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排序方式: 共有65条查询结果,搜索用时 15 毫秒
1.
《Expert systems with applications》2014,41(18):8049-8061
In this paper, we investigate the problem of time series forecasting using single hidden layer feedforward neural networks (SLFNs), which is optimized via multiobjective evolutionary algorithms. By utilizing the adaptive differential evolution (JADE) and the knee point strategy, a nondominated sorting adaptive differential evolution (NSJADE) and its improved version knee point-based NSJADE (KP-NSJADE) are developed for optimizing SLFNs. JADE aiming at refining the search area is introduced in nondominated sorting genetic algorithm II (NSGA-II). The presented NSJADE shows superiority on multimodal problems when compared with NSGA-II. Then NSJADE is applied to train SLFNs for time series forecasting. It is revealed that individuals with better forecasting performance in the whole population gather around the knee point. Therefore, KP-NSJADE is proposed to explore the neighborhood of the knee point in the objective space. And the simulation results of eight popular time series databases illustrate the effectiveness of our proposed algorithm in comparison with several popular algorithms. 相似文献
2.
《工程(英文)》2018,4(4):471-478
Cycling is an eco-friendly method of transport and recreation. With the intent of reducing the energy cost of cycling without providing an additional energy source, we have proposed the use of a torsion spring for knee-extension support. We developed an exoskeleton prototype using a crossing four-bar mechanism as a knee joint with an embedded torsion spring. This study evaluates the passive knee exoskeleton using constant-power cycling tests performed by eight healthy male participants. We recorded the surface electromyography over the rectus femoris muscles of both legs, while the participants cycled at 200 and 225 W on a trainer with the developed wheel-accelerating system. We then analyzed these data in time–frequency via a continuous wavelet transform. At the same cycling speed and leg cadence, the median power spectral frequency of the electromyography increases with cycling load. At the same cycling load, the median power spectral frequency decreases when cycling with the exoskeleton. Quadriceps activity can be relieved despite the exoskeleton consuming no electrical energy and not delivering net-positive mechanical work. This fundamental can be applied to the further development of wearable devices for cycling assistance. 相似文献
3.
The aims were to evaluate the inter-method reliability of a registration sheet for patient handling tasks, to study the day-to-day variation of musculoskeletal complaints (MSC) and to examine whether patient handling tasks and psychosocial factors were associated with MSC.Nurses (n = 148) fulfilled logbooks for three consecutive working days followed by a day off. Low back pain (LBP), neck/shoulder pain (NSP), knee pain (KP), psychosocial factors (time pressure, stress, conscience of the quality of work) and patient transfers and care tasks were reported.The logbook was reliable for both transfer and care tasks. The numbers of nurses reporting MSC and the level of pain increased significantly during the three working days (15%-30% and 17%-37%, respectively) and decreased on the day off. Stress and transfer task were associated with LPB and transfer tasks were associated with KP.Our results confirm a relationship between work factors and MSC and indicate that logs could be one way to obtain a better understanding of the complex interaction of various nursing working conditions in relation to MSC. 相似文献
4.
《Ergonomics》2012,55(3):310-316
The aim of this study was to compare the validity of self-reporting and video-recording as methods of measuring the duration of knee-straining work postures, and to evaluate the reproducibility of timings of the video-recordings. Thirty-nine carpenters and 33 floorlayers were video-filmed while working, and were asked immediately afterwards to quantify the amount of time spent in knee-straining positions. The investigators recorded the periods of knee-straining work with a stopwatch during playback of the video-film, and the agreement between the two investigators' measurements was studied in 13 pairs of measurements. The video observation method was very effective for timing knee-strain work. Furthermore, Spearman's correlation coefficient (0.88) indicated a good association between observed and self-reported knee-straining work. Estimation of self-reported kneestraining work collected by interview showed good correlation with measurements of video-recordings. When judging the repeatability of timings of kneestraining work from the video-recordings, a high level of agreement was seen between the two observers in the 13 dual measurements of time spent in knee-straining work positions. 相似文献
5.
《Ergonomics》2012,55(8):899-909
Peak impact forces, measured from seven male carpetlayers using a knee-kicker over 39 trials were 2933?N (SD 397), taking 9·5?ms (SD ± 1·1) to reach peak. The knee-kicking cycle involved high knee decelerations of 880?m.s?2 (SD ±271). Angles at peak force for the knee (63° SD ± 10°) and hip (80° SD ± 35°) showed considerable variation between individuals. Kneeling forces on the non-kicking leg during the kick cycle were 894?N: comparative forces were 368?N and 476?N measured during use of the power stretcher and crab re-stretcher, respectively. Under dynamic conditions the effective mechanical advantage of the knee-kicker was less than 1·0. In comparison, the mechanical advantage of the power stretcher was approximately 14 times greater over the stretch action. When tested with a crab re-stretcher, the breaking strength of the smooth-edge to which the carpet attaches averaged 2384?N (SD ± 245). Design guidelines for an improved carpet stretching device are provided. 相似文献
6.
