全文获取类型
收费全文 | 4109篇 |
免费 | 647篇 |
国内免费 | 114篇 |
专业分类
化学 | 2233篇 |
晶体学 | 5篇 |
力学 | 49篇 |
综合类 | 8篇 |
数学 | 21篇 |
物理学 | 754篇 |
无线电 | 1800篇 |
出版年
2024年 | 15篇 |
2023年 | 167篇 |
2022年 | 94篇 |
2021年 | 194篇 |
2020年 | 178篇 |
2019年 | 170篇 |
2018年 | 123篇 |
2017年 | 176篇 |
2016年 | 225篇 |
2015年 | 243篇 |
2014年 | 295篇 |
2013年 | 325篇 |
2012年 | 283篇 |
2011年 | 294篇 |
2010年 | 259篇 |
2009年 | 220篇 |
2008年 | 231篇 |
2007年 | 198篇 |
2006年 | 206篇 |
2005年 | 161篇 |
2004年 | 142篇 |
2003年 | 122篇 |
2002年 | 69篇 |
2001年 | 57篇 |
2000年 | 62篇 |
1999年 | 61篇 |
1998年 | 53篇 |
1997年 | 37篇 |
1996年 | 26篇 |
1995年 | 29篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1970年 | 1篇 |
排序方式: 共有4870条查询结果,搜索用时 15 毫秒
91.
《Arabian Journal of Chemistry》2020,13(2):3934-3945
A hierarchical nanostructure consisting of uniform copper oxide nanowires vertically grown on three-dimensional copper framework (CuO NWs/3D-Cu foam) was prepared by a two-step synthetic process. The uniform CuO NWs anchored onto the 3D foam exhibited outstanding electrocatalytic activity towards hydrogen peroxide reduction due to the unique one‐dimensional direction with its excellent catalytic activity and large surface area of 3D substrate, which enhanced electroactive sites and charge conductivity. As a result, a wide linear detection range of 1 µM–1 mM, good sensitivity of 8.87 µA/(mM ⋅ cm2), low detection limit of 0.98 µM, and rapid response time of 5 s to hydrogen peroxide were achieved under a working potential of −0.4 V in phosphate buffer solution (pH of 7.4). In addition, the CuO NWs/3D-Cu foam material showed excellent selectivity to hydrogen peroxide and good resistance against poisonous interferents, including ascorbic acid, dopamine, urea, uric acid, and potassium chloride. Furthermore, the CuO NWs/3D-Cu foam presented good reproducibility, stability, and accurate detection for hydrogen peroxide in real sample; therefore, it may be considered to be a potential free-standing hydrogen peroxide sensor in practical analysis applications. 相似文献
92.
E. C. C. Vasconcellos F. R. Petersen K. M. Evenson 《International Journal of Infrared and Millimeter Waves》1981,2(4):705-711
We report for the first time wavelength, relative polarization, and frequency measurements for 47 new cw FIR laser lines in the wavelength region from 120 to 1714 m, all obtained by optically pumping CD2F2 with a CO2 laser. Relative output powers were also measured. For comparison, the 189.8 m line pumped by RI(34) is nearly five times as efficient as the 118.8 m methyl alcohol line.Contribution of the U.S. Government, not subject to copyright. 相似文献
93.
E. C. C. Vasconcellos A. Scalabrin F. R. Petersen K. M. Evenson 《International Journal of Infrared and Millimeter Waves》1981,2(3):533-539
Twenty-four new submillimeter laser lines in fully deuterated methyl alcohol (CD3OD) in the wavelength range from 52 to 328 m have been obtained in a Fabry-Perot FIR resonator by optically pumping the methanol with a cw CO2 laser. We have made accurate wavelength measurements and have determined the relative polarization of most of the known CD3OD laser lines. The frequencies of 13 of the strongest lines were also measured.Contribution of the U.S. Government, not subject to copyright. 相似文献
94.
The spectral characteristics of mini-optically pumped NH3 cavity laser emission at 67.2μm was studied. It was found that the spectrum of 67.2μm emission was duality. With low power
CO2-9R(30) pumping condition (lp<1MW/cm2), the spectrum appeared to be two wide FIR laser lines (∼4.6GHz for each line), which were the result of competition of multi-Raman
processes. With high power pumping condition (lp>2MW/cm2), the spectrum extended to be a very wide band (∼14GHz), which was the result of the combination of the competition and interaction
enhancement of Raman processes. The wide band spectral characteristics of 67.2 μm would be significant to the tuning of NH3 OPFIRL.
