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61.
Lars Ole Kornum 《Rheologica Acta》1979,18(1):178-192
Summary The rheological properties and their functional dependencies, involved in the flow behavior of coatings during application and drying, are discussed. From the available rheometrical techniques a characterization of coatings is proposed, which reflects the most important rheological parameters with respect to the application process. This characterization includes measurement of (i) the change of viscosity during the drying period, (ii) the viscosity of the coating, ready for application, in the shear range from below 1 s–1 to more than 10000 s–1, (iii) the thixotropic recovery of viscosity at a shear rate below 1 s–1 following shearing at a shear rate, where all structures are broken, or being at least 3 decades higher than the measuring rate, (iv) the stress relaxation from a low shear rate where relaxation times are largest or from a realistically high shear rate, and (v) the change in the composition of the material during drying in terms of evaporation.This characterization is found to be closely related to many of the different flow problems occurring in the application process. It may be extended more fully to elucidate specific problems, since the present characterization has been limited in order to make it a useful tool in routine work. For the same reason versatile rotational viscometers, normally used in coatings laboratories, are the most advanced instruments required for the characterization. This characterization, furthermore, is consistent with theoretical approaches to rheology, thereby giving access to an extension of the validity of the measurements on theoretical grounds and to use of extensive knowledge of how well-defined materials behave and interact in the design of coatings with a certain flow behavior. The framework of the characterization is found to be crucial in relating application process and rheology, whereas the specific measurements can be made in various ways.
Paper, presented at the Annual Conference of the Deutsche Rheologische Gesellschaft in Berlin, May 8–10, 1978.
With 3 figures 相似文献
Zusammenfassung Die rheologischen Eigenschaften und ihre funktionellen Abhängigkeiten, welche das Fließverhalten von Anstrichstoffen während deren Applikation und Trocknung beeinflussen, werden besprochen. Mit Hilfe von gebräuchlichen rheometrischen Verfahren wird eine Charakterisierung von Anstrichstoffen vorgeschlagen, welche die wichtigsten rheologischen Parameter in Verbindung mit dem Applikationsprozeß berücksichtigt. Diese Charakterisierung umfaßt folgende Messungen: 1. Die scheinbare Viskosität während der Trocknung, 2. die Viskosität des Anstrichstoffes unmittelbar vor dessen Applikation, im Bereich von Schergeschwindigkeiten von unter 1 s–1 bis über 10000 s–1, 3. die thixotrope Rückbildung der Viskosität bei einer Schergeschwindigkeit unter 1 s–1, gemessen nach Beendigung einer Scherbeanspruchung mit einer Geschwindigkeit, welche die gesamte Struktur aufzubrechen imstande war oder mindestens 3 Zehnerpotenzen höher liegt als die Meßgeschwindigkeit, 4. die Spannungsrelaxation, ausgehend von einer niedrigen Schergeschwindigkeit, wo die Relaxationszeiten am größten sind, oder von einer realistisch hohen Schergeschwindigkeit, und 5. die Veränderung des Materials während seiner Trocknung infolge Verdampfung seiner flüchtigen Anteile.Diese Charakterisierung wurde zu vielen verschiedenen Fließproblemen, wie sie während des Applikationsprozesses vorkommen, in enger Beziehung stehend gefunden. Sie könnte erweitert werden, um noch speziellere Probleme deuten zu können, doch ist die Charakterisierung als nützliches Hilfsmittel für Routinearbeiten begrenzt. Aus dem gleichen Grunde wurden für die Charakterisierung keine Instrumente vorgeschlagen, die komplizierter als Rotationsviskosimeter sind.Die vorliegende Charakterisierung ist in Übereinstimmung mit den theoretischen Grundlagen der Rheologie, so daß die Meßergebnisse auf theoretischer Basis verallgemeinert werden können. Für die Formulierung von Anstrichstoffen mit gemessenem Fließverhalten endlich können die Kenntnisse über Verhalten und Wechselwirkung theoretisch definierter Stoffe mit Nutzen angewandt werden.Der oben gegebene Charakterisierungsrahmen erwies sich als entscheidend für die Anwendbarkeit der Rheologie auf den Applikationsprozeß, die spezifischen Messungen hingegen können auf verschiedene Weise ausgeführt werden.
Paper, presented at the Annual Conference of the Deutsche Rheologische Gesellschaft in Berlin, May 8–10, 1978.
With 3 figures 相似文献
62.
Explicit constructions and properties of generalized shift-invariant systems in $L^{2}(\mathbb {R})$
Ole Christensen Marzieh Hasannasab Jakob Lemvig 《Advances in Computational Mathematics》2017,43(2):443-472
Generalized shift-invariant (GSI) systems, originally introduced by Hernández et al. and Ron and Shen, provide a common frame work for analysis of Gabor systems, wavelet systems, wave packet systems, and other types of structured function systems. In this paper we analyze three important aspects of such systems. First, in contrast to the known cases of Gabor frames and wavelet frames, we show that for a GSI system forming a frame, the Calderón sum is not necessarily bounded by the lower frame bound. We identify a technical condition implying that the Calderón sum is bounded by the lower frame bound and show that under a weak assumption the condition is equivalent with the local integrability condition introduced by Hernández et al. Second, we provide explicit and general constructions of frames and dual pairs of frames having the GSI-structure. In particular, the setup applies to wave packet systems and in contrast to the constructions in the literature, these constructions are not based on characteristic functions in the Fourier domain. Third, our results provide insight into the local integrability condition (LIC). 相似文献
63.