New method for simultaneous anatomical and functional studies of articular joints and its application to the human knee 总被引:3,自引:0,他引:3
Martelli S 《Computer methods and programs in biomedicine》2003,70(3):223-240
In this paper a new methodology is described for the acquisition and computer elaboration of joint anatomy and motion data and the study of their correlation. The method uses a particular commercial electrogoniometer never used before for biomechanic investigations and software developed by the author for numerical interpolations and interactive display of the anatomical structures during joint motion. The original data acquisition protocol and computer elaboration software are described in detail, the theoretical and experimental accuracy of the method is reported and the original features and potential benefits of this approach in the field of joint biomechanics are discussed. Finally an experimental application for geometrical and functional analysis of the knee is presented as a practical example. 相似文献
7.
MR imaging of baker cysts—prevalence and relation to internal derangements of the knee 总被引:3,自引:0,他引:3
Rationale and objectives: To evaluate the prevalence of popliteal cysts in patients studied with magnetic resonance (MR) imaging. Cyst presence and
volume will be related to other internal derangement of the knee.Materials and methods: Three hundred and eighty-two consecutive patients with a MR study of the knee were included. Images were obtained in the
three spatial orthogonal planes and evaluated through consensus. Four categories were established for the Baker cyst and synovial
fluid (absence, minimum, moderate and massive), and the presence of meniscal, cruciate ligaments and cartilage lesions were
recorded. Statistical analysis was carried out with bivariate analysis (χ2 of Pearson and Gamma tests).Results: From the 382 patients, 145 had Baker cysts (38.0%). Cyst content was minimum in 99, moderate in 34 and massive in 12. Joint
effusion was observed in 269 patients (70.4%), being minimal in 140 patients, moderate in 119 and massive in ten. Meniscal
lesions were observed in 195 patients (51%), while 58 patients (15%) had a cruciate ligament lesion. Baker cyst has a statistically
significant direct relationship with the presence and quantity of synovial fluid (P=0.002) and with the presence and type of meniscal lesion (P=0.01) but not with cruciate ligaments or cartilage lesions.Conclusions: The prevalence of Baker cysts in MR studies of the knee is high. Its presence and volume are related to the quantity of
synovial fluid, and to the presence and severity of meniscal lesions. 相似文献
8.
Mezzanine surfaces can be made from concrete, bar grate, or composite materials. Anecdotal data indicate that mezzanines in distribution centers made from composite materials, due to their increased compliance, may be a more comfortable working surface. Prior research suggested that a measure of tibial shock, peak tibial acceleration, could potentially discriminate the biomechanical differences between these surfaces. The objective of this study was to quantify differences in tibial accelerations as 27 people walked on mezzanines constructed from concrete and a wood composite material. Accelerometers were attached bilaterally to the shins of volunteers, and data were collected as they walked 30.5 m on each surface at their normal walking speed, a faster-than-normal walking speed, and a slower-than-normal walking speed. Peak acceleration values obtained from the leg with the highest values were compared. On average, the peak acceleration values were 5% higher on the concrete mezzanine as compared with the wood composite mezzanine (p = .036). These findings suggest that individuals working on mezzanines in distribution centers constructed from composite surfaces would potentially experience less discomfort associated with long exposure periods on these surfaces. 相似文献
9.
10.
The mechanisms of UHMWPE wear at the tibiofemoral articulation of a total knee replacement are potentially highly dependent on the cyclic direction of motion, the relative amounts of rolling versus sliding, and the loading of the contacting surfaces as previously described for hip components [3]. The simulated wear rate, for a standard test protocol utilizing the Insall-Burstein®1 II Modular Knee System (IB-II) knee prosthesis, for normal walking gait was found to be 17.0 mg/106 cycles on a Boston AMTI knee simulator. When the anterior/posterior (A/P) translation input was reduced by 50%, the wear rate was reduced approximately 37% to 10.6 mg/106 cycles. Eliminating either the A/P translation or tibial rotation reduced the wear rate to 1.7 mg/106 cycles and 0.69 mg/106 cycles, respectively. These results cannot be explained by sliding distance effects alone and suggest that the UHMWPE wear rate is sensitive to other parameters, such as the magnitude of multidirectional shear motion and the ratio of rolling/sliding contact kinematics in combination with the applied load. 相似文献