全文获取类型
收费全文 | 125996篇 |
免费 | 20912篇 |
国内免费 | 13929篇 |
专业分类
化学 | 66204篇 |
晶体学 | 1071篇 |
力学 | 6226篇 |
综合类 | 609篇 |
数学 | 10781篇 |
物理学 | 40230篇 |
无线电 | 35716篇 |
出版年
2024年 | 546篇 |
2023年 | 3209篇 |
2022年 | 3996篇 |
2021年 | 5063篇 |
2020年 | 5134篇 |
2019年 | 4527篇 |
2018年 | 4090篇 |
2017年 | 3996篇 |
2016年 | 5645篇 |
2015年 | 5978篇 |
2014年 | 7217篇 |
2013年 | 9099篇 |
2012年 | 10776篇 |
2011年 | 10906篇 |
2010年 | 7793篇 |
2009年 | 7787篇 |
2008年 | 8384篇 |
2007年 | 7467篇 |
2006年 | 7139篇 |
2005年 | 5981篇 |
2004年 | 4200篇 |
2003年 | 3459篇 |
2002年 | 3177篇 |
2001年 | 2762篇 |
2000年 | 2525篇 |
1999年 | 2801篇 |
1998年 | 2393篇 |
1997年 | 2219篇 |
1996年 | 2163篇 |
1995年 | 1828篇 |
1994年 | 1609篇 |
1993年 | 1337篇 |
1992年 | 1190篇 |
1991年 | 1001篇 |
1990年 | 777篇 |
1989年 | 586篇 |
1988年 | 451篇 |
1987年 | 363篇 |
1986年 | 358篇 |
1985年 | 300篇 |
1984年 | 185篇 |
1983年 | 132篇 |
1982年 | 113篇 |
1981年 | 66篇 |
1980年 | 49篇 |
1979年 | 22篇 |
1971年 | 1篇 |
1957年 | 32篇 |
1936年 | 1篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Jihua Zhang Xi WangWeidong Yu Tao FengFumin Zhang Zhihong ZhengQiong Li Xianghuai Liu 《Solid State Communications》2003,127(4):289-293
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips. 相似文献
122.
Fei Chang Dongheng Zhang Haijian Yang Haibin Song 《Journal of organometallic chemistry》2004,689(5):936-946
The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene. 相似文献
123.
124.
125.
Calculations and detailed first principle and thermodynamic analyses have been performed to understand the formation mechanism of K2Ti6O13 nanowires (NWs) by a hydrothermal reaction between bulk Na2Ti3O7 crystals and a KOH solution. It is found that direct ion exchange between K+ and Na+ plus H+ interactions with [TiO6] octahedra in Na2Ti3O7 promote the formation of an intermediate H2K2Ti6O14 phase. The large lattice mismatch between this intermediate phase and the bulk Na2Ti3O7 structure, and the large energy reduction associated with the formation of this intermediate phase, drive the splitting of the bulk crystal into H2K2Ti6O14 NWs. However, these NWs are not stable because of large [TiO6] octahedra distortion and are subject to a dehydration process, which results in uniform K2Ti6O13 NWs with narrowly distributed diameters of around 10 nm. 相似文献
126.
127.
128.
van Driel W.D. van Gils M.A.J. Xuejun Fan Zhang G.Q. Ernst L.J. 《Components and Packaging Technologies, IEEE Transactions on》2008,31(2):260-268
Exposed pad packages were introduced in the late 1980s and early 1990s because of their excellent thermal and electrical performance. Despite these advantages, the exposed pad packages experience a lot of thermo-hygro-mechanical related reliability problems during qualification and testing. Examples are die lift, which occurs predominantly after moisture sensitivity level conditions, and die-attach to leadframe delamination leading to downbond stitch breaks during temperature cycling. In this chapter, nonlinear finite element (FE) models using fracture mechanics based J-integral calculations are used to assess the reliability problems of the exposed pad package family. Using the parametric FE models any geometrical and material effects can be explored to their impact on the occurrence diepad delamination, and dielift. For instance the impact of diepad size is found to be of much less importance as the impact of die thickness is. Using the fracture mechanics approach, the starting location for the delamination from thermo-hygro-mechanical point of view is deducted. The results indicate that when diepad delamination is present, cracks are likely to grow beneath the die and dielift will occur. The interaction between dielift and other failure modes, such as lifted ball bonds, are not found to be very significant. The FE models are combined with simulation-based optimization methods to deduct design guidelines for optimal reliability of the exposed pad family. 相似文献
129.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
130.
Xin Sun Qiang Lu Moroz V. Takeuchi H. Gebara G. Wetzel J. Shuji Ikeda Changhwan Shin Tsu-Jae King Liu 《Electron Device Letters, IEEE》2008,29(5):491-493
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control). 相似文献