篇 |
2022年 | 149篇 |
2021年 | 177篇 |
2020年 | 148篇 |
2019年 | 181篇 |
2018年 | 188篇 |
2017年 | 155篇 |
2016年 | 277篇 |
2015年 | 231篇 |
2014年 | 332篇 |
2013年 | 642篇 |
2012年 | 836篇 |
2011年 | 996篇 |
2010年 | 691篇 |
2009年 | 645篇 |
2008年 | 836篇 |
2007年 | 731篇 |
2006年 | 759篇 |
2005年 | 611篇 |
2004年 | 504篇 |
2003年 | 440篇 |
2002年 | 370篇 |
2001年 | 542篇 |
2000年 | 452篇 |
1999年 | 274篇 |
1998年 | 228篇 |
1997年 | 203篇 |
1996年 | 237篇 |
1995年 | 206篇 |
1994年 | 179篇 |
1993年 | 142篇 |
1992年 | 143篇 |
1991年 | 160篇 |
1990年 | 140篇 |
1989年 | 99篇 |
1988年 | 90篇 |
1987年 | 58篇 |
1986年 | 66篇 |
1985年 | 94篇 |
1984年 | 77篇 |
1983年 | 60篇 |
1982年 | 78篇 |
1981年 | 83篇 |
1980年 | 70篇 |
1979年 | 76篇 |
1978年 | 73篇 |
1977年 | 86篇 |
1976年 | 73篇 |
1975年 | 69篇 |
1973年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A domain partitioning algorithm for minimizing or maximizing a Lipschitz continuous function is enhanced to yield two new, more efficient algorithms. The use of interval arithmetic in the case of rational functions and the estimates of Lipschitz constants valid in subsets of the domain in the case of others and the addition of local optimization have resulted in an algorithm which, in tests on standard functions, performs well. 相似文献
82.
The surface properties of nanofibres are of importance in various applications. In this work, electrospun polyamide nanofibres were used as substrates for creating functional nanostructures on the nanofibre surfaces. A RF magnetron sputter coating was used to deposit the functional layer of titanium dioxide (TiO2) onto the nanofibres. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and environmental scanning electron microscopy (ESEM) were employed to study the topography, grain structure and wetting of the nanofibre surfaces, respectively. The AFM results indicated a significant difference in the morphology of the nanofibres before and after the TiO2 sputter coating. The XRD analysis showed the amorphous structures of the TiO2 deposition layer. XPS spectra reflected the chemical features of the deposited nanostructures. The ESEM observation revealed that the surface wettability of TiO2 sputter coated nanofibres was significantly improved after UV irradiation. 相似文献
83.
We investigate carrier dynamics in a passive InAs/InP quantum dot (QD) waveguide using 255 fs optical pulses at a central wavelength of 1568 nm. We observe strong anisotropy of absorption saturation for different polarizations. Pump-probe measurements indicate the presence of carrier relaxation dynamics on a timescale in the order of tens of picoseconds due to cascaded relaxation of carriers generated by two-photon absorption (TPA) from the bulk region to the QDs via the wetting layer. These relaxation timescales are much longer than in QD amplifiers. Our observations are supported by a rate-equation model which includes TPA, showing good agreement with the pump-probe measurements. 相似文献
84.
We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging. 相似文献
85.
D. Liu Y. Li R. An Y. Dou H. Yang Q. Gong 《Applied Physics A: Materials Science & Processing》2006,84(3):257-260
We studied the influence of focusing depth on the index change threshold and damage threshold of silica glass irradiated by a focused 120 fs laser beam. Both thresholds increased with the focusing depth. The aspect ratio of the waveguide cross section can be selected by changing the focusing depth. A 5 mm long waveguide was written at the depth of 2100 μm, which was single mode at 632.8 nm and exhibited propagation loss of 0.56 dB/cm. The refractive index change was calculated to be ∼2.47×10-3. The influence of the focusing depth should be considered in multi-layer devices as shown in the fabrication of a 3×3 waveguide array. PACS 42.62.-b; 42.82.Et; 81.05.Kf 相似文献
86.
Polyethylene oxide (PEO) based polymer electrolytes with BaTiO3 as filler and Li(C2F5SO2)2N as salt have been examined in lithium polymer batteries. The aluminum disolution potential in PEO-Li(C2F5SO2)2N was estimated to be 4.1 V vs. Li/Li+ at 80 °C, which was compared to that of 3.8 V vs. Li/Li+ in PEO-Li(CF3SO2)2N. The electrical conductivity of the system was measured as a function of O/Li ratio. The highest conductivity was observed
in O/Li=8. The conductivity was 1.65×10−3 S/cm at 80 °C and 1.5×10−5 S/cm at 25 °C. The interfacial resistance of Li/polymer electrolyte/Li annealed at 80 °C for 15 days was lower than 100 Ωcm2.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001. 相似文献
87.
Iron oxide catalyst with spinel structure used for dehydrogenation of ethylbenzene is one kind of important catalyst in petrochemical industry. In this work several series of industrial catalyst were prepared with different components and different manufacturing processes. Mössbauer Spectroscopy has been used to determine the optimal components and the better manufacturing process for spinel structure formation. The results may prove useful for producing the industrial dehydrogenation catalyst with better catalytic property. 相似文献
88.
89.
90.
Organically modified solid-state silicates (ORMOSILS) doped with a new laser dye 1,3,5,7,8-pentamethylpyrromethene-2,6-disulfonate-BF2 complex (pyrromethene 556) have been synthesized by a sol-gel method and the compositional effects on pore characteristics, fluorescence and lasing properties have been investigated. It is found that the use of dimethylsulfoxide and γ-glycidoxypropyltrimethoxysilane could greatly change the structure properties of sol-gel derived ORMOSILS cage, and thus the fluorescence and lasing properties of the materials could improve significantly. A successful laser oscillation from this dye-doped ORMOSILS sample has been achieved upon pumping with a Q-switched frequency-doubled Nd:YAG laser at 532 nm. A slope efficiency of 54% with a useful lifetime greater than 10,000 shots has been demonstrated at a pump repetition rate of 1 Hz and a pump intensity of 1 J/cm2 by using the new ORMOSILS cage on our newly designed laser system. Our results have shown that it is possible to obtain a high-efficiency with a long-lifetime for a compact new laser device by low cost dye-doped solid-state ORMOSILS. 相似文献