全文获取类型
收费全文 | 1582篇 |
免费 | 89篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 5篇 |
综合类 | 16篇 |
化学工业 | 402篇 |
金属工艺 | 14篇 |
机械仪表 | 26篇 |
建筑科学 | 131篇 |
矿业工程 | 22篇 |
能源动力 | 21篇 |
轻工业 | 260篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
武器工业 | 1篇 |
无线电 | 65篇 |
一般工业技术 | 225篇 |
冶金工业 | 284篇 |
自动化技术 | 192篇 |
出版年
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 35篇 |
2020年 | 35篇 |
2019年 | 47篇 |
2018年 | 34篇 |
2017年 | 38篇 |
2016年 | 44篇 |
2015年 | 40篇 |
2014年 | 54篇 |
2013年 | 134篇 |
2012年 | 75篇 |
2011年 | 118篇 |
2010年 | 63篇 |
2009年 | 65篇 |
2008年 | 62篇 |
2007年 | 71篇 |
2006年 | 60篇 |
2005年 | 58篇 |
2004年 | 63篇 |
2003年 | 41篇 |
2002年 | 50篇 |
2001年 | 21篇 |
2000年 | 27篇 |
1999年 | 43篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 32篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1972年 | 6篇 |
1970年 | 6篇 |
1967年 | 5篇 |
排序方式: 共有1674条查询结果,搜索用时 31 毫秒
101.
Davis RH Zhao Y Galvin KP Wilson HJ 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2003,361(1806):871-894
Solid-solid contacts due to microscopic surface roughness in viscous fluids were examined by observing the translational and rotational behaviours of a suspended sphere falling past a lighter sphere or down an inclined surface. In both cases, a roll-slip behaviour was observed, with the gravitational forces balanced by not only hydrodynamic forces but also normal and tangential solid-solid contact forces. Moreover, the nominal separation between the surfaces due to microscopic surface roughness elements is not constant but instead varies due to multiple roughness scales. By inverting the system, so that the heavy sphere fell away from the lighter sphere or the plane, it was found that the average nominal separation increases with increasing angle of inclination of the plane or the surface of the lighter sphere from horizontal; the larger asperities lift the sphere up from the opposing surface and then gravity at large angles of inclination is too weak to pull the sphere back down to the opposing surface before another large asperity is encountered. The existence of microscopic surface roughness and solid-solid contacts is shown to modify the rheological properties of suspensions. For example, the presence of compressive, but not tensile, contact forces removes the reversibility of sphere-sphere interactions and breaks the symmetry of the particle trajectories. As a result, suspensions of rough spheres exhibit normal stress differences that are absent for smooth spheres. For the conditions studied, surface roughness reduces the effective viscosity of a suspension by limiting the lubrication resistance during near-contact motion, and it also modifies the suspension microstructure and hydrodynamic diffusivity. 相似文献
102.
Regional evaporation estimates from flux tower and MODIS satellite data 总被引:10,自引:0,他引:10
Two models were evaluated for their ability to estimate land surface evaporation at 16-day intervals using MODIS remote sensing data and surface meteorology as inputs. The first was the aerodynamic resistance-surface energy balance model, and the second was the Penman-Monteith (P-M) equation, where the required surface conductance is estimated from remotely-sensed leaf area index. The models were tested using 3 years of evaporation and meteorological measurements from two contrasting Australian ecosystems, a cool temperate, evergreen Eucalyptus forest and a wet/dry, tropical savanna. The aerodynamic resistance-surface energy balance approach failed because small errors in the radiative surface temperature translate into large errors in sensible heat, and hence into estimates of evaporation. The P-M model adequately estimated the magnitude and seasonal variation in evaporation in both ecosystems (RMSE = 27 W m− 2, R2 = 0.74), demonstrating the validity of the proposed surface conductance algorithm. This, and the ability to constrain evaporation estimates via the energy balance, demonstrates the superiority of the P-M equation over the surface temperature-based model. There was no degradation in the performance of the P-M model when gridded meteorological data at coarser spatial (0.05°) and temporal (daily) resolution were substituted for locally-measured inputs.The P-M approach was used to generate a monthly evaporation climatology for Australia from 2001 to 2004 to demonstrate the potential of this approach for monitoring land surface evaporation and constructing monthly water budgets from 1-km to continental spatial scales. 相似文献
103.
