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排序方式: 共有299条查询结果,搜索用时 31 毫秒
91.
Beate Hiller 《LWT》2008,41(6):1140-1144
The effect of borate, phosphate and tris buffer on the extend of enzymatic oligomerisation of sodium caseinate and whey protein isolate is described. The study revealed that buffer systems enhance the enzymatic oligomerisation of milk protein monomers by lactoperoxidase, lipoxygenase and β-galactosidase. Compared to water, higher amounts of protein polymers (>2×106 g/mol) using borate buffer and higher amounts of protein oligomers (2×104-2×106 g/mol) using phosphate or tris buffer were observed. Oligomerisation effects, which were originally attributed to the catalytic activity of enzymes, were shown to be in part the result of a complex interaction between buffer, protein and enzyme systems. 相似文献
92.
Beate Bollig 《Information Processing Letters》2003,86(3):143-148
Branching programs are a well-established computation model for Boolean functions, especially read-once branching programs (BP1s) have been studied intensively. A very simple function f in n2 variables is exhibited such that both the function f and its negation ¬f can be computed by Σ3p-circuits, the function f has nondeterministic BP1s (with one nondeterministic node) of linear size and ¬f has size O(n4) for oblivious nondeterministic BP1s but f requires nondeterministic graph-driven BP1s of size . This answers an open question stated by Jukna, Razborov, Savický, and Wegener [Comput. Complexity 8 (1999) 357-370]. 相似文献
93.
The appropriate selection and application of quantitative structure-activity relationships (QSARs) for the prediction of toxicity is based on the prior assignment of a chemical to its mode of toxic action. This classification is often derived from structural characteristics with the underlying assumption that chemically similar compounds have similar mechanisms of action, which is often but not necessarily the case. Instead of using structural characteristics for classification toward a mode of toxic action, we used Escherichia coli based bioanalytical assays to classify electrophilic chemicals. Analyzing a series of reactive organochlorines, epoxides, and compounds with an activated double bond, three subclasses of reactive toxicity were distinguished: "glutathione depletion-related toxicity", "DNA damage", and "unspecific reactivity". For both subsets of specifically reacting compounds a direct correlation between effects and chemical reactivity was found. Reaction rate constants with either glutathione or 2'-deoxyguanosine, which was used as a model for complex DNA, served well to set up preliminary QSARs for either glutathione depletion-related toxicity or toxicity based on DNA damage in the model organism E. coli. The applicability of QSARs for electrophilic chemicals based on mechanistically relevant reaction rate constants is a priori limited to a small subset of compounds with strictly identical mechanism of toxic action and similar metabolic rates. In contrast, the proposed bioanalytical assays not only allowed the experimental identification of molecular mechanisms underlying the observable toxicity but also their toxicity values are applicable to quantitatively predict toxic effects in higher organisms by linear correlation models, independent of the assigned mode of toxic action. 相似文献
94.
Colchicine is a naturally occurring alkaloid used in human and veterinary medicine. It shows genotoxicity in in vitro and in vivo systems even at low concentrations. Therefore, no ADI has been established, and colchicine has been included in Annex IV of Council Regulation (EEC) No. 2377/90. No abuse of this drug in intensive livestock farming has yet been reported. However, there may be a natural route of entry for this compound into the food chain when Colchicum autumnale is consumed by animals kept outdoors. To address this concern, we developed and validated a highly sensitive and selective quantitative LC-ESI-MS-MS method for the detection of colchicine in sheep serum and milk. For sample pretreatment, all samples were liquid-liquid extracted with phosphate buffer (pH 8.0) and dichloromethane. LC separation was carried out on an RP C18 column employing a 0.5% formic acid/acetonitrile gradient system. The recoveries in both matrixes at a concentration range from 0.0005 to 1 mg/L were >80% with RSDs of <10%. The applicability of the method was demonstrated in serum and the corresponding milk samples from Albanian sheep. After exposure to C. autumnale, the animals showed clinical signs of intoxication. Significant concentrations (up to 1 mg/L) of the drug were found in serum as well as in milk samples. 相似文献
95.
Summary Formula size and depth are two important complexity measures of Boolean functions. We study the tradeoff between those two
measures:
We give an infinite set of Boolean functions and show for nearly each of them: There is no formula over “and”, “or”, “negation”
computing it optimal with respect to both measures. That implies a logarithmic lower bound on circuit depth. 相似文献
96.
