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71.
Stress-strain curves of single crystals of magnesia compressed in the [100] direction are reported at temperatures from –196° to 1200°C.; curves are also shown for different rates of loading at room temperature. The crystals show considerable ductility at all temperatures and at room temperature can be deformed plastically about 6% before fracture at stresses which are about one-quarter of reported polycrystalline fracture strengths. The macroscopic yield drops apparently exponentially from an extrapolated value of 50,000 lb. per sq. in. at absolute zero to about 4500 lb. per sq. in. at temperatures of 900°C. and higher. Heat-treatment has an appreciable effect on the yield stress. The resistance of the material to deformation increases with the number of slip systems and bands activated because of the barriers to dislocation movements which occur at slip band intersections. At about 2 to 3% strain, stress concentrations begin to be relieved by small internal cracks which are not easily propagated. This effect is extensive before final macroscopic failure of the crystal occurs. Preliminary creep tests above the macroscopic yield stress and in the temperature range 800° to 1000°C. show large instantaneous plastic deformations followed by slow constant-rate creep. 相似文献
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Abstract One method to overcome the notorious efficiency problems of logical reasoning algorithms in AI has been to combine a general-purpose reasoner with several special-purpose reasoners for commonly used subtasks. In this paper we are using Schubert's (Schubert et al. 1983, 1987) method of implementing a special-purpose class reasoner. We show that it is possible to replace Schubert's preorder number class tree by a preorder number list without loss of functionality. This form of the algorithm lends itself perfectly towards a parallel implementation,1 and we describe design, coding and testing of such an implementation. Our algorithm is practically independent of the size of the class list, and even with several thousand nodes learning times are under a second and retrieval times are under 500 ms. 相似文献
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基于天然砂分计筛余百分率,采用再生细骨料按照0~0.315 mm、0~0.63 mm、0~1.25 mm、0~2.5 mm和0~5.0 mm不同粒级逐级取代天然砂制作再生砂浆,测定其在0.55、0.60、0.65水灰比下7d、14d和28 d的抗折抗压强度和微观形貌.试验结果表明:再生砂浆试件的抗折抗压强度均大于空白试件,且随着再生细骨料逐级取代率的提高而增大;当再生细骨料100%逐级取代天然砂时,龄期为14 d时的再生砂浆的强度增长最大;28 d时,再生砂浆抗压强度的降低幅度随着水灰比的增加而增加,但抗折强度的降低幅度却随着水灰比的增加而减小;随水化龄期的增加,再生砂浆中水化产物不断增多,界面过渡区越来越密实. 相似文献
75.
MELINDA J. SEMON CHARLES G. EDWARDS DAVID FORSYTH CO DINN 《Australian Journal of Grape and Wine Research》2001,7(1):52-59
Malolactic fermentations (MLF) were induced in a commercially prepared Washington State Chardonnay must to evaluate the influence of timing of inoculation and pre-culture conditions of Oenococcus oeni strains MCW, EQ-54, and WS-8. The must (pH 3.62, 21.5°Brix) was divided into lots and inoculated with Saccharomyces cerevisiae strain CY3079. Strains of O. oeni were pre-cultured by growing in diluted juice or by re-hydration of freeze-dried strains. Bacteria were inoculated into the musts before (Day 0) or after completion of the alcoholic fermentation (Day 22). Yeast populations exceeded 107 cfu/mL in all fermentations that proceeded to dryness. However, the viability of most strains of O. oeni quickly declined after inoculation regardless of the timing of inoculation or the strain used. MLF was induced in the wines inoculated with strains EQ-54 and WS-8 but not with MCW, and the rate depended on the time of inoculation. The method used to prepare bacterial starter cultures had no apparent influence on the completion of MLF. Values for volatile acidity were slightly higher (P< 0.05) in wines inoculated with O. oeni before alcoholic fermentation compared with those inoculated after alcoholic fermentation. 相似文献
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CHARLES A. SANTO 《Journal of Urban Affairs》2007,29(5):455-479
ABSTRACT: A host of empirical studies have indicated that stadiums and arenas have no significant impact on metropolitan area income or employment. In light of this evidence, the continued proliferation of public investment in sports facilities begs the question: Is there some other justification for this spending, or are policymakers simply acting against the public interest (either irrationally, or in response to political‐economic influences)? A possibility that has not been fully explored is the notion that stadiums and teams generate tangible and intangible consumption benefits that could support some level of public investment. This research builds on a small foundation of literature that is moving discussion beyond the economic catalyst debate by providing an empirical measure of the consumption benefits that accrue to a region as the result of hosting a major league sports team. A contingent valuation survey is used to quantify the consumption benefits that would be associated with the relocation of a major league baseball team to Portland, Oregon. An empirical measure of the region's aggregate willingness to pay for the benefits associated with hosting a team is disaggregated into option and existence values, which can then be compared to any proposed level of public contribution to a new stadium. The findings indicate that consumption benefits would only support a capital investment of approximately $74 million; a figure far smaller than the typical stadium subsidy. The majority of projected benefits are associated with expected public goods and externalities, rather than anticipated attendance, indicating that an equitable financing plan should employ nonuser revenue sources. The level of projected benefits does not vary by locality within the metropolitan area, which argues for a regional cost‐sharing approach. The willingness of residents to pay for stadium construction is tempered by a concern about other pressing social needs in the Portland area and a reaction to the current tax climate. 相似文献
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JEFFRI C. BOHLSCHEID XIAO-DONG WANG D. SCOTT MATTINSON CHARLES G. EDWARDS 《Journal of food quality》2006,29(1):1-15
A modified headspace solid phase microextraction (HS‐SPME) method was compared with Amberlite® XAD‐2 resin for the extraction of volatile compounds. In the HS‐SPME method, volatiles were extracted using an 85 μm polyacrylate fiber from wines that contained a standardized amount of ethanol (10% v/v), NaCl (0.325 g/mL) and internal standards (dodecanol and nonanoic acid). Both extraction procedures yielded high relative recoveries (>92%) and reproducibilities (coefficient of variations ≤ 11%) for the different higher alcohols, esters and medium‐chain fatty acids. Overall, limits of detection for the HS‐SPME and XAD‐2 methods were below sensory threshold concentrations. HS‐SPME and XAD‐2 performed similarly in the analysis of a Riesling wine; however, the HS‐SPME method did not require organic solvents and was generally quicker to perform. In applying the HS‐SPME method, differences in concentrations of volatile compounds produced in Riesling and Chenin blanc wines by 11 different yeast strains were noted. 相似文献