全文获取类型
收费全文 | 11319篇 |
免费 | 1884篇 |
国内免费 | 1169篇 |
专业分类
化学 | 5877篇 |
晶体学 | 86篇 |
力学 | 727篇 |
综合类 | 65篇 |
数学 | 1127篇 |
物理学 | 3433篇 |
无线电 | 3057篇 |
出版年
2024年 | 30篇 |
2023年 | 263篇 |
2022年 | 297篇 |
2021年 | 456篇 |
2020年 | 438篇 |
2019年 | 394篇 |
2018年 | 330篇 |
2017年 | 340篇 |
2016年 | 489篇 |
2015年 | 523篇 |
2014年 | 567篇 |
2013年 | 807篇 |
2012年 | 902篇 |
2011年 | 965篇 |
2010年 | 720篇 |
2009年 | 692篇 |
2008年 | 779篇 |
2007年 | 618篇 |
2006年 | 685篇 |
2005年 | 510篇 |
2004年 | 395篇 |
2003年 | 337篇 |
2002年 | 317篇 |
2001年 | 262篇 |
2000年 | 282篇 |
1999年 | 247篇 |
1998年 | 237篇 |
1997年 | 219篇 |
1996年 | 227篇 |
1995年 | 177篇 |
1994年 | 150篇 |
1993年 | 143篇 |
1992年 | 115篇 |
1991年 | 88篇 |
1990年 | 85篇 |
1989年 | 62篇 |
1988年 | 48篇 |
1987年 | 37篇 |
1986年 | 40篇 |
1985年 | 26篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 513 毫秒
41.
一种多径环境下基于四阶累积量的阵列扩展测向方法 总被引:3,自引:0,他引:3
本文分析了基于四阶累积量的测向方法不能正确测量多径信号方向的原因,提出了一种多径环境下的基于四阶累积量的新型测向方法。该方法利用零点领处理方法抑制多径信号,然后采用四阶累积量进行阵列扩展测向。计算机模拟结果表明该方法在多径环境下具有良好的性能并且可能实现对足够多的信号进行测向。 相似文献
42.
43.
Nghiem S.V. Kwok R. Yueh S.H. Gow A.J. Perovich D.K. Chih-Chien Hsu Kung-Han Ding Jin Au Kong Grenfell T.C. 《Geoscience and Remote Sensing, IEEE Transactions on》1998,36(1):111-124
To investigate effects of diurnal thermal cycles on C-band polarimetric backscatter and millimeter-wave emission from sea ice, the authors carried out a winter experiment at the outdoor geophysical research facility (GRF) in the cold regions research and engineering laboratory (CRREL), the ice sheet grew from open sea water to a thickness of 10 cm in 2.5 days, during which they took polarimetric backscatter data with a C-band scatterometer, interlaced with brightness temperature measurements at 90 GHz in conjunction with meteorological and sea ice characterizations. The initial ice growth in the late morning was slow due to high insolation. As the air temperature dropped during the night, the growth rate increased significantly. Air temperature changed drastically from about -12 to -36°C between day and night, the diurnal thermal cycle repeated itself the next day and the growth rate varied in the same manner. Ice temperature profiles clearly show the diurnal response in the ice sheet with a lag of 2.5 h behind the time of the maximum short-wave incident solar radiation. The diurnal cycles are also evident in the millimeter-wave brightness temperature data, measured sea ice backscatter revealed substantial diurnal variations up to 6 dB with repeatable cycles in synchronization with the temperature cycles and the brightness temperature modulations, the diurnal cycles in backscatter indicate that the dominant scattering mechanism related to thermodynamic processes in sea ice is reversible, a diurnal backscatter model based on sea ice electrodynamics and thermodynamics explains the observed diurnal signature. This work shows that diurnal effects are important for inversion algorithms to retrieve sea ice geophysical parameters from remote sensing data acquired with a satellite synthetic aperture radar (SAR) or scatterometer on Sun-synchronous orbits 相似文献
44.
采用连续波电光检测法,对GaAs/GaAlAs双异质结激光器列阵有源区进行定点测量,实验结果反映了发光区内及发光区外电场随电流变化的不同规律。文中对实验结果给出了合理解释。 相似文献
45.
46.
47.
Ross Anderson Cunsheng Ding Tor Helleseth Torleiv Klove 《Designs, Codes and Cryptography》1998,15(2):111-124
Previous researchers have designed shared control schemes with a view to minimising the likelihood that participants will conspire to perform an unauthorised act. But, human nature being what it is, systems inevitably fail; so shared control schemes should also be designed so that the police can identify conspirators after the fact. This requirement leads us to search for schemes with sparse access structures. We show how this can be done using ideas from coding theory. In particular, secret sharing schemes based on geometric codes whose dual [n,k,d] codes have d and n as their only nonzero weights are suitable. We determine their access structures and analyse their properties. We have found almost all of them, and established some relations among codes, designs and secret-sharing schemes. 相似文献
48.
In this paper, a construction of optimal constant composition codes is developed, and used to derive some series of new optimal
constant composition codes meeting the upper bound given by [13]. 相似文献
49.
Hong-Nian Li Xiao-Xiong WangWang-Feng Ding 《Journal of Electron Spectroscopy and Related Phenomena》2006
Using X-ray photoemission measurements, we have determined the attenuation length of C 1s photoelectrons in C60 film to be 21.5 Å with the incident photon energy of Mg Kα radiation. The inelastic mean free path calculated with the TPP-2M algorithm coincides fairly well with the experimentally determined attenuation length, indicating the validity of the algorithm to fullerene and fullerides. The inelastic mean free paths for some fullerides, i.e. K3C60, K6C60, Ba4C60, Sm2.75C60 and Sm6C60 are calculated to help the quantitative analyses of the photoemission spectra for these compounds. 相似文献
50.
一种高性能的适用于AVS的二维整数逆变换实现结构 总被引:1,自引:0,他引:1
针对AVS视频标准中的整数逆变换,本文提出了一种高性能的硬件实现方案.本方案采用两个一维逆变换核和4个16(16的双口SRAM.通过合理控制SRAM的读写方式,避免了数据的预处理与后处理,流水线的深度也得到减少.在列变换时,改变数据运算次序,从而保证了4个双口SRAM不影响运算速度.处理8(8的数据块,本结构仅需要37个时钟,与传统的实现方案相比,在同等运算速度下,面积节约28%.实验表明该结构适用于采用AVS标准的HDTV编解码器. 相似文献