全文获取类型
收费全文 | 939篇 |
免费 | 49篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 262篇 |
金属工艺 | 9篇 |
机械仪表 | 18篇 |
建筑科学 | 20篇 |
矿业工程 | 2篇 |
能源动力 | 39篇 |
轻工业 | 166篇 |
水利工程 | 8篇 |
石油天然气 | 6篇 |
无线电 | 65篇 |
一般工业技术 | 135篇 |
冶金工业 | 79篇 |
原子能技术 | 6篇 |
自动化技术 | 161篇 |
出版年
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 52篇 |
2020年 | 20篇 |
2019年 | 37篇 |
2018年 | 23篇 |
2017年 | 32篇 |
2016年 | 27篇 |
2015年 | 36篇 |
2014年 | 39篇 |
2013年 | 75篇 |
2012年 | 52篇 |
2011年 | 70篇 |
2010年 | 44篇 |
2009年 | 53篇 |
2008年 | 52篇 |
2007年 | 41篇 |
2006年 | 31篇 |
2005年 | 29篇 |
2004年 | 30篇 |
2003年 | 20篇 |
2002年 | 16篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 8篇 |
1998年 | 29篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1964年 | 1篇 |
1960年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有989条查询结果,搜索用时 31 毫秒
81.
Alfonso Baños Juan I. Mulero Antonio Barreiro Miguel A. Davó 《International journal of control》2016,89(10):1985-2007
Impulsive dynamical systems is a well-established area of dynamical systems theory, and it is used in this work to analyse several basic properties of reset control systems: existence and uniqueness of solutions, and continuous dependence on the initial condition (well-posedness). The work scope is about reset control systems with a linear and time-invariant base system, and a zero-crossing resetting law. A necessary and sufficient condition for existence and uniqueness of solutions, based on the well-posedness of reset instants, is developed. As a result, it is shown that reset control systems (with strictly proper plants) do not have Zeno solutions. It is also shown that full reset and partial reset (with a special structure) always produce well-posed reset instants. Moreover, a definition of continuous dependence on the initial condition is developed, and also a sufficient condition for reset control systems to satisfy that property. Finally, this property is used to analyse sensitivity of reset control systems to sensor noise. This work also includes a number of illustrative examples motivating the key concepts and main results. 相似文献
82.
Abstract To study the behaviour of anisotropic media in reflection when illuminated by natural light, an ‘indicating surface of natural reflectance’ is defined. The use of such a surface is proposed, and its statistical parameters are given. The expressions that relate these parameters to the refractive indices of the incident medium and to the principal indices of the medium under observation have been deduced for the case of uniaxial media. Those corresponding to uniaxial transparent substances are presented here. 相似文献
83.
Sixto Malato Julin Blanco Alfonso Vidal Diego Alarcn Manuel I. Maldonado Julia Cceres Wolfgang Gernjak 《Solar Energy》2003,75(4):329-336
The technical feasibility and performance of photocatalytic degradation of four water-soluble pesticides (diuron, imidacloprid, formetanate and methomyl) have been studied at pilot scale in two well-defined systems which are of special interest because natural-solar UV light can be used for them: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors specially designed for solar photocatalytic applications. The initial concentration tested with imidacloprid, formetanate and methomyl was 50 and 30 mg/l with diuron, and the catalyst concentrations were 200 mg/l and 0.05 mM with TiO2 and iron, respectively. Total disappearance of the parent compounds, 90% mineralisation and toxicity reduction below the threshold (EC50) have been attained with all pesticides tested. All these results have contributed to an evaluation of photocatalytic treatment capacity and comments on the main parameters of TiO2 and Fe separation from the treated water. 相似文献
84.
