全文获取类型
收费全文 | 4969篇 |
免费 | 789篇 |
国内免费 | 548篇 |
专业分类
化学 | 3411篇 |
晶体学 | 46篇 |
力学 | 349篇 |
综合类 | 24篇 |
数学 | 623篇 |
物理学 | 1853篇 |
出版年
2024年 | 25篇 |
2023年 | 103篇 |
2022年 | 165篇 |
2021年 | 202篇 |
2020年 | 200篇 |
2019年 | 195篇 |
2018年 | 187篇 |
2017年 | 139篇 |
2016年 | 277篇 |
2015年 | 230篇 |
2014年 | 261篇 |
2013年 | 382篇 |
2012年 | 478篇 |
2011年 | 456篇 |
2010年 | 308篇 |
2009年 | 290篇 |
2008年 | 307篇 |
2007年 | 250篇 |
2006年 | 248篇 |
2005年 | 211篇 |
2004年 | 185篇 |
2003年 | 162篇 |
2002年 | 132篇 |
2001年 | 111篇 |
2000年 | 94篇 |
1999年 | 100篇 |
1998年 | 75篇 |
1997年 | 74篇 |
1996年 | 74篇 |
1995年 | 61篇 |
1994年 | 45篇 |
1993年 | 45篇 |
1992年 | 27篇 |
1991年 | 38篇 |
1990年 | 35篇 |
1989年 | 26篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1974年 | 2篇 |
1944年 | 4篇 |
1943年 | 1篇 |
1942年 | 3篇 |
1941年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有6306条查询结果,搜索用时 15 毫秒
911.
Jianying Dai Wenqing Zhang Tiantian Li Ling Bai Wenya He Lifei Ji Huilan Shi Xin Zhang 《Electroanalysis》2019,31(7):1381-1389
Exploration of cost‐effective, high‐performance and durable multifunctional electrocatalysts is of significant importance for renewable energy conversion and storage. In this work, a simple strategy is developed to tailor the nickel metal with the collaboration of nitrogen‐doped graphene and single‐walled carbon nanotubes. The resulted nickel catalyst exhibits superior trifunctional activities for oxygen evolution, hydrogen evolution and oxygen reduction reactions in the same electrolyte, even comparable to commercial Pt/C and RuO2 respectively, which can be attributed to the synergistic advantages between nickel, nitrogen and carbon, mainly including abundant integrated active sites achieved by the irregular charge distribution among C?N and Ni?N coupling centers. Such remarkable effects on trifunctional catalysis elicit the efficient overall water splitting, and endow the assembled zinc‐air battery with a good performance. These highlight the metallic nickel as an advanced multifunctional electrocatalysts with integrated sites developed from the collaboration of two different carbon nanomaterials. 相似文献
912.
Shuo Li Hedan Bai Robert F. Shepherd Huichan Zhao 《Angewandte Chemie (International ed. in English)》2019,58(33):11182-11204
Soft materials possess several distinctive characteristics, such as controllable deformation, infinite degrees of freedom, and self‐assembly, which make them promising candidates for building soft machines, robots, and haptic interfaces. In this Review, we give an overview of recent advances in these areas, with an emphasis on two specific topics: bio‐inspired design and additive manufacturing. Biology is an abundant source of inspiration for functional materials and systems that mimic the function or mechanism of biological tissues, agents, and behaviors. Additive manufacturing has enabled the fabrication of materials and structures prevalent in biology, thereby leading to more‐capable soft robots and machines. We believe that bio‐inspired design and additive manufacturing have been, and will continue to be, important tools for the design of soft robots. 相似文献
913.
Effect of a negative Poisson ratio in the tension of ceramics 总被引:1,自引:0,他引:1
The effect of a negative Poisson ratio is experimentally revealed in the tension deformation of a natural layered ceramic. This effect can increase the volume strain energy per unit volume by 1100% and, simultaneously, decrease the deformation strain energy per unit volume by about 44%, so that it effectively enhances the deformation capacity by about 1 order of magnitude in the tension of the material. The present study also shows that the physical mechanisms producing the effect are attributed to the climbing on one another of the nanostructures in the natural material, which provides a guide to the design of synthetic toughening composites. 相似文献
914.
Synthesis and characterization of a novel two-component organogelator based on ion-bonded discotic complex 总被引:1,自引:0,他引:1
Kang Tao Tiayuan Wu Dairen Lu Ruke Bai Hongfei Li Lijia An 《Journal of Molecular Liquids》2008,142(1-3):118-123
A novel ion-bonded discotic complex was prepared from 2,3,6,7,10,11-hexakis(N,N-dimethylaminopropylaminocarbonylmethoxy)triphenylene (HDTP) and 4′-dodecyloxybiphenyl-4-carboxylic acid (DBC) by ionic self-assembly (ISA) route and characterized by Fourier transform infrared (FTIR) spectrum. We found that the complex can self-assemble into stable gels in aromatic hydrocarbons. Nanofibers with diameters of 50–130 nm were observed in the gels by transmission electron micrograph (TEM). The FTIR data in conjunction with UV–vis and fluorescence spectra suggested that the aggregation of the complex into elongated fibers in solution was induced by a directional extended network of hydrogen bonds and π–π interactions. Based on the experiment analysis, we proposed a tentative model of the self-assembly of this two-component gel-phase material. 相似文献
915.
