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31.
Summary An overview ofvariational inequality andvariational equality formulations for frictionless contact and frictional contact problems is provided. The aim is to discuss the state-of-the-art
in these two formulations and clearly point out their advantages and disadvantages in terms of mathematical completeness and
practicality. Various terms required to describe the contact configuration are defined.Unilateral contact law and classical Coulomb’s friction law are given.Elastostatic frictional contact boundary value problem is defined. General two-dimensional frictionless and frictional contact formulations for elastostatic
problems are investigated. An example problem of a two bar truss-rigid wall frictionless contact system is formulated as an
optimization problem based on the variational inequality approach. The problem is solved in a closed form using the Karush-Kuhn-Tucker
(KKT) optimality conditions. The example problem is also formulated as a frictional contact system. It is solved in the closed
form using a new two-phase analytical procedure. The procedure avoids use of the incremental/iterative techniques and user
defined parameters required in a typical implementation based on the variational equality formulation. Numerical solutions
for the frictionless and frictional contact problems are compared with the results obtained by using a general-purpose finite
element program ANSYS (that uses variational equality formulation). ANSYS results match reasonably well with the solutions
of KKT optimality conditions for the frictionless contact problem and the two-phase procedure for the frictional contact problem.
The validity of the analytical formulation for frictional contact problems (with one contacting node) is verified. Thevariational equality formulation for frictionless and frictional, contact problems is also studied in detail. The incremental/iterative Newton-Raphson
scheme incorporating the penalty approach is utilized. Studies are conducted to provide insights for the numerical solution
techniques. Based on the present study it is concluded that alternate formulations and computational procedures need to be
developed for analysis of frictional contact problems. 相似文献
32.
Several commercial applications, such as online comparison shopping and process automation, require integrating information that is scattered across multiple websites or XML documents. Much research has been devoted to this problem, resulting in several research prototypes and commercial implementations. Such systems rely on wrappers that provide relational or other structured interfaces to websites. Traditionally, wrappers have been constructed by hand on a per-website basis, constraining the scalability of the system. We introduce a website structure inference mechanism called compact skeletons that is a step in the direction of automated wrapper generation. Compact skeletons provide a transformation from websites or other hierarchical data, such as XML documents, to relational tables. We study several classes of compact skeletons and provide polynomial-time algorithms and heuristics for automated construction of compact skeletons from websites. Experimental results show that our heuristics work well in practice. We also argue that compact skeletons are a natural extension of commercially deployed techniques for wrapper construction. 相似文献
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M. H. M. Akmal A. R. M. Warikh U. A. A. Azlan M. A. Azam T. J. S. Anand T. Moriga 《Journal of Electroceramics》2016,37(1-4):50-57
Sodium potassium niobate (KNN) is the most promising candidate for lead-free piezoelectric material, owing to its high Curie temperature and piezoelectric coefficients among the non-lead piezoelectric. Numerous studies have been carried out to enhance piezoelectric properties of KNN through composition design. This research studied the effects of yttrium concentrations and lattice site occupancy preference in KNN films. For this research, the yttrium-doped KNN thin films (mol% = 0, 0.1, 0.3, 0.5, 0.7 and 0.9) were fabricated using the sol-gel spin coating technique and had revealed the orthorhombic perovskite structures. Based on the replacement of Y3+ ions for K+/ Na+ ions, it was found that the films doped with 0.1 to 0.5 mol% of yttrium had less lattice strain, while films with more than 0.5 mol% of Y3+ ions had increased strain due to the tendency of Y3+ to occupy the B-site in the perovskite lattice. Furthermore, by analysing the vibrational attributes of octahedron bonding, the dopant occupancy at A-site and B-site lattices could be identified. O-Nb-O bonding was asymmetric and became distorted due to the B-site occupancy of yttrium dopants at high dopant concentrations of >0.5 mol%. Extra conduction electrons had resulted in better resistivity of 2.153× 106 Ω at 0.5 mol%, while higher resistivity was recorded for films prepared with higher concentration of more than 0.5 mol%. The introduction of Y3+ improved the grain distribution of KNN structure. Further investigations indicated that yttrium enhances the surface smoothness of the films. However, at high concentrations (0.9 mol%), the yttrium increases the roughness of the surface. Within the studied range of Y3+ , the film with 0.5 mol% Y3+ represented a relatively desirable improvement in dielectric loss, tan δ and quality factor, Qm. 相似文献
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Abstract Correlation properties of light scattered by a moving diffuser are determined by studying the spectral characteristics of the light that emerges from two pinholes placed after the diffuser. These properties are used to determine the correlation functions of the heights of diffuser surface and the speed of the diffuser. The phase of the light on the two pinholes after it has passed through the moving diffuser, is also determined. 相似文献
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Antifungal activity of five different essential oils in vapour phase for the control of Colletotrichum gloeosporioides and Lasiodiplodia theobromae in vitro and on mango
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Anand Babu Perumal Periyar Selvam Sellamuthu Reshma B. Nambiar Emmanuel Rotimi Sadiku 《International Journal of Food Science & Technology》2016,51(2):411-418
Mango fruit has high commercial value; however, major postharvest losses are encountered throughout the supply chain due to postharvest diseases. These results lead to the search for natural fungicide for postharvest diseases control. The antifungal effects of five essential oils (thyme, clove, cinnamon, anise and vitex) were assessed by disc volatilisation method. Thyme oil vapours at 5 μL per Petriplate, and clove and cinnamon oil at 8 μL per Petriplate showed 100% growth inhibition of mango pathogens in vitro. GC/MS analysis of essential oil showed thymol (23.88), o‐cymol (23.88) and terpinolene (23.88) as the major constituents of thyme oil. Clove and cinnamon oils contain 3‐allyl‐2‐methoxyphenol (37.42%) and benzofuran 3‐methyl (17.97%), respectively. Thyme oil as a fumigant at 66.7 μL L?1 showed a significant (P < 0.05) inhibition on postharvest pathogens of mango fruits stored at 25 °C for 6 days. Results of our study suggest the possibility of using thyme oil as an alternate natural fungicide to manage postharvest diseases in mango. 相似文献
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Extant research on information technology (IT) adoption and continuance has not adequately modeled the times of adoption by individuals. This study argues that individuals adopt an innovation at different times and are likely to be influenced by different factors over time. The theoretical models are empirically validated using data gathered at three points in time through surveys of 132 users of a new innovation. The results indicate that the innovation attributes and individual characteristics influence individuals’ intentions to adopt the innovation during the early stage, and the innovation attributes and contextual factors impact the individuals’ intentions during the later stage. 相似文献