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排序方式: 共有1747条查询结果,搜索用时 15 毫秒
851.
To investigate the precision achieved by human measurement on a digitizing board, 100 healthy volunteers (46 women, mean age 36 +/- 12 years) were asked to measure 15 times on artificial pattern composed of 15 points. A high precision digitizing board (programmed to the technical accuracy of +/- 50 microns) was used, and mean and maximum errors in measuring the same distance repeatedly and relocalizing the same point repeatedly were obtained for each volunteer. A median mean and maximum error of 0.2 mm and 1.0 mm were found for repeated distance measurement. When simulating QT dispersion measurement (measuring the same distance 12 times), median value of 20 ms was obtained for ECGs of 25 mm/s paper speed. The study concludes that human precision of operating a digitizing board is rather poor. A recommendation is given to use either a computer screen for manual measurement of ECGs or to provide an operator of the digitizing board with an immediate feedback of the precision and measurement stability achieved so that erroneous measurement can be actively rejected. 相似文献
852.
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854.
Barry M. Verdegan Brian W. Schwandt Stephen L. Fallon Joe Malik 《Filtration+Separation》1997,34(10):1061-1064
In oil filtration, particles must attach to the filter medium, typically fibres. Attachment is a function of the chemical and physical properties of both the contaminant and the filter medium. Cellulose and synthetic filter media are commonly used in oil filtration. The contaminants include wear metal particles, silica and soot. Because of differences in size and in physical and chemical characteristics, significant differences in contaminant attachment and removal are expected. Experiments were conducted in which filters were challenged with contaminants exhibiting different physical and chemical characteristics. It was found that contaminant shape, roughness and size distribution influence removal. Indirect evidence suggests that chemical interactions also influence removal. The structure of the filter medium mediates these effects. 相似文献
855.
856.
Hung Manh Ho Adnan Anwar Malik Jiro Kuwano Hafiz Muhammad Awais Rashid 《Soils and Foundations》2021,61(3):874-885
This study investigates the load transfer mechanism that includes the effect of helix bending deflection on end-bearing capacity, distribution of ground pressure under the helix and soil deformation around the screw pile. The helix to shaft diameter ratio of 2.5 and 2.8 with a strong helix and a weak helix were used. The model ground was prepared with fine sand at 80% of relative density. To investigate the load transfer mechanism, the experimental tests were modelled in a 3D finite element code. A good agreement between the experimental and numerical approaches was found. The numerical analyses showed that large influence zone exists under screw pile with strong helix, which resulted in higher mobilized soil shear strength that contributed to higher end-bearing capacity. In the case of strong helix, uniform pattern of pressure distribution was observed under the central shaft and the helix. Similar pattern of pressure distribution under the central shaft was observed in weak helix case but the pattern of pressure distribution under the helix changed from uniform to triangular to trapezoidal at various stages during the load test. The normalized end-bearing capacity decreased linearly with the increase in normalized helix bending deflection in both approaches, i.e. experimental and numerical. 相似文献
857.
Shahzeb Ullah Khan Muhammad Zafar Riaz Ullah Abdelaaty A. Shahat Mushtaq Ahmad Shazia Sultana Khafsa Malik 《Microscopy research and technique》2021,84(1):42-55
In this study we have discussed pollen morphology of 14 mimosaceous species belonging to five genera by using light microscopy (LM) and scanning electron microscopy (SEM). The palynological features of species were determined by both qualitative and quantitative characters. The qualitative characters include pollen shape, colpi arrangement, and exine sculpturing. Oblate spheroidal shaped pollens were noted in Albizia procera, Albizia lebbeck, Acacia tortilis, Acacia ampliceps, and Acacia modesta, subprolate shaped pollen in Leucaena leucocephala, Prosopis julifera, and Acacia nilotica, prolate pollen in Acacia farnesiana and Prosopis glandulosa while spheroidal, sub spheroidal and sub oblate pollen grains were observed in Acacia catechu, Mimosa himalayana, Prosopis cineraria, respectively. Sparsely foveolate, reticulate, scabrate, and scrobiclate exine sculpturing were observed. Colpi with sunken ornamentation were seen in P. cineraria, P. glandulosa, P. juliflora, and L. leucocephala while colpi were absent in rest of the studied species. The quantitative characters were statistically studied using SPSS software. The current study gives important morpho‐palynological characters for identifying and validation of close related and similar taxa which will aid to the phylogenetic analysis of Mimosaceae family. 相似文献
858.
All these years, several studies have been carried out to find feasible, viable and dominant alternate source to fossil fuels, with the primary interest of enhancing engine performance and reducing exhaust tail pipe emissions. The present work enumerates the performance and emission characteristics of low-heat rejection engine (LHRE) coated with the alumina–zirconia (Al2O3–ZrO2) composite. Experimental results proved improvement in brake thermal efficiency, brake-specific fuel consumption and well-to-wheel reduction of carbon monoxide, hydrocarbon and smoke emission for coated engine (CE) in comparison with uncoated engine (UCE). Neat diesel, new high-potential punnai methyl ester and its diesel blends were used as test fuels. However, in the experimental study, oxides of nitrogen increased for CE than UCE. 相似文献
859.
Saransh Malik Sangmi Moon Bora Kim Cheolwoo You Huaping Liu Intae Hwang 《Wireless Personal Communications》2014,74(2):773-788
We propose an adaptive modulation and coding (AMC) scheme using relay protocols AF, DF and DMF. The AMC scheme is used for improving the throughput and reliability of a communication system, using different modulation and coding schemes. We analyze the performance of relay protocols with the AMC scheme and observe that relay protocols with the AMC scheme are capable of providing better average throughput at a lower signal to noise ratio (SNR) level as compared to the conventional scheme with no AMC. We perform Monte Carlo simulations based on 3GPP long term evolution-advanced parameters to prove the performance comparison of adaptive modulation and coding scheme (MCS) relay protocols with non-adaptive MCS relay protocols. The simulation results of the proposed system with adaptive MCS prove that among the amplify-and-forward (AF), decode-and-forward (DF) and de-modulate-and-forward (DMF), the DMF protocol performs best, at a lower SNR value and higher average throughput. 相似文献
860.
Saransh Malik Bora Kim Sangmi Moon Cheolwoo You Huaping Liu Jeong-Ho Kim Intae Hwang 《Wireless Personal Communications》2014,77(4):2945-2958
In this paper, an adaptive relay scheme of hybrid relay system is proposed based on channel state information of the received signal-to-noise ratio (SNR) at the relay node. hybrid relay system is comprised of amplify-and-forward, decode-and-forward and demodulate-and-forward together in cooperative networks. The relay protocols are selected adaptively, on the basis of power allocation (PA) constraint, or the SNR value at previous hop. Thus multihop performance of the relay system can be improved by applying PA allocation scheme. The simulation results show that the performance of the novel hybrid relay protocol can be improved significantly compared to the conventional hybrid system in terms of error performance and link efficiency. 相似文献