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51.
Young?Tae?Im Seung?Tae?ChoiEmail author Tae?Sang?Park Jae?Hyun?Kim 《Journal of Mechanical Science and Technology》2004,18(1):12-19
Using LSM (laser scanning method), the radius of curvature due to thermal deformation in polyimide film coated on Si substrate
is measured. Since the polyimide film shows viscoelastic behavior, i.e., the modulus and deformation of the film vary with
time and temperature, we estimate the relaxation modulus and the residual stresses of the polyimide film by measuring the
radius of curvature and subsequently by performing viscoelastic analysis. The residual stresses relax by an amount of 10%
at 100°C and 20% at 150°C for two hours. 相似文献
52.
M. E. Karabin F. Barlat R. Becker 《International Journal of Mechanical Sciences》2003,45(9):2004-1503
Many bulk forms of metal products are quenched after heat treatment in order to preserve material characteristics. Rapid quenching results in large thermal stress gradients that lead to high levels of residual stress. For products such as plates and extrusions, stretching by a few percent can reduce these stresses, but the stresses are not completely relieved. This report presents a simplified analytical model of the stress relief process illustrating the effects of through-thickness property gradients on residual stress after stretching. The basic conclusion is that for plates with uniform yield surface shapes through the thickness, the through-thickness residual stress range after stress relief is equal to the strength range in the direction of stretch. In extrusions, the bow after stress relief is proportional to this strength range. Cases are also considered in which the yield surface shapes range from isotropic to anisotropic through the thickness. Plastic anisotropy can perturb the effect of strength range on residual stress. 相似文献
53.
Dong Ho Bae Chul Han Kim Seon Young Cho Jung Kyun Hong Chon Liang Tsai 《Journal of Mechanical Science and Technology》2002,16(9):1054-1064
Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the
development or refinement of welded product designs. Various researchers have studied several thermal models associated with
the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated.
These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict
the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately
determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared.
Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts
wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results
in reasonable agreement with the experimental data. 相似文献
54.
In this study, residual stress distribution in multi-stacked film by MEMS (Micro-Electro Mechanical System) process is predicted
using Finite Element method FEMi. We develop a finite element program for residual stress analysis (RESA) in multi-stacked
film. The RESA predicts the distribution of residual stress field in multi-stacked film. Curvatures of multistacked film and
single layers which consist of the multi-stacked film are used as the input to the RESA. To measure those curvatures is easier
than to measure a distribution of residual stress. To verify the RESA. mean stresses and stress gradients of single and multilayers
are measured. The mean stresses are calculated from curvatures of deposited wafer by using Stoney’s equation. The stress gradients
are calculated from the vertical deflection at the end of cantilever beam. To measure the mean stress of each layer in multi-stacked
film, we measure the curvature of wafer with the left film after etching layer by layer in multi-stacked film. 相似文献
55.
Ok Sam Kim 《Journal of Mechanical Science and Technology》1998,12(6):1126-1134
Single crystal silicon (SCS) is used in a variety of microsensor applications in which stresses and other mechanical effects
may dominate device performance. One of major problems associated with the manufacturing processes of the microaccelerometer
based on the tunneling current concept is temperature gradient and thermal stressess. This paper deals with finite element
analyses of residual stresses causing popping up, which are induced in micromachining processes of a microaccelerometer. The
authors model temperature-dependent mechanical properties during focused ion beam (FIB) cutting and Pt deposition processes.
The maximum thermal strain of 0.0012 occurred at the readout gap of the microaccelerometer during the Pt deposition process.
The stress produced during the heating process of FIB cut was also found to be about 33–36 MPa and cooling process the maximum
equivalent stress of about 34MPa still at the right corner of readout gap. The calculated maximum displacement occurred at
the readout gap was 0.14 μm. This is still smaller than the popping up of about 2 μm observed in the experiment. The reason for this popping up phenomenon in munufacturing processes of microaccelerometer may
be the bending of the whole wafer or it may come from the way the underetch occurs. Different SOI material and a new geometry
of the accelerometer are under investigation. We want to seek after the real cause of this pop up phenomenon and diminish
this by changing munufacturing processes of microaccelerometer. 相似文献
56.
表面微机械微小量程压力传感器采用多晶硅薄膜等有内应力的敏感膜片时,应力往往会使膜片的力学灵敏度大大下降,无法满足微量程测量的要求。波纹膜片可以消除或减小应力来提高灵敏度,但是其波纹结构本身又会造成力学灵敏度下降,从而部分抵消了应力消除的效果。提出一种新型深盆腔膜片结构,在消除应力的同时实现了比平膜片还高的力学灵敏度,可以提高微压传感器和微麦克风的灵敏度。采用解析和有限元 两种方法相结合的方法,对该种膜片进行了分析和研究。对比平膜和波纹膜结构,显示了深盆腔膜在力学灵敏度方面的显著提高。 相似文献
57.
本文对由 Ce~(4 )引发的、在真丝上的 MMA(甲基丙烯酸甲酯)接技共聚的反应体系,进行了研究。实验结果表明,接枝反应的速率取决于引发剂及单体的浓度,反应温度和真丝性质的差异。此外,还研究了不同种类稀土离子 Ce~(4 )和硫酸铜浓度对该反应速率的影响。 相似文献
58.
从受扭圆轴M—φ图的相互换算公式出发,利用Nadai公式,推导出大直径受扭圆轴经弹塑性状态后的残余剪应力计算公式,计算简便、准确,在理论上较好地解决了这一问题,并弥补了各种实测法的不足。 相似文献
59.
The apparent cohesion due to soil suction plays an important role in maintaining the stability of steep unsaturated soil slopes with deep ground water table. In this paper, a modified direct shear box is used to determine the relationships between the value of this additional cohesion and the associated soil suction. The apparatus incorporates a miniature tensiometer which allows for the simple and direct measurement of suction during shearing. The soil-water characteristic curves and shearing behavior of intact residual soils, being low-to-medium plasticity silts, as well as silty sand, taken from four landslide-prone areas in Thailand, have been investigated. The relatively low air-entry suctions (0–7 kPa) and bimodality of the soil-water characteristic curves gives an indication of the structured pore size distribution of the materials tested. Samples with higher suction tend to display stronger bonding at particle contacts and thus are more brittle. The shear strength is found to increase nonlinearly with suction, though linearization can be reasonably assumed for suction below around 30 kPa. Prediction of shear strength based on soil-water characteristic curves agrees better with ultimate than peak values. A simple equation is proposed for the minimum ultimate strength that can be expected in an unsaturated residual soil with a suction lower than about 30 kPa. 相似文献
60.