Harrison JA Kartha KP Fournier EJ Lowary TL Malet C Nilsson UJ Hindsgaul O Schenkman S Naismith JH Field RA 《Organic & biomolecular chemistry》2011,9(5):1653-1660
Systematically modified octyl galactosides and octyl N-acetyllactosamines were assessed as inhibitors of, and substrates for, T. cruzi trans-sialidase (TcTS) in the context of exploring its acceptor substrate binding site. These studies show that TcTS, which catalyses the α-(2→3)-sialylation of non-reducing terminal β-galactose residues, is largely intolerant of substitution of the galactose 2 and 4 positions whereas substitution of the galactose 6 position is well tolerated. Further studies show that even the addition of a bulky sugar residue (glucose, galactose) does not impact negatively on TcTS binding and turnover, which highlights the potential of 'internal' 6-substituted galactose residues to serve as TcTS acceptor substrates. Results from screening a 93-membered thiogalactoside library highlight a number of structural features (notably imidazoles and indoles) that are worthy of further investigation in the context of TcTS inhibitor development. 相似文献
64.
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68.
Ole Toft Sørensen 《Journal of Thermal Analysis and Calorimetry》2005,80(3):793-794
Summary An enormous development has taken place within the last five years in synchronous teaching over the Internet, i.e. both the teacher and the students are simultaneously in direct communication with each other as in a normal class-room or auditorium. With this concept it is possible to communicate orally, to exchange Power Point Presentations, documents, programmes and live web-camera pictures. It is even possible to use an electronic black board on which both the teacher and the students can work simultaneously. The great advantage with this type of teaching is that it is not restricted to a single class-room/auditorium with limited access, but in a virtual room accessible to everybody in principle all over the world, and which certainly open up new possibilities in teaching. The purpose of this paper is to present and to discuss the concept of virtual class-room teaching, how the system operates in practice, its advantages and, finally, how its inherent limitations can be overcome. 相似文献
69.
The copper- and heme-containing nitrite reductases (NiRs) are key enzymes in denitrification. Their subunits contain two distinct redox-active metal centers, an electron-accepting site and a nitrite-reducing site, to carry out the single-electron reduction of nitrite to nitric oxide. Catalytic cycles of both enzyme families employ intramolecular electron transfer that can be rate-determining for their activity. Herein, we report results comparing these two enzyme families in order to resolve the different mechanisms controlling intramolecular electron transfer in these proteins. 相似文献
70.
Lone Skov Henrik Hansen Henning C. Dittmar Jonathan N. W. N. Barker Jan C. Simon Ole Baadsgaard 《Photochemistry and photobiology》1998,67(6):714-719
Sensitization on skin exposed to acute low-dose UVB irradiation separates normal humans into two phenotypically distinct groups: One group, following sensitization on UVB-irradiated skin, develops contact sensitivity, designated UVB resistant (UVB-R) and the second group, following sensitization on UVB-irradiated skin, fails to develop contact sensitivity, designated UVB susceptible (UVB-S). To investigate whether UVB susceptibility in humans is related to antigen-presenting activity in the skin we studied the effect of UVB irradiation on the number and function of the epidermal antigen-presenting cells in volunteers identified as UVB-R and UVB-S. Single cell suspensions of epidermal cells from control skin and skin exposed to 3 minimal erythema doses (MED) of UVB 3 days previously were stained for Langerhans cells (CD1a+HLA-DR+) and epidermal macrophages (CD1a-HLA-DR+). The UVB exposure of the skin significantly decreased the percentage of Langerhans cells (UVB-R: n = 7, P < 0.02, UVB-S: n = 6, P < 0.03) and increased the percentage of epidermal macrophages (UVB-R: n = 7, P < 0.03, UVB-S: n = 6, P < 0.03) however to the same degree in both the UVBR and the UVB-S group. To study the effect on Langerhans cell alloreactivity, epidermal cells were harvested immediately after UVB irradiation. However, in both UVB-R and UVB-S subjects the Langerhans cell alloreactivity was blocked to the same degree immediately after UVB irradiation compared to nonirradiated epidermal cells. To determine the effect of UVB irradiation on epidermal macrophages, epidermal cells were harvested 3 days after UVB irradiation. Irradiated epidermal cells from both UVB-R and UVB-S subjects demonstrated a strong antigen-presenting capacity compared to epidermal cells from control skin leading to activation of T cells that mainly secrete interferon (1FN)-γ and not interleukin (IL)-4. In conclusion we found that UVB susceptibility was not correlated with the number of Langerhans cells or epidermal macrophages in the skin at the same time of sensitization. Neither was it correlated with the capacity of Langerhans cells nor UVB-induced epidermal macrophages to activate T cells in vitro. 相似文献