全文获取类型
收费全文 | 1448篇 |
免费 | 37篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 35篇 |
综合类 | 1篇 |
化学工业 | 311篇 |
金属工艺 | 24篇 |
机械仪表 | 25篇 |
建筑科学 | 66篇 |
矿业工程 | 3篇 |
能源动力 | 15篇 |
轻工业 | 200篇 |
水利工程 | 9篇 |
无线电 | 92篇 |
一般工业技术 | 166篇 |
冶金工业 | 384篇 |
原子能技术 | 13篇 |
自动化技术 | 142篇 |
出版年
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 41篇 |
2015年 | 20篇 |
2014年 | 41篇 |
2013年 | 38篇 |
2012年 | 45篇 |
2011年 | 54篇 |
2010年 | 36篇 |
2009年 | 50篇 |
2008年 | 37篇 |
2007年 | 42篇 |
2006年 | 36篇 |
2005年 | 27篇 |
2004年 | 25篇 |
2003年 | 27篇 |
2002年 | 31篇 |
2001年 | 22篇 |
2000年 | 36篇 |
1999年 | 21篇 |
1998年 | 107篇 |
1997年 | 62篇 |
1996年 | 56篇 |
1995年 | 49篇 |
1994年 | 22篇 |
1993年 | 33篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 28篇 |
1987年 | 15篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1976年 | 23篇 |
1975年 | 10篇 |
1974年 | 11篇 |
1972年 | 8篇 |
排序方式: 共有1486条查询结果,搜索用时 15 毫秒
91.
In an open mobile health (mHealth) sensing system, users will be able to seamlessly pair sensors with their cellphone and expect the system to just work. This ubiquity of sensors, however, creates the potential for users to accidentally wear sensors that are not paired with their own cellphone. Our method probabilistically detects this situation by finding correlations between embedded accelerometers in the cellphone and sensor. We evaluate our method over a dataset of seven individuals with sensors in various positions on their body and experimentally show that our method is capable of achieving an accuracy of 85%. 相似文献
92.
Corrosion protection of steel reinforcement in concrete structures by cathodic protection (CP) is a cost effective, reliable, and widely accepted method to stop and prevent the corrosion of the steel reinforcement. The efficiency of CP is usually monitored by the “24 h, 100 mV depolarization criterion,” a purely empirical criterion whose implementation is cost and labor intensive and that does not allow online control of CP. Within an extended research project on CP applied to concrete members of a highway bridge exposed to penetrating moisture, three sets of macrocells (MC), each composed of five MC sensors, were installed in conjunction with concrete resistance sensors and silver/silver chloride reference cells. Chloride profiles were determined from the cored or drilled powder originating from the installation of sensors and from drilling cores. Corrosion currents, steel potentials, and concrete resistance were monitored over a period of 1 year before, after installing the CP systems (which remained switched off for half a year for evaluating the effect of the conductive coating), and after start-up of the CP systems. The CP systems applied consist of a moisture resistant conductive coating. As expected CP has a pronounced effect on local MC currents: Anodic MC currents were reduced or changed into cathodic currents, whereas cathodic currents were only weakly influenced. By adjusting the applied protection current all anodic MC currents may be changed into cathodic MC currents. Results indicate that the 100 mV depolarization criterion is a conservative criterion in atmospherically exposed concrete; it is not reliable in strongly wetted concrete. There was no consistent correlation between the CP induced changes in the local MC currents and 24 h depolarization values indicating that large potential shifts induced by CP do not necessarily imply overprotection. Results show that monitoring MC currents before, during, and after CP operation allows to demonstrate in a transparent way the effect of CP on the corrosion of the steel reinforcement. Online monitoring of MC currents is proposed as a viable and comprehensible method to monitor and control the efficiency of CP. 相似文献
93.
