全文获取类型
收费全文 | 100448篇 |
免费 | 11105篇 |
国内免费 | 7209篇 |
专业分类
电工技术 | 7839篇 |
综合类 | 8370篇 |
化学工业 | 13691篇 |
金属工艺 | 6603篇 |
机械仪表 | 7021篇 |
建筑科学 | 6411篇 |
矿业工程 | 3068篇 |
能源动力 | 2785篇 |
轻工业 | 10537篇 |
水利工程 | 3180篇 |
石油天然气 | 3011篇 |
武器工业 | 1154篇 |
无线电 | 12263篇 |
一般工业技术 | 11283篇 |
冶金工业 | 5680篇 |
原子能技术 | 1912篇 |
自动化技术 | 13954篇 |
出版年
2024年 | 560篇 |
2023年 | 1587篇 |
2022年 | 3637篇 |
2021年 | 4801篇 |
2020年 | 3365篇 |
2019年 | 2536篇 |
2018年 | 2843篇 |
2017年 | 3204篇 |
2016年 | 2965篇 |
2015年 | 4129篇 |
2014年 | 5324篇 |
2013年 | 6599篇 |
2012年 | 8019篇 |
2011年 | 8696篇 |
2010年 | 8092篇 |
2009年 | 7539篇 |
2008年 | 7778篇 |
2007年 | 7217篇 |
2006年 | 6210篇 |
2005年 | 5066篇 |
2004年 | 3693篇 |
2003年 | 2651篇 |
2002年 | 2578篇 |
2001年 | 2297篇 |
2000年 | 1826篇 |
1999年 | 942篇 |
1998年 | 1084篇 |
1997年 | 632篇 |
1996年 | 554篇 |
1995年 | 372篇 |
1994年 | 258篇 |
1993年 | 250篇 |
1992年 | 166篇 |
1991年 | 145篇 |
1990年 | 126篇 |
1989年 | 157篇 |
1988年 | 102篇 |
1987年 | 87篇 |
1986年 | 75篇 |
1985年 | 60篇 |
1984年 | 41篇 |
1983年 | 36篇 |
1982年 | 42篇 |
1981年 | 47篇 |
1980年 | 57篇 |
1979年 | 30篇 |
1977年 | 65篇 |
1976年 | 114篇 |
1975年 | 20篇 |
1951年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Sehyun Park Okajima Y. Hirokawa J. Ando M. 《Antennas and Propagation, IEEE Transactions on》2005,53(9):2865-2871
This work proposes a dual-polarized planar antenna; two post-wall slotted waveguide arrays with orthogonal 45/spl deg/ linearly-polarized waves interdigitally share the aperture on a single layer substrate. Uniform excitation of the two-dimensional slot array is confirmed by experiment in the 25 GHz band. The isolation between two slot arrays is also investigated in terms of the relative displacement along the radiation waveguide axis in the interdigital structure. The isolation is 33.0 dB when the relative shift of slot position between the two arrays is -0.5/spl lambda//sub g/, while it is only 12.8 dB when there is no shift. The cross-polarization level in the far field is -25.2 dB for a -0.5/spl lambda//sub g/ shift, which is almost equal to that of the isolated single polarization array. It is degraded down to -9.6 dB when there is no shift. 相似文献
82.
Microstructures of hundreds of micron thick poly(styrene-block-isoprene) copolymer films solution-cast in a cylindrical tube with the solvent evaporation controlled were investigated by transmission electron microscope (TEM), small angle X-ray scattering (SAXS) and optical microscope (OM). In a block copolymer with cylindrical polyisoprene microdomains, the orientation of the cylinders was varied along radial direction of the cylindrical tube. Highly aligned hexagonal arrays of in-plane polyisoprene cylinders were formed with their cylindrical axis parallel to the circumference of the tube in the regimes close to the wall edge. In contrast randomly ordered microdomains were observed at the center of the tube. We have also found that the orientation depends on the solvent evaporation rate and an intermediate rate (∼2.3 nL/s) provides the best orientation. In the case of a block copolymer with a bicontinuous double gyroid structure, we obtained a globally ordered microstructure where [111] crystallographic direction was parallel to the circumference of the tube. For both block copolymers, the area of highly ordered arrays of nanoscopic domains is over 1 mm2. Development of the orientation was explained by coupling two orthogonal fields: (1) The flow of a solution induced by strong capillary force at a meniscus between the cylindrical tube wall and the block copolymer solution and (2) the solvent evaporation. 相似文献
83.
