全文获取类型
收费全文 | 401篇 |
免费 | 9篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 54篇 |
金属工艺 | 7篇 |
机械仪表 | 4篇 |
建筑科学 | 12篇 |
矿业工程 | 3篇 |
能源动力 | 24篇 |
轻工业 | 16篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 34篇 |
一般工业技术 | 113篇 |
冶金工业 | 108篇 |
自动化技术 | 27篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 17篇 |
2012年 | 13篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 18篇 |
2008年 | 8篇 |
2007年 | 23篇 |
2006年 | 6篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 10篇 |
2001年 | 13篇 |
2000年 | 4篇 |
1999年 | 15篇 |
1998年 | 27篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1949年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有410条查询结果,搜索用时 15 毫秒
1.
Skim and whole milk powders were manufactured at lab scale by spray freeze drying (SFD), using liquid nitrogen as the cryogen. The polydispersity of droplet/particle sizes was limited using an encapsulator nozzle to atomize the feed. Particle morphology was examined using a scanning electron microscope. Samples were compared with equivalent spray-dried powders in tests of wettability and dissolution in water. The spray freeze-dried powders were found to be highly porous, with a uniform structure of pores throughout the entire particles. When tested in water, SFD skim milk powders wetted roughly three times as fast as industrially spray-dried agglomerated skim milk powders and were observed to dissolve rapidly by breaking down into smaller particles. 相似文献
2.
The results of study of the effects of yttria stabilization (0–6 mol.%) on the room-temperature fracture behavior and toughening mechanisms in zirconia-reinforced MoSi2 are presented in this paper. Transformation toughening is shown to occur only in composites reinforced with zirconia particles stabilized with 2 mol.% yttria. However, the fracture toughness levels are comparable in the other composites with yttria levels between 0 and 6 mol.%. Toughening in the other composites is attributed to the combined effects of residual stress, microcrack shielding/anti-shielding and/or crack deflection. A rigorous micromechanics-based model is presented for the estimation of residual stress levels in brittle materials reinforced with phases that can transform during cooling or under stress. The model is applied successfully to the rationalization of the observed fracture and toughening phenomena. 相似文献
3.
Developing competency-based methods for near-real-time air combat problem solving assessment 总被引:1,自引:0,他引:1
Air combat scenarios present unique problems where the solution is not obvious. An advanced networked simulation environment can be used to train high-level cognitive air combat skills such as problem solving. A problem in the development of principled and construct oriented assessment is related to determining the level of specificity of the assessment. We present a detailed discussion of the definition of critical competencies associated with combat mission problem solving performance, and we describe our approach to develop and implement an embedded performance assessment system that maps outcomes to these competencies. Finally, we discuss the implications for our approach for comprehensive assessment and discuss our goals for an evaluation of the competency-based approach to assessment. 相似文献
4.
This paper examines the current status and methodologies of study of material and system reliability in Microelectromechanical Systems (MEMS). This includes: a review of the current literature in the area of MEMS regarding failure analysis experimental investigations; testing methods and philosophies for material characterization and possible mechanistic analytical solutions for estimating material properties. The paper proposes a reliability framework that encompasses all the available information. This statistical platform will enable the MEMS design engineer to distill all the available information in the literature into a stand-alone semi-empirical material reliability model, and a holistic system-level model for a complete system. 相似文献
5.
K. T. Venkateswara Rao W. O. Soboyejo R. O. Ritchie 《Metallurgical and Materials Transactions A》1992,23(8):2249-2257
A study has been made of the role of ductile-phase toughening on the ambient temperature fracture toughness and fatigue-crack
propagation behavior of a molybdenum disilicide intermetallicmatrix composite reinforced with 20 vol pct niobium spheres.
Using disk-shaped compact DC(T) samples, only moderate improvements (∼24 pct) in fracture toughnessK
lcvalues were found for the composite compared to the unreinforced MoSi2 matrix material. Moreover, (cyclic) fatigue- crack propagation was seen at stress intensities as low as 75 to 90 pct ofK
Ic, with growth rates displaying a high dependency (∼14) on the applied stress-intensity range. The lack of significant toughening
due to the incorporation of ductile Nb particles is associated with an absence of crack/particle interactions. This is attributed
to the formation of a weak reaction-layer interface and elastic mismatch stresses at the crack tip between the Nb and MoSi2, both factors which favor interfacial debonding; moreover, the spherical morphology of Nb phase stabilizes cracking around
the particle. Results suggest that increasing the aspect ratio of the distributed Nb rein- forcement phase with attendant
interfacial debonding and eliminating possible Nb-phase em- brittlement due to interstitial impurity contamination are critical
factors for the successful development of tougher Nb/MoSi2 structural composites.
Formerly with McDonnell
Formerly with McDonnell 相似文献
6.