Ruff Holly A.; Saltarelli Lisa M.; Capozzoli Mary; Dubiner Karen 《Canadian Metallurgical Quarterly》1992,28(5):851
If an activity during manipulative play is exploratory, it should, in contrast to other activity, be used differentially for objects that vary in novelty. In a study of 5-mo-olds, different definitions of exploratory mouthing were tested, and results suggest that mouthing followed immediately by a look fulfilled some criteria for an exploratory activity. In the next study of 5- to 11-mo-olds, mouthing with looks after and examining, a measure of visual–manipulative inspection, met the criteria for exploratory activity; other kinds of mouthing and visual–manipulatory activity did not. Exploratory mouthing decreased with age, and examining increased. The exploratory function of mouthing apparently was not due to concurrent manual activity providing haptic information. The conclusion is that some activities are exploratory and information-gathering and other activities are nonexploratory and serve other functions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
Alfonso Centuori 《电子产品世界》2005,(23):123-124
可再充电电池常常被用来为诸如数码相机、PDA、移动电话和MP3播放机等便携式设备供电. 相似文献
86.
Maria Ariza-Avidad Alejandra Nieto Alfonso Salinas-Castillo Luis F Capitan-Vallvey Gordon M Miskelly Michael J Sailor 《Nanoscale research letters》2014,9(1):410
We report the monitoring of porous silicon (pSi) degradation in aqueous solutions using a consumer-grade digital camera. To facilitate optical monitoring, the pSi samples were prepared as one-dimensional photonic crystals (rugate filters) by electrochemical etching of highly doped p-type Si wafers using a periodic etch waveform. Two pSi formulations, representing chemistries relevant for self-reporting drug delivery applications, were tested: freshly etched pSi (fpSi) and fpSi coated with the biodegradable polymer chitosan (pSi-ch). Accelerated degradation of the samples in an ethanol-containing pH 10 aqueous basic buffer was monitored in situ by digital imaging with a consumer-grade digital camera with simultaneous optical reflectance spectrophotometric point measurements. As the nanostructured porous silicon matrix dissolved, a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from red to green. While the H coordinate in the hue, saturation, and value (HSV) color space calculated using the as-acquired photographs was a good monitor of degradation at short times (t < 100 min), it was not a useful monitor of sample degradation at longer times since it was influenced by reflections of the broad spectral output of the lamp as well as from the narrow rugate reflectance band. A monotonic relationship was observed between the wavelength of the rugate reflectance peak and an H parameter value calculated from the average red-green-blue (RGB) values of each image by first independently normalizing each channel (R, G, and B) using their maximum and minimum value over the time course of the degradation process. Spectrophotometric measurements and digital image analysis using this H parameter gave consistent relative stabilities of the samples as fpSi > pSi-ch. 相似文献
87.
Enrique Castillo Alfonso Fernández-Canteli Dieter Siegele 《International Journal of Fracture》2014,187(1):159-172
A crack growth model that allows us to obtain the S–N curves from the crack growth rate curves is presented in an attempt to harmonize the stress based and fracture mechanics approaches in lifetime prediction of long cracks propagation. First, using the Buckingham theorem, the crack growth rate curve $\frac{da}{dN}-\varDelta K$ is defined over all its range as a cumulative distribution function based on a normalized dimensionless stress intensity factor range $\varDelta K^+$ . Then, a relevant theorem is derived that provides an alternative to self-similarity allowing significant reduction of experimental planning. In this way, different $a-N$ crack growth curves for different stress ranges $\varDelta \sigma $ and initial crack lengths $a_0$ can be obtained from a particular crack growth curve under some conditions. The S–N field is obtained from the crack growth curves, showing the close relation between the fracture mechanics and stress approaches. Finally, the model is applied to a particular set of experimental data to obtain the crack growth rate curve and the S–N curves of a certain material for a subsequent fatigue lifetime assessment 相似文献
88.
