全文获取类型
收费全文 | 30705篇 |
免费 | 1880篇 |
国内免费 | 73篇 |
专业分类
电工技术 | 433篇 |
综合类 | 35篇 |
化学工业 | 7071篇 |
金属工艺 | 1217篇 |
机械仪表 | 1751篇 |
建筑科学 | 571篇 |
矿业工程 | 10篇 |
能源动力 | 1244篇 |
轻工业 | 2691篇 |
水利工程 | 122篇 |
石油天然气 | 23篇 |
武器工业 | 1篇 |
无线电 | 5017篇 |
一般工业技术 | 6643篇 |
冶金工业 | 2137篇 |
原子能技术 | 402篇 |
自动化技术 | 3290篇 |
出版年
2024年 | 32篇 |
2023年 | 379篇 |
2022年 | 579篇 |
2021年 | 977篇 |
2020年 | 687篇 |
2019年 | 715篇 |
2018年 | 966篇 |
2017年 | 983篇 |
2016年 | 1147篇 |
2015年 | 927篇 |
2014年 | 1377篇 |
2013年 | 1984篇 |
2012年 | 2100篇 |
2011年 | 2615篇 |
2010年 | 1875篇 |
2009年 | 1869篇 |
2008年 | 1643篇 |
2007年 | 1328篇 |
2006年 | 1179篇 |
2005年 | 987篇 |
2004年 | 897篇 |
2003年 | 839篇 |
2002年 | 766篇 |
2001年 | 671篇 |
2000年 | 600篇 |
1999年 | 565篇 |
1998年 | 941篇 |
1997年 | 552篇 |
1996年 | 509篇 |
1995年 | 324篇 |
1994年 | 242篇 |
1993年 | 205篇 |
1992年 | 154篇 |
1991年 | 124篇 |
1990年 | 102篇 |
1989年 | 115篇 |
1988年 | 93篇 |
1987年 | 75篇 |
1986年 | 69篇 |
1985年 | 56篇 |
1984年 | 49篇 |
1983年 | 41篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 36篇 |
1979年 | 20篇 |
1977年 | 29篇 |
1976年 | 43篇 |
1975年 | 19篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Namhyoung Kim Kyu-Hwan Jung Yong Seog Kim Jaewook Lee 《Expert systems with applications》2012,39(15):11839-11845
The present paper explores the possible application of a new ensemble model. The model, which is based on multiple SVM classifiers, is employed to address churner identification problems in the mobile telecommunication industry, a sector in which the role of customer retention program becomes increasingly important due to its very competitive business environment. In particular, the current study introduces a uniformly subsampled ensemble (USE) model of SVM classifiers, not only to reduce the computational complexity of large-scale data, but also to boost the reliability and accuracy of calibrated models on data sets with highly skewed class distributions. According to our experiments, the performance of the USE SVM model is superior compared to all single and ensemble models. It is more scalable than well-known ensemble models as well. 相似文献
92.
Kyung-Hoon Hyun Sangkyu Lee Chae-Woong Cho Ungyu Paik Dae-Hwan Kim Eun-Sang Na Jea-Gun Park 《Journal of Electroceramics》2006,17(2-4):351-354
An attempt was made to improve the conventional lamination process in the multilayered ceramic capacitors (MLCCs) fabrication by adapting a solvent treatment on the BaTiO3 green sheets. During the lamination process, additional particle rearrangement in the BaTiO3 green block was stimulated by solvent treatment. This rearrangement resulted in a more compact structure of the BaTiO3 green sheets compared to that obtained through the conventional lamination process. The overall thickness of BaTiO3/Ni/BaTiO3 laminates was also reduced after solvent treatment. It is suggested that miniaturization in the fabrication of MLCCs can be improved by adapting a solvent treatment during the lamination process. 相似文献
93.
H.C. Ji P.K.J. Park Hoon Kim J.H. Lee Y.C. Chung 《Photonics Technology Letters, IEEE》2006,18(8):950-952
We propose and demonstrate a novel technique to monitor the frequency offset between the optical source and delay interferometer (DI) for direct-detection differential phase-shift-keying (DPSK) systems. In this scheme, a phase-modulated tone is applied to DPSK signals at the transmitter and then detected after being converted into an amplitude-modulated tone at the DI to be used for the monitoring signal. Our experimental demonstration shows that the monitoring range and sensitivity of the proposed scheme are measured to be /spl plusmn/2 GHz and /spl sim/10 MHz, respectively, which we believe are good enough to be used either to generate alarm signals for the frequency offset monitoring or to control the feedback loop of the DI. 相似文献
94.
A continuous-wave hybrid AlGaInAs-silicon evanescent laser 总被引:1,自引:0,他引:1
A.W. Fang Hyundai Park R. Jones O. Cohen M.J. Paniccia J.E. Bowers 《Photonics Technology Letters, IEEE》2006,18(10):1143-1145
We report a novel laser architecture, the hybrid silicon evanescent laser (SEL), that utilizes offset AlGaInAs quantum wells (QWs) bonded to a silicon waveguide. The silicon waveguide is fabricated on a silicon-on-insulator wafer using a complimentary metal-oxide-semiconductor-compatible process, and is subsequently bonded with the AlGaInAs QW structure using low temperature O/sub 2/ plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum temperature for CW operation is 60/spl deg/C. The maximum single-sided fiber-coupled CW output power at room temperature is 4.5 mW. 相似文献
95.
