全文获取类型
收费全文 | 1229篇 |
免费 | 89篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 322篇 |
金属工艺 | 23篇 |
机械仪表 | 28篇 |
建筑科学 | 46篇 |
矿业工程 | 5篇 |
能源动力 | 38篇 |
轻工业 | 190篇 |
水利工程 | 4篇 |
石油天然气 | 1篇 |
无线电 | 149篇 |
一般工业技术 | 223篇 |
冶金工业 | 49篇 |
原子能技术 | 6篇 |
自动化技术 | 217篇 |
出版年
2024年 | 3篇 |
2023年 | 19篇 |
2022年 | 31篇 |
2021年 | 34篇 |
2020年 | 33篇 |
2019年 | 49篇 |
2018年 | 54篇 |
2017年 | 34篇 |
2016年 | 67篇 |
2015年 | 45篇 |
2014年 | 63篇 |
2013年 | 114篇 |
2012年 | 80篇 |
2011年 | 90篇 |
2010年 | 60篇 |
2009年 | 69篇 |
2008年 | 74篇 |
2007年 | 38篇 |
2006年 | 43篇 |
2005年 | 39篇 |
2004年 | 30篇 |
2003年 | 31篇 |
2002年 | 28篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有1318条查询结果,搜索用时 15 毫秒
91.
Jaime González‐Buesa Ana Ferrer‐Mairal Rosa Oria María L. Salvador 《Packaging Technology and Science》2013,26(7):413-421
Most experimental systems for measuring the permeability of microperforated polymeric films are static, mainly because in dynamic systems the small differences in pressure on both sides of the perforation may result in serious errors in the measurements. The O2 and CO2 transmission rate through microperforations of different sizes (from 40 × 30 to 350 × 110 µm) were determined in a static and in a dynamic system. In the latter case, rather than the diffusive flow, the hydrodynamic flow generated by the difference in pressure was measured (between 5 and 90 mbar). This was determined by applying Bernouilli's theorem and an experimental equation potentially relating the area of the microperforation with the transmission rate. A comparison of the transmission rates obtained in both cases gives coefficients of determination close to one (>0.993). This means that measuring the hydrodynamic flow can be considered as an alternative for the quantification of the diffusive flow through a microperforation. This is a simple and quick methodology that does not require expensive equipment. Furthermore, this feature enables commercial leak detection equipment to be used to quantify diffusive transmission rates through microperforations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
92.
G. Pacheco-Malagn Norma. A. Sanchez-Flores J. Saniger-Blesa L. Baos P. Prez-Romo Jaime S. Valente Mara de L. Guzman-Castillo F. Hernndez-Beltrn Jos J. Fripiat 《Microporous and mesoporous materials》2007,100(1-3):70-76
This contribution deals with the synthesis of a silicon-rich ZSM-5 obtained from an amorphous organo-alumino-silicic gel. The gel was formed by reacting a mechanical mixture of RHA (rice hull ash), silica’s source, and of natural clinoptilolite, source of alumina, with glycerol during 2 h at 200 °C. After a maturation period of one day at 60 °C, the reaction product was hydrolyzed by a tetra-propyl-ammonium (TPA) solution and then aged for two days at 135 °C in a stainless steel autoclave. After washing and drying, the X-ray pattern showed a well crystallized ZSM-5. The textural analysis of the slowly calcined solid at 500 °C for 4 h, and the SEM micrographies evidence that the zeolite was supported on mesoporous silica. The proportion of both components depends on the tunable hydrolysis conditions. 相似文献
93.
Open DRM and the Future of Media 总被引:1,自引:0,他引:1
This article offers an analysis of the various methods for implementing interoperable digital rights management platforms. 相似文献
94.
José Cheel Cristina Theoduloz Jaime A. Rodríguez Peter D.S. Caligari Guillermo Schmeda-Hirschmann 《Food chemistry》2007,102(1):36-44
The total phenolic, flavonoid and anthocyanin content of achenes (true fruit) and thalamus (receptacle) from the native South American Fragaria chiloensis ssp. chiloensis (f. patagonica and f. chiloensis), Fragaria vesca and Fragaria x ananassa cv. Chandler was determined by spectrophotometric means. Highest phenolic content was found in F. vesca while lowest content was measured for white strawberry (F. chiloensis ssp. chiloensis, f. chiloensis). The total anthocyanin and total flavonoid contents in the samples investigated was lower for the white strawberry and higher in F. x ananassa cv. Chandler. Total flavonoid content showed a better correlation than total anthocyanins with the free radical scavenging effect of the extracts measured by means of the DPPH discoloration assay. In the superoxide anion assay all the acetone extracts of strawberries showed similar activity. The data presented in this study demonstrate that the amount of phenolic compounds differ significantly between species and subspecies and determine the free radical scavenging activity of fruits. On a w/w basis, higher total phenolics including flavonoids was found in achenes. The highest total anthocyanin content was found in the achenes of F. chiloensis and F. vesca, while F. ananassa presented higher antocyanin content in thalamus. The main anthocyanin in thalamus of F. ananassa (95%) were pelargonidin derivatives which were also present in F. chiloensis ssp. chiloensis f. patagonica (62.6%) but were not detected in F. vesca and F. chiloensis ssp. chiloensis f. chiloensis. In F. vesca and F. chiloensis ssp. chiloensis f. chiloensis only cyanidin derivatives were found both in thalamus and achenes. 相似文献
95.
De La Cruz-Blas C.A. Lopez-Martin A. Carlosena A. Jaime Ramirez-Angulo 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2005,52(7):376-379
A current-mode CMOS RMS-DC converter is presented. The basic building blocks are based on a novel approach to design current-mode computational cells. In such an approach, the large-signal V-I characteristic of class-AB transconductors is conveniently exploited leading to a very regular and compact implementation. A proper biasing scheme in such transconductors allows operation with supply voltage as low as V/sub GS/+2V/sub DSsat/. Measurement results from a practical prototype are presented in order to demonstrate the technique proposed here. 相似文献
96.
