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61.
M. Grujicic B. Pandurangan C.-F. Yen B. A. Cheeseman 《Journal of Materials Engineering and Performance》2012,21(11):2207-2217
Johnson-Cook strength material model is frequently used in finite-element analyses of various manufacturing processes involving plastic deformation of metallic materials. The main attraction to this model arises from its mathematical simplicity and its ability to capture the first-order metal-working effects (e.g., those associated with the influence of plastic deformation, rate of deformation, and the attendant temperature). However, this model displays serious shortcomings when used in the engineering analyses of various hot-working processes (i.e., those utilizing temperatures higher than the material recrystallization temperature). These shortcomings are related to the fact that microstructural changes involving: (i) irreversible decrease in the dislocation density due to the operation of annealing/recrystallization processes; (ii) increase in grain-size due to high-temperature exposure; and (iii) dynamic-recrystallization-induced grain refinement are not accounted for by the model. In this study, an attempt is made to combine the basic physical-metallurgy principles with the associated kinetics relations to properly modify the Johnson-Cook material model, so that the model can be used in the analyses of metal hot-working and joining processes. The model is next used to help establish relationships between process parameters, material microstructure and properties in friction stir welding welds of AA5083 (a non-age-hardenable, solid-solution strengthened, strain-hardened/stabilized Al-Mg-Mn alloy). 相似文献
62.
Abstract In this study the hydraulic characteristics and the start‐up of anaerobic rotating biological contactor (AnRBC) were investigated experimentally and theoretically. Results of tracer study showed that the AnRBC reactor is a well‐mixed reactor in the first and second stages. Start‐up of the AnRBC reactor was successfully carried out using high strength synthetic wastewaters at hydraulic retention time of 21.6 hours, organic surface loading of 111.4 g‐COD/m2?d, organic volumetric loading of 13.33 Kg‐COD/m3?d, disk rotational speed of 12 rpm and 100% disk submergence. In the steady‐state operating condition, the removal efficiencies of soluble COD and BOD could be up to 71% and 76% for the inlet COD and BOD concentrations of 12,000 and 7,267 mgL‐1, respectively. The microscopic observations after start‐up of the AnRBC reactor showed that the acetogenic bacteria are significant in the first two stages while the methanogenic bacteria predominate in the last two stages. 相似文献
63.
A study on the formation of a measurement scale for the environmental quality of Taiwan’s long-term care institutions by the Delphi method 总被引:1,自引:0,他引:1
Yen Ping Hsieh Yen Wen Hsieh Chia Ching Lin Chien Wen Yeh Sing Chiao Chang 《Journal of Housing and the Built Environment》2012,27(2):169-186
This study used a two-round modified Delphi technique with a questionnaire survey in order to reach a consensus for the questionnaire; the survey was conducted from September to December 2009. The six indicators for the environmental quality of long-term care institutions in Taiwan are (1) indoor environmental quality, (2) safety equipment for the prevention and management of disasters occurring in residents?? daily lives, (3) provision for assistive devices for residents?? daily use, (4) provision for privacy and individualized space, (5) provision for comfortable and decorated indoor environments, and (6) provision for social interaction space. The scale included 34 items with an acceptable number of panel members and acceptable construct validity. Panel members all highly approved of Indicators 1, 2, and 6. Although they approved of Indicator 3, they suggested that caregivers at institutions should replace the functions of living assistive devices. They approved of Indicator 5; however, they questioned the method for providing comfortable and decorated environments. They approved of Indicator 4; however, they suggested that private space need not be provided in the living room of the institution. In terms of long-term care institution environments in Taiwan, Indicators 1, 2, and 6 were important for protecting residents?? physical and psychological well-being and improving their social interactions. Indicator 3, although important, could be directly replaced by caregivers. Indicator 5 required more implementation methods, while Indicator 4, the living room of the institution, was considered unnecessary. 相似文献
64.
M. Grujicic B. Pandurangan B. A. Cheeseman C.-F. Yen 《Journal of Materials Engineering and Performance》2012,21(9):1813-1823
Spallation is a fracture mode commonly observed in ballistically/blast-wave-loaded structures. The interaction between decompression waves generated within the target structure produces tensile stresses which, if of a sufficient magnitude, may cause material damage and ultimate fracture (spallation). In this study, the phenomenon of spall-fracture is analyzed within a one-dimensional Lagrangian framework. Two distinct analyses are carried out. Within the first analysis, decompression waves are treated as decompression shocks, which simplified the analysis and enabled the formation of spallation-strength-based material index. In the second analysis, decompression waves are treated as smooth (centered simple) waves. This increased the fidelity of the computational analysis, but the material-selection procedure could be done only numerically and an explicit formulation of the spallation-strength-based material-selection index could not be carried out. Overall, the two analyses yielded similar results for the spallation-strength-based material-selection criterion suggesting that the simpler (decompression shock based) one is still adequate for use in the material-selection process. 相似文献
65.