A miniature UWB planar monopole antenna with 5-GHz band-rejection filter and the time-domain characteristics 总被引:2,自引:0,他引:2
Young Jun Cho Ki Hak Kim Dong Hyuk Choi Seung Sik Lee Seong-Ook Park 《Antennas and Propagation, IEEE Transactions on》2006,54(5):1453-1460
A planar monopole antenna with a staircase shape and small volume (25/spl times/26/spl times/1 mm/sup 3/) is proposed in this paper. With the use of a half-bowtie radiating element, the staircase-shape, and a modified ground plane structure, the proposed antenna has a very wide impedance bandwidth measured at about 11.6 GHz (2.9-14.5 GHz, bandwidth ratio about 1:5) below VSWR 2 including the WLAN band notched in the vicinity of 5 GHz. An omnidirectional radiation pattern is obtained. The group delay which is an indication of linearity between two proposed antennas is less than 1 ns. The electrical characteristics in terms of frequency and time domains and physical ones of the proposed antenna make it attractive for use in ultrawideband (UWB) systems. 相似文献
96.
Young-Suk Kim Chan-Il Kim Jun-Young Park Kyung-Hoan Na 《Metallurgical and Materials Transactions A》2005,36(1):169-176
The atomic force microscopy (AFM)-based nanolithographic technique is currently used to directly machine material surfaces
and fabricate nanocomponents for microelectromechanical systems (MEMS) devices. In the current study, three-dimensional molecular
dynamic (MD) simulations with potentials based on the Morse function were performed to evaluate the effect of crystallographic
factors and process variables on the nanodeformation characteristics of the nanolithography processing of monocrystalline
copper. Moreover, the effects of process variables (tool shape, cutting speed, and ploughing depth) on the nanostructural
pattern are investigated. The simulation results revealed that the crystal orientation and ploughing direction had a significant
influence on varying the forces (cutting force, thrust force, and width-direction force); the nature of the nanodeformation
ahead of the tool; and the surface quality of the machined material. 相似文献
97.
A new LDPC decoding algorithm aided by segmented cyclic redundancy checks for magnetic recording channels 总被引:2,自引:0,他引:2
Yeong-Hyeon Kwon Mi-Kyung Oh Dong-Jo Park 《IEEE transactions on magnetics》2005,41(7):2318-2320
We introduce a new low-density parity-check (LDPC) decoding algorithm that exploits the cyclic redundancy check (CRC) information of data segments. By using the error detection property of the CRC, we can successively decode data segments of a codeword corrupted by random errors and erasures. The key idea is that the messages from the variable nodes with correct checksum are fixed to deterministic log likelihood ratio values during LDPC iterative decoding. This approach improves the decoding speed and codeword error rate without significant modification of the LDPC decoding structure. Moreover, the CRC is also used for an early stopping criterion of LDPC decoding. Simulation results verify our claims. 相似文献
98.
J. H. Song I. K. Park Y. S. Shin J. H. Kim S. W. Hong B. T. Min H. D. Kim 《Nuclear Engineering and Design》2003,222(1):1051-15
This paper discusses the results of steam explosion experiments using reactor material carried out under “Test for Real cOrium Interaction with water (TROI)” program. About 4–9 kg of corium melt jet is delivered into a sub-cooled water pool at atmospheric pressure. Spontaneous steam explosions are observed in four tests among six tests. The dynamic pressure, dynamic load, and morphology of debris clearly indicate the cases with steam explosion. The initial conditions and results of the experiments are discussed. 相似文献
99.
It is generally assumed in the mechanistic film dryout model that the critical heat flux (CHF) arises when liquid film calculated from evaporation, droplet entrainment and deposition gets dryout. The dryout of film is usually assumed when film thickness becomes zero. However, it was indicated that the complete dryout assumption can estimate CHF well for uniform heating case but cannot simulate accurately for non-uniform heating case. The critical film thickness concept may be an appropriate approach physically because there is a possibility of instantaneous disappearance of liquid film when it gets very thin. Therefore, a critical dryout film thickness correlation was developed to properly model dryout phenomenon together with MARS code based on experimental data. The modified version of MARS implementing a newly developed critical dryout film thickness correlation was assessed using various dryout data including those of non-uniform heating case and flow reduction transient test. The prediction results showed improved agreement with the experimental data. 相似文献
100.
Based on the dynamic anti-windup strategy, an alternative control methodology for state constrained systems is presented. The proposed method is an a posteriori approach for state constrained systems, which is differentiated from the usual a priori approach. That is, first a linear controller is designed to show a desirable nominal performance by ignoring state constraints. Then, an additional compensator is introduced to account for state constraints. By minimizing a reasonable performance index, a dynamic compensator is derived explicitly, which is expressed in plant and controller parameters. The proposed method not only provides a graceful performance degradation, but it also guarantees the total stability of the resulting systems. An illustrative example is given to show the effectiveness of the proposed method. 相似文献