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31.
Norbert J. M. Kuipers Antonie A. C. M. Beenackers 《Polymer Engineering and Science》1996,36(16):2108-2118
A mathematical model is presented for non-Fickian diffusion of a penetrant A into a granular glassy polymer containing a reactive group B, resulting in the desired product P. Further, both a consecutive reaction between A and P (producing X) and a parallel reaction between A and C (producing Y) are incorporated, with C initially present in the particle. The swelling of the polymer, induced by the penetrant, is described by power-law kinetics for the velocity of the swelling front. Kinetics are considered to be first order in each of the two reactants. Concentration profiles in the particle and selectivity to desired product are calculated as function of the swelling behavior of the polymer grain. In case of a consecutive reaction the local concentration of P reaches a maximum value independent of the swelling rate. However, the position of the maximal concentration of P moves towards the center of the grain with a rate depending on the kinetics of swelling. For Case II diffusion this velocity equals the velocity of the advancing front between glassy and rubbery polymer. The selectivity of the desired reaction decreases with decreasing swelling rate. A low swelling rate also results in an inhomogeneous product distribution within the granule. A criterion is derived predicting under what conditions the consecutive reaction can be neglected and a pure product is obtained. The analysis further reveals that both a more homogeneous product and a higher selectivity toward a desired product can be obtained by realizing preswelling of the polymer with an inert swelling agent. For Case II diffusion the concentration profiles of the side product of the parallel reaction, Y, are flat in the rubbery part of the polymer. This is caused by the relatively low swelling rate allowing Y to redistribute in the swollen polymer. If additional C is continuously supplied from the gas phase, then the selectivity decreases continuously with increasing conversion of B. 相似文献
32.
Investigations on the Amylose Determination in High Protein Starch Source Materials, Especially Peas. The proposed utilization of amylose rich starches requires different methods of amylose determination. In addition to laboratory methods also simple tests are important to that. Because the discussed legume starches are hardly investigated, first of all the suitability of the amperometric iodine titration had to be checked. Then a more easier work was described. In the case of routine analyses a modified test procedure was compared with the method of iodine titration. 相似文献
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A non-conserved sequence in the 5'region of the CYH2 intron from Saccharomyces cerevisiae controls splicing efficiency of the pre-mRNA 总被引:2,自引:0,他引:2
Ulrike Swida Eduardo Thüroff Edith Steindert Norbert F. Kufer 《Yeast (Chichester, England)》1988,4(3):209-217
The CYH2 gene from Saccharomyces cerevisiae containing one 510 bp intron is spliced inefficiently. We have shown previously that a non-conserved sequence within the intron is responsible for this low splicing efficiency. Using synthetic oligonucleotides comprising the identified region we show in this report that a very short region contains the specificity to act negatively on the splicing efficiency of the CYH2 gene. Furthermore, this sequence influences the splicing efficiency only when it is placed close to the 5' splice site of the gene. Investigations with chimeric CYH2/beta-actin genes show that this sequence acts independent from its natural surroundings. We propose that this sequence might interact with splicing factor(s). 相似文献
35.
Coal-derived liquids are susceptible to oxidative degradation. Two different weight ratios of SRC-I/SRC-II blends, with or without phenol derivatives, have been subjected to accelerated ageing studies. Viscosity, infrared, elemental analysis, molecular weight determination, and solvent analysis are used to examine the properties of the degradation products. On ageing, there is a large increase in the amount of toluene-insoluble material, decrease in oil components, and a relatively constant amount of asphaltenes. The oxygen content increases in the aged toluene-insoluble and asphaltene fractions, and a new absorption at ≈1700 cm?1 (the C = 0 group) appears in these two fractions only. On the addition of phenol itself and the less hindered phenol derivatives, the original hydrogen-bonding between the acidic and basic fuctional groups in the coal liquids is apparently disrupted because the added phenol can now interact with the proton-accepting species in the liquids, thus leading to a lower viscosity. This does not mean that the unhindered phenols retard the rate of ageing. The original hydrogen-bonding in the coal-derived liquid now gives way to a new hydrogen-bonding, and ageing occurs with the latter. The more hindered phenol derivatives are not as effective as phenol in disrupting the original hydrogen-bonding in the coal-derived liquids. 相似文献
36.
