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排序方式: 共有1062条查询结果,搜索用时 109 毫秒
991.
S.C. Goh C.H. Chia S. Zakaria M. Yusoff C.Y. Haw Sh. Ahmadi N.M. Huang H.N. Lim 《Materials Chemistry and Physics》2010
In this work, CoFe2O4 nanocrystals with high saturation magnetization (Ms) and high coercivity (Hc) have been fabricated via a simple hydrothermal method and without subsequent calcination. The resulting CoFe2O4 nanocrystals are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry, differential scanning calorimetry and vibrating sample magnetometry. The results indicate that CoFe2O4 nanocrystals are single crystal and the average crystallite size is increasing with the hydrothermal temperature. The electron micrographs show that the nanocrystals are well-dispersed and possess uniform size. The shape of CoFe2O4 nanocrystals is transformed from spherical into rod by increasing the hydrothermal temperature. The nanocrystals show relatively high Ms of 74.8 emu g−1 and Hc of 2216 Oe, as compared to previous reported results. The obtained results reveal the applicability of this method for efficiently producing well crystallized and relatively high magnetic properties CoFe2O4 nanocrystals as compared to other methods. More importantly, it does not require further calcination processes. 相似文献
992.
Richard Ritikos Boon Tong Goh Khairul Anuar Mat Sharif Muhamad Rasat Muhamad Saadah Abdul Rahman 《Thin solid films》2009,517(17):5092-4957
Multilayer thin films consisting of a-CNx:H/nc-Si:H layers prepared by radio-frequency plasma enhanced chemical vapour (r.f. PECVD) deposition technique were studied. High optical reflectivity at a specific wavelength is one of major concern for its application. By using this technique, a-CNx:H/nc-Si:H multilayered thin films (3-11 periods) were deposited on substrates of p-type (111) crystal silicon and quartz. These films were characterized using ultra-violet-visible-near infrared (UV-Vis-NIR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field effect scanning electron microscopy (FESEM) and AUGER electron spectroscopy (AES). The multilayered films show high reflectivity and wide stop band width at a wavelength of approximately 650 ± 60 nm. The FTIR spectrum of this multilayered structure showed the formation of Si-H and Si-H2 bonds in the nc-Si:H layer and CC and N-H bonds in a-CNx:H layer. SEM image and AES reveal distinct formation of a-CNx:H and nc-Si:H layers in the cross section image with a decrease in interlayer cross contamination with increasing number of periods. 相似文献
993.
ABSTRACT: Incidences of foodborne outbreaks involving enterohemorrhagic Escherichia coli strains with mutations in a key regulatory gene, rpoS , have been reported. Incentives, if any, for losing this regulatory function are not clear since the RpoS regulator is required for the expression of several environmental stress tolerance genes. RpoS also positively regulates 2 of the 3 acid-resistance systems of E. coli under aerobic growth conditions and enables the pathogen to survive gastric acid challenge. We selected 7 enterohemorrhagic E. coli isolates, 6 of which are known to carry defective rpoS gene, and then analyzed resistance to synthetic gastric juice after the strains were inoculated on fresh-cut lettuce and stored under modified atmosphere packaging (MAP) conditions. Subatmospheric oxygen partial pressures in MAP enabled all 6 rpoS- defective isolates to induce acid resistance over the 8-d storage period if the temperature was ≥ 15 °C. No acid resistance was induced for MAP-stored lettuce left at temperatures ≤ 10 °C or for lettuce packed and stored under aerobic conditions. The data underscore the impending danger of abusive storage temperatures especially with regard to the application of MAP to extend the shelf life of fresh produce. The results also highlight the biological significance of having multiple acid-resistance pathways and the complex regulatory network of enterohemorrhagic E. coli strains. 相似文献
994.
K.P. Pramoda N.T.T. Linh P.S. Tang W.C. Tjiu S.H. Goh C.B. He 《Composites Science and Technology》2010
Poly(methyl methacrylate) (PMMA) nano composites were synthesized by melt compounding technique. Different graphite loadings were investigated, including some treated with poly(vinylidene fluoride) (PVDF). A homogeneous dispersion of graphite throughout the PMMA matrix was observed under microscopic analysis. Thermo-gravimetric analysis showed the incorporation of graphite resulted in improvement of thermal stability of neat PMMA. Dynamic mechanical thermal analysis also showed a significant improvement in the storage modulus over the temperature range of 25–150 °C. Coating the graphite with a small amount of PVDF was found to further extend the improvement in the modulus of the PMMA nano composite at 1 wt.% graphite loading. 相似文献
995.
