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排序方式: 共有508条查询结果,搜索用时 9 毫秒
1.
We present uniaxial tensile test results for 30–50 nm thick freestanding aluminum films. Young’s modulus and ductility were found to decrease monotonically with grain size. Reverse Hall–Petch behavior was observed with no appreciable room temperature creep. Non-linear elasticity with small irreversible deformation was observed for 50 nm thick specimens. 相似文献
2.
The feasibility of applying a chemical method based on the formation of 2-alkylcyclobutanone to samples of irradiated soft cheese (Brie and Camembert) was investigated. Significant quantities of 2-dodecylcyclobutanone (DCB) and 2-tetradecylcyclobutanone (TCB) were detected in both types of irradiated cheese and are proposed as qualitative markers. Other members of the cyclobutanone family (decyl- and tetradecenyl-) are also thought to be present but could not be substantiated due to a lack of authentic standards. These compounds were absent from the unirradiated samples. Results also show a significant linear relationship between the irradiation dose (1 to 8 kGy) and the amount of DCB and TCB detected in the cheese. 相似文献
3.
4.
M.N. Haque 《Cement and Concrete Research》1980,10(1):13-22
The paper briefly reviews the concepts of dry lean concrete (DLC), roller compacted concrete (RCC) and Econocrete and their possible applications for the construction of subbase in pavement, concrete gravity dam and fill etc. The effects of differing quantities of fraction passing 75 μm on the strength and workability of concrete are reported. The 28 days compressive strength of all-in-aggregate concrete decreased at 1 and 5% silt contents whereas it increased at 10% silt as compared to the silt free concrete exposed to continuous air curing. It was observed that the water curing of all-in-aggregate concrete dramatically improved the compressive strength of the concrete as compared to the air curing. It is also reported that the variations in the pulse velocity on the concrete with differing silt content and curing regimes followed similar pattern of that of the variations in the compressive strength. 相似文献
5.
Q. Ahsan A. S. M. A. Haseeb E. Haque J. P. Celis 《Journal of Materials Engineering and Performance》2003,12(3):304-311
This paper describes an investigation on the failure of a large leaded bronze bearing that supports a nine-ton roller of a
plastic calendering machine. At the end of the normal service life of a good bearing, which lasted for seven years, a new
bearing was installed. However the new one failed catastrophically within a few days, generating a huge amount of metallic
wear debris and causing pitting on the surface of the cast iron roller. Following the failure, samples were collected from
both good and failed bearings. The samples were analyzed chemically and their microstructures examined. Both samples were
subjected to accelerated wear tests in a laboratory type pin-on-disk apparatus. During the tests, the bearing materials acted
as pins, which were pressed against a rotating cast iron disk. The wear behaviors of both bearing materials were studied using
weight loss measurement. The worn surfaces of samples and the wear debris were examined by light optical microscope, scanning
electron microscope, and energy-dispersive x-ray microanalyzer. It was found that the laboratory pin-on-disk wear data correlated
well with the plant experience. It is suggested that the higher lead content (∼18%) of the good bearing compared with 7% lead
of the failed bearing helped to establish a protective transfer layer on the worn surface. This transfer layer reduced metal-to-metal
contact between the bearing and the roller and resulted in a lower wear rate. The lower lead content of the failed bearing
does not allow the establishment of a well-protected transfer layer and leads to rapid wear. 相似文献
6.
Genetic algorithm-based motion estimation schemes play a significant role in improving the results of H.264/AVC standardization efforts when addressing conversational and non-conversational video applications. In this paper, we present a robust motion estimation scheme that uses a noble genetic trail bounded approximation (GTBA) approach to speed up the encoding process of H.264/AVC video compression and to reduce the number of bits required to code frame. The proposed algorithm is utilized to enhance the fitness function strength by integrating trail information of motion vector and sum of absolute difference (SAD) information into a fitness function. Experimental results reveal that the proposed GTBA resolves conflict obstacles with respect to both the number of bits required to code frames and the execution time for estimation. 相似文献
7.