Survey on the content of vitisin A and hydroxyphenyl-pyranoanthocyanins in Tempranillo wines 总被引:1,自引:0,他引:1
Michael Rentzsch Michael Schwarz Peter Winterhalter Dora Blanco-Vega Isidro Hermosín-Gutiérrez 《Food chemistry》2010
Little is known about the content and development of pyranoanthocyanins, pigments mainly formed during red wine ageing, in commercial wines. Some of the major pyranoanthocyanins in a wide selection of 1–10 years-old Spanish Tempranillo wines and also in a 29 years wide-vertical series of Tempranillo wines from an individual cellar have been determined. Great variability in pyranoanthocyanin concentrations was found (range, mg/l): vitisin A, 0–10.76; pinotin A, 0–4.26; and malvidin 3-glucoside-4-vinylphenol, 0.03–1.37. Vitisin A and malvidin 3-glucoside-4-vinylphenol were already present in 1–2 years-old wines, whereas pinotin A was only detectable in a few of the 1 and 2 years-old wines. Vitisin A tended to decrease with wine age, while hydroxyphenyl-pyranoanthocyanins showed the reverse trend. However, the aforementioned trends were interrupted by various temporary maxima, most likely due to some “refreshment” of the oldest wines (i.e., addition of young wine), as suggested by unexpected high concentrations of malvidin 3-glucoside, in contrast to the results found in the wine vertical series. The effects of addition of young wine on aged wine pyranoanthocyanin concentrations were confirmed by wine refreshment experiments. 相似文献
94.
95.
96.
97.
This paper is motivated by the performance evaluation of circulating vertical conveyor systems (CVCSs). CVCSs are bulk queues of transportation type. These material handling systems feature generally distributed inter-arrival times, which can be longer than the bulk service time. This leads to interdependencies between the number of arrivals in consecutive service intervals and the number of loads in the queue. We propose a new discrete-time approach for the steady-state analysis of such bulk service queues of transportation type with general arrival and service processes and finite server and limited queue capacities. The approach is based on a finite Markov chain that generates complete probability distributions for the key performance measures, including the queue length, waiting time and departing batch size. The proposed approach is exact in the cases of discrete-time slots, e.g. as in communication systems. We investigate the discretisation error that arises if the approach is used as an approximation for the continuous time using a numerical comparison to a discrete-event simulation. Moreover, we examine the impact of arrival stream variability on the system performance and compare the positive effects of a higher frequency of server visits with the effects arising from larger pickup capacities. 相似文献
98.
Comparing Different Synthesis Procedures for Carbide‐Derived Carbon‐Based Structured Catalyst Supports
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Different approaches were analyzed to combine the tuneable micropore structure of carbide‐derived carbons with a foam‐like secondary porosity. The resulting structured catalyst supports were characterized in detail and applied in the model reaction of ethene hydrogenation. Preparation methods studied were dip‐coating using polytetrafluoroethylene as binder on cellular metal structures, a chemical vapor deposition coating of the metal structures with thin carbide layers and subsequent conversion to carbide‐derived carbon, and the partial or full conversion of carbide foams to carbon/carbide composites. For the binder method, optimal parameters for stable slurry preparation as well as for calcination of the slurry were obtained. It could further be demonstrated that the conversion of carbide foams into carbon/carbide composites leads to an appreciation between decreasing mechanical strength and increasing specific surface area. 相似文献
99.
J. Großfeld und K. Schwarz 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1938,76(3):232-233
Kurze Zusammenfassung Ein als nicht nachweisbar bezeichneter gelber Farbstoff erwies sich als unlöslich in den üblichen Lösungsmitteln, aber als löslich in alkalisch reagierenden Flüssigkeiten. Er ließ sich aus Teigwaren durch Verreiben mit schwach ammonikalischem, verdünnten Alkohol ausziehen und aus dieser Lösung nach Ansäuern und Abdestillieren des Alkohols auf Wolle ausfärben. 相似文献
100.
Investigations of tantalum coatings on steel by vacuum plasma spraying In this work the possibilities of the production of tantalum coatings by vacuum plasma spraying were investigated. Suitable parameters of the vacuum plasma spraying process were determined, and the quality of vacuum plasma sprayed tantalum coatings was evaluated with regard to chemical composition, adhesion strength, density and corrosion behaviour. To obtain high-quality coatings it was necessary to apply sufficient plasma power as well as an optimal injection of spraying powder into the plasma torch. A complete melting of the tantalum powder particles could not he achieved. The coatings obtained showed a good adhesion strength but a low formability (ductility). The corrosion resistance against HCL and HNO3 was evaluated by curves of the current density versus potential. With the aid of the passive current density it was determined that the corrosion resistance of the sprayed coatings was not as excellent as of compact tantalum. The increased surface roughness was not significant with respect to the corrosion behaviour. The reduced corrosion resistance could be caused probably by a high oxygen content of the tantalum powder, especially by oxides around individual powder particles. In contrast to tantalum, vacuum plasma sprayed titanium coatings showed the same corrosion resistance as compact titanium under the same testing conditions. 相似文献