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排序方式: 共有782条查询结果,搜索用时 15 毫秒
81.
Elsayed-Ali OH Abdel-Fattah T Elsayed-Ali HE 《Journal of hazardous materials》2011,185(2-3):1550-1557
Zeolites are used in environmental remediation of soil or water to immobilize or remove toxic materials by cation exchange. An experiment was conducted to test the use a low electric field to direct the toxic cations towards the zeolite. An electrokinetic cell was constructed using carbon electrodes. Synthetic Linde Type A (LTA) zeolite was placed in the cell. Copper(II) chloride dissolved in water was used as a contaminant. The Cu(2+) concentration was measured for ten hours with and without an applied electric field. The removal of the Cu(2+) ions was accelerated by the applied field in the first two hours. For longer time, the electric field did not improve the removal rate of the Cu(2+) ions. The presence of zeolite and applied electric field complicates the chemistry near the cathode and causes precipitation of Cu(2+) ions as copper oxide on the surface of the zeolite. With increased electric field the zeolite farther away from the cathode had little cation exchange due to the higher drift velocity of the Cu(2+) ions. The results also show that, in the LTA Zeolite A pellets, the cation exchange of Cu is limited to a shell of several tens of micrometers. 相似文献
82.
The effect of gypsum in slag-blended cement on free and restrained shrinkage of concrete subjected to various curing conditions
is presented in this paper. Added gypsum in slag-blended cements was found to increase the autogenous shrinkage of concrete
up to 56 days. However, added gypsum caused small reduction in the long-term shrinkage when the concrete was exposed to drying.
Slag concretes with 3% added gypsum content, when exposed to drying at the age of 24 h, exhibited more cracking tendency than
comparable concrete with 0% added gypsum. This is attributed to the increased shrinkage evolution of slag concrete with 3%
gypsum content at early ages. However, if moist cured for 7 days, increasing the amount of gypsum from 3 to 5% in slag-blended
cement reduced the cracking tendency. It is concluded that the beneficial effect of increasing gypsum in reducing cracking
tendency in slag concrete is only favourable if moist cured for 7 days. 相似文献
83.
Erläuterung des Sprühraffinationsverfahrens, bei dem eine Schmelze mit inertem Gas verdüst wird und die entstehenden Metalltropfen durch eine Raffinationsschlacke fallen. Erörterung der Gesetzmäßigkeiten für die Stoffaustauschvorgänge zwischen Metalltropfen und Schlacke. Bestimmung der mittleren Tropfengröße beim Versprühen von kohlenstoffgesättigtem Roheisen. Untersuchung der Wirkung der Sprühraffination am Beispiel der Entschwefelung des Roheisens mit Schlacken des Systems CaO–CaF2–Al2O3 bei 1600 °C. Ermittlung des Stoffübergangskoeffizienten des Schwefels für den umgekehrt transitorischen Phasenkontakt und Vergleich mit Werten bei anderen Techniken des Phasenkontaktes Metall-Schlacke. 相似文献
84.
Michael Day Tarek Saab 《今日电子》2005,(12):71-72,75
发光二极管(LED)在各种终端设备中已经被广泛使用,从汽车前照灯、交通信号灯、文字显示器、广告牌及大屏幕视频显示器,到普通及建筑照明和LCD背光等最新应用,LED的迅速采用使得最普通的设备也需要重新设计。随着LED效率与亮度的增加以及成本的减少,LED有可能会取代消费类应用中的传统照明技术。本文通过比较采用基于LED的LCD背光的大屏幕显示器中所使用的一些技术,阐述如何解决在使用LED时所面对的一些设计挑战。 相似文献
85.
Tarek S. Kayed 《Materials Research Bulletin》2003,38(3):533-538
The effects of boron doping on the formation and properties of the Tl-based superconductors have been studied. Up to 10 wt.% boron has been added to the oxides having the nominal composition, Tl1.8Ba2Ca2.2Cu3Ox, by the usual solid-state reaction method. Boron additions in the range 0.8-1.0% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of boron additions eliminate the Tl-2223 phase, reduce the fraction of Tl-2212 phase and cause separate non-superconducting phases to be formed. The formation of non-superconducting phases does not allow us to obtain pure Tl-2212 phase. 相似文献
86.
