全文获取类型
收费全文 | 1888篇 |
免费 | 62篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 52篇 |
综合类 | 9篇 |
化学工业 | 520篇 |
金属工艺 | 36篇 |
机械仪表 | 57篇 |
建筑科学 | 46篇 |
矿业工程 | 7篇 |
能源动力 | 46篇 |
轻工业 | 224篇 |
水利工程 | 19篇 |
石油天然气 | 4篇 |
无线电 | 122篇 |
一般工业技术 | 276篇 |
冶金工业 | 195篇 |
原子能技术 | 23篇 |
自动化技术 | 317篇 |
出版年
2022年 | 14篇 |
2021年 | 37篇 |
2020年 | 20篇 |
2019年 | 23篇 |
2018年 | 23篇 |
2017年 | 35篇 |
2016年 | 57篇 |
2015年 | 37篇 |
2014年 | 51篇 |
2013年 | 96篇 |
2012年 | 82篇 |
2011年 | 91篇 |
2010年 | 75篇 |
2009年 | 91篇 |
2008年 | 80篇 |
2007年 | 76篇 |
2006年 | 55篇 |
2005年 | 50篇 |
2004年 | 53篇 |
2003年 | 46篇 |
2002年 | 56篇 |
2001年 | 39篇 |
2000年 | 34篇 |
1999年 | 29篇 |
1998年 | 35篇 |
1997年 | 37篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 25篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 26篇 |
1982年 | 12篇 |
1981年 | 18篇 |
1980年 | 19篇 |
1979年 | 28篇 |
1978年 | 21篇 |
1977年 | 16篇 |
1975年 | 16篇 |
1974年 | 27篇 |
1973年 | 12篇 |
1971年 | 12篇 |
排序方式: 共有1953条查询结果,搜索用时 15 毫秒
81.
Newsted JL Nakanishi J Cousins I Werner K Giesy JP 《Environmental science & technology》2002,36(22):4761-4769
An assessment of HFE-7500, a 'segregated' hydrofluoroether, was conducted to evaluate the potential for exposure to and subsequent effects on humans and wildlife in Japan. The segregated hydrofluoroethers belong to a class of fluorochemicals currently being proposed as replacements for traditional fluorochemicals (CFCs and PFCs) that are currently being used in several industries, in particular, the semiconductor industry. These traditional compounds have been implicated as ozone-depleting or potent "greenhouse gases". The segregated hydrofluoroethers have useful physical and chemical properties, but do not contribute to ozone depletion and have lower "global warming potential" (GWP) indices. Although the physical properties of these materials (low H2O solubility and high vapor pressure) suggest there would be a very low level of risk to aquatic systems, a thorough analysis had not been previously performed. Predicted environmental concentrations (PECs) of HFE-7500 in Japan were determined with the Higashino model, a Gausian puff and plume model that used an approximation of environmental releases to the atmosphere as input to the model. Allowable concentrations to protect aquatic life, wildlife, and humans from noncancer effects were determined as detailed in USEPA's final Water Quality Guidance for the Great Lakes Systems. Potential risk to ecological receptors and humans was determined by calculating hazard quotients and margins of safety. The results of the risk assessment indicate that HFE-7500 poses no significant risk to either aquatic or terrestrial wildlife species or humans living in the Japanese environment. The least margin of safety for any ecological receptor was 100,000, and a margin of safety greater than 100,000,000 for most receptors indicated that HFE-7500 poses no threat to human health. Because of a scarcity of toxicity and exposure data, the risk assessment was based on very conservative assumptions. Therefore, the actual margins of safety for both humans and wildlife could have been 100- to 1,000-fold greater if additional data were available such that less stringent uncertainty factors could be applied. These results suggest that the environmental impact of HFE-7500 should be inconsequential based on the marked improvement in its atmospheric properties relative to the traditional compounds currently in use. Given the short atmospheric lifetime and low global warming potential of this material, its replacement of CFCs and PFCs would result in a net improvement of environmental health and safety. 相似文献
82.
Kurt P. Judmann 《e & i Elektrotechnik und Informationstechnik》2002,119(11):a16-a16
Sciencenews10-Jahr-Feier
Institut für Maschinelles Sehen und Darstellen 相似文献83.
Leith EN Mills KD Grannell S Dilworth DS Athey BD Lopez J 《Journal of the Optical Society of America. A, Optics, image science, and vision》2002,19(3):532-536
The method of Fourier optics is applied to the problem of time-gated imaging through scattering media. Tb adapt the problem to this treatment, appropriate alterations are made: The continuous medium is replaced by a cascade of thin scatterers, and a spatial filtering process is substituted for the conventional gating processes. Closed-form solutions are derived. 相似文献
84.
Keisuke Omae In-Tae Bae Muneyuki Naito Manabu Ishimaru Yoshihiko Hirotsu James A. Valdez Kurt E. Sickafus 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2006,250(1-2):300-302
We have performed high-dose Fe ion implantation into Si and characterized ion-beam-induced microstructures as well as annealing-induced ones using transmission electron microscopy (TEM) and grazing-incidence X-ray diffraction (GIXRD). Single crystals of Si(1 0 0) substrate were irradiated at 623 K with 120 keV Fe+ ions to a fluence of 4 × 1017 cm−2. The irradiated samples were then annealed in a vacuum furnace at temperatures ranging from 773 K to 1073 K. Cross-sectional TEM observations and GIXRD measurements revealed that a layered structure is formed in the as-implanted specimen with ε-FeSi, β-FeSi2 and damaged Si, as component layers. A continuous β-FeSi2 layer was formed on the topmost layer of the Si substrate after thermal annealing. 相似文献
85.