Montella A Aria M D'Ambrosio A Galante F Mauriello F Pernetti M 《Accident; analysis and prevention》2011,43(6):2072-2084
Aim of the study was to investigate, by means of a driving simulator experiment, drivers’ behaviour in terms of speed, deceleration, and lateral position on major approaches of rural intersections in relation to different perceptual cues.In the experiment, ten different design conditions with and without speed-reducing treatments along the approach to the intersection were tested. Twenty-three drivers drove a test route two times and data from the second drive were used for comparison. The order of the ten design conditions was counterbalanced for all the drivers to minimize the presentation order effect. Three different data analysis techniques were used: (a) cluster analysis of speed and lateral position data, (b) statistical tests of speed and lateral position data, and (c) categorical analysis of deceleration behaviour patterns.The most effective treatments were the dragon teeth markings (based on the principle of optical road narrowing), the colored intersection area (based on the principle of intersection highlighting), and the raised median island (based on the principle of physical road narrowing). These measures, in comparison to the base intersection, produced: (1) a significant speed reduction starting from 250 m before the intersection in the range between 13 and 23 km/h, (2) a significant change in the deceleration behaviour with a reduction in the proportion of drivers which did not decelerate, and (3) a shift away from the intersection of the deceleration beginning. Given the significant effects on drivers’ behaviour, the dragon teeth markings, the colored intersection area, and the raised median island are strongly recommended for real world implementation. 相似文献
89.
Otero P Alfonso A Alfonso C Rodríguez P Vieytes MR Botana LM 《Analytical chemistry》2011,83(15):5903-5911
Chromatographic techniques coupled to mass spectrometry is the method of choice to replace the mouse bioassay (MBA) to detect marine toxins. This paper evaluates the influence of different parameters such as toxin solvents, mass spectrometric detection method, mobile-phase-solvent brands and equipment on okadaic acid (OA), dinophysistoxin-1 (DTX-1), and dinophysistoxin-2 (DTX-2) quantification. In addition, the study compares the results obtained when a toxin is quantified against its own calibration curve and with the calibration curve of the other analogues. The experiments were performed by liquid chromatography (LC) and ultraperformance liquid chromatography (UPLC) with tandem mass spectrometry detection (MS/MS). Three acetonitrile brands and two toxin solvents were employed, and three mass spectrometry detection methods were checked. One method that contains the transitions for azaspiracid-1 (AZA-1), azaspiracid-2 (AZA-2), azaspiracid-3(AZA-3), gimnodimine (GYM), 13-desmethyl spirolide C (SPX-1), pectenotoxin-2 (PTX-2), OA, DTX-1, DTX-2, yessotoxin (YTX), homoYTX, and 45-OH-YTX was compared in both instruments. This method operated in simultaneous positive and negative ionization mode. The other two mass methods operated only in negative ionization mode, one contains transitions to detect DTX-1, OA DTX-2, YTX, homoYTX, and 45-OH-YTX and the other only the transitions for the toxins under study OA, DTX-1, and DTX-2. With dependence on the equipment and mobile phase used, the amount of toxin quantified can be overestimated or underestimated, up to 44% for OA, 46% for DTX-1, and 48% for DTX-2. In addition, when a toxin was quantified using the calibration curve of the other analogues, the toxin amount obtained is different. The maximum variability was obtained when DTX-2 was quantified using either OA or a DTX-1 calibration curve. In this case, the overestimation was up to 88% using the OA calibration curve and up to 204% using the DTX-1 calibration curve. In summary, the correct quantification of DSP toxins by MS detection depends on multiple factors. Since these factors are not taken into account in a validated protocol, these results question the convenience of having MS/MS as a reference method for protecting consumers of marine toxins, moreover if toxicity of each group is considered independently and total toxicity is not summed anymore as it is in the MBA. 相似文献
90.
何谓永恒城市与火车之间的爱恨情仇/关系源远流长,有过激情四溢的乐章,也有过痛苦折磨的片断,有过甜蜜美好的瞬间,也有公诸于众的背叛。而今,两者之间的关系历经变化,今非昔比。然而在巴伦西亚的杰昆·索罗拉火车站,城市与火车之间的激情烈焰仍在燃烧。新车站在允许高速火车进行停靠的同时,完成了将铁轨迁入地下的工程: 相似文献