全文获取类型
收费全文 | 21598篇 |
免费 | 2729篇 |
国内免费 | 2156篇 |
专业分类
化学 | 2863篇 |
晶体学 | 112篇 |
力学 | 545篇 |
综合类 | 207篇 |
数学 | 1510篇 |
物理学 | 6830篇 |
无线电 | 14416篇 |
出版年
2024年 | 71篇 |
2023年 | 226篇 |
2022年 | 486篇 |
2021年 | 752篇 |
2020年 | 654篇 |
2019年 | 505篇 |
2018年 | 519篇 |
2017年 | 796篇 |
2016年 | 907篇 |
2015年 | 1100篇 |
2014年 | 1699篇 |
2013年 | 1711篇 |
2012年 | 1641篇 |
2011年 | 1559篇 |
2010年 | 1124篇 |
2009年 | 1295篇 |
2008年 | 1536篇 |
2007年 | 1587篇 |
2006年 | 1304篇 |
2005年 | 1065篇 |
2004年 | 917篇 |
2003年 | 827篇 |
2002年 | 669篇 |
2001年 | 554篇 |
2000年 | 483篇 |
1999年 | 385篇 |
1998年 | 319篇 |
1997年 | 312篇 |
1996年 | 233篇 |
1995年 | 222篇 |
1994年 | 169篇 |
1993年 | 164篇 |
1992年 | 131篇 |
1991年 | 114篇 |
1990年 | 57篇 |
1989年 | 58篇 |
1988年 | 94篇 |
1987年 | 45篇 |
1986年 | 23篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 25篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1959年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
51.
O. Gravrand E. De Borniol S. Bisotto L. Mollard G. Destefanis 《Journal of Electronic Materials》2007,36(8):981-987
This paper aims at studying the feasibility of very long infrared wavelength (VLWIR) (12–18 μm) focal plane arrays using n-on-p planar ion-implanted technology. To explore and analyze the feasibility of such VLWIR detectors, a set of four Cd
x
Hg1−x
Te LPE layers with an 18 μ cutoff at 50 K has been processed at Defir (LETI/LIR–Sofradir joint laboratory), using both our “standard” n-on-p process and our improved low dark current process. Several 320 × 256 arrays, 30-μm pitch, have been hybridized on standard Sofradir readout circuits and tested. Small dimension test arrays characterization
is also presented. Measured photonic currents with a 20°C black body suggest an internal quantum efficiency above 50%. Typical
I(V) curves and thermal evolution of the saturation current are discussed, showing that standard photodiodes remain diffusion
limited at low biases for temperatures down to 30 K. Moreover, the dark current gain brought by the improved process is clearly
visible for temperatures higher than 40 K. Noise measurements are also discussed showing that a very large majority of detectors
appeared background limited under usual illumination and biases. In our opinion, such results demonstrate the feasibility
of high-performance complex focal plane arrays in the VLWIR range at medium term. 相似文献
52.
The lattice profile analyzes the intrinsic structure of pseudorandom number sequences with applications in Monte Carlo methods and cryptology. In this paper, using the discrete Fourier transform for periodic sequences and the relation between the lattice profile and the linear complexity, we give general formulas for the expected value, variance, and counting function of the lattice profile of periodic sequences with fixed period. Moreover, we determine in a more explicit form the expected value, variance, and counting function of the lattice profile of periodic sequences for special values of the period. 相似文献
53.
54.
小波提升算法是一种新的双正交小波构造方法,通过预测算子,确定高频信息,并初步确定低频信息,然后通过更新算子,对初步确定的低频信息进行修正,从而确定低频信息。它在空域对信号进行变换,完成了对信号频域的分析。在图像处理中,基于离散小波变换的提升算法比传统的卷积算法运算简单,实时性好,易于实现,因而被新一代图像压缩标准JPEG2000所采用。文中简要介绍了小波提升算法的原理,分析了其特点,并介绍了JPEG2000标准中采用的W5/3、D9/7两种小波的提升格式和实现算法。 相似文献
55.
A 320×240 CMOS image sensor is demonstrated,which is implemented by a standard 0.6 μm 2P2M CMOS process.For reducing the chip area,each 2×2-pixel block shares a sample/hold circuit,analog-to-digital converter and 1-b memory.The 2×2 pixel pitch has an area of 40 μm×40 μm and the fill factor is about 16%.While operating at a low frame rate,the sensor dissipates a very low power by power-management circuit making pixel-level comparators in an idle state.A digital correlated double sampling,which eliminates fixed pattern noise,improves SNR of the sensor, and multiple sampling operations make the sensor have a wide dynamic range. 相似文献
56.
57.
数码相机CMOS图像传感器的特性参数与选择 总被引:2,自引:0,他引:2
介绍了数码相机的核心器件———CMOS图像传感器的特性参数和在数码相机设计过程中CMOS图像传感器的选择。选择CMOS图像传感器,不仅需要考虑包括传感器的尺寸、像素总数和有效像素数、最小照度、动态范围、灵敏度、分辨力、光电响应不均匀性以及光谱响应等在内的特性参数,而且还要考虑电源管理和功耗、模数转换位数、开发的简便性以及成本等因素。 相似文献
58.
59.
60.
M. Missous C. Mitchell J. Sly K. T. Lai R. Gupta S. K. Haywood 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):496
Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on InxGa(1−x)As−InyAl(1−y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of 420°C to produce structures that are suitable for both emission and detection in the 2–5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In0.84Ga0.16As/AlAs/In0.52Al0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ–Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2–7 μm) in three structures of differing In0.84Ga0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ–Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated. 相似文献