Abstract. In this journal, Chen and Hirschheim have provided a historical analysis of positivist and interpretivist research paradigms and methodologies in the 10 years following the much cited work of Orlikowski and Baroudi. In this paper, we investigate the mysterious case of the missing paradigm – that of the critical approach to information systems (IS) research. We take Chen and Hirschheim's survey as our starting point and aim to fill the gap left by the absence of the critical paradigm in their analysis and make some criticisms of their method. Recent years have seen the growth of IS research that consciously adopts a critical perspective. This paper charts the development of critical IS research over the period of 1991–2001, adding some comments on more recent developments. We conclude by critically reflecting on the current development of critical research in the field of IS. 相似文献
104.
Bahram Parvin Qing Yang Ju Han Hang Chang Bjorn Rydberg Mary Helen Barcellos-Hoff 《IEEE transactions on image processing》2007,16(3):615-623
Saliency is an important perceptual cue that occurs at different levels of resolution. Important attributes of saliency are symmetry, continuity, and closure. Detection of these attributes is often hindered by noise, variation in scale, and incomplete information. This paper introduces the iterative voting method, which uses oriented kernels for inferring saliency as it relates to symmetry. A unique aspect of the technique is the kernel topography, which is refined and reoriented iteratively. The technique can cluster and group nonconvex perceptual circular symmetries along the radial line of an object's shape. It has an excellent noise immunity and is shown to be tolerant to perturbation in scale. The application of this technique to images obtained through various modes of microscopy is demonstrated. Furthermore, as a case example, the method has been applied to quantify kinetics of nuclear foci formation that are formed by phosphorylation of histone gammaH2AX following ionizing radiation. Iterative voting has been implemented in both 2-D and 3-D for multi image analysis. 相似文献
105.
Joseph G. Davis E. Subrahmanian Suresh Konda Helen Granger Michael Collins Arthur W. Westerberg 《Information Systems Frontiers》2001,3(3):377-392
The provision of computer support for collaborative work is a central concern for Information Systems (IS) research and practice. In this paper we present the details of an information flow study undertaken in the household division of a large European design and manufacturing company (Delta). The goal of the study was to elicit user requirements for a computer system to facilitate the collaborative work of new product design teams. These requirements form the basis for the design and development of a Web-based LIRÉ (Living Repository) prototype system, the functionalities, features, and rationale of which are discussed. We also present the results of the evaluation of LIRÉ by the users at Delta and our observations on enhancing the sophistication and usefulness of this class of system. A production version based on the prototype but using commercially available software is currently in use by the New Product Development group at Delta. 相似文献
106.
Jorge López-Cuevas Howard Jones Helen V. Atkinson 《Journal of the American Ceramic Society》2000,83(12):2913-2918
The sessile drop method has been used to determine the time dependence of the contact angle at 850°C in vacuo for Ag–28 wt% Cu, Ag–35 wt% Cu–1.5 wt% Ti, and Ag–27 wt% Cu–12 wt% In–2 wt% Ti on vitreous and devitrified fused quartz substrates. Nonwetting behavior (θ > 90°) was observed for Ag–28 wt% Cu on both substrates with no evident effect of time at temperature. The silica substrate structure, whether crystalline or amorphous, as well as its surface condition, whether smooth or rough, made no significant difference. In contrast, with Ag–35 wt% Cu–1.5 wt% Ti and Ag–27 wt% Cu–12 wt% In–2 wt% Ti the contact angle continuously decreased with time for both silica substrates, and the structure and surface condition of the substrates had a negligible effect in the case of Ag–27 wt% Cu–12 wt% In–2 wt% Ti, which produced essentially the same contact angles on both silica substrates at a given time of hold at 850°C. The contact angles produced by Ag–35 wt% Cu–1.5 wt% Ti on devitrified fused quartz were consistently higher than those produced on the vitreous substrates, with increasing holding time at 850°C. This is attributable to the presence of extensive cracks in the α-cristobalite layer at the surface of the devitrified substrates, which obstruct wetting and spreading. These results, when correlated with the wettability of preoxidized silicon carbide by the same alloys reported in previous work, could account for the adverse effect on wetting of the high-temperature silica films formed on the surface of the SiC in that work. 相似文献
107.