An investigation of crack closure and the propagation of semi-elliptical fatigue cracks in Q1N (HY80) pressure vessel steel 总被引:1,自引:0,他引:1
The results of an experimental investigation of the effect of crack closure on the propagation of semi-elliptical fatigue cracks are presented. Load-shedding fatigue threshold tests were carried out at stress ratios of 0.2, 0.35, 0.5 and 0.7. Crack closure was measured at the surface and depth positions using backface strain gauges, near-tip gauges, and a clip gauge. Differences between the surface and depth growth behaviour are explained by considerations of the effects of the transition from plane stress conditions at the surface to plane strain conditions at the depth. The effects of stress ratios are attributed largely to differences in the crack opening displacement, which result in asperities coming into contact to induce roughness-induced crack closure. 相似文献
7.
A dimensional analysis based on four parameters has been developed previously to predict injection pressure; clamp force, and bulk temperature for the injection molding of amorphous materials in center-gated disk-shaped cavities. In this paper geometric and semicrystalline-materials approximations are introduced and tested for extending the previous analysis to include multigated thin cavities and semicrystalline materials. The combination of these approximations and the previous analysis, known hereafter as the Radial Flow Method (RFM), greatly simplifies the analysis of mold filling. The geometric approximation, which is based on a simple model for the axial stress distribution in the cavity, is shown to give reasonable predictions when compared with experimental data and a numerical two-directional flow simulation for the filling of an off-center-gated rectangular cavity with acrylonitrilebutadiene-styrene copolymer (ABS). The semicrystallinematerials approximation, in which heat capacity and viscosity changes during crystallization are neglected, is shown to give good agreement with experimental data for the filling of a center-gated disk-shaped cavity with polypropylene. As an illustration, the Radial Flow Method is used to analyze the molding of a large, thin-wall automobile interior trim panel. The inlet melt temperature, mold-wall temperature, part thickness, injection rate, viscosity and gate locations are varied in a series of calculations to determine the relative effectiveness of these variables in lowering the injection pressure and Clamp force. The results obtained with the Radial Flow Method are in good agreement with those obtained by a finiteelement simulation of two-directional flow. 相似文献
8.
Background
Leptin and its soluble receptor (sOB-R) are important to regulation of body composition but there are no data on the developmental variations in these plasma variables and their relationship with body composition measurements, 相似文献9.
T. Pankiw M. L. Winston E. Plettner K. N. Slessor J. S. Pettis O. R. Taylor 《Journal of chemical ecology》1996,22(4):605-615
The composition of the five-component honey bee queen mandibular gland pheromone (QMP) of mated European honey bee queens was compared to those of virgin and drone-laying (i.e., laying only haploid unfertilized eggs that develop into males), European queens and Africanized mated queens. QMP of mated European queens showed significantly greater quantities of individual components than all queen types compared, except for a significantly greater quantity of 9-hydroxy-(E)-2-decenoic acid (9-HDA) found in Africanized queens. Glands of European drone-laying queens contained quantities intermediate between virgin and mated queens, reflecting their intermediate reproductive state and age. QMP ontogeny shifts from a high proportion of 9-keto-(E)-2-decenoic acid (ODA) in young unmated queens to roughly equal proportions of ODA and 9-HDA in mated queens. A biosynthetic shift occurs after mating that results in a greater proportion of 9-HDA, methylp-hydroxybenzoate (HOB), and 4-hydroxy-3-methoxyphenylethanol (HVA) production, accompanied by a decreased proportion of ODA. Africanized QMP proportions of ODA and 9-HDA were significantly different from European queens. A quantitative definition of a queen equivalent of QMP is proposed for the various queen types, and a standard queen equivalent for mated European honeybee queen mandibular gland pheromone is adopted as 200µg ODA, 80µg 9-HDA, 20µg HOB, and 2 µg HVA. 相似文献
10.
The business value of information technology as measured by technical efficiency: Evidence from country-level data 总被引:1,自引:0,他引:1
The value of information technology (IT) in a business production process has long been a debatable issue. Explanation of the so-called “productivity paradox” has been one of the central topics in this arena. Much work has focused on firm-level analyses. This paper investigates IT contribution at a country level, using production theory in microeconomics. It negates the relationship between IT value and productivity based on grouping of countries, when the individual analytical method is applied and technical efficiency is used as the performance criterion. Findings obtained by applying stochastic production frontiers to a comprehensive country-level panel data set suggest that the IT contributions, as determined by the increase or decrease in the technical efficiency, to individual countries differ in magnitude from a production frontier to another, but are robust. It also shows that IT spending does not necessarily improve technical efficiencies of individual countries, regardless of whether they are developed or developing countries, and that given technological changes, the so-called productivity paradox may exist in a country, no matter whether it is a developed or developing nation. Finally, the significant implications of the findings are presented. 相似文献