全文获取类型
收费全文 | 1574篇 |
免费 | 56篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 21篇 |
综合类 | 1篇 |
化学工业 | 329篇 |
金属工艺 | 45篇 |
机械仪表 | 54篇 |
建筑科学 | 44篇 |
矿业工程 | 2篇 |
能源动力 | 87篇 |
轻工业 | 97篇 |
水利工程 | 16篇 |
石油天然气 | 10篇 |
无线电 | 159篇 |
一般工业技术 | 334篇 |
冶金工业 | 200篇 |
原子能技术 | 4篇 |
自动化技术 | 229篇 |
出版年
2023年 | 11篇 |
2022年 | 19篇 |
2021年 | 35篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 45篇 |
2015年 | 24篇 |
2014年 | 53篇 |
2013年 | 93篇 |
2012年 | 60篇 |
2011年 | 85篇 |
2010年 | 70篇 |
2009年 | 80篇 |
2008年 | 77篇 |
2007年 | 67篇 |
2006年 | 41篇 |
2005年 | 48篇 |
2004年 | 28篇 |
2003年 | 41篇 |
2002年 | 42篇 |
2001年 | 25篇 |
2000年 | 17篇 |
1999年 | 23篇 |
1998年 | 37篇 |
1997年 | 28篇 |
1996年 | 36篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 20篇 |
1985年 | 23篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有1632条查询结果,搜索用时 15 毫秒
81.
82.
83.
This paper describes a PC based centralized monitoring of the running condition of a multi-machine system. This kind of monitoring from remote central location is one of the primary requirements in today’s era of automation. The convergence of embedded system like microcontroller/DSP/FPGA, etc., now-a-days, is adding a new dimension to enhance the capability of the PC based data acquisition. In this present approach, conditions of different parameters of each motor have been measured by dedicated microcontroller based hardware. All these units are connected in a network using bus topology. All parameters are communicated to a remote PC through this bus where user friendly state-of-the-art developed software stores it for display and analysis purposes. 相似文献
84.
Impact-toughened, compatibilized binary blends of styrene-maleic anhydride (SMA) copolymer/amine functionalized ethylene-propylene (amine-EP) polymer and ternary blends consisting of SMA/amine-EP/high density polyethylene (HDPE) are described. In both blends 0.02 to 4 μm range rubbery inclusions, which toughen the SMA matrix, are formed. SMA sub-inclusions exist in the amine-EP phase. In the ternary blend substantially all of the polyethylene is embedded in the EP phase. Compatibilization of the SMA and the commingled polyolefin phase is promoted by a graft copolymer formed by the reaction of amine groups on the EP with the maleic anhydride groups on the SMA. We describe the morphology, rheology, aging characteristics and impact properties of these blends. SMA modification by SMA-g-(amine-EP) polymers formed in situ in the melt, with HDPE, has not been previously reported. 相似文献
85.
A method of tracking the peak power points for a variable speed wind energy conversion system 总被引:24,自引:0,他引:24
In this paper, a method of tracking the peak power in a wind energy conversion system (WECS) is proposed, which is independent of the turbine parameters and air density. The algorithm searches for the peak power by varying the speed in the desired direction. The generator is operated in the speed control mode with the speed reference being dynamically modified in accordance with the magnitude and direction of change of active power. The peak power points in the P-/spl omega/ curve correspond to dP/d/spl omega/=0. This fact is made use of in the optimum point search algorithm. The generator considered is a wound rotor induction machine whose stator is connected directly to the grid and the rotor is fed through back-to-back pulse-width-modulation (PWM) converters. Stator flux-oriented vector control is applied to control the active and reactive current loops independently. The turbine characteristics are generated by a DC motor fed from a commercial DC drive. All of the control loops are executed by a single-chip digital signal processor (DSP) controller TMS320F240. Experimental results show that the performance of the control algorithm compares well with the conventional torque control method. 相似文献
86.
An experimental study has been performed to detect the occurrence of nanosized carbon particulates below the soot laden zone of a co-flowing partially premixed flame. Samples have been extracted from different points across the flame and passed through DI water. Absorption and fluorescence spectroscopies have been performed with the collected water suspensions. The occurrence of carbon nanoparticles is evident across the inner flame front. In addition, evidence of naphthalene has also been found inside the inner rich premixed flame. The concentration of naphthalene decreases while that of the carbon nanoparticles increases as the inner flame front is reached. The stability of the nanoparticles in the sample has been ensured by observing that the change in fluorescence quantum yield from the sample over a long duration is small. The band gap energy has been evaluated using the absorption data to characterize the likely structures of the particles in the collected suspension. Two kinds of particles having different zones of band gap energy are found in the flame. Dynamic light scattering measurements show that the particle size grows with the increase in height in the lower part of the flame. While, at 3 and 6 mm elevations the particles are observed to be below 2.5 nm in diameter, the particles at 10 mm elevation are found in the size range of 2.5-5.5 nm. 相似文献
87.