E. A. Essock, W. K. Krebs, and J. R. Prather (1997) found that detection of grid patterns by the fingers was best for longitudinal, then oblique, and, last, horizontal orientations. They suggested that the anisotropy is due to the number of cortical neurons tuned to a stimulus orientation. The contribution of E. H. Weber (1834/1996) deserves mention. He found that the 2-point threshold on the arm was lower for horizontal than for longitudinal orientations. He (1852/1965) explained this by elongated "sensory circles"—areas of skin served by single nerve fibers. The elongation followed the axis of the main sensory nerves (longitudinal in the arm). Horizontal acuity was finer because the stimulus interval covered more separate fibers. This account is similar to modern ideas on elongated receptive fields, although the locus is peripheral rather than central. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
Helen F. Nahrung Rachel Waugh Richard Andrew Hayes 《Journal of chemical ecology》2009,35(9):1043-1053
Hybridization is an important biological phenomenon that can be used to understand the evolutionary process of speciation
of plants and their associated pests and diseases. Interactions between hybrid plants and the herbivores of the parental taxa
may be used to elucidate the various cues being used by the pests for host location or other processes. The chemical composition
of plants, and their physical foliar attributes, including leaf thickness, trichome density, moisture content and specific
leaf weight were compared between allopatric pure and commercial hybrid species of Corymbia, an important subtropical hardwood taxon. The leaf-eating beetle Paropsis atomaria, to which the pure taxa represented host (C. citriodora subsp. variegata) and non-host (C. torelliana) plants, was used to examine patterns of herbivory in relation to these traits. Hybrid physical foliar traits, chemical profiles,
and field and laboratory beetle feeding preference, while showing some variability, were generally intermediate to those exhibited
by parent taxa, thus suggesting an additive inheritance pattern. The hybrid susceptibility hypothesis was not supported by
our field or laboratory studies, and there was no strong relationship between adult preference and larval performance. The
most-preferred adult host was the sympatric taxon, although this species supported the lowest larval survival, while the hybrid
produced significantly smaller pupae than the pure species. The results are discussed in relation to plant chemistry and physical
characteristics. The findings suggest a chemical basis for host selection behavior and indicate that it may be possible to
select for resistance to this insect pest in these commercially important hardwood trees. 相似文献
109.
Matthew J. Watson Helen M. Chan Martin P. Harmer Hugo S. Caram 《Journal of the American Ceramic Society》1998,81(8):2053-2060
The reaction-bonded aluminum oxide process begins with aluminum, Al2 O3 , and usually ZrO2 powders that have been attrition-milled in an organic liquid. The attrition-milled powder is then compacted and heat-treated in air to produce polycrystalline, Al2 O3 -based ceramics. Safety considerations have made it desirable for the milling liquid to be changed from acetone to a less-flammable solvent. In this paper, mineral spirits, ethanol, and mineral spirits that contains 2 wt% stearic acid are presented as viable alternatives to acetone. The effects of changing the milling liquid on the reaction process and the properties of the final fired ceramic are investigated. 相似文献
110.
Compton Scott N.; Burns Barbara J.; Egger Helen L.; Robertson Elizabeth 《Canadian Metallurgical Quarterly》2002,70(6):1240
This article reviews the empirical literature on psychosocial, psychopharmacological, and adjunctive treatments for children between the ages of 6 and 12 with internalizing disorders. The aim of this review was to identify interventions that have potential to prevent substance use disorders in adolescence by treating internalizing disorders in childhood. Results suggest that a variety of behavioral, cognitive-behavioral, and pharmacological interventions are effective in reducing symptoms of childhood depression, phobias, and anxiety disorders. None of the studies reviewed included substance abuse outcomes. Thus, little can be said about the relationship between early treatment and the prevention of later substance use. The importance of evaluating the generalizability of research-supported interventions to community settings is highlighted and recommendations for future research are offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献