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51.
One of the most useful geosynthetics in soil reinforcement is geogrid due to its high tensile strength, having a great influence on soil skeleton reinforcement and eventually, increasing bearing capacity of the foundation. In this research, a series of 36 repeated plate load tests have been carried out to investigate the scale effect on geogrid-reinforced soil, tending to further understanding of the behaviour of geogrid-reinforced soil system. Four different soil grains sizes, two different geogrid's aperture sizes (with roughly the same tensile strength) and three different loading plate sizes are the variables considered. During the tests, the applied loading and soil surface settlements were recorded to evaluate the systems' response. As it was expected, the reinforced soil exhibited higher bearing capacity than the unreinforced status, up to 635%. The results show that increasing loading plate size and soils' particle size fortify the response of foundation, especially in reinforced status, against the loading plate penetration. The results further focused on the important role of scale effect on the response of reinforced foundation. It was understood that the optimum nominal aperture size of geogrids should be about 4 times of medium grain size of soil. Also, it was found out that in order to acquisition of highest reinforcement benefits, the footing's width should be in the range 13–25 (20 in average) times of medium grain size of the backfill. Finally, to achieve the best results, it is recommended that the aperture size of geogrids should be selected roughly 0.2 times of footing width. 相似文献
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53.
本文结合云霄翔球广场一期工程静压PHC管桩施工实例,对2#楼主楼采用先引孔后压桩法施工技术和施工工艺,使桩端穿过砂层及卵石层进入持力层深度及有效桩长满足设计及规范要求,以保证施工质量和工期。 相似文献
54.
为验证4~5 MW风电增速箱轴承性能,研制一台轴承试验机。该试验机可以通过载荷谱控制轴承旋转方向、转速、承受的轴向和径向载荷以及润滑油流量来模拟轴承实际工况,并使用测量轴承振动和温度的方法来侧面反映轴承的实时状态。使用变频器控制变频调速电机使轴承变速变向,液压比例伺服阀可变精准加载,润滑比例流量阀调整润滑油流量,铂热电阻温度传感器测量轴承温度,加速度传感器配合振动采集模块测量轴承振动。试验机可以通过加快轴承转速和增大轴承载荷的方法,只需要普通寿命试验几十分之一的时间就足以完成强化寿命试验。通过50 000 min的测试,试验机运行平稳、可靠性良好,数据正常,达到了设计目的。 相似文献
55.
为测量不同温度下轴承的摩擦力矩,基于传递法测量原理,设计一种新型轴承摩擦力矩测量设备。设备中保温箱下层的工艺孔使用密封结构进行密封,并针对被测轴承与测量主轴对接时产生的冲击问题,设计新型类鼠盘式可分离夹具,实现对接时的平稳过渡。使用LabVIEW编写相关运动控制、数据采集、控制界面程序。经程序计算处理后,获取轴承摩擦力矩值、变化曲线等数据。最后,使用该设备对SKF7207深沟球轴承进行摩擦力矩测量。结果表明:设备最大重复测量误差为0.000 49 N·m,重复性较好,满足设计要求。 相似文献
56.
《Soils and Foundations》2019,59(6):2206-2219
Soil-cement columns are widely used to improve soft ground, and the bearing capacity of the formed composite ground is a key design parameter. The currently employed design method was developed for composite grounds under rigid footings, whilst the bearing capacity behavior of composite grounds under earth fills with different degrees of stiffness has rarely been investigated. Hence, the present study attempts to fill this gap. In this investigation, 1-g laboratory model tests are conducted to compare the bearing capacity behavior of composite grounds under a rigid footing and under embankment fill, based on which a numerical model that can capture the strain-softening behavior of soil-cement columns is established. The calibrated numerical model is further employed to perform 144 analyses. The results indicate that the failure mode of composite grounds differs for different types of earth fills: soil failure occurs prior to column failure under soft clay and dredged slurry, whereas column failure is the primary failure mode for composite grounds under embankment fill. This difference in failure mode of composite grounds can be explained using soil arching theories. For different failure modes, different bearing capacity efficiency factors should be used in design. 相似文献
57.
《Soils and Foundations》2019,59(5):1280-1291
This study focuses on the impact of relative density on the bearing capacity of unsaturated sand using both theoretical predictions and measurements from physical modeling tests. The theoretical predictions incorporate the effective stress, quantified using the suction stress concept and friction angles obtained from direct shear tests on unsaturated sand specimens at different relative densities and degrees of saturation, into conventional bearing capacity equations. The suction stress values inferred from the failure envelopes were found to match well with values predicted from the soil-water retention curves for sands with different relative densities. Moreover, the bearing capacity values measured in physical modeling experiments involving loading of a circular footing atop unsaturated silty sand layers having different initial degrees of saturation matched well with the predicted bearing capacity values from an effective-stress based model. As expected, the bearing capacity was greater for soils with increasing relative density, but an interesting observation is that a transition from general to local shear failure occurred at a certain combination of relative density and degree of saturation. For the silty sand tested, this transition occurred at a relative density of 0% for degrees of saturation between 4 and 16% and at a relative density of 40% for degrees of saturation between 30 and 90%. General shear failure was always observed at relative densities of 70 and 90%. 相似文献
58.
《CIRP Annals》2019,68(1):385-388
A novel semi-active joint for connecting mechanical (i.e., sliding/rolling) bearings or guideways to an ultra-precision motion stage is presented. The semi-active joint enables the benefits of bearing/guideway friction on in-position stability while avoiding its adverse effects on rapid ultra-precision positioning. The joint is equipped with solenoids that switch its stiffness from low, during settling, to high once the stage gets into position. A two-step scheme is implemented to mitigate adverse effects of switching on positioning performance. Experiments demonstrate up to 81% and 60% improvements in settling time and in-position stability, respectively, compared to cases with solely low- or high-stiffness joints. 相似文献
59.
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