Jaime Ortiz Edgar Uquiche Paz Robert Nalda Romero Vilma Quitral Catherine Llantén 《European Journal of Lipid Science and Technology》2009,111(4):320-327
The nutritional composition of the edible seaweeds Codium fragile, Gracilaria chilensis and Macrocystis pyrifera was determined, including amino acid and fatty acid contents along with tocol and carotenoid contents. The results indicated that the three algae C. fragile, G. chilensis and M. pyrifera showed a high range of protein contents (13.7–10.8%), amino acid contents (1879.6–1417.7 mg/100 g dry algae) and a low content in lipids (0.7–15.0%). The most abundant fatty acids in C. fragile and G. chilensis were linolenic, oleic, and linoleic acid. δ‐Tocopherol and α‐tocopherol (677.8 and 453.5 µg/g lipid, respectively) were found in C. fragile, while in G. chilensis and M. pyrifera, γ‐tocotrienol and α‐tocopherol (263.5 and 1327.7 µg/g lipid, respectively) were found. In addition, in C. fragile and G. chilensis β‐carotene was the principal carotenoid found (197.9 and 113.7 µg/g dry algae, respectively) compared with M. pyrifera (17.4 µg/g dry algae). The composition of macronutrients (minerals, carbohydrate‐type dietetic fiber, proteins; low in lipids) and micronutrients (essential amino acids, PUFA of balanced n‐6/n‐3 proportion, β‐carotene and α‐tocopherol as source of vitamins A and E), corroborate the nutritional and biological potential of the studied algae, which constitute useful raw materials for the development of diets or ingredients for human and animal nutrition. 相似文献
97.
Low-Voltage Super class AB CMOS OTA cells with very high slew rate and power efficiency 总被引:1,自引:0,他引:1
Lopez-Martin A.J. Baswa S. Jaime Ramirez-Angulo Carvajal R.G. 《Solid-State Circuits, IEEE Journal of》2005,40(5):1068-1077
A simple technique to achieve low-voltage power-efficient class AB operational transconductance amplifiers (OTAs) is presented. It is based on the combination of class AB differential input stages and local common-mode feedback (LCMFB) which provides additional dynamic current boosting, increased gain-bandwidth product (GBW), and near-optimal current efficiency. LCMFB is applied to various class AB differential input stages, leading to different class AB OTA topologies. Three OTA realizations based on this technique have been fabricated in a 0.5-/spl mu/m CMOS technology. For an 80-pF load they show enhancement factors of slew rate and GBW of up to 280 and 3.6, respectively, compared to a conventional class A OTA with the same 10-/spl mu/A quiescent currents and /spl plusmn/1-V supply voltages. In addition, the overhead in terms of common-mode input range, output swing, silicon area, noise, and static power consumption, is minimal. 相似文献
98.
Jaime Ramírez-Angulo Author Vitae Author Vitae Antonio Lopez-Martin Author Vitae Author Vitae 《Integration, the VLSI Journal》2008,41(4):539-543
A simple dynamic biasing scheme to extend the input/output range of cascode amplifiers is introduced. It requires minimum extra hardware and no additional power consumption. A dynamic biased telescopic op-amp is discussed as an application example. Experimental results of a fabricated test chip in 0.5 μm CMOS technology are presented that verify the proposed technique. 相似文献
99.
The Multimode Resource‐Constrained Project Scheduling Problem for Repetitive Activities in Construction Projects 下载免费PDF全文
J. D. García‐Nieves J. L. Ponz‐Tienda A. Salcedo‐Bernal E. Pellicer 《Computer-Aided Civil and Infrastructure Engineering》2018,33(8):655-671
In construction projects, resource availability might limit the implementation of ideal schedules. Especially, when repetitive activities are involved, traditional resource‐constrained project scheduling problem (RCPSP) models fail to allocate the resource consumption in an efficient manner. Besides, actual models only provide local optimal solutions and do not incorporate activity acceleration routines. To fulfill this gap, partially, a mathematical optimization model, the multimode RCPSP for repetitive activities in construction projects, is proposed and solved to optimality; it takes into account acceleration routines under real construction scenarios using spreadsheets. The article shows a complete computational experimentation over a real construction project, considering several scenarios of resource availabilities and continuity conditions. The model allows analyzing the resources efficiency indexes comparing them to resource consumptions, continuity of activities, and objective functions that reveal that fragmented activities do not provide better resource efficiency outcomes. 相似文献
100.
Andrea D. Adamczak Adam A. Spriggs Danielle M. Fitch Walid Awad Charles A. Wilkie Jaime C. Grunlan 《应用聚合物科学杂志》2010,115(4):2254-2261
High‐temperature polymers are being used for a broad range of applications, such as composite matrices for structural applications (e.g., high speed aircraft). Polyimides are a special class of polymers that meet the thermal and oxidative stability requirements for high temperature composite aerospace applications. A weight loss study was performed on a fluorinated polyimide resin and its carbon fiber composite in an effort to determine its thermal stability and degradation mechanisms. Experiments were conducted using a preheated oven and thermogravimetric analysis to obtain the weight loss. Regardless of the method used, the resin and composite exhibited excellent thermal stability (less than 1% weight loss) below 430°C, regardless of 2–20 min of exposure. After 20 min of exposure at 510°C, the composite remained relatively stable with only 5.3% weight loss using the oven technique, whereas the neat polyimide sustained 12.6%. When degradation occurred, it was found to be the result of thermolysis and oxidation (to a lesser extent). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献