The Sn-Cu eutectic alloy has been produced by rapid solidification using the melt-spinning technique, and both Zn and Bi have
been added individually to it, in the ratio 0.5 wt.%. X-ray diffraction (XRD) analysis and differential thermal analysis (DTA)
have been carried out. Resistivity, Vickers microhardness (HV), and yield stress (σy) have been measured. Also a new method for measuring creep has been described using a HV tester. The creep measured by this
method is termed “microcreep.” It is a quick, nondestructive method and requires a small sample, about 1 cm2, with thickness 1 mm or less. The results show that formation of Cu39Sn11 occurs due to the addition of both Zn and Bi. The addition of Zn increases HV and σy, but slightly lowers the creep resistance; however, the addition of Bi deteriorates the creep resistance. Also, it is found
that the creep rate of as-quenched melt-spun alloys is high. 相似文献
87.
Estimation of solar radiation components incident on Helwan site using neural networks 总被引:3,自引:1,他引:2
Field testing carried out for solar energy applications is costly, time consuming and depends heavily on prevailing weather conditions. Adequate security and weather protection must be provided at the test site. Measurements may also suffer from delays that can be caused by system failures and bad weather. To overcome these problems the need for accurate model becomes evermore important. To achieve such prediction task, an artificial neural network, ANN, model is regarded as a cost-effective technique superior to traditional statistical methods. In this paper, Levenberg optimization function is adopted to predict insolation data in different spectral bands for Helwan (Egypt) monitoring station. The predicted values were then compared with the actual values and presented in terms of usual statistics. The results hint that, the ANN model predicted infrared, ultraviolet, and global insolation with a good accuracy of approximately 95%, 93% and 96%, respectively. In addition, ANN model was tested to predict the same components for Aswan over an 11 month period. The predicted values of the ANN model compared to the actual values for Aswan produced an accuracy of 95%, 91% and 92%, respectively. Data for Aswan were not included as a part of ANN training set. Hence, these results demonstrate the generalization capability of this approach over unseen data and its ability to produce accurate estimates. 相似文献
88.
Eryl D. Owen Tarek N. Al-Akil 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1977,27(1):241-247
The interaction between dilute aqueous solutions of the disazo dye Brilliant Orange and the triphenylmethane dye Crystal Violet results in a decrease in the absorption of Crystal Violet in the region 550–600 nm and the appearance of a new absorption at 494 nm. The decrease in absorbance at 590 nm is characteristic of the metachromic interactions of Crystal Violet with a wide variety of polyanion substrates while the increase at 494 nm is due to the conversion of Brilliant Orange from its azo to its hydrazone tautomer. The relative effects of a variety of organic solvents in reversing the interaction has been investigated. 相似文献
89.
The rotational isomeric state model was employed to provide a better understanding of the role of chain microstructure on the conformational behavior of homogeneous ethylene-1-olefin copolymers. The chain microstructure was assembled in accordance with the copolymerization theory using a set of conditional probabilities in direct relation to the reactivity ratios and the feed compositions of the comonomers. The catalytic inversion influence on the tacticity of the polymeric microstructure was also taken into account by considering the replication probability during the Monte Carlo simulation. Statistical weight factors of the rotational isomeric states were evaluated using molecular dynamics runs of the various homopolymers according to the earlier work of Mattice et al. Probability distribution surfaces constructed by the integration of the molecular dynamics trajectories of sufficient length to sample all of the conformational space indicated the increase of the probability of g±t joint states at the expense of g±g± pairs with the increase in the side chain length of the 1-olefin comonomers. It was also indicated that this behavior had a maximum around poly(1-butene)/poly(1-hexene) with an apparent reversal in case of poly(1-octene) due to the side chain crowding, which forces the chain to favor more of the g±g± joint states. The characteristic ratios calculated for the copolymers on the basis of the rotational isomeric state model also indicated the increased extension of the polymer backbone with the increase in the side chain length. The lower characteristic ratio calculated for the octene polymers may, in fact, explain the experimental observation that poly(1-octene) has a lower melting point than those of other poly(1-olefin)s of shorter side chains. A complete account of the role of tacticity on the characteristic ratio and the radial distribution function is also given. 相似文献
90.
Legierungsverfahren zur Einbringung von Metallen seltener Erden in Versuchsschmelzen. Abhängigkeit der Schwefelabsenkung vom Zusatz dieser Metalle zum Stahl. Ermittlung von Zugfestigkeit, Streckgrenze, Bruchdehnung, Brucheinschnürung und Kerbschlagzähigkeit in Abhängigkeit von der Probenlage (längs, quer und in Dickenrichtung) bei unterschiedlich abgesenkten Schwefelgehalten. 相似文献