全文获取类型
收费全文 | 412902篇 |
免费 | 5827篇 |
国内免费 | 1386篇 |
专业分类
电工技术 | 7704篇 |
综合类 | 349篇 |
化学工业 | 62041篇 |
金属工艺 | 14286篇 |
机械仪表 | 11872篇 |
建筑科学 | 11641篇 |
矿业工程 | 869篇 |
能源动力 | 11119篇 |
轻工业 | 43835篇 |
水利工程 | 3312篇 |
石油天然气 | 1837篇 |
武器工业 | 13篇 |
无线电 | 55398篇 |
一般工业技术 | 76637篇 |
冶金工业 | 74986篇 |
原子能技术 | 5568篇 |
自动化技术 | 38648篇 |
出版年
2021年 | 2670篇 |
2019年 | 2436篇 |
2018年 | 3840篇 |
2017年 | 3906篇 |
2016年 | 4147篇 |
2015年 | 3429篇 |
2014年 | 5721篇 |
2013年 | 19289篇 |
2012年 | 10208篇 |
2011年 | 14699篇 |
2010年 | 11291篇 |
2009年 | 12893篇 |
2008年 | 13924篇 |
2007年 | 14293篇 |
2006年 | 12781篇 |
2005年 | 11967篇 |
2004年 | 11581篇 |
2003年 | 11285篇 |
2002年 | 10915篇 |
2001年 | 11139篇 |
2000年 | 10274篇 |
1999年 | 10774篇 |
1998年 | 24022篇 |
1997年 | 17598篇 |
1996年 | 13912篇 |
1995年 | 10980篇 |
1994年 | 9775篇 |
1993年 | 9354篇 |
1992年 | 7123篇 |
1991年 | 6790篇 |
1990年 | 6397篇 |
1989年 | 6107篇 |
1988年 | 5860篇 |
1987年 | 4884篇 |
1986年 | 4836篇 |
1985年 | 5979篇 |
1984年 | 5602篇 |
1983年 | 4833篇 |
1982年 | 4496篇 |
1981年 | 4447篇 |
1980年 | 4209篇 |
1979年 | 4080篇 |
1978年 | 3771篇 |
1977年 | 4549篇 |
1976年 | 6097篇 |
1975年 | 3116篇 |
1974年 | 3011篇 |
1973年 | 2890篇 |
1972年 | 2318篇 |
1971年 | 2003篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
A coupled-mode analysis of superimposed holographic transmission gratings in single-mode planar optical waveguides is presented. The diffraction characteristics are shown to be sensitive to the polarization of the incident wave, the angular separation of the output waves and the relative index modulation between the gratings. The coupling between gratings affects the diffraction efficiencies and decreases the angular and wavelength selectivities. Nevertheless, good channel separation and high fanout can be obtained together 相似文献
962.
This paper develops and demonstrates by computer simulations new nonlinear system stochastic techniques to determine the amplitude-domain and frequency-domain properties of nonlinear systems as described in nonlinear differential equations of motion. From measurements of input excitation data and output response data, this new method, based upon multiple-input/single-output (MI/SO) linear analysis of reverse dynamic systems, allows for the efficient identification of different nonlinear systems. Nonlinear systems simulated here include Duffing, Van der Pol, Mathieu, and Dead-Band systems. Features of this new method are: (1) it can be implemented using established MI/SO linear procedures and computer programs; (2) it determines nonlinear system amplitude properties separate from nonlinear system frequency properties; (3) it quantifies relative contributions from different nonlinear terms by using appropriate coherence functions; (4) it gives results that are independent of the input or output probability distributions, spectral properties, and input excitation levels. 相似文献
963.
964.
