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71.
Modern high performance adhesives are designed to offer an optimized balance of elasticity,toughness and plastic deformation capacity for the individual fields of application in e.g. the building and construction or transportation and vehicle industry. The long-term life prediction for adhesive joints based on laboratory tests requiring only days,weeks,or months is still a demanding challenge. Testing in practice is carried out with the intention of accelerating time dependent aging effects that may occur in a bonded joint during its service time. Initial strength values of bonded joints,such as shear or peel properties can often be obtained from the adhesive manufacturers or retrieved from literature. They are useful to compare different adhesives and to demonstrate the effect of parameters such as bond line thickness,overlap length or curing conditions,and,in some cases,the surface state. On the other hand only few data are available describing the mechanical long-term properties of adhesives related to creep and relaxation under static load conditions. Due to the nature of the polymer network of organic adhesives their viscoelastic-plastic deformation behavior is strongly time-and temperature dependent. The objective of this paper is to illustrate effective methods for investigating and predicting the creep and relaxation properties of adhesively bonded joints in the long-term region and for creating basic data for the design and engineering with adhesives. 相似文献
72.
MICROALGAE AS A SOURCE OF FATTY ACIDS 总被引:2,自引:0,他引:2
Microalgae are a very diverse group of organisms that consist of both prokaryotic and eukaryotic forms. Although most microalgae are phototrophic, some species are also capable of heterotrophic growth. Some species of microalgae can be induced to overproduce particular fatty acids through simple manipulations of the physical and chemical properties of the culture medium. As a result of the profound differences in cellular organization and growth modes and the ability to manipulate their fatty acid content, microalgae represent a significant source of unusual and valuable lipids and fatty acids.
The utilization of microalgal lipids and fatty acids as food components requires that these organisms be grown at large scale under controlled conditions. Several growth systems have been developed for large scale growth of phototrophic microalgae using either natural sunlight or artificial light, but their lack of control of culturing parameters or their high cost of operation have limited their utility for the production of food products. Instead, large scale cultivation of heterotrophic microalgae using classical fermentation systems provides consistent biomass produced under highly controlled conditions at low cost.
Microalgae contain many of the major lipid classes and fatty acids found in other organisms. However, they are also the principal producers in the biosphere of some polyunsaturated fatty acids, especially docosahexaenoic acid (DHA). The high DHA content found in some algae is currently being utilized to supplement infant formula to enable it to more closely resemble human breast milk. Thus, the commercialization of DHA from microalgae demonstrates the value of these organisms as a source of useful fatty acids. 相似文献
The utilization of microalgal lipids and fatty acids as food components requires that these organisms be grown at large scale under controlled conditions. Several growth systems have been developed for large scale growth of phototrophic microalgae using either natural sunlight or artificial light, but their lack of control of culturing parameters or their high cost of operation have limited their utility for the production of food products. Instead, large scale cultivation of heterotrophic microalgae using classical fermentation systems provides consistent biomass produced under highly controlled conditions at low cost.
Microalgae contain many of the major lipid classes and fatty acids found in other organisms. However, they are also the principal producers in the biosphere of some polyunsaturated fatty acids, especially docosahexaenoic acid (DHA). The high DHA content found in some algae is currently being utilized to supplement infant formula to enable it to more closely resemble human breast milk. Thus, the commercialization of DHA from microalgae demonstrates the value of these organisms as a source of useful fatty acids. 相似文献
73.
HELEN A. GRUBER PAUL L. KRONICK PETER R. BUECHLER MARY V. HANNIGAN 《Journal of food science》1990,55(6):1506-1509
Collagen, elastin and residual actomyosin in connective tissue of some lower grades of beef were determined from the contents of hydroxy-proline, valine and glutamic acid, using three simultaneous equations based on amounts of these amino acids found in the pure proteins. The complete amino-acid profiles of the connective tissues agreed with the calculated protein compositions. Connective tissues were removed from the meat by dissection, and sequential saline extractions removed sarcoplasmic and myofibrillar proteins. Glycoproteins were removed by extraction with half-saturated calcium hydroxide; collagen, by autoclaving. Changes in composition after extraction or au-toclaving were confirmed by histological investigations. 相似文献
74.
PAUL WHYTE JOHN DANIEL COLLINS KEVINA McGILL CLAIRE MONAHAN 《Journal of Food Safety》2002,22(1):55-65
Commercial immersion chilling systems used in poultry processing are a major source in the cross-contamination of carcasses with pathogenic microorganisms. In the current study, the efficacy of a chlorine based bactericidal compound, sodium dichloroisocyanurate (NADCC), to control contamination between carcasses was compared to the more traditional sodium hypochlorite solutions in a simulated carcass immersion chilling system. The addition of either sodium dichloroisocyanurate or sodium hypochlorite to the immersion chill tank water at concentrations of 50 ppm or more significantly reduced total aerobic mesophilic (37C) and psychrophilic (22C) counts when compared to corresponding untreated water samples in which dressed broiler carcasses had been immersed ( P < 0.01). Both compounds significantly reduced the numbers of fecal coliforms and thermophilic campylobacters in the immersion water samples compared to corresponding control samples ( P < 0.01). In contrast to the control water samples, salmonellae were not detected in immersion water samples treated with either of the chlorine based compounds. 相似文献
75.