Automated audio segmentation and classification play important roles in multimedia content analysis. In this paper, we propose an enhanced approach, called the correlation intensive fuzzy c-means (CIFCM) algorithm, to audio segmentation and classification that is based on audio content analysis. While conventional methods work by considering the attributes of only the current frame or segment, the proposed CIFCM algorithm efficiently incorporates the influence of neighboring frames or segments in the audio stream. With this method, audio-cuts can be detected efficiently even when the signal contains audio effects such as fade-in, fade-out, and cross-fade. A number of audio features are analyzed in this paper to explore the differences between various types of audio data. The proposed CIFCM algorithm works by detecting the boundaries between different kinds of sounds and classifying them into clusters such as silence, speech, music, speech with music, and speech with noise. Our experimental results indicate that the proposed method outperforms the state-of-the-art FCM approach in terms of audio segmentation and classification. 相似文献
8.
Conventional annealing is a slow, high temperature process that involves heating atoms uniformly, i.e., in both defective and crystalline regions. This study explores an electrical alternative for energy efficiency,where moderate current density is used to generate electron wind force that produces the same outcome as the thermal annealing process. We demonstrate this on a zirconium alloy using in-situ electron back scattered diffraction(EBSD) inside a scanning electron microscope(SEM) and juxtaposing the results with that from thermal annealing. Contrary to common belief that resistive heating is the dominant factor, we show that 5 × 10~4 A/cm~2 current density can anneal the material in less than 15 min at only135?C. The resulting microstructure is essentially the same as that obtained with 600?C processing for360 min. We propose that unlike temperature, the electron wind force specifically targets the defective regions, which leads to unprecedented time and energy efficiency. This hypothesis was investigated with molecular dynamics simulation that implements mechanical equivalent of electron wind force to provide the atomistic insights on defect annihilation and grain growth. 相似文献
9.
Microscale materials testing using MEMS actuators 总被引:4,自引:0,他引:4
Small size scale and high resolutions in force and displacement measurements make MEMS actuators appropriate for micromechanical testing. In this paper, for the first time, we present methodologies for uniaxial tensile and cantilever bending testing of both micrometer- and submicrometer-scale freestanding specimens using MEMS actuators. We also introduce dry fabrication processes for the specimens. The methodologies allow freestanding single or multilayered thin-film specimens to be fabricated separately from the MEMS actuators. For the uniaxial tension test, tensile forces are applied by lateral comb drive actuators capable of generating a total load of 383 μN at 40 V with resolutions on the order of 3 nN. A similar actuator is used in the bending test, with load resolution of 58 nN and spring constant of 0.78 N/m. The tensile testing methodology is demonstrated with the testing of a 110-nm-thick freestanding aluminum specimen. The cantilever bending experiment is performed on a 100-nm-thick aluminum specimen. The experimental setups can be mounted in a SEM (and also in a TEM after modifications for tensile testing) for in situ observation of materials behavior under different environmental conditions. Remarkable strengthening is observed in all the specimens tested compared to their bulk counterparts in both tensile and bending experiments. Experimental results highlight the potential of MEMS actuators as a new tool for materials research 相似文献
10.
F. Gulshan Q. Ahsan A. S. M. A. Haseeb E. Haque 《Journal of Failure Analysis and Prevention》2005,5(3):67-72
A failure analysis of superheater tube supports of the primary reformer in a local fertilizer factory is presented. A number
of tube supports failed at approximately half of their designed service life. Following the failure, the factory was visited,
and relevant information and samples were collected. The samples were investigated in the laboratory by chemical analysis,
macro- and microhardness measurements, macro-and micrometallographic examinations, and X-ray diffractometry. The analysis
showed the supports were fabricated from HH-type heat-resisting alloy and that the failure mode was high-temperature creep.
The microstructure of the alloy showed the presence of massive intergranular as well as intragranular σ-phase and intragranular
needle-shaped M23C6 carbides. It was also concluded from the formation of massive σ-phase in the tube that the failure was hastened because the
supports were operating at approximately 800 °C. The alloy composition led to the formation of σ-phase under the operating
conditions of the reformer, and the use of an alloy with a higher concentration of austenite-stabilizing element(s) could
have avoided the failure. 相似文献