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31.
Janet Feigenspan Christian Kästner Sven Apel Jörg Liebig Michael Schulze Raimund Dachselt Maria Papendieck Thomas Leich Gunter Saake 《Empirical Software Engineering》2013,18(4):699-745
Software-product-line engineering aims at the development of variable and reusable software systems. In practice, software product lines are often implemented with preprocessors. Preprocessor directives are easy to use, and many mature tools are available for practitioners. However, preprocessor directives have been heavily criticized in academia and even referred to as “#ifdef hell”, because they introduce threats to program comprehension and correctness. There are many voices that suggest to use other implementation techniques instead, but these voices ignore the fact that a transition from preprocessors to other languages and tools is tedious, erroneous, and expensive in practice. Instead, we and others propose to increase the readability of preprocessor directives by using background colors to highlight source code annotated with ifdef directives. In three controlled experiments with over 70 subjects in total, we evaluate whether and how background colors improve program comprehension in preprocessor-based implementations. Our results demonstrate that background colors have the potential to improve program comprehension, independently of size and programming language of the underlying product. Additionally, we found that subjects generally favor background colors. We integrate these and other findings in a tool called FeatureCommander, which facilitates program comprehension in practice and which can serve as a basis for further research. 相似文献
32.
Clinical applications of glass-ceramics in dentistry 总被引:3,自引:0,他引:3
Höland W Rheinberger V Apel E van 't Hoen C Höland M Dommann A Obrecht M Mauth C Graf-Hausner U 《Journal of materials science. Materials in medicine》2006,17(11):1037-1042
Glass-ceramics featuring special properties can be used as a basis to develop biomaterials. It is generally differentiated
between highly durable biomaterials for restorative dental applications and bioactive glass-ceramics for medical use, for
example, bone replacements. In detail, this paper presents one biomaterial from each of these two groups of materials.
In respect to the restorative dental biomaterials, the authors give an overview of the most important glass-ceramics for clinical
applications. Leucite, leucite-apatite, lithium disilicate and apatite containing glass-ceramics represent biomaterials for
these applications. In detail, the authors report on nucleation and crystallization mechanisms and properties of leucite-apatite
glass-ceramics. The mechanism of apatite nucleation is characterized by a heterogeneous process. Primary crystal phases of
α - and β -NaCaPO4 were determined.
Rhenanite glass-ceramics represent biomaterials with high surface reactivity in simulated body fluid, SBF, and exhibit reactive
behaviour in tests with bone cells. Cell adhesion phenomena and cell growth were observed. Suitable colonization and proliferation
and differentiation of cells as a preliminary stage in the development of a material for bone regeneration applications was
established. The authors conclude that the processes of heterogeneous nucleation and crystallization are important for controlling
the required reactions in both biomaterial groups. 相似文献
33.
Effective thermal properties of an isotactic polypropylene (α‐iPP) injection moulded part by a multiscale approach 下载免费PDF全文
G. Laschet M. Apel J. Wipperfürth C. Hopmann M. Spekowius R. Spina 《Materialwissenschaft und Werkstofftechnik》2017,48(12):1213-1219
In injection moulding processes, the melt undergoes a complex deformation and cooling history, which results in an inhomogeneous distribution of crystalline superstructures in semi‐crystalline thermoplastics, which significantly influences their final mechanical and thermal properties. In this paper we describe the determination of local effective thermal properties of a moulded part via a multiscale simulation approach. First a macroscopic filling and heat transfer simulation is performed followed by a microstructure evolution calculation on the micro‐scale. Then, the effective thermal properties are derived via a two‐level homogenization scheme. The results show that the effective thermal conductivity is anisotropic and that it varies asymmetrically over the analysed plate sections. 相似文献
34.
Sven Apel Christian Kästner Armin Größlinger Christian Lengauer 《Automated Software Engineering》2010,17(3):251-300
A feature-oriented product line is a family of programs that share a common set of features. A feature implements a stakeholder’s requirement and represents a design decision or configuration option. When added to a program,
a feature involves the introduction of new structures, such as classes and methods, and the refinement of existing ones, such
as extending methods. A feature-oriented decomposition enables a generator to create an executable program by composing feature
code solely on the basis of the feature selection of a user—no other information needed. A key challenge of product line engineering
is to guarantee that only well-typed programs are generated. As the number of valid feature combinations grows combinatorially
with the number of features, it is not feasible to type check all programs individually. The only feasible approach is to
have a type system check the entire code base of the feature-oriented product line. We have developed such a type system on
the basis of a formal model of a feature-oriented Java-like language. The type system guaranties type safety for feature-oriented
product lines. That is, it ensures that every valid program of a well-typed product line is well-typed. Our formal model including type system is sound and complete. 相似文献
35.
