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1.
Microscopic examination of the microstructure and deformation of conventional and auxetic foams 总被引:1,自引:0,他引:1
Auxetic materials have a negative Poisson’s ratio, that is, they expand laterally when stretched longitudinally. One way of
obtaining a negative Poisson’s ratio is by using a re-entrant cell structure. Auxetic foam was fabricated from a conventional
polymeric foam. Assuming similar mechanical properties for the solid material comprising the foams, the principle variable
affecting the properties of the foam is the geometry of the cells. This means that the unusual mechanical properties of auxetic
foams are attributed to the deformation characteristics of re-entrant microstructures. In this paper, the results of optical-
and scanning electron-microscopic studies of the geometrical parameters for the different foams examined are presented. Examples
of the microstructural deformation mechanisms observed are also presented. Comparison between the conventional foams and their
auxetic conversions are also made.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
2.
This study examines whether the patterns of muscle activity measured from the masticatory muscles during a chew are sufficiently reproducible to form the basis of a characterisation of chewing behaviour, and whether they express the degree of variation evident between individuals. Electromyograph (EMG) readings of the repetitive activity involved in chewing gum were analyzed for 10 subjects, each on three separate occasions. For each individual the temporal aspects of the chew cycle (duration of the activity burst, period between bursts of activity and duration of the complete cycle) were reproducible between EMG recording sessions. Consistency was also found for amplitude aspects of the EMG record: mean voltage within the activity burst, maximum voltage, and the area under the EMG trace. For all six parameters there was significant variation between subjects. The study showed that variations in the chewing pattern, as occur for chewing on opposite sides of the mouth, were reflected in the 6 EMG parameters examined, and that the changes elicited were different for each individual. Moreover, encouraging subjects to concentrate on the act of chewing caused them to modify their chewing pattern, highlighting the importance of avoiding such attention when assessing habitual chewing behaviour. 相似文献
3.
ANN M. GUENTERT RABI H. MOHTAR RICHARD H. LINTON MARK TAMPLIN JOHN B. LUCHANSKY 《Journal of food process engineering》2006,29(1):89-117
Listeria monocytogenes grows at refrigeration temperatures (5C or below) and tolerates various environmental stressors. The Food and Drug Administration specifies a zero tolerance for this pathogen in certain ready‐to‐eat processed foods. Modeling its dynamic behavior to fluctuation in temperature at various pH levels is critical to the safety of food. This study presents linear and nonlinear models to predict the behavior of L. monocytogenes in pH‐modified chicken salad at various cold storage and temperature abuse conditions. A linear model of the kinetics accounting for simple and interactive effects of storage time, temperature and pH was developed. Predictions of the linear model were inconsistent with laboratory observations. The limitations of the linear model were reflected in the poor correlation of model predictions to the observed values (r2 = 0.58). A proposed nonlinear model was therefore used to model the observed data. The four model parameters (N(0), Cc(0), kmax and Nres ) were optimized for each of the nine treatments. Correlation coefficient (r2) values ranged from 0.70 (pH 5.2, 7.2C) to 0.99 (pH 4.0, 21.1C), indicating an improved accuracy. Developing a functional and validated microbial predictive model for chicken salad requires further analyses and collection of data at additional pH and temperature values to determine a single set of parameter values that would represent the microbial behavior at the full range of pH and temperatures observed under storage conditions. Future experiments should address the adaptive nature of L. monocytogenes, as the response to environmental stressors affects the survival of the organism in food systems. 相似文献
4.
Defatted field pennycress (Thlaspi arvense L.) seedmeal was found to completely inhibit seedling germination/emergence when added to a sandy loam soil containing wheat (Triticum aestivum L.) and arugula [Eruca vesicaria (L.) Cav. subsp. sativa (Mill.) Thell.] seeds at levels of 1.0% w/w or higher. Covering the pots with Petri dishes containing the soil-seedmeal mixture decreased germination of both species at the lowest application rate (0.5% w/w), suggesting that the some of the phytotoxins were volatile. CH2Cl2, MeOH, and water extracts of the wetted seedmeal were bioassayed against wheat and sicklepod (Senna obtusifolia (L.) H. S. Irwin & Barneby) radicle elongation. Only the CH2Cl2 extract was strongly inhibitory to both species. Fractionation of the CH2Cl2 extract yielded two major phytotoxins, identified by gas chromatography–mass spectrometry and NMR as 2-propen-1-yl (allyl) isothiocyanate (AITC) and allyl thiocyanate (ATC), which constituted 80.9 and 18.8%, respectively, of the active fraction. When seeds of wheat, arugula and sicklepod were exposed to volatilized AITC and ATC, germination of all three species was completely inhibited by both compounds at concentrations of 5 ppm or less. In field studies, where seedmeal was applied at 0.50, 1.25, and 2.50 kg/m2 and tarped with black plastic mulch, all of the treatments significantly reduced dry weight of bioassay plants compared to the tarped control, with the highest seedmeal rate decreasing dry matter to less than 10% of the control 30 d after seedmeal application. Field pennycress seedmeal appears to offer excellent potential as a biofumigant for high-value horticultural crops for both conventional and organic growers.Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable. 相似文献
5.