Supported by theNatural Science Foundation of Guangdong Province, P.R. China. 相似文献
95.
Development of Two‐Channel Phosphorescent Core–Shell Nanoprobe for Ratiometric and Time‐Resolved Luminescence Imaging of Intracellular Oxygen Levels 下载免费PDF全文
96.
This paper addresses two versions of a lifetime maximization problem for target coverage with wireless directional sensor networks. The sensors used in these networks have a maximum sensing range and a limited sensing angle. In the first problem version, predefined sensing directions are assumed to be given, whereas sensing directions can be freely devised in the second problem version. In that case, a polynomial-time algorithm is provided for building sensing directions that allow to maximize the network lifetime. A column generation algorithm is proposed for both problem versions, the subproblem being addressed with a hybrid approach based on a genetic algorithm, and an integer linear programming formulation. Numerical results show that addressing the second problem version allows for significant improvements in terms of network lifetime while the computational effort is comparable for both problem versions. 相似文献
97.
金属纳米结构对光谱响应及折射率灵敏度的影响 总被引:1,自引:0,他引:1
推导了任意形状金属纳米结构对复杂环境折射率的局域表面等离子体共振(LSPR)光谱响应的解析解,给出了体折射率和局部折射率灵敏度公式,并进行了详细的理论分析和数值验证。结果表明,金属纳米结构的光谱响应与被分析物厚度呈指数增长关系,并与被分析物的折射率、敏感层厚度、金属纳米结构的材料和形状等因素有关。被分析物折射率越高,光谱响应越大。敏感层越厚,局部折射率灵敏度越差。同时,尖锐的金属纳米结构形状可以获得更大的体折射率灵敏度。对金属纳米结构光谱响应及折射率灵敏度的研究对制作高灵敏度LSPR传感器具有重要的指导意义。 相似文献
98.
Yasin Cotur Michael Kasimatis Matti Kaisti Selin Olenik Charis Georgiou Firat Güder 《Advanced functional materials》2020,30(16)
A highly flexible, stretchable, and mechanically robust low‐cost soft composite consisting of silicone polymers and water (or hydrogels) is reported. When combined with conventional acoustic transducers, the materials reported enable high performance real‐time monitoring of heart and respiratory patterns over layers of clothing (or furry skin of animals) without the need for direct contact with the skin. The approach enables an entirely new method of fabrication that involves encapsulation of water and hydrogels with silicones and exploits the ability of sound waves to travel through the body. The system proposed outperforms commercial, metal‐based stethoscopes for the auscultation of the heart when worn over clothing and is less susceptible to motion artefacts. The system both with human and furry animal subjects (i.e., dogs), primarily focusing on monitoring the heart, is tested; however, initial results on monitoring breathing are also presented. This work is especially important because it is the first demonstration of a stretchable sensor that is suitable for use with furry animals and does not require shaving of the animal for data acquisition. 相似文献
99.
Jianhua Yan Yuhui Han Shuhui Xia Xiao Wang Yuanyuan Zhang Jianyong Yu Bin Ding 《Advanced functional materials》2019,29(51)
BaTiO3 crystals are attractive materials due to their high dielectric properties, but they are brittle and inelastic ceramics, which limits their broader applications in emerging fields, such as flexible electronics. A scalable strategy for the fabrication of ultra‐flexible crystalline BaTiO3 nanofiber (NF) films by a sol–gel electrospinning method, followed by a brief calcination, is reported. It facilitates the formation of perovskite BaTiO3 crystals with intricate grain boundaries at a low temperatures by growing them within polymer NF templates. The ceramic films have a polymer‐like softness of 50 mN, a large Young's modulus of 61 MPa, and an elastic strain of 0.9%. Moreover, they have a low density of 28 mg cm?3 and demonstrate superior softness without fracture after deformation. Piezoelectric sensors fabricated based on these films exhibit a high sensitivity of 80 ms with an output voltage of 1.05 V at a pressure of 100 kPa. This approach allows for the large‐scale fabrication of flexible BaTiO3 crystal NF films. 相似文献
100.