Kurt Beyer 《AI & Society》2002,16(3):278-287
This narrative describes the making of a German electrical engineer, Kurt Beyer, into a micro-entrepreneur. He set for himself
the goal of sailing around the world in his own vessel – without being able to afford to buy such a ship. Many people in Germany
have in recent years started to build their own sea-going vessels in order to escape from the creativity-stifling and restrictive
patterns of their lives and work. Only a few of them have ever finished building their vessels. Firstly, this report describes
the experiences of one of those few who have made it. Secondly, it tells the story of how this engineer himself turned into
a micro-entrepreneur during the period of yacht-building and how later he started his own charter enterprise, centred around
his yacht. Following the model of entrepreneurship described by Dassen-Housen in this issue of AI & Society, the narrative illustrates what it means to run such an enterprise in view of the international competition. Here follows
the narrative of the engineer and ship-builder himself (translated by D. Brandt). 相似文献
86.
The objective of this study is to investigate experimentally and theoretically whether sodium carbonate (Na2CO3) salt is suitable for establishing a salinity gradient in a salt-gradient solar-pond (SGSP). For this purpose, a small-scale prismatic solar-pond was constructed. Experiments were conducted in the laboratory under the incident radiation from two halogen-lamps acting as a solar simulator. Furthermore, a one-dimensional transient mathematical model that describes the heat and mass transfer behaviour of the SGSP was developed. The differential equations obtained were solved numerically using a finite-difference method. It was found from the experiments that the density gradient, achieved using sodium carbonate salt, can suppress convection from the bottom to the surface of the pond. 相似文献
87.
Pipp Sandra; Shaver Phillip; Jennings Sybillyn; Lamborn Susie; Fischer Kurt W. 《Canadian Metallurgical Quarterly》1985,48(4):991
Assessed 100 undergraduates' developmental theories about their affective relationships with their parents, using a retrospective method. Ss used drawings and questionnaire ratings to portray their relationships with parents at 5 points between infancy and the present. From infancy to their current age, Ss portrayed their relationships in 2 major ways: They perceived themselves as gaining in responsibility, dominance, independence, and similarity from infancy to the present, whereas they portrayed their parents as experiencing a decline on these dimensions. For variables indicating closeness and love, however, there was a striking discontinuity in these linear trends: Although Ss perceived linear trends from infancy to adolescence, they depicted their current relationships as involving a great deal more love and closeness. They also portrayed their relationships with mothers and fathers somewhat differently. More responsibility was felt toward the mothers and they were portrayed as especially friendly, but Ss felt more similar to their fathers, whom they perceived as dominant. Results suggest that late adolescents construct theories of the affective components of their relationships with their parents to serve the needs of separation while maintaining a close affective tie to the parents. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
Kurt Heyns und Helmut Koch 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1971,145(2):76-84
Zusammeufassung Zur Überprüfung des Auftretens von Nitrosaminen [2] im Rahmen der Maillard-Reaktion wurden die flüchtigen Produkte verschiedener Glucose-Aminosäure-Modell-gemische durch Kombination von Gaschromatographie and Massenspektrometrie, Polarographie und Dünnschicht-Chromatographie untersucht. Das Auftreten von Nitrosaminen kann durch die Ergebnisse eindeutig ausgeschlossen werden.
The problem of formation of nitrosamines by reacting monosaccharides with aminoacids (maillard-reaction)
Summary For proving the formation of nitrosamines applying maillardconditions [2] we tested the volatile reaction products of various glucose-aminoacid mixtures by coupling gas chromatography and mass spectrometry, polarography and thin-layer chromatography. The appearence of nitrosamines could undoubtedly be excluded according to the results.相似文献
89.
90.
Anthony J. Bur Steven C. Roth Mark A. Spalding Daniel W. Baugh Kurt A. Koppi Walter C. Buzanowski 《Polymer Engineering and Science》2004,44(11):2148-2157
We used a temperature‐sensitive fluorescent dye, perylene, to monitor the true resin temperature during extrusion of polycarbonate. The measurement involved doping polycarbonate with perylene and detecting fluorescence with an optical sensor that accesses a standard instrumentation port on a barrel of a single‐screw extruder. The sensor's confocal optics design permits fluorescence intensity measurements as a function of position. Using a previously established calibration function, temperature and temperature gradients were obtained from the measured fluorescence. Because the origin of the measurement is the fluorescent dye molecule that is soluble in the resin, this method allows temperature measurement of the polymer without interference from the surrounding metal parts. With the sensor looking over the screw, temperature profiles from the barrel wall to the core of the screw were obtained as a function of screw speed, screw design and resin melt flow rate. Polym. Eng. Sci. 44:2148–2157, 2004. © 2004 Society of Plastics Engineers. 1 This paper is a contribution from the National Institute of Standards and Technology, and, thus, is not subject to copyright in the United States. 相似文献