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991.
Visualization of embedded carbon nanotubes (CNTs) in polymer using a scanning electron microscope (SEM) has been established as a convenient technique to evaluate CNT dispersion. This technique is known as voltage contrast imaging and is different from material contrast and topographic contrast imaging. By investigating CNT/epoxy composites the voltage contrast imaging theory is further understood. Trapping of electrons at the CNT/epoxy interface induces a local potential difference which enhances the image contrast. By coating the composite with a polymer film of different thicknesses the imaging depth (i.e. from how deep the CNTs can be seen) is determined to be up to 250 nm, and is a function of the accelerating voltage of the SEM. Visibility of CNTs is found to be sensitive to the CNT dispersion and concentration, as well as to the accelerating voltage. 相似文献
992.
993.
994.
Tom Gießgen Andreas Mittelbach Daniel Hche Mikhail Zheludkevich Karl U. Kainer 《工业材料与腐蚀》2019,70(12):2247-2255
An advanced mathematical approach to describe the influence of corrosion products on the corrosion rate is presented here. The related model can be used as input equation for numerical predictive corrosion simulations or simply as an empirical model, to extrapolate experimental data of corrosion tests to longer times and to interpret the physical parameters behind. This semiempirical model assumes that a constant share of the dissolved metal precipitates on the surface and hinders the diffusion processes. Hence, the effective corrosion rate decreases exponentially with increasing dissolution. The explicit corrosion progress over time is derived by time integration on a newly developed, time dependent corrosion rate equation. The derived expression can be effortlessly implemented in existing for example finite element method, which is demonstrated for the uniform corrosion of a zinc surface. Furthermore, this approach is qualitatively compared with other empirical models for corrosion products and the validity is demonstrated by fitting of experimental data. A very good agreement between experiment and theory can be achieved for various materials and environments considering no change of the driving corrosion mechanism. 相似文献
995.
996.
K. Vijai Anand R. Mohan R. Mohan Kumar M. Karl Chinnu 《Journal of Experimental Nanoscience》2014,9(3):261-271
ZnS nanoparticles have been synthesised at low temperature by short reaction (80°C for 2?h) via wet chemical route. The nanoparticles were stabilised using hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The average particle size calculated from X-ray diffraction studies was about 4?nm with cubic zincblende structure. The presence of HMTA in the synthesised ZnS nanoparticles was confirmed by FTIR studies. A significant blue shift was observed in the optical absorption band edge for the ZnS nanoparticles as compared to the bulk, indicating a strong quantum confinement. The room temperature photoluminescence (PL) spectrum showed a broad green emission peak at around 502?nm. The photocatalytic property of HMTA-stabilised ZnS nanoparticles were investigated on the decolourisation of methylene blue aqueous solution under UV light irradiation. 相似文献
997.
Coherent distortion risk measures are applied to capture the possible violation of a restriction in linear optimization problems whose parameters are uncertain. Each risk constraint induces an uncertainty set of coefficients, which is proved to be a weighted-mean trimmed region. Thus, given a sample of the coefficients, an uncertainty set is a convex polytope that can be exactly calculated. We construct an efficient geometrical algorithm to solve stochastic linear programs that have a single distortion risk constraint. The algorithm is available as an R-package. The algorithm’s asymptotic behavior is also investigated, when the sample is i.i.d. from a general probability distribution. Finally, we present some computational experience. 相似文献
998.
Russell H. Jones Charles H. Henager Jr. Charles A. Lewinsohn Charles F. Windisch Jr. 《Journal of the American Ceramic Society》2000,83(8):1999-2005
Ceramic-matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements have been made in the creep resistance of SiC fibers and, hence, in the high-temperature properties of SiC fiber/SiC (SiCf /SiC) composites; however, more must be known about the stability of these materials in oxidizing environments before they are widely accepted. Experimental weight change and crack growth data support the conclusion that the oxygen-enhanced crack growth of SiCf /SiC occurs by more than one mechanism, depending on the experimental conditions. These data suggest an oxidation embrittlement mechanism (OEM) at temperatures <1373 K and high oxygen pressures and an interphase removal mechanism (IRM) at temperatures of ≳700 K and low oxygen pressures. The OEM results from the reaction of oxygen with SiC to form a glass layer on the fiber or within the fiber–matrix interphase region. The fracture stress of the fiber is decreased if this layer is thicker than a critical value ( d > d c ) and the temperature below a critical value ( T < T g ), such that a sharp crack can be sustained in the layer. The IRM results from the oxidation of the interfacial layer and the resulting decrease of stress that is carried by the bridging fibers. Interphase removal contributes to subcritical crack growth by decreasing the fiber-bridging stresses and, hence, increasing the crack-tip stress. The IRM occurs over a wide range of temperatures for d < d c and may occur at T > T g for d > d c . This paper summarizes the evidence for the existence of these two mechanisms and attempts to define the conditions for their operation. 相似文献
999.
Karl Seifert 《Holz als Roh- und Werkstoff》1964,22(7):267-275
1000.
Psychologists bring great value to health care systems, but our ethnocentrism regarding the medical community often limits our effectiveness as agents of change. Based on experience in developing pain management services within the Department of Veterans Affairs health care system, we discuss cultural issues as central to effective systems change and provide specific recommendations for psychologists aspiring to change organized health care systems, such as the Department of Veterans Affairs. Consideration is given to the misfit of the biomedical model to chronic pain, “physics envy” affecting the authority accorded psychology, and societal stigmatization of psychopathology. A process-based definition of cultural competence is recommended as improving on psychology's intrinsic group-based notion of culture in engaging the medical community. The systems thinking literature is sampled in summarizing practical recommendations that include identifying features of local medical culture and power dynamics between psychology and medicine that can be modified by engaging stakeholders in an interpersonally effective manner. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献