全文获取类型
收费全文 | 3860篇 |
免费 | 101篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 29篇 |
综合类 | 3篇 |
化学工业 | 596篇 |
金属工艺 | 56篇 |
机械仪表 | 49篇 |
建筑科学 | 155篇 |
矿业工程 | 24篇 |
能源动力 | 42篇 |
轻工业 | 420篇 |
水利工程 | 41篇 |
石油天然气 | 7篇 |
无线电 | 159篇 |
一般工业技术 | 471篇 |
冶金工业 | 1495篇 |
原子能技术 | 14篇 |
自动化技术 | 414篇 |
出版年
2022年 | 29篇 |
2021年 | 64篇 |
2020年 | 36篇 |
2019年 | 45篇 |
2018年 | 58篇 |
2017年 | 58篇 |
2016年 | 59篇 |
2015年 | 47篇 |
2014年 | 76篇 |
2013年 | 195篇 |
2012年 | 141篇 |
2011年 | 207篇 |
2010年 | 140篇 |
2009年 | 174篇 |
2008年 | 161篇 |
2007年 | 178篇 |
2006年 | 149篇 |
2005年 | 132篇 |
2004年 | 116篇 |
2003年 | 121篇 |
2002年 | 108篇 |
2001年 | 65篇 |
2000年 | 72篇 |
1999年 | 72篇 |
1998年 | 67篇 |
1997年 | 76篇 |
1996年 | 85篇 |
1995年 | 67篇 |
1994年 | 75篇 |
1993年 | 91篇 |
1992年 | 83篇 |
1991年 | 32篇 |
1990年 | 68篇 |
1989年 | 74篇 |
1988年 | 49篇 |
1987年 | 66篇 |
1986年 | 66篇 |
1985年 | 71篇 |
1984年 | 43篇 |
1983年 | 49篇 |
1982年 | 37篇 |
1981年 | 40篇 |
1980年 | 33篇 |
1979年 | 34篇 |
1978年 | 16篇 |
1977年 | 28篇 |
1976年 | 20篇 |
1975年 | 26篇 |
1974年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有3975条查询结果,搜索用时 78 毫秒
1.
William M. Pitts Martin Werrel Marco Fernandez Mary A. Long Evan A. Eisenberg James Filliben Cory D. Runyon 《火与材料》2021,45(1):127-154
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF. 相似文献
2.
3.
Matthew O'Sullivan Daire
hUallachin Patrícia Oliveira Antunes Eleanor Jennings Mary Kelly‐Quinn 《河流研究与利用》2019,35(2):146-158
Cattle access to streams has been linked globally with degradation of stream water quality, driven largely by bank erosion and resultant instream, fine sediment deposition. The majority of evidence on such effects is however based in arid and semiarid regions of the United States and Australia, with few studies relating to cool temperate climates such as Northwest Europe. In this study, “Quorer” resuspendable sediment samples were taken from riffle geomorphic units upstream (control) and at two points downstream (pressure and recovery) of cattle access points in headwater streams in agricultural catchments in Ireland to assess levels of deposited stream sediment. Samples were taken in April/May (2016) prior to the grazing season and in October (2016) at the end of the grazing season. Sites in good‐high ecological status catchments and less than good ecological status catchments were included in the study. Higher levels of sediment were found downstream of cattle access points in both good‐high status and less than good status catchments; however, the impacts of access points were spatially confined to, in most cases, the area immediately downstream of the point of access. There was a strong correlation between deposited sediment mass and organic matter (OM) mass, with levels of OM increasing linearly with deposited sediment mass. Levels of measured sediment were negatively correlated with riparian habitat health (measured using a qualitative habitat assessment). The results of this study highlight the need for measures to prevent cattle access to headwater streams where access points can be many in order to manage local habitat quality and downstream water quality issues. 相似文献
4.
Shruti Deshmukh Stephen Burbine Erin Keaney Shib Shankar Banerjee Artee Panwar Christopher Peters Mary Herndon Derrick Rockosi Joey Mead Carol Barry 《Polymer Engineering and Science》2020,60(11):2782-2792
Highly-filled polymer systems include color masterbatches, feedstocks for powder injection molding, and rigid sheets with high levels of flame retardants, but they have not been explored for flexible sheet. This work investigated the (a) selecting a polymer matrix with enough melt strength and flexibility to form a stable sheet with high filler loading, (b) the maximum achievable filler loading for the sheet, and (c) optimizing the process of extruding a highly-filled flexible polymer system. Extrusion grade low-density polyethylene (LDPE) provided sufficient flexibility and permitted a maximum filler loading of 36 vol% (~78 wt%). Good dispersion of the nanoparticle filler, however, required two passes through multiple screw extruders and a small reduction in the viscosity of the LDPE. Sheet with thickness of 415 μm, surface roughness of <1 μm, and sufficient flexibility was extruded continuously at a rate of 10 m/min., but it required a more traditional coat hanger manifold to prevent filler hang up in the sheet die. The filler particles were distributed uniformly through the core and skin of the sheet, giving the sheet good mechanical properties. 相似文献
5.