Pure titanium and Ti-6Al-4V were exposed at 750°C in an H2/H2O/H2S PO
210–18 Pa and PS
210–1 Pa), H2/H2O (PO
210–18 Pa) and air environments for up to 240 hr. The corrosion kinetics, obtained by the discontinuous gravimetric method, showed that the sulfidation/oxidation kinetics were linear for Ti and linear-parabolic for Ti-6Al-4V in the H2/H2O/H2S environment. Both materials obeyed parabolic rate laws in the H2/H2O atmosphere after a transient period, and linear-parabolic rate laws in air. After exposure to the H2/H2O/H2S atmosphere, the titanium specimen displayed a double scale of TiO2 with an intervening TiS2 film between the double-layered scale of TiO2 and the substrate. Ti-6Al-4V also contained a double layer of TiO2 together with a stratum consisting of Al2S3, TiS2 and vanadium sulfide at the junction of the inner TiO2 layer and substrate. Some Al2O3 precipitated in the external portion of the outer TiO2 layer. Following oxidation in the low-PO
2 atmosphere a double-layered oxide of TiO2 scale formed on both Ti and Ti-6Al-4V. The scale on Ti-6Al-4V also contained an -Al2O3 film situated between the outer and inner (TiO2) layers. For both materials, multilayered-scale formation characterized air oxidation. In detail a multilayered oxide scale of TiO2 formed on the air-oxidized Ti, while a multilayered oxide scale with alternating layers of Al2O3/TiO2 developed on Ti-6Al-4V oxidized in air. 相似文献
88.
We present in this paper a new energy-efficient communication scheme called CNS (Compression with Null Symbol) that combines the power of data compression and communication through silent symbol. The concept of communication through silent symbol is borrowed from the energy efficient schemes proposed in Sinha (Proceedings
of 6th IEEE consumer communications and networking conference (CCNC), Las Vegas, pp. 1–5, 2009), Ghosh et al. (Proceedings
of 27th IEEE international performance computing and communications conference (IPCCC), USA, pp. 85–92, 2008), and Sinha and
Sinha (Proceedings of international conference on distributed computing and internet technologies (ICDCIT), LNCS, pp. 139–144,
2008). We show that the average theoretical energy saving at the transmitter by CNS is 62.5%, assuming an ideal channel and
for equal likelihood of all possible binary strings of a given length. Next, we propose a transceiver design that uses a hybrid
modulation scheme utilizing FSK and ASK so as to keep the cost/complexity of the radio devices low. Considering an additive
white gaussian noise (AWGN) channel and a non-coherent detection based receiver, CNS shows a saving in transmitter energy
by 30% when compared to binary FSK, for equal likelihood of all possible binary strings of a given length. Simultaneously,
there is a saving of 50% at the receiver for all types of data modulation due to halving of the transmitted data duration,
compared to binary encoding. In contrast, RBNSiZeComm proposed in Sinha (Proceedings of 6th IEEE consumer communications and
networking conference (CCNC), Las Vegas, pp. 1–5, 2009), TSS proposed in Ghosh et al. (Proceedings of 27th IEEE international
performance computing and communications conference (IPCCC), USA, pp. 85–92, 2008) and RZE proposed in Sinha and Sinha (Proceedings
of international conference on distributed computing and internet technologies (ICDCIT), LNCS, pp. 139–144, 2008) generate
average transmitter energy savings of about 41, 20, and 35.2%, respectively. Also, at the receiver side, while RBNSiZeComm
does not generate any saving, TSS and RZE produce about 36.9 and 12.5% savings on an average, respectively. Considering certain
data types that may occur in the context of some wireless sensor networks (WSN) based applications (e.g., remote healthcare, agricultural WSNs, etc.), our simulation results demonstrate that for
AWGN noisy channels, the transmitter side savings vary from about 33–50% on an average, while for RBNSiZeComm, this saving
is about 33–61% on the same data set (Sinha in Proceedings of 6th IEEE consumer communications and networking conference (CCNC),
Las Vegas, pp. 1–5, 2009). Thus, taking into account the low cost/complexity of the proposed transceiver, these results clearly
establish that CNS can be a suitable candidate for communication in low power wireless sensor networks, such as in remote
healthcare applications, body area networks, home automation, WSNs for agriculture and many others. 相似文献
89.
A. Datta S. Dutta S.K. Pal R. Sen 《Journal of Materials Processing Technology》2013,213(12):2339-2349
Tool condition monitoring by machine vision approach has been gaining popularity day by day since it is a low cost and flexible method. In this paper, a tool condition monitoring technique by analysing turned surface images has been presented. The aim of this work is to apply an image texture analysis technique on turned surface images for quantitative assessment of cutting tool flank wear, progressively. A novel method by the concept of Voronoi tessellation has been applied in this study to analyse the surface texture of machined surface after the creation of Voronoi diagram. Two texture features, namely, number of polygons with zero cross moment and total void area of Voronoi diagram of machined surface images have been extracted. A correlation study between measured flank wear and extracted texture features has been done for depicting the tool flank wear. It has been found that number of polygons with zero cross moment has better linear relationship with tool flank wear than that of total void area. 相似文献
90.
Implementation of monitoring strategy for increasing the efficiency of groundwater pollutant source characterization is often necessary, especially when only inadequate and arbitrary concentration measurement data are initially available. Two main parameters that need to be estimated for efficient and accurate characterization of groundwater pollution sources are: location of the source and the time when the source became active. Complexities involved with the explicit estimation of the time of start and source activity have not been addressed so far in previous studies. The main complexity arises due to the fact that the spatial location and time of activity are inter-related. Therefore, specifying one and solving for the other simplifies the source characterization problem. Hence, in this study, both the source location and time of initiation are treated as unknowns. The developed methodology uses dynamic time warping distance in the linked simulation-optimization model to address some complex issues in designing a monitoring network to efficiently estimate source characteristics including the time of first activity of unknown groundwater source. Performance of the developed methodology is evaluated on illustrative contaminated aquifer. These evaluation results demonstrate the potential use of the developed methodology. 相似文献