全文获取类型
收费全文 | 1749274篇 |
免费 | 48734篇 |
国内免费 | 18875篇 |
专业分类
电工技术 | 51209篇 |
技术理论 | 56篇 |
综合类 | 25533篇 |
化学工业 | 319923篇 |
金属工艺 | 80057篇 |
机械仪表 | 60687篇 |
建筑科学 | 69972篇 |
矿业工程 | 22141篇 |
能源动力 | 58839篇 |
轻工业 | 123336篇 |
水利工程 | 19561篇 |
石油天然气 | 58580篇 |
武器工业 | 2720篇 |
无线电 | 226309篇 |
一般工业技术 | 307778篇 |
冶金工业 | 148066篇 |
原子能技术 | 36676篇 |
自动化技术 | 205440篇 |
出版年
2022年 | 18715篇 |
2021年 | 27351篇 |
2020年 | 20960篇 |
2019年 | 21836篇 |
2018年 | 22552篇 |
2017年 | 23064篇 |
2016年 | 28923篇 |
2015年 | 28692篇 |
2014年 | 43471篇 |
2013年 | 104814篇 |
2012年 | 52794篇 |
2011年 | 65931篇 |
2010年 | 58865篇 |
2009年 | 66616篇 |
2008年 | 59101篇 |
2007年 | 55339篇 |
2006年 | 60482篇 |
2005年 | 52659篇 |
2004年 | 49429篇 |
2003年 | 48427篇 |
2002年 | 46756篇 |
2001年 | 42677篇 |
2000年 | 42016篇 |
1999年 | 42021篇 |
1998年 | 41376篇 |
1997年 | 38801篇 |
1996年 | 36973篇 |
1995年 | 33281篇 |
1994年 | 30945篇 |
1993年 | 29326篇 |
1992年 | 27862篇 |
1991年 | 24413篇 |
1990年 | 24450篇 |
1989年 | 23224篇 |
1988年 | 21630篇 |
1987年 | 19662篇 |
1986年 | 18897篇 |
1985年 | 22064篇 |
1984年 | 22367篇 |
1983年 | 20250篇 |
1982年 | 19269篇 |
1981年 | 19249篇 |
1980年 | 17847篇 |
1979年 | 18479篇 |
1978年 | 17662篇 |
1977年 | 17053篇 |
1976年 | 17561篇 |
1975年 | 15921篇 |
1974年 | 15476篇 |
1973年 | 15544篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The phenomenon of persistent tunneling photoconductivity was studied using the tunneling spectroscopy technique at liquid-helium temperature: the separation between the unoccupied levels in a δ-doped layer at the GaAs surface decreased after illumination. This decrease was due to an increase in the width of the quantum well of the δ-doped layer. For photon energies hv exceeding the GaAs band gap E g , this increase in the width of the quantum well was related to the accumulation of positive charge in the depth of GaAs induced by the generation of the electron-hole pairs and photoionization of deep centers. For hv < E g (including the case of CO2 laser), only photoionization is important. The experimental data agree with the self-consistent calculations. The critical temperature for the effect has been determined (T c = 45 K); at higher temperatures, the effect disappears. 相似文献
992.
The problem of synthesis of an isotropic reradiator providing for the transparency of a circular perfectly conducting cylinder illuminated by a TE-polarized plane wave is investigated. A general solution to the problem of diffraction from the cylinder with a reradiator is obtained, and a system of nonlinear equations for the synthesis problem is derived. Numerical solution of the synthesis problem is illustrated by a number of examples. 相似文献
993.
This letter presents a new polarizer which has a simple comb structure inside a circular waveguide. The electrical performance of the proposed comb polarizer is optimized by a circular waveguide radius and by the physical parameters of the comb plates. This polarizer is suitable for providing good performance in millimeter‐band application because of its simple structure and low fabrication cost. In our experiments the dual‐band comb polarizer designed in band 1(K) and band 2(Ka) showed good electrical performance without any tuning elements. 相似文献
994.
