全文获取类型
收费全文 | 480篇 |
免费 | 24篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 198篇 |
金属工艺 | 8篇 |
机械仪表 | 12篇 |
建筑科学 | 10篇 |
矿业工程 | 4篇 |
能源动力 | 17篇 |
轻工业 | 98篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 9篇 |
一般工业技术 | 85篇 |
冶金工业 | 17篇 |
自动化技术 | 35篇 |
出版年
2023年 | 12篇 |
2022年 | 23篇 |
2021年 | 35篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 11篇 |
2014年 | 26篇 |
2013年 | 32篇 |
2012年 | 43篇 |
2011年 | 44篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 21篇 |
2007年 | 13篇 |
2006年 | 17篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有504条查询结果,搜索用时 15 毫秒
101.
102.
The author examined relations among demographic risk (income, maternal education, single-parent status), growth in temperament (fear, irritability, effortful control), and parenting (rejection, inconsistent discipline) across 3 years and the prediction of children's adjustment problems in a community sample (N=190; ages 8-12 years at Time 1). Family income was related to higher initial levels of fear, irritability, rejection, and inconsistency and lower effortful control but was not related to changes in these variables. Higher initial rejection predicted increases in child fear and irritability. Higher initial fear predicted decreases in rejection and inconsistency. Higher initial irritability predicted increases in inconsistency, and higher initial effortful control predicted decreases in rejection. When growth of parenting and temperament were considered simultaneously, increases in effortful control and decreases in fear and irritability predicted lower Time 3 internalizing and externalizing problems. Increases in rejection and inconsistent discipline predicted higher Time 3 externalizing, although sometimes the effect appeared to be indirect through temperament. The findings suggest that temperament and parenting predict changes in each other and predict adjustment during the transition to adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
A simple procedure is developed for the selection of pultruded structural shapes to be used as beam-columns in structural design. The design equations are then validated by comparison with experimental data gathered during beam-column testing of wide-flange and I-beam pultruded structural shapes. The design procedure accounts for axial load eccentricity and bending action induced by lateral loads and end-moments. The design equations are set in the context of load and resistance factor design, considering both strength and serviceability. This paper addresses the methodology to determine the resistance factors, which should be used with properly selected load-factors accounting for the variability and uncertainty of the loads. The design equations use section-properties, such as the bending stiffness (EI), which must be measured and supplied by industry. It is found that the section-properties used in the design of beams and columns are sufficient for the design of beam-columns. Therefore, the cost and time involved in testing structural shapes are minimized. This paper also addresses the means by which section-properties can be generated effectively and inexpensively. 相似文献
104.
María P. Albano Liliana B. Garrido 《Journal of Materials Synthesis and Processing》2002,10(4):211-218
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. 相似文献
105.
Schottky diodes were built on different polycrystalline diamond films grown by Microwave Plasma and Hot Filament Chemical Vapor Deposition and their electrical properties were studied. The barrier height increased with the diamond film quality and the corresponding ideality factor decreased. Even though the lower-quality HFCVD film displayed poor rectifying properties, it was found to be much less sensitive to variations in the operating conditions (air vs. vacuum). The activation energies of the films depend on morphological parameters, as preferable grain size or orientation. The bulk conduction also depends on the quality of the deposited films, changing from ohmic to trap-free or shallow trap SCLC and SCLC with an exponential distribution of traps. The hypothesis of using the electrical measurements as an indicator for film quality has been discussed. 相似文献
106.
Aqueous tape casting of yttria stabilized zirconia 总被引:2,自引:0,他引:2
Tape casting process was used to produce yttria stabilized zirconia (YSZ) substrates in an aqueous system with poly(vinylalcohol) (PVA) and glycerine as binder and plasticizer, respectively. Various compositions of YSZ slips with different amounts of PVA and glycerine and consequently different solid/liquid ratios were prepared. The influence of the slip composition on the rheological properties of the slips was studied. In addition, the effect of the slip composition on the properties of the green and sintered tapes was investigated. PVA and glycerine did not affect the dispersion properties of the YSZ powder. Glycerine additions enhanced the flexibility of the green tapes but also produced a decrease in the tensile strength. The increase in the PVA content increased the tensile strength but resulted in a markedly decrease in the green density of the tapes. A correlation between the green and sintered density was found. The anisotropic sintering shrinkage parallel and perpendicular to the casting direction increased with increasing the PVA content. The slip compositions with 5 wt% PVA produced green tapes with satisfactory tensile strength. They had the highest sintered density, the lower sintering shrinkage and the lesser shrinkage anisotropy. 相似文献
107.