Coordinating Multiple Agents via Reinforcement Learning 总被引:2,自引:0,他引:2
Gang?ChenEmail author Zhonghua?Yang Hao?He Kiah Mok?Goh 《Autonomous Agents and Multi-Agent Systems》2005,10(3):273-328
In this paper, we attempt to use reinforcement learning techniques to solve agent coordination problems in task-oriented environments. The Fuzzy Subjective Task Structure model (FSTS) is presented to model the general agent coordination. We show that an agent coordination problem modeled in FSTS is a Decision-Theoretic Planning (DTP) problem, to which reinforcement learning can be applied. Two learning algorithms, coarse-grained and fine-grained, are proposed to address agents coordination behavior at two different levels. The coarse-grained algorithm operates at one level and tackle hard system constraints, and the fine-grained at another level and for soft constraints. We argue that it is important to explicitly model and explore coordination-specific (particularly system constraints) information, which underpins the two algorithms and attributes to the effectiveness of the algorithms. The algorithms are formally proved to converge and experimentally shown to be effective. 相似文献
996.
Goh JC Lee PV Ng P 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2002,216(6):359-368
Rapid prototyping (RP) technology has been used recently as a means for automated socket fabrication. Although the technology has proven to be promising and has truly automated the socket fabrication process, the structural integrity of RP sockets remains questionable. For the long term, unsupervised use of these 'unconventional' sockets, their material properties and structural integrity must be determined. This study investigated the structural integrity of polypropylene sockets manufactured using a polymer deposition technique, in which a socket is formed by a continuous strand of partially melted polypropylene that is spirally deposited according to the socket's cross-sectional contour. To investigate the problem of delamination of the socket, the tensile properties of the socket material were determined according to ASTM D638-99. The ultimate tensile strength was found to be approximately 13-23 per cent lower than that of polypropylene sheets that are at present normally used for socket fabrication. In order to improve the load-bearing capacity of the socket, it was reinforced using a double-wall arrangement at the distal region, where failure normally occurs. The structural integrity of the complete prosthesis was then investigated according to ISO 10328 (loading condition II). The prosthesis passed the static loading test registering only 12 mm permanent deformation, and it successfully completed a preliminary cyclic test of 250,000 cycles with no observable failure. 相似文献
997.
Summary The Brillouin spectrum of polyethylene has been measured as a function of temperature. Slope discontinuities of opposite directions have been observed in the Brillouin shift and width near the glass transition temperature. The former is attributed to a corresponding discontinuity in the temperature coefficient of specific volume, while the latter to the onset of long-range coordinated molecular motion near the transition region. 相似文献
998.
DF Kallmes AJ Evans RJ Woodcock RA Omary JE Dix BC McNulty CA Holder JE Dion 《Canadian Metallurgical Quarterly》1996,200(2):403-405
PURPOSE: To optimize parameters with computed tomographic angiography for the detection of cerebral aneurysms. MATERIALS AND METHODS: Model aneurysms were placed randomly at various branch points and scanned multiple times with spiral technique. The final analysis included 63 branch points and 22 aneurysms. Each spiral scan used a different parameter combination. Collimation ranged from 1.5 to 4.0 mm and pitch ranged from 1:1 to 1.5:1. Images were constructed with shaded surface display (SSD) and maximum intensity projection (MIP) algorithms and were interpreted by three readers for the presence or absence of aneurysm. RESULTS: The receiver operating characteristic (ROC) curve area for 1.5-mm collimation was greater than those of 3- or 4-mm collimation (P < .01 and P < .001, respectively). There was no statistically significant difference in the ROC curve areas between 3- and 4-mm collimation (P = .37). There was no statistically significant decrease in ROC curve area when increasing pitch from 1:1 to 1.5:1 for any value of collimation (P = .96). For all parameter combinations the ROC curve areas for SSD images was greater than that of MIP images (P < .0001). CONCLUSION: For cerebral aneurysm detection, narrow collimation is superior to wider collimation. Mild increases in pitch do not substantially degrade diagnostic accuracy. SSD offers improved diagnostic accuracy over MIP display in this model. 相似文献
999.
The disturbance rejection problem for structured systems is solved. A graph is associated with such a structured system. Disturbance rejection is shown to be solvable by state feedback whenever the control inputs reach the outputs more quickly than the disturbances in the associated graph. The infinite structure of a structured system is characterized in terms of input-output paths in the associated graph 相似文献
1000.
Copolymers of allyl methacrylate with methyl methacrylate or n-butyl methacrylate were synthesized by group transfer polymerization. The pendant allyl groups of the copolymers were then
hydrobrominated, followed by reaction with sodium azide. Fullerene was incorporated via an addition reaction of fullerene
with azide group. The resulting fullerene-containing poly(alkyl methacrylate)s have fairly narrow polydispersities.
Received: 17 September 1997/Revised version: 4 November 1997/Accepted: 7 November 1997 相似文献