Kiang S.-Z. Baker R.L. Sullivan G.J. Chiu C.-Y. 《IEEE transactions on image processing》1992,1(2):162-169
A pruning algorithm of P.A. Chou et al. (1989) for designing optimal tree structures identifies only those codebooks which lie on the convex hull of the original codebook's operational distortion rate function. The authors introduce a modified version of the original algorithm, which identifies a large number of codebooks having minimum average distortion, under the constraint that, in each step, only modes having no descendents are removed from the tree. All codebooks generated by the original algorithm are also generated by this algorithm. The new algorithm generates a much larger number of codebooks in the middle- and low-rate regions. The additional codebooks permit operation near the codebook's operational distortion rate function without time sharing by choosing from the increased number of available bit rates. Despite the statistical mismatch which occurs when coding data outside the training sequence, these pruned codebooks retain their performance advantage over full search vector quantizers (VQs) for a large range of rates. 相似文献
965.
Four parameters are defined to measure the performance of a teletext system, namely, the probability of delivering a message within specified time, the transmission efficiency, the average number of errors per page, and the throughput. Each of them is derived and computational results are presented taking the UK teletext system as an example. These parameters are compared in their ability to characterize the performance of the teletext system 相似文献
966.
967.
Collusion attacks are a major issue in fingerprinting schemes for copyright protection. A new class of codes, called scattering codes, is presented which can be used to control colluders' strategy in collusions of size up to 3. Scattering codes can be combined with dual Hamming codes to obtain 3-secure fingerprinting codes much shorter than those resulting from Boneh-Shaw's general construction 相似文献
968.
The purpose of this paper is to study the relationship between the oxygen concentration and brightness degradation in ZnS:TbOF green thin-film electroluminescent (EL) devices. The characteristics including crystallinity, optical, and electrical properties were discussed. The brightness-voltage (B-V) measurement results shelved that with higher oxygen-content in ZnS:TbOF phosphor layer, lower brightness was measured. It was consistent with the poor crystallinity, worse photoluminescent intensity, and easier to get moisture in the oxygen-rich (O/Tb>1) phosphor film. Furthermore, deep level transient spectroscopy (DLTS) measurements identified that when the O/Tb ratio was greater than 1, the oxygen-related deep hole traps EH1 and/or EH2 could be detected in the ZnS:TbOF phosphor layer. These E H1 and/or EH2 traps were believed to be the main killers for the brightness of the device since they capture most of the holes from the generated electron-hole pairs. This evidence strongly supports that the modified energy transfer model is more dominant than direct impact excitation during the luminescent process 相似文献
969.
M Pan J Suárez de Lezo A Medina M Romero E Hernández J Segura F Melian F Wangüemert M Landin F Benítez M Amat F Velasco A Torres 《Canadian Metallurgical Quarterly》1997,80(10):1336-1338
Two hundred twenty-eight patients with successful coronary stent implantation were randomized either to protamine administration and femoral sheath removal (group I, n = 117) or no heparin neutralization and delayed sheath removal (group II, n = 111). The hospital stay after treatment was shorter in patients receiving protamine; therefore, protamine use for neutralizing circulating heparin may be safely administered immediately after stent implantation. 相似文献
970.
Z Amma E Kis M Józan-Jilling G Wagner T Gesztesi 《Canadian Metallurgical Quarterly》1997,138(29):1859-1861
Two chronic haemodialyzed patients with digitalis intoxication are reported. One of them took digoxin 0.25 mg three times daily for an unknown period and the other took digitoxin 0.1 mg twice daily for two weeks. The symptoms of intoxication were mainly concealed by uremic syndrome. The diagnosis was established by noticed sinus bradycardia, first- and second-degree atrioventricular block in ECG and the determination of sera levels of glycosides (serum digoxin concentration was 7.36 ng/ml, serum digitoxin concentration was 46.5 ng/ml) in both cases. Considering the probable long elimination period of digitalis and the potentially life-threatening situation the patients were given digoxin-specific antibody (Fab) fragments with potassium replacement therapy. The symptoms disappeared within a few hours after therapy, side effects and rebound toxicity did not develop. In connection with these cases the aim of this report is to publish a method which can reverse the life-threatening digitalis intoxication in patients suffering from renal failure as well. As to the above method, the authors have not found any similar case reports in the Hungarian medical literature. 相似文献