Diogo A. B. Fernandes Liliana F. B. Soares João V. Gomes Mário M. Freire Pedro R. M. Inácio 《International Journal of Information Security》2014,13(2):113-170
In the last few years, the appealing features of cloud computing have been fueling the integration of cloud environments in the industry, which has been consequently motivating the research on related technologies by both the industry and the academia. The possibility of paying-as-you-go mixed with an on-demand elastic operation is changing the enterprise computing model, shifting on-premises infrastructures to off-premises data centers, accessed over the Internet and managed by cloud hosting providers. Regardless of its advantages, the transition to this computing paradigm raises security concerns, which are the subject of several studies. Besides of the issues derived from Web technologies and the Internet, clouds introduce new issues that should be cleared out first in order to further allow the number of cloud deployments to increase. This paper surveys the works on cloud security issues, making a comprehensive review of the literature on the subject. It addresses several key topics, namely vulnerabilities, threats, and attacks, proposing a taxonomy for their classification. It also contains a thorough review of the main concepts concerning the security state of cloud environments and discusses several open research topics. 相似文献
108.
Comment on “The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric‐Dielectric System” 下载免费PDF全文
A comparison between 2D and 3D Finite Element Method based simulations on the tunability properties of ferroelectric – linear dielectric composites is presented. Dependences of the effective permittivity and tunability on the concentration of the linear phases are presented and it is shown that there are important differences between the two approaches. The appropriateness of such simulations in describing realistic composite systems is discussed, too. 相似文献
109.
Nunzia La Maida Manuela Pellegrini Esther Papaseit Clara Prez-Ma Lourdes Poyatos Mireia Ventura Liliana Galindo Francesco Paolo Busard Simona Pichini Magí Farr Emilia Marchei 《International journal of molecular sciences》2020,21(24)
The consumption of synthetic cannabinoids (SCs) has significantly increased in the last decade and the analysis of SCs and their metabolites in human specimens is gaining interest in clinical and forensic toxicology. A pilot study has been carried out using a combination of an initial last generation gas chromatography-mass spectrometry (GC-MS) screening method for the determination of JWH-122, JWH-210, UR-144) in oral fluid (OF) of consumers and an ultra-high performance liquid chromatography high resolution mass spectrometry (UHPLC-HRMS) confirmatory method for the quantification of the parent compounds and their metabolites in the same biological matrix. OF samples were simply liquid-liquid extracted before injecting in both chromatographic systems. The developed methods have been successfully validated and were linear from limit of quantification (LOQ) to 50 ng/mL OF. Recovery of analytes was always higher than 70% and matrix effect always lower than 15% whereas intra-assay and inter-assay precision and accuracy were always better than 16%. After smoking 1 mg JWH-122 or UR-144 and 3 mg JWH-210, maximum concentration of 4.00–3.14 ng/mL JWH-122, 8.10–7.30 ng/mL JWH-210 ng/mL and 7.40 and 6.81 ng/mL UR-144 were measured by GC-MS and UHPLC-HRMS respectively at 20 min after inhalation. Metabolites of JWH 122 and 210 were quantified in OF by UHPLC-HRMS, while that of UR144 was only detectable in traces. Our results provide for the first time information about disposition of these SCs and their metabolites in consumers OF. Last generation GC-MS has proven useful tool to identify and quantify parent SCs whereas UHPLC-HRMS also confirmed the presence of SCs metabolites in the OF of SCs consumers. 相似文献
110.
Roberto Fanigliulo Paolo Bondioli Laura Fornaciari Liliana Folegatti Renato Grilli Stefano Benigni Igor Calderari Daniele Pochi 《European Journal of Lipid Science and Technology》2021,123(12):2100116
This paper aims at investigating the possibility of replacing conventional hydraulic fluids with refined olive pomace oil added with a common food grade antioxidant, as hydraulic fluid for agricultural machinery. The fluid efficiency test is carried out using an experimental test rig based on a hydraulic system designed to apply severe work cycles (pressure values up to 40 MPa; temperatures up to 100 °C) to small oil volumes with the aim of strongly accelerating the ageing of the tested fluid. The fluid, added with 2 g kg−1 of antioxidant, apparently does not undergo any changes in chemical-physical properties and maintains stable the technical performance of the test equipment during 530 h work cycle. This research has four different goals: i) to contribute to the circular economy, by using olive oil byproducts in agricultural environment; ii) to contribute to the reduction of environmental contamination by substituting petroleum products with natural biodegradable ones; iii) to contribute to avoid the presence of mineral products (such as saturated hydrocarbons, which could accumulate in human organs, and aromatic hydrocarbons, which are potentially genotoxic), as a residue in food products and in vegetable oils. iv) to identify alternative market possibilities for such a by-product. Practical applications : The results of the study seem to indicate the possibility of using the olive pomace oil as hydraulic fluid, for example, in agricultural machinery, opening new market perspectives which would increase its added value. 相似文献