Sung-Hoon An U-Yeol Park Kyung-In Kang Moon-Young Cho Hun-Hee Cho 《Canadian Metallurgical Quarterly》2007,21(4):259-264
Total conceptual cost estimates and the assessment of the quality of these estimates are critical in the early stages of a building construction project. In this study, the support vector machine (SVM) model for assessing the quality of conceptual cost estimates is proposed, and the application of SVM in construction areas is investigated. The results show that the SVM model assessed the quality of conceptual cost estimates slightly more accurately than the discriminant analysis model. This shows that using the SVM has potential in construction areas. In addition, the SVM model can assist clients in their evaluation of the quality of the estimated cost and the probability of exceeding the target cost, and in their decision on whether or not it is necessary to seek a more accurate estimate in the early stages of a project. 相似文献
84.
发展和深化了集对分析(SPA)基础理论,并在此基础上探讨了基于集对分析的模式识别方法,给出了集对模式识别的三个判定原则,这对SPA的发展及其在模式识别中的应用提供了理论支持。 相似文献
85.
86.
Fast DCT algorithm with fewer multiplication stages 总被引:1,自引:0,他引:1
Yeonsik Jeong Imgeun Lee Hak Soo Kim Kyu Tae Park 《Electronics letters》1998,34(8):723-724
A novel fast DCT scheme with reduced multiplication stages and fewer additions and multiplications is proposed. The proposed algorithm is structured so that most multiplications tend to be performed at the final stage, which reduces the propagation error that could occur in the fixed-point computation. Minimisation of the multiplication stages can further decrease the error 相似文献
87.
88.
This study demonstrates that the use of high field 1H NMR spectroscopy permits individual detection of phosphatidylcholine and sphingomyelin molecules at the surface of native low density lipoprotein (LDL) particles. Distinct behaviour was observed for the choline head group -N(CH3)3 resonances of these different phospholipids revealing preferential immobilisation for phosphatidylcholine. This suggests the existence of reversible and irreversible phosphatidylcholine-apolipoprotein B interactions and is consistent with microdomain formation at the surface monolayer of LDL. The novel resonance assignment and results show that 1H NMR can provide efficient and practical means for future studies on the structure and dynamics at the LDL surface. 相似文献
89.
The majority of patients with soft tissue or bone sarcomas of the upper extremity can be treated today with limb-saving procedures using combined modality therapies. For patients with a tumor in the shoulder area, sometimes an interscapulothoracic amputation is the only radical surgical treatment. However, in selected cases, in which the tumor does not involve the neurovascular bundle, a limb-sparing alternative might be the Tikhoff-Linberg resection. Normal function of the hand and forearm, with reasonable function of the elbow, can be maintained by this procedure. Four case histories are reported. 相似文献
90.
Jun-Hee Hong Jong-Keun Park 《Power Systems, IEEE Transactions on》1995,10(4):1789-1797
This paper presents a method of obtaining transmission network equivalents from the network's response to a pulse excitation signal. The proposed method is based on modal decomposition representation for the large-scale interconnected system. In this framework we use Prony analysis to identify the network function of the system and to decompose the large system into a parallel combination of simple first-order systems. As a result the network function of the transmission network can be identified easily, and a Thevenin-type of discrete-time filter model can be generated. It can reproduce the driving-point impedance characteristic of the network. Furthermore, the proposed model can be implemented into the EMTP in a direct manner. The simulation results with the full system representation and the developed equivalent system showed a good agreement 相似文献