全文获取类型
收费全文 | 1006篇 |
免费 | 156篇 |
国内免费 | 66篇 |
专业分类
电工技术 | 135篇 |
综合类 | 82篇 |
化学工业 | 39篇 |
金属工艺 | 96篇 |
机械仪表 | 116篇 |
建筑科学 | 65篇 |
矿业工程 | 14篇 |
能源动力 | 17篇 |
轻工业 | 9篇 |
水利工程 | 16篇 |
石油天然气 | 18篇 |
武器工业 | 10篇 |
无线电 | 121篇 |
一般工业技术 | 360篇 |
冶金工业 | 42篇 |
原子能技术 | 4篇 |
自动化技术 | 84篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 43篇 |
2021年 | 32篇 |
2020年 | 49篇 |
2019年 | 42篇 |
2018年 | 35篇 |
2017年 | 47篇 |
2016年 | 34篇 |
2015年 | 51篇 |
2014年 | 64篇 |
2013年 | 68篇 |
2012年 | 62篇 |
2011年 | 70篇 |
2010年 | 67篇 |
2009年 | 52篇 |
2008年 | 55篇 |
2007年 | 47篇 |
2006年 | 42篇 |
2005年 | 35篇 |
2004年 | 46篇 |
2003年 | 41篇 |
2002年 | 29篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 29篇 |
1997年 | 21篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 14篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1985年 | 2篇 |
排序方式: 共有1228条查询结果,搜索用时 15 毫秒
1.
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
2.
G. MENEGHETTI P. LAZZARIN 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(2):95-106
The paper presents an expression useful to estimate the notch stress intensity factor (NSIF) from finite element analyses carried out by using a mesh pattern with a constant element size. The evaluation of the NSIF from a numerical analysis of the local stress field usually requires very refined meshes and then large computational effort. The usefulness of the presented expression is that (i) only the elastic peak stress numerically evaluated at the V‐notch tip is needed and no longer the whole stress–distance set of data; (ii) the adopted meshes are rather coarse if compared to those necessary for the evaluation of the whole local stress field. The proposed expression needs the evaluation of a virtual V‐notch tip radius, i.e. the radius which would produce the same elastic peak stress than that calculated by FEM at the sharp V‐notch tip by means of a given mesh pattern. Once such a radius has been theoretically determined for a given geometry, the expression can be applied in a wide range of notch depths and opening angles. 相似文献
3.
选用水面舰艇用945钢和潜艇用921A钢,研究了不同焊缝外形尺寸对爆炸试验中三缺口试样的中央缺口开裂行为的影响。通过大量的试验数据,确定了开裂判据e≤e_m,为试验前预示中央缺口开裂与否提供了可靠的依据。 相似文献
4.
爆破切口形状对细高建筑物倒塌效果的影响 总被引:12,自引:7,他引:5
分析了爆破拆除细高建筑物时产生偏斜,前冲和后坐的原因,提出采用梯形和倒梯形爆破切口以准确控制倒塌方法,前冲和后坐。 相似文献
5.
6.
7.
0 IntroductionSelf-shielded flux cored wire is a newly developedwelding material used without gas protection. Use of suchcored wires has grown rapidly in developed countriesbecause of the following advantages: simple use, goodwind resistance ability, lower cost resulted from highproductivity and strong desulfurization ability[1]. Self-shielded flux cored wires are preferred for on-site weldingsuch as ship and barge building, storage tank, bridge,offshore oil platform buildings and so on[2 -3].… 相似文献
8.
This article discusses a technique based on combination of multimode resonators (MMR) and complementary split ring resonators (CSRR) to design multi notch‐bands ultra wide‐band (UWB) band‐pass filters (BPF). The proposed structure consists of two parallel multimode resonators, resulting in a dual notch‐band UWB BPF, integrated with a single cell of CSRR to realize the third notch‐band. The mechanism of realizing the notch‐bands is mathematically presented and a triple notch‐bands UWB BPF is designed, simulated and fabricated. The overall size of the proposed filter is reported to be around 36 × 7.7 mm2 where a size reduction of around 35% is demonstrated in comparison to the conventional filter. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:375–381, 2014. 相似文献
9.
Satellite navigation suffers from performance degradation in the presence of narrowband interference. We present a Global Positioning System(GPS) receiver anti-jamming algorithm based on the neural network. The method combines the adaptive notch filter with the Back Propagation(BP) neural network. We first use the two order lattice infinite impulse response adaptive notch filter to eliminate-out-of-band jamming, then use the BP neural network predictor to estimate and cancel jamming. We analyze three aspects of algorithm performance which include acquired satellite numbers,signal-to-noise improvements and iteration numbers. Simulation results show that the method can effectively suppress narrowband interference and has a better anti-jamming capacity and a faster convergence speed. 相似文献
10.
以V型件弯曲和回弹过程为分析研究对象,通过对V型件弯曲及回弹过程的有限元数值模拟,分析获得了成形参数对V型件弯曲回弹的影响规律。结果表明:回弹角随弯曲角及材料的硬化系数的增大而增大,随材料的变形程度及硬化指数的增大而减小。 相似文献