Abstract This study investigats a new approach‐the sequential approach‐ in job shop scheduling. The objective is to minimize the total of lateness cost and set‐up cost in job shops. Whenever a scheduling decision has to be made as to which job should receive the next processing, this approach considers each cost sequentially. One of the two costs is considered first, and every time all waiting jobs must be examined in terms of this cost, and only those jobs qualified would the second cost apply to and from which a job would be selected for processing. This investigation was carried out by using GASP IV simulation under a variety of job shop situations. The effectiveness of this approach and job selection mechanism constitute the main theme of this study. 相似文献
66.
Abstract The effects of buoyancy forces on the laminar boundary layer flow and heat transfer along vertically moving cylinders are analyzed for the cases of prescribed surface temperature and prescribed wall heat flux in power of streamwise distance. Local similarity solutions are obtained to show the effects of buoyancy parameters and the transverse curvature of the cylinder on the surface friction and heat transfer rate. 相似文献
67.
New business models and applications have been continuously developed and popularized on the Internet. In recent years, a number of applications including blogs, Facebook, iGoogle, Plurk, Twitter, and YouTube known as Web 2.0 have become very popular. These aforementioned applications all have a strong social flavor. However, what social factors exert an influence onto their use is still unclear and remains as a research issue to be further investigated. This research studies four social factors and they are subjective norm, image, critical mass, and electronic word-of-mouth. A causal model of the satisfaction and continuance intention of Web 2.0 users as a function of these four social factors is proposed. Results indicate that user satisfaction with Web 2.0 applications significantly affects electronic word-of-mouth, which in turn significantly influences their continuance intention. In addition, subjective norm, image and critical mass all have a significant impact onto satisfaction, which in turn has an indirect significant influence on electronic word-of-mouth. Finally, all social factors have a significant direct impact on continuance intention. Finally, implications for service providers and researchers are discussed. 相似文献
68.
Evaluating the criteria for human resource for science and technology (HRST) based on an integrated fuzzy AHP and fuzzy DEMATEL approach 总被引:2,自引:0,他引:2
This study intends to use a combination of fuzzy Analytic Hierarchy Process (AHP) and fuzzy Decision-making Trial and Evaluation Laboratory (DEMATEL) method in human resource for science and technology (HRST). Specifically, this study first uses AHP to evaluate the weighting for each criterion and then use DEMATEL method to establish contextual relationships among those criteria. We find out Infrastructure might be more critical since it is a cause and will directly influence human resource for science and technology performance. For human resource for science and technology (HRST), improving Infrastructure might be a better choice for the long period of time. Moreover, Education, R&D Expenses and Immediate output are more important second-tier criteria than Value, Cooperation, Labor Market, Human Capital and Intermediate output. Therefore, the improvement should be started with Infrastructure, particularly on identification of the Education, R&D Expenses and Immediate output. 相似文献
69.
Yen‐Ting Lin Ting‐Wei Yeh Yoshitake Nakajima P. Daniel Dapkus 《Advanced functional materials》2014,24(21):3162-3171
GaN nanorod formation on Ga‐polar GaN by continuous mode metalorganic chemical vapor deposition selective area growth (MOCVD SAG) is achieved under a relatively Ga‐rich condition. The Ga‐rich condition, provided by applying a very low V/III ratio, alters the growth rates of various planes of the defined nanostructure by increasing relative growth rate of the semi‐polar tilted m‐plane {1–101} that usually is the slowest growing plane under continuous growth conditions. This increased growth rate relative to the non‐polar m‐plane {1–100} and even the c‐plane (0001), permits the formation of GaN nanorods with nonpolar sidewalls. In addition, a new growth mode, called the NH3‐pulsed mode, is introduced, utilizing the advantages of both the continuous mode and the lower growth rate pulsed mode to form nanorods. Finally, nanorods grown under the different growth modes are compared and discussed. 相似文献
70.
Tzu Hsuan Chiang Mei Yun Chen Meng Hsien Li Ming Yu Yen 《Journal of Materials Science》2013,48(20):6994-7003
The study investigated the use of ethylene glycol to form α-MoO3 from molybdic acid wastewater by thermal treatment at 300 °C for 1 h. The color change, pH values, and residual molybdenum concentration in the wastewater were dependent on the reaction times that were used. The results of UV–visible and Fourier transform infrared (FTIR) spectroscopy were used to explain the reaction process. During the treatment process, the morphologies of the constituents were observed using scanning electron microscopy. In this work, X-ray photoelectron spectroscopy and transmission electron microscopy demonstrated that when the molybdenum oxide powder was treated thermally at 300 °C, the material exhibited crystallinity, and the peaks were indexed to correspond with the (002) and (200) crystallographic planes, which were identified as orthorhombic molybdenum trioxide (α-MoO3). In addition, the FTIR and X-ray photoelectron spectroscopy confirmed that α-MoO3 powder had been synthesized. 相似文献