分析 在中国入世的大背景下中德经济合作的前景。论述了中国经济向世界开放会对中德互补性的经济合作创造新的潜力,及其面临的机遇和风险。 相似文献
97.
Beate Balzer Martin K. M. Hruschka Ludwig J. Gauckler 《Journal of the American Ceramic Society》2001,84(8):1733-1739
Electrostatically stabilized alumina suspensions can be destabilized by the enzyme-catalyzed decomposition of urea (direct coagulation casting). Depending on the conditions, this reaction can shift the pH of a suspension to the buffer pH of the reaction products or increase the ionic strength at the buffer pH. The coagulation for both mechanisms was investigated using in situ rheological measurements. Using a vane tool in oscillation mode, the measuring conditions were optimized to find a reasonable method for time-dependent measurements. Constant parameters (stress or strain) proved to be unsuitable, because the linear viscoelastic region shifted considerably during the coagulation. Furthermore, the gel structure produced on coagulation via increase of ionic strength (Δ I ) was very sensitive to the oscillation. Therefore, for long-time experiments, a short continuous measurement with a low strain was followed by amplitude sweeps with increased intervals to determine the linear values of G ' and G ". In this way, the increase of the moduli G ' and G " could be followed for longer times, and it was possible to demonstrate two results. First, the final G ' of the network was about 10 times higher for Δ I -coagulated material than for suspensions coagulated via pH shift (ΔpH). Second, particle rearrangement processes took place in Δ I -coagulated networks even after the chemical changes were finished, whereas ΔpH-coagulated samples were "frozen-in" when approaching the isoelectric point and showed no further physical changes afterward. 相似文献
98.
Determining properties of cement‐based materials by inverse analysis. The direct experimental determination of certain material properties of cement‐based materials is technically difficult or even impossible. In such cases, a combined application of experimental and numerical methods might be required. The material properties are thereby determined by inverse analyses of experiments. In the field of material testing, two examples for properties which may be determined by inverse analysis are the strain softening curve and the moisture dependent water vapour diffusion coefficient, respectively. These material properties are of special importance for the characterisation of structural durability. Sufficient accuracy and efficiency of an inverse analysis may only be achieved if an adequate physical model of the experiment and a suitable optimisation method are used. For the problems to be solved here, evolutionary algorithms have proved to be appropriate means for the optimisation. The principle of the inverse analysis is explained and two example applications are presented. The latter are the determination of softening curves on the basis of fracture tests and the determination of diffusion coefficients on the basis of drying experiments. 相似文献
99.
100.
Beate Krause Hana Lerch Andreas Hotho Alexander Ro?nagel Gerd Stumme 《Informatik-Spektrum》2012,35(5):12-23
Soziale Tagging-Systeme geh?ren zu den in den vergangenen Jahren entstandenen Web2.0-Systemen. Sie erm?glichen es Anwendern,
beliebige Informationen in das Internet einzustellen und untereinander auszutauschen. Je nach Anbieter verlinken Nutzer Videos,
Fotos oder Webseiten und beschreiben die eingestellten Medien mit entsprechenden Schlagw?rtern (Tags). Die damit einhergehende
freiwillige Preisgabe oftmals pers?nlicher Informationen wirft Fragen im Bereich der informationellen Selbstbestimmung auf.
Dieses Grundrecht gew?hrleistet dem Einzelnen, grunds?tzlich selbst über die Preisgabe und Verwendung seiner pers?nlichen
Daten zu bestimmen. Für viele Funktionalit?ten, wie beispielsweise Empfehlungsdienste oder die Bereitstellung einer API, ist
eine solche Kontrolle allerdings schwierig zu gestalten. Oftmals existieren keine Richtlinien, inwieweit Dienstanbieter und
weitere Dritte diese ?ffentlichen Daten (und weitere Daten, die bei der Nutzung des Systems anfallen) nutzen dürfen. Dieser
Artikel diskutiert anhand eines konkreten Systems typische, für den Datenschutz relevante Funktionalit?ten und gibt Handlungsanweisungen
für eine datenschutzkonforme technische Gestaltung. 相似文献