全文获取类型
收费全文 | 3006篇 |
免费 | 437篇 |
国内免费 | 188篇 |
专业分类
电工技术 | 281篇 |
综合类 | 406篇 |
化学工业 | 385篇 |
金属工艺 | 109篇 |
机械仪表 | 284篇 |
建筑科学 | 328篇 |
矿业工程 | 209篇 |
能源动力 | 129篇 |
轻工业 | 79篇 |
水利工程 | 72篇 |
石油天然气 | 176篇 |
武器工业 | 42篇 |
无线电 | 275篇 |
一般工业技术 | 294篇 |
冶金工业 | 126篇 |
原子能技术 | 10篇 |
自动化技术 | 426篇 |
出版年
2024年 | 6篇 |
2023年 | 55篇 |
2022年 | 96篇 |
2021年 | 121篇 |
2020年 | 135篇 |
2019年 | 119篇 |
2018年 | 103篇 |
2017年 | 98篇 |
2016年 | 141篇 |
2015年 | 106篇 |
2014年 | 163篇 |
2013年 | 207篇 |
2012年 | 247篇 |
2011年 | 232篇 |
2010年 | 181篇 |
2009年 | 144篇 |
2008年 | 156篇 |
2007年 | 206篇 |
2006年 | 166篇 |
2005年 | 154篇 |
2004年 | 129篇 |
2003年 | 92篇 |
2002年 | 99篇 |
2001年 | 72篇 |
2000年 | 55篇 |
1999年 | 52篇 |
1998年 | 59篇 |
1997年 | 39篇 |
1996年 | 47篇 |
1995年 | 40篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 18篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有3631条查询结果,搜索用时 15 毫秒
91.
We consider a continuous multi-facility location-allocation problem that aims to minimize the sum of weighted farthest Euclidean distances between (closed convex) polygonal and/or circular demand regions, and facilities they are assigned to. We show that the single facility version of the problem has a straightforward second-order cone programming formulation and can therefore be efficiently solved to optimality. To solve large size instances, we adapt a multi-dimensional direct search descent algorithm to our problem which is not guaranteed to find the optimal solution. In a special case with circular and rectangular demand regions, this algorithm, if converges, finds the optimal solution. We also apply a simple subgradient method to the problem. Furthermore, we review the algorithms proposed for the problem in the literature and compare all these algorithms in terms of both solution quality and time. Finally, we consider the multi-facility version of the problem and model it as a mixed integer second-order cone programming problem. As this formulation is weak, we use the alternate location-allocation heuristic to solve large size instances. 相似文献
92.
This paper presents an adjustable robust security constrained economic dispatch (SCED) model with wind power uncertainties. First, the scenario based adjustable robust SCED model is presented. It considers multiple scenarios from historical data as well as the spatial correlation among wind farms. Then, the proposed SCED model becomes an optimization problem with a large amount of constraints which is skillfully solved using a lift-and-project minimum volume enclosing ellipsoid (MVEE) based convex hull. Furthermore, the proposed model is transformed into a second order cone programming (SOCP) model by the use of participation factors to generate adjustable generation outputs and thus guarantee the energy balance. In order to further reduce the computational complexity, the inactive constraints reduction strategy is proposed to quickly eliminate inactive SOC security constraints before solving the model. Numerical results of IEEE 14-bus and 118-bus test systems as well as the practical Polish power systems with several wind farms show that the proposed model can achieve better economies. Moreover, more than 82% of security constraints are identified as inactive in various cases of the simulation, and the proposed inactive constraints reduction strategy is promising for improving the computational performance. 相似文献
93.
Experimental investigation and numerical modelling of the fire performance for epoxy resin carbon fibre composites of variable thicknesses 下载免费PDF全文
This paper applies a unique integrated approach to determine the flammability properties of a composite material (epoxy with carbon fibre) and compares its fire behaviour at two different thicknesses (2.1 and 4.2 mm) by performing small scale (thermo‐gravimetric analysis (TGA)/Fourier transform infrared radiation) and meso‐scale tests (cone calorimeter). For small‐scale tests, experiments were conducted in nitrogen using TGA coupled to gas analysis by Fourier transform infrared radiation. These results allow the determination of thermal stability, main degradation temperature and main gaseous emissions released during the thermal degradation. For meso‐scale tests, experiments were carried out using a cone calorimeter with sample dimensions of 100 × 100 mm at five heat fluxes (30, 40, 50, 60 and 70 kW/m2). The results show that the ignition time increases with an increase in the thickness of the material. Relative hazard classification of the fire performance of the current composites has also been compared with other materials using parameters obtained elsewhere. In addition, the effective ignition, thermal and pyrolysis properties obtained from the ignition and mass loss rate experiments for the 4.2‐mm thick samples were used in a numerical model for pyrolysis to predict well ignition times, back‐surface temperatures and mass pyrolysis rates for all heat fluxes as well as for the 2.1‐mm thick samples. Note that the ignition temperature obtained in the cone agrees with the main degradation temperature in the TGA. The flammability properties deduced here can be used to predict the heat release rate for real fire situations using CFD modelling. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
94.