Toughening by Monoclinic Zirconia 总被引:1,自引:0,他引:1
The toughening induced by monoclinic ZrO2 in the absence of microcracking was investigated, using ZnO as the host material. Toughness levels Kc in excess of the host toughness Kc M were achieved, attaining a peak toughness Kc /Kc M ∼1.7, at monoclinic ZrO2 volume concentrations 0.2. This toughening is attributed to crack/particle interactions, associated with the deflection and bowing of the crack by the residual strain field around the monoclinic ZrO2 particles. 相似文献
6.
Failure Mechanisms in Ceramic-Fiber/Ceramic-Matrix Composites 总被引:2,自引:0,他引:2
Mechanisms of failure in a unidirectional Sic-fibe/glass-ceramic composite are investigated using in situ observations during tensile and flexural loading. These experiments show that failure in tension occurs in several stages (similar to certain other brittle fiber composites): multiple matrix cracking, followed by fiber fracture and pullout. In flexural loading the failure process is more complex. Consequently, the flexural test cannot be used for measurement of tensile strength (although it can be used for measurement of the stress for matrix cracking). The application of conventional fracture mechanics to describe tensile failure is discussed. The in situ observations provide direct indication of the importance of frictional bonding between the matrix and fibers. Some novel methods for measuring the frictional forces and residual stresses are investigated, and the influence of surface damage on strength is assessed. 相似文献
7.
P. E. EVANS 《Journal of the American Ceramic Society》1970,53(7):365-369
Compression creep measurements at constant load on ZrO2 -6 mol% Sc2 O3 (grain size ∼1 μm), ZrO2 -6 mol% Y2 O3 (grain size ∼17 μm), and heat-treated ZrO2 -6 mol% Sc2 O3 (grain size ∼2 μm) yield activation energies of 89, 86, and 74 kcal/mol, respectively. The creep rates are linearly proportional to the inverse square of the grain size of the material. A stress exponent, n , of 1.5 was found for the scandia-doped zirconia and two regimes, with n =1 and 6, were found for the yttria-doped zirconia. These data, supported by metallographic evidence, are interpreted as showing that n =1 is associated with cation diffusion control of creep, n =6 with local propagation of inter-crystalline cracks, and n =1.5 with a transition region. 相似文献
8.
Sectioning vitrified cells and tissues for cryo‐electron microscopy is more challenging than room‐temperature sectioning of plastic‐embedded samples. As the sample must be kept very cold (130 °C) and because there is no liquid upon which the sections can float as they are cut, transferring the sections from the knife edge to a grid is one of the more difficult steps in the process. We employed a micromanipulator to hold and control the cryo‐sections as they come off the knife. This allows slower cutting speeds than are typically used in vitreous cryo‐sectioning and contributes to better control during cutting, which facilitates repeatable placement of a ribbon of sections onto a grid. The ribbon is kept under tension during the entire cutting process, which may decrease folding and/or compression, features that are inherent to vitreous sections. Furthermore, the added control afforded by this technique makes it easier for multiple ribbons to be placed on a single grid, thereby increasing the number of sections that can be examined and imaged during a microscopy session. It even allows for serial cryo‐electron microscopy. As such, this approach is an advance in the cryo‐microtomy of vitreous sections. 相似文献
9.
This paper attempts to give a brief overview of the concept of design for environment (DfE) as part of the concurrent engineering philosophy. DfE includes designing for recyclability, reuseability, durability, and maintainability. DfE also promotes the reduction of energy consumption and product emissions as a means of environmental consciousness. As part of this research into DfE, five Hunter Valley–based Australian businesses were used as case studies in an attempt to discover what role DfE plays in local Australian industry. 相似文献
10.
A sub-tropical intertidal wetland in Moreton Bay, Queensland, Australia (27°52'S, 153° 23'E) was physically modified in 1985 to manage a mosquito breeding problem. Monitoring before and after modification was done using field and remote sensing techniques. Images from large scale colour infrared aerial photography were analysed to evaluate impacts of the modification. Analysis was by subtracting and classifying digitized images taken before and after modification. The resulting ‘difference type images’ showed the types of change and their nature. These images indicated also the spatial extent of the changes. The site has become wetter as a result of increased tidal flushing, indicated by reduced spectral values. The area modified has changed less than the adjacent mangrove inlet which floods the area. Mangroves have increased in size and spatial extent, with increased spectral values generally. The changes are consistent with reported mangrove changes in other local areas and thus are unlikely to be a direct effect of runnelling. 相似文献