全文获取类型
收费全文 | 25949篇 |
免费 | 2257篇 |
国内免费 | 1545篇 |
专业分类
电工技术 | 629篇 |
综合类 | 2562篇 |
化学工业 | 1716篇 |
金属工艺 | 2768篇 |
机械仪表 | 1644篇 |
建筑科学 | 6144篇 |
矿业工程 | 916篇 |
能源动力 | 785篇 |
轻工业 | 712篇 |
水利工程 | 1127篇 |
石油天然气 | 785篇 |
武器工业 | 178篇 |
无线电 | 1262篇 |
一般工业技术 | 5544篇 |
冶金工业 | 1432篇 |
原子能技术 | 294篇 |
自动化技术 | 1253篇 |
出版年
2024年 | 76篇 |
2023年 | 208篇 |
2022年 | 476篇 |
2021年 | 568篇 |
2020年 | 737篇 |
2019年 | 625篇 |
2018年 | 552篇 |
2017年 | 805篇 |
2016年 | 831篇 |
2015年 | 890篇 |
2014年 | 1398篇 |
2013年 | 1410篇 |
2012年 | 1537篇 |
2011年 | 1812篇 |
2010年 | 1428篇 |
2009年 | 1687篇 |
2008年 | 1568篇 |
2007年 | 1930篇 |
2006年 | 1638篇 |
2005年 | 1495篇 |
2004年 | 1154篇 |
2003年 | 1146篇 |
2002年 | 947篇 |
2001年 | 810篇 |
2000年 | 720篇 |
1999年 | 552篇 |
1998年 | 457篇 |
1997年 | 424篇 |
1996年 | 315篇 |
1995年 | 295篇 |
1994年 | 236篇 |
1993年 | 193篇 |
1992年 | 175篇 |
1991年 | 116篇 |
1990年 | 123篇 |
1989年 | 118篇 |
1988年 | 72篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 28篇 |
1984年 | 38篇 |
1983年 | 30篇 |
1982年 | 32篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
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
23.
24.
In the present study, attempts are made to extend the application of the mechanical model for the fatigue crack initiation (FCI) and the FCI life formula of metallic notched elements in laboratory air to those in the corrosive environment. The test results and analysis of the corrosion FCI (CFCI) life of aluminum alloys and Ti---6A1---4V show that the expression of the CFCI life obtained by modifying the FCI life formula in laboratory air can give a good fit to the test results of the CFCI life. The salt water (3.5% NaCl) environment has no effects on the CFCI resistant coefficient compared with the FCI resistant coefficient in laboratory air. However, 3.5% NaCl environment greatly decreases the CFCI threshold of aluminum alloy, but has little effect on the CFCI threshold of Ti---6A1---4V. The loading frequency ranging from 1 Hz to 10 Hz has no appreciable effect on the CFCI life, and thus, the CFCI threshold of aluminum alloys investigated. Hence, the expression for the CFCI life of metallic notched elements proposed in this study is a better one, which reveals a correlation between the CFCI life and the governing parameters, such as, the geometry of the notched elements, the nominal stress range, the stress ratio, the tensile properties and the CFCI threshold. However, this new expression of the CFCI life needs to be verified by more test results. 相似文献
25.
X. Wang S. B. Lambert 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(12):1637-1655
Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%. 相似文献
26.
Y. N. Lenets 《Fatigue & Fracture of Engineering Materials & Structures》1997,20(2):249-256
Abstract— The behaviour of fatigue cracks in an Al-alloy under cyclic compression, either with or without overloads, was studied. For constant-amplitude compressive cycling, a non-catastrophic (saturation) character of the fatigue crack behaviour was confirmed, with the final depth of a crack depending on the applied load level. Single (tensile or compressive) intermittent overloads were shown to re-activate a previously arrested crack while reversed (tensile—compressive or compressive—tensile) ones were also shown to maintain continual fatigue crack extension under otherwise fully compressive cycling. 相似文献
27.
In this paper,a sequential algorithm computing the aww vertex pair distance matrix D and the path matrix Pis given.On a PRAM EREW model with p,1≤p≤n^2,processors,a parallel version of the sequential algorithm is shown.This method can also be used to get a parallel algorithm to compute transitive closure array A^* of an undirected graph.The time complexity of the parallel algorithm is O(n^3/p).If D,P and A^* are known,it is shown that the problems to find all connected components,to compute the diameter of an undirected graph,to determine the center of a directed graph and to search for a directed cycle with the minimum(maximum)length in a directed graph can all be solved in O(n^2/p logp)time. 相似文献
28.
本文报导了最近研制成功的用于提高国产氩离子激光器相干长度的相干扩展器。利用这种基于F-P理论的相干扩展器可以使国产氩离子激光器的相干长度由不足5cm一下提高到m的量级,功率损耗在25%~40%之间,有着很好的应用前景。 相似文献
29.
关于后张预应力混凝土结构优化设计的几个问题 总被引:1,自引:1,他引:0
结合UP软件编程实践,本文对后张预应力混凝土结构计算程序中引入优化功能的意义进行了论述,提出了预应力筋与普通钢筋之间的最优搭配关系,优化原点概念及相关影响因素,列出了优化计算程序所应涉及的基本计算内容,并对当前后张预应力混凝土结构设计中的一些观点提出了不同意见。 相似文献
30.
通过对耐热耐蚀合金Incoloy 80 0H的性能分析 ,指出它与普通奥氏体不锈钢相比具有较优的抗氧化性能、耐蚀性和高温蠕变强度。针对催化裂化装置同轴式沉降再生器内部所用Incoloy 80 0H焊件易出现裂纹的问题进行分析 ,认为在施焊过程中由于合金凝固时有低熔点金属或化合物的液态膜残留在晶界区 ,该合金具有高的焊接热裂纹敏感性 ,若焊材选择不当 ,焊丝填充不充分、缺少保护气等将导致晶间裂纹产生。提出了该合金采用TIG焊接防止热裂纹产生的措施。 相似文献