全文获取类型
收费全文 | 94899篇 |
免费 | 12106篇 |
国内免费 | 9176篇 |
专业分类
化学 | 48520篇 |
晶体学 | 708篇 |
力学 | 4754篇 |
综合类 | 544篇 |
数学 | 8767篇 |
物理学 | 26366篇 |
无线电 | 26522篇 |
出版年
2024年 | 384篇 |
2023年 | 2194篇 |
2022年 | 2749篇 |
2021年 | 3433篇 |
2020年 | 3282篇 |
2019年 | 3112篇 |
2018年 | 2750篇 |
2017年 | 2545篇 |
2016年 | 3695篇 |
2015年 | 4022篇 |
2014年 | 4797篇 |
2013年 | 6263篇 |
2012年 | 7387篇 |
2011年 | 7488篇 |
2010年 | 5443篇 |
2009年 | 5457篇 |
2008年 | 5759篇 |
2007年 | 5251篇 |
2006年 | 5036篇 |
2005年 | 4386篇 |
2004年 | 3368篇 |
2003年 | 2744篇 |
2002年 | 2440篇 |
2001年 | 2159篇 |
2000年 | 2083篇 |
1999年 | 2212篇 |
1998年 | 1954篇 |
1997年 | 1674篇 |
1996年 | 1688篇 |
1995年 | 1513篇 |
1994年 | 1353篇 |
1993年 | 1198篇 |
1992年 | 1062篇 |
1991年 | 898篇 |
1990年 | 730篇 |
1989年 | 593篇 |
1988年 | 478篇 |
1987年 | 402篇 |
1986年 | 352篇 |
1985年 | 340篇 |
1984年 | 239篇 |
1983年 | 207篇 |
1982年 | 171篇 |
1981年 | 127篇 |
1980年 | 94篇 |
1979年 | 69篇 |
1978年 | 65篇 |
1977年 | 64篇 |
1976年 | 64篇 |
1973年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
本文论述了寄生电容不敏感型开关电容四象限模拟乘法器的设计,并提出了一种新型的电路结构,分析了它的性能,以及元器件的非理想特性对其性能的影响和采取的补偿方法。 相似文献
92.
微波辐射电镜生物样品制备方法研究 总被引:2,自引:1,他引:1
本文报道一种快速微波辐射电镜样品制备方法──水浴法,以及这个方法在动植物样品超薄切片制备中的应用。实验结果表明,水浴法使得样品可以接受相对较长时间的微波辐射而不致造成任何损伤,浸泡液和样品的温度控制简单而且准确,样品处理的结果内外均匀一致,超微结构保存优秀,完全可与常规制样法和Login法的结果相媲美,而且在某些方面水浴法要优于常规法和Login法。 相似文献
93.
94.
95.
Wang F.-Y. Gildea K. Jungnitz H. Chen D.D. 《Industrial Electronics, IEEE Transactions on》1994,41(6):641-653
The manufacturing message specification (MMS) is the ISO standard communication protocol specific to manufacturing. To analyze MMS design and performance, service unit automats are introduced to represent individual MMS services, while service connection Petri Nets (PNs) are constructed from these automats to describe MMS service connections and processes. This approach makes MMS protocol specification and analysis possible in terms of well-developed concepts and methods in PN theory. It leads to a distributed and hierarchical model of MMS software system by integrating service connection PNs. A generalized stochastic PN for MMS performance evaluation is obtained by incorporating service parameters and time factors into the model. A technique based on T-invariants is used to simplify the performance analysis 相似文献
96.
Ma Z.J. Chen J.C. Liu Z.H. Krick J.T. Cheng Y.C. Hu C. Ko P.K. 《Electron Device Letters, IEEE》1994,15(3):109-111
It has been reported that high-temperature (~1100°C) N2 O-annealed oxide can block boron penetration from poly-Si gates to the silicon substrate. However, this high-temperature step may be inappropriate for the low thermal budgets required of deep-submicron ULSI MOSFETs. Low-temperature (900~950°C) N2O-annealed gate oxide is also a good barrier to boron penetration. For the first time, the change in channel doping profile due to compensation of arsenic and boron ionized impurities was resolved using MOS C-V measurement techniques. It was found that the higher the nitrogen concentration incorporated at Si/SiO2 interface, the more effective is the suppression of boron penetration. The experimental results also suggest that, for 60~110 Å gate oxides, a certain amount of nitrogen (~2.2%) incorporated near the Si/SiO2 interface is essential to effectively prevent boron diffusing into the underlying silicon substrate 相似文献
97.
Shye Lin Wu Chung Len Lee Tan Fu Lei Chen C.F. Chen L.J. Ho K.Z. Ling Y.C. 《Electron Device Letters, IEEE》1994,15(4):120-122
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device 相似文献
98.
Chih-Yao Huang Ming-Jer Chen 《Electron Devices, IEEE Transactions on》1994,41(10):1806-1810
This work reports the development of design model for n-well guard rings in a CMOS process utilizing a low-doped epitaxial layer on a highly doped substrate. The validity of the model has been judged by a wide range of experimental data measured from the fabricated n-well guard ring structures with guard ring width as parameter. From the model developed, guidelines have been drawn to minimize the guard ring width while critically suppressing the amount of electrons escaping from the guard ring 相似文献
99.
Chen W.L. Munns G.O. East J.R. Haddad G.I. 《Electron Devices, IEEE Transactions on》1994,41(2):155-161
InP-based resonant tunneling hot electron transistors (RHET's) were studied systematically using chemical beam epitaxy (CBE) for the first time. All the RHET's studied have a highly strained AlAs/In0.75Ga0.25As/AlAs resonant tunneling double barrier as a hot electron injector, and an InP collector barrier with or without InGaAsP graded layers. The highest transport ratio (α) observed is 0.98, and the highest peak-to-valley current ratios (PVR's) measured are 20 and 200 in the collector current and base current, respectively, at 80 K. A self-consistent simulation is used as a reference to optimize the hot electron injector and to explain the ballistic transport. An energy spectrometer technique was applied to the RHET's for resolving the hot electron energy distribution which showed a full width at half maximum (FWHM) of around 58 meV, indicating ballistic transport of electrons. Finally, room temperature transistor action was also observed with a β of 4 and a cutoff frequency of 31 GHz 相似文献
100.
Load-capacity interference and the bathtub curve 总被引:1,自引:0,他引:1
Load-capacity (stress-strength) interference theory is used to derive a heuristic failure rate for an item subjected to repetitive loading which is Poisson distributed in time. Numerical calculations are performed using Gaussian distributions in load and capacity. Infant mortality, constant failure rate (Poisson failures), and aging are shown to be associated with capacity variability, load variability, and capacity deterioration, respectively. Bathtub-shaped failure rate curves are obtained when all three failure types are present. Changes in load or capacity distribution parameters often strongly affect the quantitative behavior of the failure-rate curves, but they do not affect the qualitative behavior of the bathtub curve. Neither is it likely that the qualitative behavior will be affected by the use of nonGaussian distributions. The numerical results, however, indicate that infant mortality and wear-out failures interact strongly with load variability. Thus bathtub curves arising from this model cannot be represented as simple superpositions of independent contributions from the three failure types. Only if the three failure types arise from independent failure mechanisms or in different components is it legitimate simply to sum the failure rate contributions 相似文献