Qiuyuan Feng Tingju Li Hongyun Yue Kai Qi Fudong Bai Junze Jin 《Applied Surface Science》2008,254(8):2262-2268
Ni-Al2O3 composite coatings were prepared by using sediment co-deposition (SCD) technique and conventional electroplating (CEP) technique from Watt's type electrolyte without any additives. The microstructure, hardness, and wear resistance of resulting composites were investigated. The results show that the incorporation of nano-Al2O3 particles changes the surface morphology of nickel matrix. The preferential orientation is modified from (2 0 0) plane to (1 1 1) plane. The microhardness of Ni-Al2O3 composite coatings in the SCD technique are higher than that of the CEP technique and pure Ni coating and increase with the increasing of the nano-Al2O3 particles concentration in plating solution. The wear rate of the Ni-Al2O3 composite coating fabricated via SCD technique with 10 g/l nano-Al2O3 particles in plating bath is approximately one order of magnitude lower than that of pure Ni coating. Wear resistance for SCD obtained composite coatings is superior to that obtained by the CEP technique. The wear mechanism of pure Ni and nickel nano-Al2O3 composite coatings are adhesive wear and abrasive wear, respectively. 相似文献
916.
Sun L Chen Z Ren Q Yu K Bai L Zhou W Xiong H Zhu ZQ Shen X 《Physical review letters》2008,100(15):156403
We report direct observation of the strong exciton-photon coupling in a ZnO tapered whispering gallery (WG) microcavity at room temperature. By scanning excitations along the tapered arm of the ZnO tetrapod using a micro-photoluminescence spectrometer with different polarizations, we observed a transition from the pure WG optical modes in the weak interaction regime to the excitonic polariton in the strong coupling regime. The experimental observations are well described by using the plane wave model including the excitonic polariton dispersion relation. This provides a direct mapping of the polariton dispersion, and thus a comprehensive picture for coupling of different excitons with differently polarized WG modes. 相似文献
917.
基于各向异性扩散的红外图像噪声滤波算法 总被引:13,自引:5,他引:8
抑制红外焦平面阵列探测器噪声时,为了有效保持边缘细节,在塔基(Tukey)扩散模型的基础上,提出了一种基于各向异性扩散的滤波算法.算法由微分法提取边界点集,利用信号和噪声的空间分布特性对图像进行预处理,从而改善了Perona-Malik(P-M)方程的病态性.建立了新的扩散系数且该系数在理论上满足Charbonnier等人构造准则.通过给定边界条件实现了有利于保持边缘的目的.该算法已在基于DSP FPGA的硬件平台上实时运行,较好地抑制了噪声,又有效地保持了边缘,处理后的图像具有良好的视觉效果. 相似文献
918.
Nanostructured Pr8Fe86−xVxB6−yCy (x=0, 1; y=0, 1) ribbons composed of Pr2Fe14B and α-Fe phases with a high coercivity are fabricated by direct melt spinning. The effects of a single addition of V and a combined addition of V and C on the structures and magnetic properties of melt-spun Pr8Fe86VB6−xCx (x=0 and 1) ribbons have been investigated. Compared with addition-free ribbons, 1 at% V addition is found to reduce the grain sizes of the samples and improve their magnetic properties due to a strong exchange coupling between the hard and the soft phase. A remanence ratio of 0.82, a coercive field of 6.2 kOe and a maximum energy product of 23.4 MGOe in melt-spun Pr8Fe85VB6 ribbons are obtained at room temperature. The combined addition of V and C is found to lead to the formation of an intermediate phase of VC at grain boundaries, which appears as a pinning barrier during magnetization and results in an increase of the coercivity value to 6.9 kOe for melt-spun Pr8Fe85VB5C ribbons. 相似文献
919.
Chunxu Bai 《Physics letters. A》2008,372(5):725-729
Spin-polarized transports of relativistic electrons through graphene-based ferromagnet/insulator/ferromagnet (FG/IG/FG) single junctions have been investigated theoretically. Large oscillating tunnel magnetoresistance (TMR) has been found in monolayer and bilayer FG/IG/FG junctions. The oscillating amplitudes of TMR do not decrease with the increase of the thickness and the height of barrier, in contrast to the exponential decay in conventional ferromagnet/insulator/ferromagnet single junction. The physical origin for such a phenomenon has also been analyzed. It is anticipated to apply such a phenomenon to design the spin-polarized electron device based on the graphene materials. 相似文献
920.
Kang Tao Dairen Lu Ruke Bai Hongfei Li Lijia An 《Macromolecular rapid communications》2008,29(17):1477-1483
We have developed a novel strategy for the preparation of ion‐bonded supramolecular star polymers by RAFT polymerization. An ion‐bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert‐butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by 1H NMR and GPC. The results show that the polymerization possesses the character of living free‐radical polymerization and the ion‐bonded supramolecular star polymers PSt, PtBA, and PSt‐b‐PtBA, with six well‐defined arms, were successfully synthesized.