INFLUENCE OF GRANULE SIZE ON VISCOSITY OF CORNSTARCH SUSPENSION 总被引:2,自引:0,他引:2
The influence of granule size and size distribution in gelatinized suspensions of 2.6% cornstarch heated at fixed temperatures between 70–90C on the power law viscosity was measured by laser diffraction. In the early stages of gelatinization, where the granule size standard deviation was less than 12 μm, dilatant behavior was observed over the shear rate range 200–1100 S −1 . At constant starch concentration and without granule rupture, suspension consistency, K, increased exponentially with granule mean diameter while the flow behavior index, n, decreased linearly with increase in the extent of gelatinization and the standard deviation of the granule size. The variation of K with granule size and that of n with standard deviation were found to be independent of temperature over 70–90C. In the later stages of gelatinization, where the granules lose their integrity, suspension viscosity progressively decreased as granule rupture continued. 相似文献
76.
A Kinetic Approach to Food Quality Prediction Using Full-History Time-Temperature Indicators 总被引:2,自引:0,他引:2
A mathematical model based on the theory of chemical kinetics was derived to predict food quality change from the response of a full-history time-temperature indicator. A first-order kinetic reaction (n = 1) was used to describe both indicator response and changes in food quality. A storage investigation of mature green tomatoes showed that the quality prediction model satisfactorily predicted changes in tomato firmness induced by variable temperature storage. Tomato firmness as predicted from the response of a LifeLines model 57 time-temperature indicator was not significantly different from the observed changes (F = 1.99, p = 0.18) for 28 days of storage. The mathematical derivation was extended to develop a quality-based interpretation of the shelf life of perishable foods. 相似文献
77.
Moisture profiles in fried samples of potato starch with different gluten contents were determined during postfrying storage. Over time, moisture migrated from the core to the crust of the sample, and the moisture content of the crust region increased. The addition of gluten caused a significant increase in oil uptake in the crust. The initial hardness of the crust significantly decreased as the gluten content increased to 10 and 30%, during the first 30 min of storage. With longer storage time (> 240 min), the crust hardness tended to increase, due to an increase in firmness of the starch sample. This behavior was less pronounced for samples with 10 and 30% gluten. The range of linear viscoelastic behavior (up to 14% strain) was determined from the initial linear zone of the stress-strain curves. Stress relaxation tests were performed in the linear and nonlinear viscoelastic regions, with a strain level of 5% and 40%, respectively. According to stress relaxation curves, samples became less elastic with the addition of gluten and more elastic with the time of storage. 相似文献
78.
CHARLES R. BARMORE JAMES F. FISHER PAUL J. FELLERS RUSSELL L. ROUSEFF 《Journal of food science》1986,51(2):415-416
Treatment of commercial grapefruit juice with Florisil (activated magnesium silicate) simultaneously reduced the content of citric acid and the bitter compounds limonin and naringin. Ascorbic acid concentration and °Brix (total soluble solids) were not altered by the Florisil treatment. Experienced taste panelists were able to differentiate between the nontreated and Florisil-treated juice on the basis of bitterness and tartness (acidity). The panelists indicated a preference for the Florisil-treated juice. 相似文献
79.
Beef spleens were freed of undesirable capsular and internal connective tissue by passage through a Beehive Model AU 4171 deboner fitted with a desinewing head. The resulting product (called mechanically separated spleen or MSS) was recovered at a 79% yield and contained 17.0% protein, 2.9% fat and 762 ppm iron. The effect of mechanical separation on protein quality was determined by protein efficiency ratio (PER). Rats fed MSS and whole spleen diets exhibited significantly greater weight gains than those fed casein. PER values for whole spleen (2.4) and MSS (2.3) were not significantly different. The PER value for casein (2.5) was significantly higher than that of MSS but not whole spleen. 相似文献
80.
In vitro iron availability (IA) from egg white meals was 14–17% of total meal iron. When mushroom (Agaricus bisporus) was added to egg white meals, IA decreased. The initially low IA from whey protein concentrate meals (<1% of meal iron) was enhanced by mushroom. Sodium benzoate or sodium bisulfite added to egg white/ mushroom meals increased IA. Addition of polyphenoloxidase (PPO) and gallic acid to egg white meals decreased IA; however, gallic acid alone increased IA. Blanching mushrooms eliminated PPO activity and increased IA of egg white/mushroom meals, but it was still less than for egg white meals. Sodium bisulfite added to blanched mushroom/egg white meals increased IA above that for egg white meals. Results are consistent with the interpretation that enzymatic browning can decrease IA. 相似文献