Evaluation of fire performance of organic fire retardant free acrylic based coatings applied on various building materials by cone calorimetric method 下载免费PDF全文
Fire performance of water‐based plaster systems containing acrylic copolymer binder and non‐flammable mineral and ceramic fillers intended for decorative coating application was determined by cone calorimetric method. The coatings were applied on common building substrate materials used in construction sector, namely, Medium Density Fibre (MDF) boards, Gypsum Boards (GIB) and Stainless Steel (SS), and the different plaster finishes attempted on these substrates were Tierrafino, Suave and Bone China respectively. Group numbers of the different test samples were also evaluated following the Kokkala method. Based on various measurements, especially heat release, smoke evolution, mass loss data and the Group number estimates, it is evident that these organic fire retardant free coatings can offer good fire safety if applied on appropriate substrates like GIB or SS. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
95.
Apparatus for the vertical orientation cone calorimeter testing of flexible polyurethane foams 下载免费PDF全文
Of concern to regulators and fire safety engineers is how flexible polyurethane foam drips and flows during burning. Specifically, flexible polyurethane foam forms a burning ‘pool’ of liquid as the foam decomposes, which can lead to accelerated flashover events. To fully study this phenomenon where the ‘pool fire’ accelerates heat release, large‐scale tests like the furniture calorimeter (American Society of Testing and Materials (ASTM) E1537) are used, and no small‐scale technique exists. In this paper, we present our work in developing a new sample holder that works with a bench‐scale heat release test, the cone calorimeter (ASTM E1354). The holder was built upon designs developed by the National Institute of Standards and Technology, which placed the foam in a cage in a vertical orientation during cone calorimeter testing. In this paper, we show the schematics for this test apparatus, as well as results obtained with this apparatus on four different flexible foams (shape memory and high‐density foam, flame retarded and non‐flame retarded). We compare the results from the vertical testing with that obtained via traditional horizontal ASTM E1354 testing. The advantages and disadvantages of this new apparatus are discussed in this paper. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
96.
Methane calibration burner and C‐factor determination with cone calorimeter – validation of the standardized calibration protocol 下载免费PDF全文
The cone calorimeter is one of the major fire tests. In its reference standard ISO 5660‐1, the apparatus (and especially a characteristic of its orifice plate mass flow meter, called C‐Factor) is calibrated using a methane burner set at 5 kW. However, measurements performed in end‐use are in the range 1–10 kW. In addition, standard proposes to check linearity at 1 and 3 kW, which means in the lowest part of the range. This communication establishes the validation of the linearity on the whole range and determines the optimal condition for C‐factor determination. It justifies the technical choices of the standard. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
97.
Psychophysical, achromatic luminance threshold, and scaling data have been analyzed and found to follow from nonlinear, hyperbolic responses of retinal cones. For short (0.1 s) stimulus duration, a stable state of visual adaptation could explain the threshold response, but for longer durations a change of adaptation had to be considered. This resulted in a contrast sensitivity that increased when the stimulus duration increased and became constant for higher test field luminances. Threshold and scaling data can thus be traced back to cone‐specific responses over a much larger range of stimulus intensity than has been anticipated earlier. The experimental results, including those for lightness and brightness scaling, have been compared with the CIELAB and the CIEDE2000 color formulas. The idea of combining cone responses with adaptive changes to describe luminance responses resulted in a common cone‐based response formula for describing both luminance thresholds and scaling data. Adaptive changes explain the reason why both Weber–Fechner and Stevens’ laws are valid. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 339–351, 2016 相似文献
98.
This paper addresses target localization problem in a cooperative 3-D wireless sensor network (WSN). We employ a hybrid system that fuses distance and angle measurements, extracted from the received signal strength (RSS) and angle-of-arrival (AoA) information, respectively. Based on range measurement model and simple geometry, we derive a novel non-convex estimator based on the least squares (LS) criterion. The derived non-convex estimator tightly approximates the maximum likelihood (ML) one for small noise levels. We show that the developed non-convex estimator is suitable for distributed implementation, and that it can be transformed into a convex one by applying a second-order cone programming (SOCP) relaxation technique. We also show that the developed non-convex estimator can be transformed into a generalized trust region sub-problem (GTRS) framework, by following the squared range (SR) approach. The proposed SOCP algorithm for known transmit powers is then generalized to the case where the transmit powers are different and not known. Furthermore, we provide a detailed analysis of the computational complexity of the proposed algorithms. Our simulation results show that the new estimators have excellent performance in terms of the estimation accuracy and convergence, and they confirm the effectiveness of combining two radio measurements. 相似文献
99.
应用二阶Lagrange插值多项式的函数逼近进行曲线图形数字化。用AutoCAD中VBA程序绘制逼近曲线,与原曲线比较,验证插值多项式系数的准确性。以无套管穿越计算为例,给出了应用步骤。通过曲线数字化,将人工查图转变为编程计算。 相似文献
100.