全文获取类型
收费全文 | 3318篇 |
免费 | 403篇 |
国内免费 | 145篇 |
专业分类
电工技术 | 51篇 |
综合类 | 53篇 |
化学工业 | 702篇 |
金属工艺 | 154篇 |
机械仪表 | 110篇 |
建筑科学 | 20篇 |
矿业工程 | 11篇 |
能源动力 | 228篇 |
轻工业 | 13篇 |
水利工程 | 1篇 |
石油天然气 | 5篇 |
武器工业 | 12篇 |
无线电 | 1333篇 |
一般工业技术 | 766篇 |
冶金工业 | 54篇 |
原子能技术 | 28篇 |
自动化技术 | 325篇 |
出版年
2024年 | 13篇 |
2023年 | 321篇 |
2022年 | 136篇 |
2021年 | 282篇 |
2020年 | 220篇 |
2019年 | 120篇 |
2018年 | 159篇 |
2017年 | 284篇 |
2016年 | 232篇 |
2015年 | 234篇 |
2014年 | 234篇 |
2013年 | 182篇 |
2012年 | 243篇 |
2011年 | 199篇 |
2010年 | 142篇 |
2009年 | 152篇 |
2008年 | 69篇 |
2007年 | 150篇 |
2006年 | 133篇 |
2005年 | 60篇 |
2004年 | 29篇 |
2003年 | 32篇 |
2002年 | 38篇 |
2001年 | 42篇 |
2000年 | 23篇 |
1999年 | 37篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 14篇 |
1988年 | 7篇 |
排序方式: 共有3866条查询结果,搜索用时 156 毫秒
21.
针对跟踪过程中目标形态不断变化或部分遮挡导致鲁棒性差的问题,提出一种基于多特征自适应融合的粒子滤波跟踪算法.该算法从视觉特征集中选取了描述能力强的2种特征,并将其按照与目标模型的多尺度相似度进行线性融合;为了减小跟踪漂移,通过计算当前目标模型与初始目标模型的多尺度相似度自适应地更新目标模型.大量仿真实验结果表明,文中算法可以鲁棒地跟踪到部分遮挡和形态变化的运动目标. 相似文献
22.
《Displays》2021
We present an efficient method for the fast calculation of computer generated hologram (CGH). The 3D object is split into sub-layers according to its depth information. A 2D all-in-focus image is generated by sequential tiling all the layers in one plane. A Fourier hologram that contains all the information of 3D object is calculated from the fast Fourier transform (FFT) of the reassembled 2D image. By multiplying a pre-calculated multifocal off-axis digital phase mask (DPM) to the Fourier hologram, the content of each layer is axially relocated to different depth in the Fourier transform optical system to reconstruct the 3D object. The computation speed of the proposed method is greatly improved with only single FFT calculation process. Both of simulation and experimental results proves the validation of the proposed method. 相似文献
23.
《Displays》2021
This study reinvestigated one of the most fundamental problems in structure light depth sensing field: correspondence retrieval of features between patterns and images. We formulate the global optimum correspondence retrieval by maximizing a conditional probability of correspondence given observed features, which is depicted by a Bayesian network. Different from traditional “code-only” based correspondence retrieval methods, the proposed Bayesian network based method exploits the positional correlations of correspondences of neighboring features, namely, the correspondences of poorly detected features are estimated with the aid of the correspondences of well detected features. The method performs especially well on challenging scenes with rich depth variations, abrupt depth changes, edges, etc. Experiments show that the proposed method increase the correspondence accuracy by about 40% on challenging scenes, compared with traditional “code-only” based correspondence retrieval methods. 相似文献
24.
The availability of a system or equipment is one of the crucial characteristics that measures the customer satisfaction and strongly influences his final choice decision between concurrent products. The aim of this work is to provide an approach to improve the products availability assessment by taking into account the safety criteria by considering the use situations at design stage. Our work focuses on the routine design of complex products. The availability is often simply estimated considering reliability and maintainability. Basically, the intrinsic availability is the probability that it is operating satisfactorily at any point in time when used under conditions stated by design specifications. The time considered includes operating time and active repair time. Thus, intrinsic availability excludes from consideration all other times in the product lifecycle such as: accident management time, storage time, administrative time or logistic time. But many studies show that the loss of availability performance is also due to accidents that occur in different unforeseeable utilization situations. This engenders stops of the system to ensure the users safety according to standards recommendations. In this purpose, we consider the structural product architecture and the different use cases that correspond to the operational states and downtimes due to stop events that may happen during the utilization like failures, maintenance tasks and accidents. Then, we propose a product behavioral analysis including the use cases to describe interactions between the product and users or maintenance operators. We use Markov chains to model the use cases corresponding to operating time (OT), maintenance time (MT) and preparing time after accidents (RT). Then these three parameters are considered to specify a generic approach to improve the availability assessment. Such an approach provides the traceability of the product behavior along its lifecycle. In this way, the main causes of stop can be identified and this may guide the designer for improving the availability of the product future versions. To validate our approach, an application is presented considering a printing line. The comparison of our simulation considering an industrial case study shows a good agreement about the influence of safety on the availability. 相似文献
25.