Dipta Mukherjee Arjun Dey A. Carmel Mary Esther Debajyoti Palai N. Sridhara Parthasarathi Bera Manjima Bhattacharya A. Rajendra Anand Kumar Sharma Anoop Kumar Mukhopadhyay 《Ceramics International》2018,44(8):8913-8921
Smooth, uniform and crystalline vanadium oxide thin films were deposited on quartz by spin coating technique with four different rpm i.e., 1000, 2000, 3000 and 4000 and subsequently post annealed at 350, 450 and 550?°C in vacuum. Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) techniques were utilized for microstructural characterizations and phase analysis, respectively, for vanadium oxide powder and deposited film. Nanorods were observed to be grown after vacuum annealing. X-ray photoelectron spectroscopy (XPS) technique was utilized to study the elemental oxidation state of deposited vanadium oxide films. Thermo-optical and electrical properties such as solar transmittance (τs), reflectance (ρs), absorptance (αs), infrared (IR) emittance (εir) and sheet resistance (Rs) of different thin films were evaluated. Based on the optical characteristics the optimized condition of the film processing was identified to be spin coated at 3000?rpm. Subsequently, the nanoindentation technique was utilized to measure hardness and Young's modulus of the optimized film. The measured nanomechanical properties were found to be superior to those reported for sputtered vanadium oxide films. Finally, temperature dependent phase transition characteristics of optimized vanadium oxide films were studied by differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition was found to occur in the range of 44–48?°C which was significantly lower than the phase transition temperature (i.e., 68?°C) of bulk VO2. 相似文献
6.
7.
Journal of Computational Electronics - Parameter identification and accurate photovoltaic (PV) modeling from basic I–V information are necessary for simulation, optimization, and control of... 相似文献
8.
Rachel A. Hegab Sibile Pardue Xinggui Shen Christopher Kevil Nicholas A. Peppas Mary E. Caldorera-Moore 《应用聚合物科学杂志》2020,137(25):48767
pH responsive hydrogels are ideal platforms for numerous therapeutic delivery applications, including oral delivery, as they are capable of overcoming the many barriers that must be considered when creating an effective drug delivery system. Understanding of the innate hydrogel network structure and its swelling behavior at environmentally relevant conditions is vital for designing hydrogel network capable of effective controlled drug release. Herein, we explored how to expand traditional techniques of swelling and pore characterization to gain better insight into the performance of anionic microparticles composed of the poly(methyl methacrylate-co-acrylic acid) with varying molar percentage of 10, 20, and 30 mol% of MMA, for controlled release of low-molecular-weight drugs. By evaluating these carrier systems at environmental conditions, we can observe changes in swelling and pore size of the anionic hydrogel networks as a function of MMA, which was then correlated with the release profiles of the small-molecular-weight drug sodium nitrate. With the correlation of the swelling behavior of the networks and the release profiles, we demonstrated how the expansion of swelling parameters at relevant pH values provides further incite for evaluating for the optimal blend for controlled release. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48767. 相似文献
9.
Mark Breheny Kyle Bowman Nasim Farahmand Ola Gomaa Taj Keshavarz Godfrey Kyazze 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2019,94(7):2081-2091
Microbial fuel cells (MFCs) produce electricity as a result of the microbial metabolism of organic substrates, hence they represent a sustainable approach for energy production and waste treatment. If the technology is to be implemented in industry, low cost and sustainable bioelectrodes must be developed to increase power output, increase waste treatment capacity, and improve service intervals. Although the current application of abiotic electrode catalysts, such as platinum and electrode binders such as Nafion leads to greater MFC performance, their use is cost prohibitive. Novel bioelectrodes which use cost effective and sustainable materials are being developed. These electrodes are developed with the intention to reduce start-up time, reduce costs, extend life-span and improve core MFC performance metrics (i.e. power density, current density, chemical oxygen demand (COD) reduction and Coulombic efficiency (CE)). Comparison of different MFC systems is not an easy task. This is due to variations in MFC design, construction, operation, and different inocula (in the case of mixed-culture MFCs). This high intra-system variability should be considered when assessing MFC data, operation and performance. This review article examines the major issues surrounding bioanode and biocathode improvement in different MFC systems, with the ultimate goal of streamlining and standardising improvement processes. © 2018 Society of Chemical Industry 相似文献
10.
Janam K. Pandya Maryssa DeBonee Maria G. Corradini Mary Ellen Camire David Julian McClements Amanda J. Kinchla 《International Journal of Food Science & Technology》2019,54(12):3196-3204
Tocotrienols are members of the vitamin E family that provide many nutritional benefits. Developing tocotrienol-fortified functional foods introduces vitamin E into consumers diets without changing their food habits. The purpose of this study was to compare the stability of tocotrienols in bulk form and six food matrices at a fixed dose (40 mg kg−1) under accelerated and conventional storage conditions. The delta- and gamma-tocotrienol content was measured using HPLC, and the sensory attributes were evaluated using triangle and hedonic tests. Tocotrienol in bulk powder was less stable under stressed conditions than in bulk oil, with the powders having approximately 40% and 80% reduction in δ- and γ- after storage and bulk oil with no significant degradation. HPLC analysis demonstrated that tocotrienol content remained unchanged in dry mix lemonade, yogurt, raw and UHT milk, and margarine over time; however, complete degradation of γ- and partial degradation (up to 50%) of δ-tocotrienol was observed in bread during ambient and stressed storage conditions. A significant decrease in the δ-tocotrienol relative concentration was also observed in HTST processed milk samples. Tocotrienol addition was not perceived, and no significant difference in the product attributes and overall liking was reported in the discrimination sensory testing. 相似文献