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排序方式: 共有571条查询结果,搜索用时 15 毫秒
1.
A monolithic microwave frequency divider IC with an operating range of 1.4?5.3 GHz was developed and fabricated in a standard bipolar technology. The circuit operates on the principle of `regenerative frequency division?. Compared to the most popular divider concepts based on a master-slave D-flip-flop, an almost twice as high input frequency can be divided, provided that the same technology is used. A further advantage is the low power consumption. 相似文献
2.
Numerical modeling of multiphase flows in microfluidics and micro process engineering: a review of methods and applications 总被引:2,自引:1,他引:1
Martin Wörner 《Microfluidics and nanofluidics》2012,12(6):841-886
This article presents a comprehensive review of numerical methods and models for interface resolving simulations of multiphase
flows in microfluidics and micro process engineering. The focus of the paper is on continuum methods where it covers the three
common approaches in the sharp interface limit, namely the volume-of-fluid method with interface reconstruction, the level
set method and the front tracking method, as well as methods with finite interface thickness such as color-function based
methods and the phase-field method. Variants of the mesoscopic lattice Boltzmann method for two-fluid flows are also discussed,
as well as various hybrid approaches. The mathematical foundation of each method is given and its specific advantages and
limitations are highlighted. For continuum methods, the coupling of the interface evolution equation with the single-field
Navier–Stokes equations and related issues are discussed. Methods and models for surface tension forces, contact lines, heat
and mass transfer and phase change are presented. In the second part of this article applications of the methods in microfluidics
and micro process engineering are reviewed, including flow hydrodynamics (separated and segmented flow, bubble and drop formation,
breakup and coalescence), heat and mass transfer (with and without chemical reactions), mixing and dispersion, Marangoni flows
and surfactants, and boiling. 相似文献
3.
Photometer measurement of polydisperse aerosols 总被引:4,自引:0,他引:4
The photometer measurement of respirable aerosol mass concentration is widely employed in air pollution monitoring. Using the Mie theory of light scattering and the built-in optical parameters of some photometers, the output signal was theoretically calculated and related to the real aerosol mass concentration.. The definition of the mass sensitivity in combination with the device calibration constants enables the photometer response bias calculation as a function of the main aerosol parameters (index of refraction, particle density, particle size distribution). The respirable fraction (Soderholm (1989) Ann. occup. Hyg. 33, 301–320; Comité Européen de Normalisation (1993) EN 481; International Standards Organisation (1993) DIS 7708; American Conference of Governmental Industrial Hygienists (1994) Cincinnati, OH, pp. 42–45) of the ambient aerosol was used as a reference concentration for the calculation of the bias. The photometer response bias maps were built for four mineral dusts and a wide range of their aerosol distributions. The method makes possible an estimation of the photometer response bias in measuring various aerosols when the instrument is calibrated against any other aerosol. 相似文献
4.
Bahador Saket Carlos Scheidegger Stephen G. Kobourov Katy Börner 《Computer Graphics Forum》2015,34(3):441-450
We investigate the memorability of data represented in two different visualization designs. In contrast to recent studies that examine which types of visual information make visualizations memorable, we examine the effect of different visualizations on time and accuracy of recall of the displayed data, minutes and days after interaction with the visualizations. In particular, we describe the results of an evaluation comparing the memorability of two different visualizations of the same relational data: node‐link diagrams and map‐based visualization. We find significant differences in the accuracy of the tasks performed, and these differences persist days after the original exposure to the visualizations. Specifically, participants in the study recalled the data better when exposed to map‐based visualizations as opposed to node‐link diagrams. We discuss the scope of the study and its limitations, possible implications, and future directions. 相似文献
5.
Darcy T. Haluzan David M. Klymyshyn Martin Börner Sven Achenbach Garth Wells Timo Mappes Jürgen Mohr 《Microsystem Technologies》2008,14(9-11):1709-1714
High aspect ratio variable capacitors have been fabricated using deep X-ray lithography and electroplating. Stiction phenomena applicable to high aspect ratio devices are presented, including the conditions for stiction to occur and the critical dimensions of structures. Actuation tests at 3 GHz are also presented and show a maximum capacitance of 0.86 pF with no actuation voltage and a minimum capacitance of 0.70 pF with an actuation voltage of 20 V just before pull-in, which gives a tuning range of 1.23:1. Corresponding Q-factor values are 49.3 and 70.8 respectively. After pull-in, the measured capacitance is 0.61 pF, corresponding to a tuning range of 1.41:1, with a maximum Q-factor of 102.9. 相似文献
6.
Christoph Weigel Valeriya Cherkasova Mathias Holz Hai Binh Phi Christian Görner Tenorio Björn Wilbertz Leonard Voßgrag Thomas Fröhlich Steffen Strehle 《Advanced Engineering Materials》2023,25(9):2201873
Ultralow expansion (ULE) glasses are of special interest for temperature stabilized systems for example in precision metrology. Nowadays, ULE materials are mainly used in macroscopic and less in micromechanical systems. Reasons for this are a lack of technologies for parallel fabricating high-quality released microstructures with a high accuracy. As a result, there is a high demand in transferring these materials into miniaturized application examples, realistic system modeling, and the investigation of microscopic material properties. Herein, a technological base for fabricating released micromechanical structures and systems with a structure height above 100 μm in ULE 7972 glass is established. Herein, the main fabrication parameters that are important for the system design and contribute thus to the introduction of titanium silicate as material for glass-based micromechanical systems are discussed. To study the mechanical properties in combination with respective simulation models, microcantilevers are used as basic mechanical elements to evaluate technological parameters and other impact factors. The implemented models allow to predict the micromechanical system properties with a deviation of only ±5% and can thus effectively support the micromechanical system design in an early stage of development. 相似文献
7.
Andreas Förner Jan Vollhüter Anna Krapf Abdullah Jamjoom Daniel Hausmann Benjamin Wahlmann Zongwen Fu Carolin Körner Steffen Neumeier Mathias Göken 《Advanced Engineering Materials》2023,25(15):2300407
By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF-EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate-like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF-EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material. 相似文献
8.
D. Bjørner 《Cybernetics and Systems Analysis》2010,46(4):609-623
In this paper, we wish to advocate that departments of computer science put emphasis on teaching programming and software
engineering based on formal methods; and more emphasis on research into formal methods for the trustworthy development of
software. We also wish to advocate that the concepts of domain science and domain engineering become an indispensable part
of the science of informatics and of software engineering. 相似文献
9.
10.
Nikolaj S. Bjørner Anca Browne Michael A. Colón Bernd Finkbeiner Zohar Manna Henny B. Sipma Tomás E. Uribe 《Formal Methods in System Design》2000,16(3):227-270
We review a number of formal verification techniques supported by STeP, the Stanford Temporal Prover, describing how the tool can be used to verify properties of several versions of the Bakery Mutual exclusion algorithm for mutual exclusion. We verify the classic two-process algorithm and simple variants, as well as an atomic parameterized version. The methods used include deductive verification rules, verification diagrams, automatic invariant generation, and finite-state model checking and abstraction. 相似文献