为了改进Zernike矩边缘检测方法对非直线边缘检测精度低的弱点,提出了一种改进的基于Zernike矩方法和Sigmoid拟合法的边缘检测方法。用Zernike矩边缘检测方法检测边缘,然后用Sigmoid拟合方法检测边缘,根据边缘类型对两种方法检测的边缘结果进行加权求和,所得结果为边缘位置。分别利用理想图像和实际工业CT图像进行了实验验证,实验结果表明对非直线边缘的检测,该方法检测精度相对于Zernike矩方法提高了一个数量级。 相似文献
26.
《Journal of the European Ceramic Society》2006,26(10-11):1957-1960
The structure evolution, sintering behavior and microwave dielectric properties of La(2−x)/3Nax(Mg1/2W1/2)O3 (x = 0–0.5) were investigated in this paper. The X-ray diffraction (XRD) results show that all samples exhibit single phase, and the structure changed from orthorhombic when 0 ≤ x < 0.3 to monoclinic phase when 0.3 ≤ x ≤ 0.5. The size and ordering degree of A/B-site domains decrease with the increase in x value. The sintering temperature of the Na-doped samples increased compared to the pure La2/3(Mg1/2W1/2)O3 (LMW) due to the estimated decrease in the concentration of A-site vacancies. The addition of Na+ ion does not affect the dielectric permittivity greatly. The Q × f value decreases with the increase in x value, although the estimated concentration of A-site vacancies decreases with increasing x, which may be ascribed to the decrease of A/B-site ordering and domain size with the increase in x. The temperature coefficient of resonant frequency changed from negative values into positive values with the increase in x value. 相似文献
27.
L. T. Guan F. G. Du G. Z. Wang Y. K. Chen M. Xiao S. J. Wang Y. Z. Meng 《Journal of Polymer Research》2007,14(3):245-251
Completely biodegradable foams of poly(propylene carbonate) (PPC) derived from carbon dioxide and propylene oxide were fabricated
using N, N′-dinitroso pentamethylene tetramine (DPT) as chemical blowing agent, and urea as the activator to lower the decomposition
temperature of DPT. Thermal decomposition behavior and gas evolution behavior of the DPT composite with various urea to DPT
ratios were investigated to optimize the composition of the blowing agent. The formulation of blowing agent mixture and foaming
condition, the foam morphologies, the molecular weight change, as well as the mechanical properties of produced PPC foams
were studied extensively. The experimental results demonstrated that the greatest blowing ratio of 14.8 can be afforded in
case 12 phr blowing agent was used at 170 °C for 30 min. Gel permeation chromatography (GPC) and thermal analysis revealed
that DPT acted as both chain-extension agent and blowing agent for PPC matrix. The molecular weight of PPC subjected to foaming
increased by 76%. The foamed PPC exhibited superior mechanical properties and can be used as packaging material for many practical
applications. 相似文献
28.
Li Dong Jun-Xi Wang Hong-Zhi Shen Dan Li Xiao-Ming Xiu Ya-Jun Gao X. X. Yi 《Quantum Information Processing》2014,13(6):1413-1424
We present two error-tolerance transmission protocols of a single-photon polarization state when bit-flip error is taken into account. For achieving the transmission target of the single-photon state, the first protocol needs to encode it to a nonmaximally entangled Bell state. Exploiting the interaction of the polarization entanglement with spatial entanglement between two photons, its success probability is 100 %. Different from the first protocol, the second one utilizes the idea of teleportation with an auxiliary Bell state. By performing quantum nondemolition measurement to analyze the parity, conventional measurement, and unitary transformation operations, the success probability of the second protocol is approximately unity. Furthermore, the second protocol can be generalized to the error-tolerance transmission of an arbitrary mixed state or the distribution of an arbitrary multi-photon entangled state. 相似文献
29.
《Journal of the European Ceramic Society》2006,26(15):3233-3239
The spark plasma sintering (SPS) behaviour of nano-sized Bi4Ti3O12 (BIT) and micron-sized CaBi2Nb2O9 (CBNO) powders is described. The densification process of both powders is very rapid, i.e. the densification occurs within a very narrow time interval (2–3 min using a heating rate of 100 °C min−1 and a pressure of 50 MPa). The BIT powder exhibits a lower densification onset temperature (∼650 °C) and higher maximum shrinkage rate (8.9 × 10−3 s−1 at 780 °C) than that of the CBNO powder (∼825 °C and 4.5 × 10−3 s−1 at 950 °C). Isothermal compaction studies revealed that fully dense nano-sized BIT compacts could be obtained within the temperature region 750 °C < Tiso < 850 °C while for Tiso > 850 °C compacts containing elongated platelet grains are formed. A new preparation route to produce highly textured compacts is described in detail. Appropriate pre-forms are prepared by spark plasma sintering (SPS) and these fully dense compacts are subject to superplastic deformation in the SPS unit to achieve a total compressive strain of ∼60%. This strain was achieved within a period of 1.5 min and with a maximum strain rates of 1.1 × 10−2 s−1 achieved at ∼840 °C and 1.3 × 10−2 s−1 at 1020 °C for the BIT and CBNO compacts, respectively. The X-ray studies showed that the Lotgering orientation factors of grains in the deformed BIT and CBNO compacts are 99% and 70%. The formation of highly textured compacts is suggested to be governed by a superplastic deformation-induced directional dynamic ripening mechanism. 相似文献
30.