全文获取类型
收费全文 | 32685篇 |
免费 | 4422篇 |
国内免费 | 1916篇 |
学科分类
工业技术 | 39023篇 |
出版年
2024年 | 117篇 |
2023年 | 727篇 |
2022年 | 1329篇 |
2021年 | 1407篇 |
2020年 | 1435篇 |
2019年 | 1163篇 |
2018年 | 1147篇 |
2017年 | 1382篇 |
2016年 | 1316篇 |
2015年 | 1421篇 |
2014年 | 1750篇 |
2013年 | 1915篇 |
2012年 | 2385篇 |
2011年 | 2518篇 |
2010年 | 1827篇 |
2009年 | 1941篇 |
2008年 | 1491篇 |
2007年 | 2019篇 |
2006年 | 1917篇 |
2005年 | 1566篇 |
2004年 | 1359篇 |
2003年 | 1155篇 |
2002年 | 930篇 |
2001年 | 843篇 |
2000年 | 657篇 |
1999年 | 565篇 |
1998年 | 431篇 |
1997年 | 516篇 |
1996年 | 335篇 |
1995年 | 270篇 |
1994年 | 229篇 |
1993年 | 172篇 |
1992年 | 187篇 |
1991年 | 129篇 |
1990年 | 145篇 |
1989年 | 125篇 |
1988年 | 60篇 |
1987年 | 35篇 |
1986年 | 17篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 14篇 |
1981年 | 3篇 |
1980年 | 22篇 |
1979年 | 9篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Y. MURAKAMI K. TAKAHASHI R. KUSUMOTO 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(6):523-531
ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔKIIth. The relationship ΔKIIth > ΔKIth caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack. 相似文献
72.
73.
梁昔明 《中南工业大学学报(英文版)》2005,12(1):93-96
An active set truncated-Newton algorithm (ASTNA) is proposed to solve the large-scale bound constrained sub-problems. The global convergence of the algorithm is obtained and two groups of numerical experiments are made for the various large-scale problems of varying size. The comparison results between ASTNA and the subspace limited memory quasi-Newton algorithm and between the modified augmented Lagrange multiplier methods combined with ASTNA and the modified barrier function method show the stability and effectiveness of ASTNA for simultaneous optimization of distillation column. 相似文献
74.
In this paper, we examine, both experimentally and theoretically, the kinetics of formation and microstructure of product
phases in thin film reactions, using the Nb/Al and Ti/Al systems as our prototypes. The results of calorimetry and microscopy
studies are interpreted using simple kinetic and morphology models. In particular, the kinetic models employed here focus
on the nucleation and growth components of the phase formation process and the morphology models provide a starting point
for the classification of product grain structures.
An erratum to this article is available at . 相似文献
75.
76.
以YAG为添加剂的气压烧结氮化硅 总被引:2,自引:1,他引:1
本文以添加YAG的反应烧结氮化硅(RBSN)为前驱体,采用气氛加压烧结的工艺,在0.5~9.0MPa氮气压力范围,研究了不同氮压对烧结体的密度、相组成、强度和显微结构的影响及其相互间的关系。研究表明,通过改变氮气压力能有效地调控材料的显微结构,材料的性能又受控于显微结构的变化。 相似文献
77.
WC对Cu/WC_P复合材料性能及组织的影响 总被引:8,自引:0,他引:8
通过WC含量对WC/Cu复合材料性能的影响,确定了冷压-烧结法制备Cu/WC材料的适宜WC含量为10vol%左右。并就WC对该材料组织和再结晶行为的影响进行了有益的探讨。 相似文献
78.
The influence of an aggressive environment (0.6 M, aerated NaCl solution) on short fatigue crack initiation and growth behaviour has been studied. The study involved three major test series, namely: air fatigue, corrosion fatigue, and intermittent air fatigue/corrosion fatigue. The above tests carried out under fully reversed torsional loading conditions at a frequency of 5 Hz, showed that it was the non-metallic inclusions which took part in crack initiation resulting from debonding at metal matrix/inclusion interface and pitting of inclusions in both air and corrosove environments, respectively. Short fatigue crack growth results in these two environments obtained by using plastic replication technique, indicated a large effect of microstructure i.e. prior austenite grain boundaries. The stage/stages at which the environmental contribution was dominant has been discussed by considering the results achieved from intermittent tests. However, the mechanisms involved in corrosion fatigue short crack growth have also been described in the light of results obtained from futher investigations carried out by conducting corrosion fatigue tests under applied cathodic potential conditions and tests on hydrogen pre-charged specimens under air fatigue and uniaxial tension conditions. 相似文献
79.
用透射电镜观察了30CrMnSiNi2A钢等温的微观组织,疲劳裂纹扩展行为、裂纹尖端塑性区和位错结构,结果表明,等温状态组织由马氏体和贝氏体组成。在一个奥氏体晶粒内一般存在四个板条领域、裂纹尖端的塑性区内存在主位错带,疲劳断裂的基本组织单元为板条晶或板条束。裂纹遇到板条束界时方向发生较大偏斜。 相似文献
80.
通过高温和室温拉伸试验,研究了变形温度和变形程度对Ti-31合金板材性能和组织的影响。结果表明,合金在750~850℃的温度下变形5%~20%空冷后,其室温机械性能均能达到材料的技术指标要求。并发现了材料在900℃的临界变形区。 相似文献