全文获取类型
收费全文 | 10714篇 |
免费 | 142篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 153篇 |
化学工业 | 633篇 |
金属工艺 | 296篇 |
机械仪表 | 62篇 |
建筑科学 | 78篇 |
矿业工程 | 1篇 |
能源动力 | 87篇 |
轻工业 | 383篇 |
水利工程 | 7篇 |
石油天然气 | 8篇 |
无线电 | 367篇 |
一般工业技术 | 304篇 |
冶金工业 | 315篇 |
原子能技术 | 89篇 |
自动化技术 | 8078篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 30篇 |
2021年 | 61篇 |
2020年 | 38篇 |
2019年 | 43篇 |
2018年 | 54篇 |
2017年 | 54篇 |
2016年 | 48篇 |
2015年 | 62篇 |
2014年 | 271篇 |
2013年 | 272篇 |
2012年 | 846篇 |
2011年 | 2385篇 |
2010年 | 1182篇 |
2009年 | 1035篇 |
2008年 | 748篇 |
2007年 | 652篇 |
2006年 | 497篇 |
2005年 | 608篇 |
2004年 | 561篇 |
2003年 | 620篇 |
2002年 | 316篇 |
2001年 | 37篇 |
2000年 | 29篇 |
1999年 | 27篇 |
1998年 | 105篇 |
1997年 | 66篇 |
1996年 | 46篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 27篇 |
1992年 | 3篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1977年 | 3篇 |
1976年 | 10篇 |
1975年 | 3篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
31.
Development of new burner technology is common practice nowadays. Standardized test codes are available to conduct tests to determine operating characteristics and thermal performance of different parts of steam generating units. This paper describes the results of testing performed to evaluate thermal efficiency of a 74.5?kW fire-tube steam generator fired with a new premixed flame burner in comparison to a typical standard-retrofit diffusion flame burner system. Two premixed flame burners sized at 7.6 and 10.1?cm were tested. Testing was performed in accordance with the ASME PTC 4.1 Power Test Code. The evaluation was conducted in the range of small- to mid-sized, natural gas-fired applications, from 1.06?to?2.64×106?kJ/h. The environmental nitrogen oxide (NOx) emissions performance was also compared for both burner technologies. The results of this evaluation indicate that firing the test boiler with the 7.6?cm new burner slightly improves unit thermal efficiency by 4.0–3.3% for a unit load ranging from approximately 1.06?to?1.79×106?kJ/h, respectively. Operation with the 10.1?cm new burner improves the thermal efficiency by approximately 1.6% at 2.32×106?kJ/h. The uncertainty in the measurements used in the efficiency calculations should account for approximately ±1.5% uncertainty in the reported gross efficiency. Reductions in NOx emissions of the order of 10% resulted from operation with the new premixed flame burners. 相似文献
32.
Nonlinear model predictive control with polytopic invariant sets 总被引:1,自引:0,他引:1
Ellipsoidal invariant sets have been widely used as target sets in model predictive control (MPC). These sets can be computed by constructing appropriate linear difference inclusions together with additional constraints to ensure that the ellipsoid lies within a given inclusion polytope. The choice of inclusion polytope has a significant effect on the size of the target ellipsoid, but the optimal inclusion polytope cannot in general be computed systematically. This paper shows that use of polytopic invariant sets overcomes this difficulty, allowing larger stabilizable sets without loss of performance. In the interests of online efficiency, consideration is focused on interpolation-based MPC. 相似文献
33.
Qing-Chang Zhong Author Vitae 《Automatica》2003,39(3):499-508
This paper generalizes the frequency-domain results on the delay-type Nehari problem in the stable case to the unstable case. The solvability condition of the delay-type Nehari problem is formulated in terms of the nonsingularity of three matrices. The optimal value γopt is the maximal γ∈(0,∞) such that one of the three matrices becomes singular. All sub-optimal compensators are parameterized in a transparent structure incorporating a modified Smith predictor. 相似文献
34.
Gilles Celeux Author VitaeFlorence ForbesAuthor Vitae Nathalie Peyrard Author Vitae 《Pattern recognition》2003,36(1):131-144
Image segmentation using Markov random fields involves parameter estimation in hidden Markov models for which the EM algorithm is widely used. In practice, difficulties arise due to the dependence structure in the models and approximations are required. Using ideas from the mean field approximation principle, we propose a class of EM-like algorithms in which the computation reduces to dealing with systems of independent variables. Within this class, the simulated field algorithm is a new stochastic algorithm which appears to be the most promising for its good performance and speed, on synthetic and real image experiments. 相似文献
35.
Determination of vitality from a non-invasive biomedical measurement for use in fingerprint scanners
Fingerprints are the oldest and most widely used biometrics for personal identification. Unfortunately, it is usually possible to deceive automatic fingerprint identification systems by presenting a well-duplicated synthetic or dismembered finger. This paper introduces one method to provide fingerprint vitality authentication in order to solve this problem. Detection of a perspiration pattern over the fingertip skin identifies the vitality of a fingerprint. Mapping the two-dimensional fingerprint images into one-dimensional signals, two ensembles of measures, namely static and dynamic measures, are derived for classification. Static patterns as well as temporal changes in dielectric mosaic structure of the skin, caused by perspiration, demonstrate themselves in these signals. Using these measures, this algorithm quantifies the sweating pattern and makes a final decision about vitality of the fingerprint by a neural network trained by examples. 相似文献
36.
37.
Lithiasis may develop in the prostate loge following prostate surgery. Calculus formation in the prostate can be ascribed basically to foreign bodies, residual adenomatous spheroids and clots or fragments of sphacelous mucosa in the presence of a stenotic area after surgery and/or infection. The diagnosis is based on the physical examination and particularly on the radiological findings. Treatment is by open surgery or endoscopic or extracorporeal lithotripsy. 相似文献
38.
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
39.
MP Romero A García-Perga?eda JM Guerrero C Osuna 《Canadian Metallurgical Quarterly》1998,12(13):1401-1408
Melatonin has been suggested as a physiological antagonist of calmodulin. In this work, we have characterized melatonin binding sites in Xenopus laevis oocyte membranes. Binding of [125I]melatonin by X. laevis oocyte membranes fulfills all criteria for binding to a receptor site. Binding was dependent on time, temperature, and membrane concentration and was stable, reversible, saturable, and specific. The binding site was also pharmacologically characterized. Stoichiometric studies showed a high-affinity binding site with a Kd of 1.18 nM. These data are in close agreement with data obtained from kinetic studies (Kd=0.12 nM). In competition studies, we observed a low-affinity binding site (Kd=63.41 microM). Moreover, the binding site was characterized as calmodulin. Thus, binding was dependent on calcium and blocked by anti-CaM antibodies in a concentration-dependent manner. Calmodulin inhibitor chlorpromazine also inhibited binding of the tracer. From these results, it is suggested that membrane-bound calmodulin acts as a melatonin binding site in Xenopus laevis oocytes, where it might couple cellular activities to rhythmic circulating levels of melatonin. This hypothesis correlates with the previous findings describing melatonin as a physiological antagonist of calmodulin. 相似文献
40.