全文获取类型
收费全文 | 15304篇 |
免费 | 2504篇 |
国内免费 | 1681篇 |
专业分类
化学 | 11356篇 |
晶体学 | 194篇 |
力学 | 816篇 |
综合类 | 73篇 |
数学 | 1540篇 |
物理学 | 5510篇 |
出版年
2024年 | 38篇 |
2023年 | 309篇 |
2022年 | 335篇 |
2021年 | 499篇 |
2020年 | 628篇 |
2019年 | 622篇 |
2018年 | 561篇 |
2017年 | 496篇 |
2016年 | 717篇 |
2015年 | 746篇 |
2014年 | 944篇 |
2013年 | 1186篇 |
2012年 | 1380篇 |
2011年 | 1478篇 |
2010年 | 1060篇 |
2009年 | 905篇 |
2008年 | 1045篇 |
2007年 | 952篇 |
2006年 | 839篇 |
2005年 | 728篇 |
2004年 | 544篇 |
2003年 | 456篇 |
2002年 | 426篇 |
2001年 | 305篇 |
2000年 | 305篇 |
1999年 | 253篇 |
1998年 | 224篇 |
1997年 | 195篇 |
1996年 | 183篇 |
1995年 | 144篇 |
1994年 | 185篇 |
1993年 | 129篇 |
1992年 | 125篇 |
1991年 | 96篇 |
1990年 | 90篇 |
1989年 | 84篇 |
1988年 | 44篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1967年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 33 毫秒
161.
The purpose of this paper is to report some experimental results with HfSiO films formed on silicon substrates by electron beam evaporation (EB-PVD) and annealed at different temperatures. The images of atomic force microscope (AFM) indicated that HfSiO film annealed at 900 °C was still amorphous, with a surface roughness of 0.173 nm. X-ray photoelectron spectroscopy (XPS) analysis revealed that the chemical composition of the film was (HfO2)3(SiO2) and Hf-Si-O bonds existed in the annealed film. Electrical measurements showed that the equivalent oxide thickness (EOT) was 4 nm, the dielectric constant was around 6, the breakdown voltage was 10 MV/cm, the fixed charge density was −1.2 × 1012 cm−2, and the leakage current was 0.4 μA/cm2 at the gate bias of 2 V for 6 nm HfSiO film. The annealing after deposition effectively reduced trapping density and the leakage current, and eliminated hysteresis in the C-V curves. Annealing also induced SiO2 growth at the interface. 相似文献
162.
Jin Kyu Park Dong Hun Lee Bok Ju Song Jae Buem Oh Hwan Kyu Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1326-1342
We have designed and synthesized novel perfluorinated polyimides with 3D controlled structure. At first, we successfully developed the new synthetic routes to diamines with pendant bulky perfluorinated aromatic units in a multi‐step synthetic procedure. Novel perfluorinated polyimides were prepared in a two‐step reaction in N‐methyl‐2‐pyrrolidinone (NMP) solution: The first step was for the synthesis of polyamic acids (PAAs) and the second reaction was for the imidization of PAA. The polymer yield was over 89% and the inherent viscosity of PAAs was in the range of 0.24–0.36 dL/g. The thin films were prepared by spin‐coating the PAA solution in NMP onto various substrates such as a Si wafer or a KBr pellet, dried at 80 °C and further cured at 230 °C. The resultant polyimides are thermally stable over 400 °C. The refractive index and birefringence of the resultant polyimides are 1.5858–1.6452 and 0.01–0.005, respectively. The refractive index of polyimide decreases with increasing the fluorine content. The copolymerization and the ether linkages into the backbone reduce the birefringence of polyimides. Surprisingly, the pendant ether linkage is not a crucial factor in reducing the polyimide birefringence. Their birefringence is comparatively very low, compared with that of previous polyimides. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1326–1342, 2006 相似文献
163.
Chae Kyu Kim Eun Seok Song Hyung Joo Kim Chiyoung Park Young Chul Kim Jai Kyeong Kim Jae Woong Yu Chulhee Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):254-263
We have synthesized conjugated dendrimer with triazine peripheries, and their luminescence properties were investigated. The dendrimers consist of dendritic triazine wedges for electron transport, distyrylbenzene core as an emitting moiety, and t‐butyl peripheral groups for good processing properties. The dendrimers have LUMO values of about ?2.7 eV possibly because of the triazine moiety with high electron affinity. Photoluminescence study indicates that energy transfer occurs from the triazine wedges to the stilbene bridge, and finally to the core chromophore units due to a cascade decrease of bandgap from the peripheral wedge to core moiety. Therefore, the emission wavelength was determined by the structure of the core unit. The energy transfer efficiency of distyrylbenzene‐cored dendrimers was about 75 and 55% for Trz‐1GD‐DSB and Trz‐2GD‐DSB, respectively. A preliminary electroluminescence property also was investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 254–263, 2006 相似文献
164.
165.
Rebuilding of metal components with laser cladding forming 总被引:4,自引:0,他引:4
Laser cladding forming (LCF) is a novel powerful tool for the repairing of metal components. Rebuilding of V-grooves on medium carbon steel substrates has been carried out with laser cladding forming technique using stainless steel powder as the cladding material. Microstructure of the deposited layers has been characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDAX), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Mechanical properties of the rebuilt V-groove samples have been evaluated by tensile and impacting tests and microhardness measurement. Experimental results show that good fusion bonding between the rebuilt layers and the substrate has been formed, and the microstructure of the cladding layers is mainly composed of fine, dense and defect-free epitaxial columnar dendrites. Due to the effect of grain size refinement, the tensile strength, impacting toughness, elongation and microhardness of the rebuilt samples have been greatly enhanced compared to those of the substrate. Microhardness is also very uniform throughout the rebuilt regions. With the growth of the deposited layers, the microhardness increases gradually. The good ductility of the deposited regions is verified by the SEM fracture analysis. 相似文献
166.
167.
168.
Semilinear Differential Inclusions in Separable Banach SpacesXueXingmei(薛星美)andSongGuozhu(宋国柱)(DepartmentofMathematics,Nanjin... 相似文献
169.
170.
宋敏 《新疆大学学报(理工版)》1993,(2)
本文考虑一类具有耗散与磁场效应的多维非线性Schrdinger型方程组的初边值问题。使用积分估计(包括L~p—L~q估计)证明了整体解的存在性。 相似文献