Inf rarotspektroskopie von Wasser in Schlacken. Chemischer Bindungszustand von Wasser in Schlacken, Abhängigkeit der integralen Extinktion der OH-Banden vom Wasserdampfpartialdruck. Wasserstoff beim ESU-Verfahren. 相似文献
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Software and Systems Modeling - Engineers commonly use paper and whiteboards to sketch and discuss ideas in early phases of requirements elicitation and software modeling. These physical media... 相似文献
40.
Norbert Fischer Siegfried Nitz und Friedrich Drawert 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1987,185(3):195-201
Zusammenfassung In grünem (Taiwan Gunpowder) und schwarzem (Ceylon high OP) Tee sind beträchtliche Mengen an Aromastoffen in glykosidischer Bindung vorhanden; ihr Anteil ist sogar höher als der an freien Aromastoffen. Hauptkomponenten sind in beiden Teesorten cis-3-Hexen-1-ol, Benzylalkohol und 2-Phenylethanol in gebundener Form, dazu im Schwarztee Linalool und im grünen Tee Geraniol. Die unterschiedlichen Anteile dieser beiden Terpenalkohole spiegeln die unterschiedlichen Tee-Varietäten wieder, denen die untersuchten Teesorten angehören: der Ceylon-Tee ist der Varietätassamica zuzuordnen, der Tee aus Taiwan der Varietätsinensis. Die Zusammensetzung der aus gebundenen Formen freisetzbaren Aromastoffe war ähnlich komplex wie die der freien Aromastoffe, wobei die Unterschiede zwischen den beiden Teesorten auf den verschiedenen Herstellungsverfahren beruhen. Das Auftreten gebundener Formen solcher Aromastoffe, die nicht originär vorhanden sind, sondern erst während der Welk- oder der Fermentationsphase gebildet werden, impliziert das Vorhandensein glykosidierender Aktivitäten im Teeblatt noch in relativ späten Stadien der Schwarzteeherstellung. Die Untersuchung der gebundenen Anteile an Aromastoffen trägt neben der Analyse der freien Aromastoffe wesentlich zum Verständnis der Reaktionen im Teeblatt wahrend der verschiedenen Produktionsstadien bei.
Auszug aus der Dissertation von N. Fischer, Technische Universitat München 1986
1. Mitteilung Chem Mikrobiol Technol Lebensm 9:87 (1985) 相似文献
Bound flavour compounds in plants 2. Part. Free and bound flavour compounds in green and black tea
Summary Green and black tea contains considerable amounts of flavour compounds which are present in glycosidic bonds, their portion being even higher than that of free flavour compounds. The main components in both of these tea varieties are 3-hexene-1-ol, benzylalcohol and 2-phenylethanol, which are present in the bound forms, and additionally linalool in black tea and geraniol in green tea. The different amounts of these terpene alcohols reflect the different varieties the teas under investigation belong to: the Ceylon tea belongs to the variety assamica, and the Taiwan tea to the variety sinensis. The composition of the flavour compounds liberated from bound forms had a similar complexity to that of the free flavour compounds, the difference being based upon the different production procedures. The occurrence of bound forms of such components that are not originally present but are produced during the withering or fermentation stage implies that glycosidating activities are still present in the tea leaf, even in a relatively late stage of the black tea production process. The investigation of the bound parts of flavour compounds delivers a valuable contribution to a better understanding of the reactions occurring in the tea leaf during the different stages of tea production.
Auszug aus der Dissertation von N. Fischer, Technische Universitat München 1986
1. Mitteilung Chem Mikrobiol Technol Lebensm 9:87 (1985) 相似文献