R. Urata R. Takahashi T. Nakahara K. Takahata H. Suzuki 《Photonics Technology Letters, IEEE》2006,18(1):67-69
We propose an optically clocked transistor array optoelectronic integrated circuit (OEIC) for both serial-to-parallel and parallel-to-serial conversion (demux/mux), enabling an interface between high-speed asynchronous burst optical labels and CMOS circuitry for optical label swapping. Dual functionality of the OEIC reduces size, power, and cost of the optical label swapper. The capability for greater than 20-Gb/s conversion operation is demonstrated. 相似文献
995.
996.
N. P. Yeliseyeva 《Journal of Communications Technology and Electronics》2006,51(4):380-384
Rigorous analytic expressions for radiation resistance R Σ of an electric dipole are obtained for three mutually orthogonal orientations of the dipole’s axis with respect to a plane metal screen or right-angle corner of infinite dimensions. Radiation resistance R Σ of the dipole oriented arbitrarily in space is calculated and analyzed as a function of the distance from the screen. 相似文献
997.
Finite sample size effect on minimum variance beamformers: optimum diagonal loading factor for large arrays 总被引:6,自引:0,他引:6
Minimum variance beamformers are usually complemented with diagonal loading techniques in order to provide robustness against several impairments such as imprecise knowledge of the steering vector or finite sample size effects. This paper concentrates on this last application of diagonal loading techniques, i.e., it is assumed that the steering vector is perfectly known and that diagonal loading is used to alleviate the finite sample size impairments. The analysis herein is asymptotic in the sense that it is assumed that both the number of antennas and the number of samples are high but have the same order of magnitude. Borrowing some results of random matrix theory, the authors first derive a deterministic expression that describes the asymptotic signal-to-noise-plus-interference ratio (SINR) at the output of the diagonally loaded beamformer. Then, making use of the statistical theory of large observations (also known as general statistical analysis or G-analysis), the authors derive an estimator of the optimum loading factor that is consistent when both the number of antennas and the sample size increase without bound at the same rate. Because of that, the estimator has an excellent performance even in situations where the quotient between the number of observations is low relative to the number of elements of the array. 相似文献
998.
A new detection algorithm (NDA) based on fuzzy cellular neural networks for white blood cell detection. 总被引:1,自引:0,他引:1
White blood cell detection is one of the most basic and key steps in the automatic recognition system of white blood cells in microscopic blood images. Its accuracy and stability greatly affect the operating speed and recognition accuracy of the whole system. But there are only a few methods available for cell detection or segmentation due to the complexity of the microscopic images. This paper focuses on this issue. Based on the detailed analysis of the existing two methods--threshold segmentation followed by mathematical morphology (TSMM), and the fuzzy logic method--a new detection algorithm (NDA) based on fuzzy cellular neural networks is proposed. NDA combines the advantages of TSMM and the fuzzy logic method, and overcomes their drawbacks. With NDA, we can detect almost all white blood cells, and the contour of each detected cell is nearly complete. Its adaptability is strong and the running speed is expected to be comparatively high due to the easy hardware implementation of FCN. Experimental results show good performance. 相似文献
999.
We report for the first time optical signal-to-noise penalties which lead to performance degradations in single-fiber long-reach optical access networks when compared to identical dual-fiber systems. A simplified architecture, with reduced optical amplifier count compared to previous work, for single-fiber operation of a symmetrical 10-Gb/s, 1024-way split, 110-km long-reach optical access network is presented and demonstrated. In addition, a possible solution to remove the optical signal-to-noise penalty is suggested 相似文献
1000.
A multi-level attention framework for tracking and segmentation of humans and objects under complex occlusions is investigated,
featuring an effective probabilistic appearance-based technique for pixel reclassification during object grouping and splitting.
A novel ’spatial-depth affinity metric’ is introduced in the conventional likelihood function, utilising information of both
spatial locations of pixels and dynamic depth ordering of the component objects in grouping. Depth ordering estimation is
achieved through a combination of top-down and bottom-up approach. Experiments on some realworld difficult scenarios of low
quality and highly compressed videos demonstrate the very promising results achieved. 相似文献