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排序方式: 共有1053条查询结果,搜索用时 203 毫秒
61.
62.
Cracks induced by external excitation on a material that has defects may generate the stress concentration phenomenon. The
stress concentration behaviour causes local buckling, which will induce the damage of the members made of this material. Thus,
developing techniques to monitor the strain variation of a cracked member is an important study. The traditional technique
(such as strain gauge) can only measure the average strain of a region. The strain variation within this region cannot be
determined. Therefore, it cannot sufficiently reflect the mechanical behaviour surrounding the crack. The Digital image correlation
technique recently developed is an image identification technique to be applied for measuring the object deformation. This
technique is capable of correlating the digital images of an object before and after deformation and further determining the
displacement and strain field of an object based on the corresponding position on the image. In this work, this technique
is applied to analyse the mechanics of a cylindrical pipe experiencing crack destruction. The fixing device is used to avoid
shaking the specimen during the pressurizing process. The image capture instruments are fixed on the stable frame to measure
the deformation of specimen accurately. Through the cylindrical pipe cracking test, the capacity of the digital image correlation
technique for surveying the strain variation in a tiny region is validated. Then, the experimental results obtained using
the digital image correlation analysis is used to demonstrate the crack development tendency in defect materials and the stress
concentration zone. 相似文献
63.
Shih Chieh Huang Jui Kung Wu Wei-Jen Hsu Hsin Hsiung Chang Hsien Yen Hung Chi Lian Lin Hung-Yuan Su Nitin Bagkar Wei-Chih Ke Hui Tung Kuo Ru-Shi Liu 《International Journal of Applied Ceramic Technology》2009,6(4):465-469
The synthesis of cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor of different sizes with uniform size distribution was carried out using solid-state reaction followed by grinding and sieving method. The effect of particle size distribution of YAG:Ce phosphors on the photoluminescence (PL) properties was investigated. The results demonstrate that the uniform size distribution and particle size affects the packaging performance in white light emitting diode (LED) applications. The YAG:Ce phosphors with different particle sizes were packaged in white LEDs using different amounts of each phosphors in order to get similar efficiency as that of commercially available YAG:Ce phosphors. It was observed that minimum amount of phosphor material is required for smaller particle size for getting the similar efficiency as that exhibited by commercially available YAG:Ce phosphors. The results are particularly interesting in view of reducing the cost of current LEDs by lowering the amount of phosphors without compromising the efficiencies of final LED package. A systematic study of YAG:Ce phosphors on the packing performance in white LEDs is reported. 相似文献
64.
Yeou-Koung Tung 《Water Resources Management》1987,1(4):241-254
Like any other resources planning and management, groundwater management is performed in a stochastic environment in which the system itself involves a number of random elements. Consequences as a result of decisions made based on analyses are not certain. This paper presents a management model using the chance-constrained framework which explicitly considers the random nature of aquifer properties. The model enables the derivation of an optimal groundwater management policy that would satisfy required operation performance reliability. Furthermore, the chance-constrained model is extended to the multi-objective optimization framework in which a tradeoff between total water supply pumpage and system performance reliability is explicitly considered. The models are applied to a hypothetical example of a steady, nonuniform, homogeneous confined aquifer. 相似文献
65.
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67.
An optimum downlink power control that maximizes the user-capacity of a Direct Sequence-Code Division Multiple Access (DS-CDMA) cellular system is proposed based on a convex programming method. First, the downlink beamforming weights for the base-station antenna-array are designed based on the maximum Signal-Interference-Ratio (SIR) criterion. Then by optimizing the downlink power subject to a fixed total transmit power constraint, we further increase the Signal-Interference-Noise-Ratio (SINR) at the mobile terminal, thus increasing the capacity of the system. With the same methodology, we can also minimize the required transmit power while satisfying the SINR threshold constraints. Additionally, a robust downlink power control approach for mitigating the performance degradation due to channel estimates error is also proposed. Computer simulations are given to demonstrate the improvement of downlink capacity, received SINR, robustness, and the minimization of the required transmit power for a DS-CDMA system with antenna-array at the base-station. 相似文献
68.
Influence of ventilation on indoor radon level 总被引:1,自引:0,他引:1
Detailed radon measurements were conducted at different residential units in Hong Kong in winter time when air-conditioners were off and also in summer time when air-conditioners were on. Ventilation rates were measured concurrently to investigate the influence of ventilation on indoor radon level. The ratio of indoor radon level to outdoor radon level was plotted against ventilation rate, and it was found that a critical value existed after which the indoor radon level could be considered identical to the outdoor level. This result is important for use in ventilation design to reduce indoor radon pollution. 相似文献
69.
70.
Yanli Qu Chow W.W.Y. Mengxing Ouyang Tung S.C.H. Li W.J. Xuliang Han 《Nanotechnology, IEEE Transactions on》2008,7(5):565-572