Gomez Alvarez-Arenas T.E. Apel P.Yu. Orelovitch O. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(11):2442-2449
The propagation of ultrasonic waves in the cylindrical micro-pores (pore diam. <1 μm) of ion-track membranes (ITMs) is studied. This membrane fabrication technique provides unique possibilities to obtain cylindrical micro-pores with a very high degree of accuracy in pore shape, size, and orientation. Several ITMs were specially produced having the same pore diameter, orientation, and geometry, but different thickness. Porosity, pore diameter, and shape were determined using scanning electron microscopy, and then the coefficient of ultrasound transmission was measured using air coupling and spectral analysis. These experimental conditions permit us to eliminate the influence of the boundary conditions and to achieve a strong decoupling between the fluid filling the pores and the solid constituent of the membrane. Hence, the velocity and the attenuation coefficient for ultrasound propagation in the pores can be measured. These parameters are compared with the predictions made by conventional theories for sound propagation in porous media and in cylindrical channels. The conclusions of this work provide a better understanding of wave propagation in micro-pores and establish the basis of an ultrasonic porometry technique for ITMs. 相似文献
36.
D. Fink J. Rojas-Chapana A. Petrov H. Tributsch D. Friedrich U. Küppers M. Wilhelm P.Yu. Apel A. Zrineh 《Solar Energy Materials & Solar Cells》2006,90(10):1458-1470
We tried to produce antibacterial and antifouling advanced packing materials and medical plasters using the nowadays-available synthetic polymer foils. For this sake, we irradiated 10-μm-thick polyethylene terephthalate (PET) and polyimide (PI) foils with energetic ions at our heavy ion accelerators in Dubna or Berlin up to fluences around 107 cm−2 and etched them subsequently so that conical tracks with diameters in the order of a few micrometer emerged. The inner walls of these tracks were coated with bilayer structures of the composition: {SiO2 nanoclusters and TiO2 nanoclusters} or {Ag films and TiO2 nanoclusters}. The nanoclustered layers with typical cluster sizes of 50–100 nm were formed by deposition of corresponding commercial colloidal solutions and subsequent baking.Upon presence of moisture and near UV light, the TiO2 acts as a photoactive OH radical producer and electron scavenger. This destroys any organic matter passing through the ion tracks towards H2O and CO2—this may be an organic gas such as ethylene vapor (important to prevent premature food ripening), or fungi, viruses, bacteria, or other microorganisms (important for sterilization). The underlying SiO2 or Ag layers prevent the polymeric substrate from being attacked by the TiO2. Furthermore, the Ag layer enhances the antibacterial activity due to the toxicity of the Ag+ ions. 相似文献
37.
Light-induced increase in the activity of maize plastid DNA-dependent RNA polymerase 总被引:1,自引:0,他引:1
Illumination of dark-grown maize plants induces a rapid rise in DNA-DEPENDENT RNA polymerase activity in plastids. Within 16 h illumination the enzyme activity is isolated plastids increases 3-4 fold as compared to other dark-grown plants illuminated for only 2 h. This change in activity is unaccompanied by either a quantitative rise in the amount of chloroplast RNA polymerase or qualitative changes in the purified enzyme. It is suggested that other factors may be present which interact either with the enzyme or the DNA template and that these factors are responsible for the light-induced enhancement of the RNA polymerase activity inplastids. 相似文献
38.
Kuster WC Jobson BT Karl T Riemer D Apel E Goldan PD Fehsenfeld FC 《Environmental science & technology》2004,38(1):221-228
The Texas Air Quality Study 2000 (TexAQS2000) investigated the photochemical production of ozone and the chemistry of related precursors and reaction products in the vicinity of Houston, TX. The colocation of four instruments for the measurement of volatile organic carbon compounds (VOCs) allowed a unique opportunity for the intercomparison of the different in-situ measuring techniques. The instruments included three gas chromatographs, each with a different type of detector, and a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) with each system designed to measure a different suite of VOCs. Correlation plots and correlation statistics are presented for species measured by more than one of these instruments. The GC instruments were all in agreement to within 10-20% (slope) with coefficients of variation (r2) of > or = 0.85. The PTR-MS agreement with other instruments was more dependent on species with some very good agreements (r2 values of approximately 0.95 for some aromatics), but isoprene, acetaldehyde and propene were substantially less highly correlated (0.55 < r2 < 0.80). At least part of these differences were undoubtedly due to the timing of sample acquisition in an environment in which VOC levels changed very rapidly on both quantitative and temporal scales. 相似文献
39.
The usual Bramble-Hilbert theory is extended for proving more refined estimates of the interpolation error. For a large class of finite elements, it is shown that one can derive benefit from the presence of small and even large angles of the elements. For bilinear shape functions on rectangular grids it is proved that interpolation and finite element approximation error coincide. As an example, we consider the finite element approximation for problems on domains containing edges. 相似文献
40.
Today's photovoltaic market is divided into multicrystalline silicon wafers from ingot casting and monocrystalline wafers from Czochralski crystals. In both cases large crystals have to be cut into thin wafer geometry. As an alternative approach the EFG process and the string ribbon process are in industrial use for the production of silicon ribbons directly out of the melt. One future alternative for a high production process is the Ribbon Growth on Substrate (RGS) process which is now in the final development stage for industrial production of silicon ribbons.In this paper we will report simulation results for the crystallisation of silicon melt in contact with a substrate. This is the basis not only for the RGS process but also for thin film processes like laser remelting of amorphous Si. The results show the general solidification behaviour at the tip region of a growing Si sheet. Different crystal growth modes are predicted resulting in different grain structures of the silicon sheet as observed experimentally. 相似文献