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61.
62.
In this paper, the average stress method for the fatigue limit evaluation of stress raising geometrical features is revised and extended. In particular, an analytical close‐form approach was used and the linear elastic stress equations were modified by taking into account the effect of nominal stress on the local stress distribution. Hence, the average tangential stress was correctly evaluated over a distance of 2a0, where a0 was El Haddad's short crack constant, for long and small notches as well as for crack‐like notches. When this model is applied to a wide range of geometrical features subjected to mode I fatigue loading, the classical shape of the curves of the Kitagawa–Takahashi diagram was obtained for changes in crack‐like notch size. Similarly, notch sensitivity was estimated by reducing the notch tip radius. The accuracy of the proposed method in predicting fatigue limits was then checked by using experimental data taken from the literature and generated on testing specimens weakened by rounded and sharp notches as well as by small artificial defects. 相似文献
63.
Naotake Noda 《热应力杂志》2013,36(2):135-147
This paper treats a transient thermoelastic contact problem in a long, circular cylinder to which a heated rigid band is bonded. The problem may be reduced to that of solving dual-integral equations. The radial, hoop, and axial stresses have singularities at the end of rigid band on the cylindrical surface. The coefficients which may determine the strength of singularities of stresses are introduced. 相似文献
64.
Peter Hndel Petr Tichavsky Sergio M. Savaresi 《International Journal of Adaptive Control and Signal Processing》1998,12(5):417-436
The performance of a recently proposed high-order adaptive notch filter (HANF) for frequency estimation and tracking is studied. An analysis technique utilizing approximations with linear filters is employed to derive closed-form performance expressions for a noisy sinusoidal input signal. Important performance measures, such as stability, noise rejection, statistical efficiency, and tracking ability, are studied in detail, and rules for the design variables are given. A study is presented where the performance of HANF is compared with the performance of a minimal order adaptive notch filter (ANF), as well as with a frequency tracker based on least squares-modelling—the multiple frequency tracker (MFT). The study reveals that HANF is a competitive alternative to ANF, but also that, in general, the MFT is the method of choice. © 1998 John Wiley & Sons, Ltd. 相似文献
65.
焊接接头的多轴疲劳强度评估是领域内的复杂课题.结合缺口应力法,利用ⅡW多轴疲劳准则对已公开发表的文献中的多轴疲劳试验数据进行了重新评估.结果表明,缺口应力系统下的比例加载与非比例加载数据点重合性较好;ⅡW推荐的单轴疲劳评估S-N曲线不适用于多轴疲劳评估,循环次数在1×104 ~1×105范围内时,可能得到偏危险的评估结果;而高于1×105次时,评估结果过于保守.基于此,拟合得到了存活率Ps=97.7%的S-N评估曲线,其疲劳等级FAT=430 MPa,斜率m=5.8,同时适用于比例加载与非比例加载,可为工程焊接结构疲劳寿命预估提供参考. 相似文献
66.
一种基于自适应陷波器的电网频率测量新方法 总被引:11,自引:5,他引:11
该文提出一种测量和跟踪电网频率变化的新方法:采用两级自适应陷波滤波器结构,第一级陷波器用来滤除谐波并得到加强的基波成分,再经过降采样处理把基波频谱拓宽后,由第二级陷波器来估计基波频率。陷波器的自适应算法是非梯度搜索的,使其运算量大大简化,适用于实时处理的场合。并通过仿真来说明该方法具有测量精度高和响应时间快的特点。 相似文献
67.
Only for steels up to grade S690QL the well‐known fact is confirmed that the fatigue strength of welded joints is independent of the material. For higher strength steels a remarkable reduction of the fatigue strength is found. Some advice is given for designers in which situations the one or the other of the various approaches for the assessment of the fatigue strength of welds could be applied. In complex, real situations even the highly sophisticated effective notch stress approach might loose its applicability. A new alternative approach is proposed for these situations. It is based on stresses in real notches and an example is presented for the familiar case of a start‐stop position. 相似文献
68.
J. A. Wang K. C. Liu D. E. McCabe & S. A. David 《Fatigue & Fracture of Engineering Materials & Structures》2000,23(11):917-927
A new method to determine fracture toughness K IC of materials is introduced. A round-rod specimen having a V-grooved spiral line with a 45° pitch is tested under pure torsion. An equibiaxial tensile/compressive stress state is effectively created to simulate conventional test methods using a compact-type specimen with a thickness equivalent to the full length of the spiral line. K IC values are estimated from the fracture load and crack length with the aid of a three-dimensional finite element analysis. K IC of 7475-T7351 aluminium is estimated to be 51.3 MPa √m, which is higher than the vendor's value in the TL orientation by ∼0.8% and higher than 0.5T compact tension (CT) value by 6%; A302B steel yields 54.9 MPa √m being higher than CT test value by ∼2%. Good agreement between the K IC values obtained by different methods indicates the proposed method is sound and reliable. 相似文献
69.
Finite element modelling was conducted on notched members subjected to proportional and non-proportional loading. A recently developed cyclic plasticity model capable of accurately describing cyclic material behaviour was implemented into a finite element code. A plate with a central hole and a shaft with a circumference groove were studied. Approximate methods for the notched problems were critically evaluated using the finite element results. 相似文献
70.
Specific features of high-cycle and ultra-high-cycle fatigue 总被引:1,自引:0,他引:1