全文获取类型
收费全文 | 39991篇 |
免费 | 4290篇 |
国内免费 | 2549篇 |
专业分类
电工技术 | 3586篇 |
综合类 | 3509篇 |
化学工业 | 4230篇 |
金属工艺 | 1912篇 |
机械仪表 | 2678篇 |
建筑科学 | 5244篇 |
矿业工程 | 2037篇 |
能源动力 | 1230篇 |
轻工业 | 1157篇 |
水利工程 | 1609篇 |
石油天然气 | 1732篇 |
武器工业 | 545篇 |
无线电 | 3446篇 |
一般工业技术 | 3902篇 |
冶金工业 | 2357篇 |
原子能技术 | 521篇 |
自动化技术 | 7135篇 |
出版年
2024年 | 144篇 |
2023年 | 443篇 |
2022年 | 870篇 |
2021年 | 1121篇 |
2020年 | 1178篇 |
2019年 | 1095篇 |
2018年 | 954篇 |
2017年 | 1340篇 |
2016年 | 1566篇 |
2015年 | 1637篇 |
2014年 | 2490篇 |
2013年 | 2412篇 |
2012年 | 2652篇 |
2011年 | 3113篇 |
2010年 | 2324篇 |
2009年 | 2428篇 |
2008年 | 2222篇 |
2007年 | 2560篇 |
2006年 | 2440篇 |
2005年 | 1963篇 |
2004年 | 1687篇 |
2003年 | 1555篇 |
2002年 | 1344篇 |
2001年 | 1115篇 |
2000年 | 849篇 |
1999年 | 712篇 |
1998年 | 549篇 |
1997年 | 476篇 |
1996年 | 362篇 |
1995年 | 339篇 |
1994年 | 275篇 |
1993年 | 209篇 |
1992年 | 184篇 |
1991年 | 123篇 |
1990年 | 142篇 |
1989年 | 95篇 |
1988年 | 92篇 |
1987年 | 64篇 |
1986年 | 54篇 |
1985年 | 167篇 |
1984年 | 264篇 |
1983年 | 304篇 |
1982年 | 218篇 |
1981年 | 317篇 |
1980年 | 125篇 |
1979年 | 54篇 |
1978年 | 44篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The apparent tensile strength of technical flax fibers was determined in single‐fiber tests at various clamping lengths (20, 40, and 80 mm) and the outcome was compared with literature data. It was demonstrated that the strength of flax at each clamping length obeyed the two‐parameter Weibull model. The failure mode and sequence were studied in situ (i.e., during loading) by SEM and acoustic emission (AE). The failure sequence (axial splitting of the technical fiber along its elementary constituents, radial cracking of the elementary fibers, multiple fracture of the elementary fibers) concluded reflected the hierarchical build‐up of the flax bast fibers. To the above failure events AE amplitude ranges were assigned. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3638–3645, 2003 相似文献
72.
Stress Heterogeneity Effect on the Strength of Silicon Nitride 总被引:1,自引:0,他引:1
François Hild Elisabeth Amer Didier Marquis 《Journal of the American Ceramic Society》1992,75(3):700-702
The experiments reported in this paper demonstrate the causes of the failure of monolithic ceramics. The specimens are made of silicon nitride and tested at room temperature. The stress field within the specimen is different for each of four series of tests that have been conducted. Fractographic observations have also been made to identify the causes of the failures. A size effect analysis is performed. 相似文献
73.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
74.
Evaluation of Slow Crack Growth Resistance in Ceramics for High-Temperature Applications 总被引:1,自引:0,他引:1
The slow (subcritical) crack growth (SCG) resistance of Si3 N4 and SiC ceramics has been evaluated by a stepwise loading test on bending bars precracked by Vickers indentation. Three highly refractory materials were selected for the evaluation: i.e., (1) high-purity Si3 N4 sintered by hot isostatic pressing (HIP) without additives and (2,3) α - and β - SiC pressureless sintered with B and C addition. Under the hypothesis of linear elastic behavior at high temperature, which was found satisfied in the present materials, the SCG resistance was expressed in terms of initial stress intensity factor critical for SCG failure within a predetermined lifetime. The present method was found useful in shortening the testing time and consistent with other traditional fatigue tests (e.g., static-fatigue test): It is recommended as a screening test for materials under research and development. Among the materials tested in the present study, the highest SCG resistance up to 1440°C was found in the high-purity Si3 N4 without additives. 相似文献
75.
王飞 《理化检验(物理分册)》2003,39(12):636-638,650
为分析研究某特钢厂用户投诉的原因及存在的问题,统计了其两年间的弹簧钢棒线材用户质量投诉,从缺陷类型及生产过程控制进行了分析,重点对多起断裂原因不明的投诉进行了深入的失效研究。结果表明,弹簧钢生产厂在设备工艺、过程控制和管理中存在很多不足,加上用户的使用工艺、材料的内外质量和规格等综合因素导致了材料的断裂失效。 相似文献
76.
介绍了锦化化工(集团)有限责任公司出现的VCM压缩机曲轴断裂事故,并从断口的部位、形貌特征,断轴的几何状态、受力状态及树料性能等方面分析了曲轴断裂的根本原因。 相似文献
77.
No authorship indicated 《Canadian Metallurgical Quarterly》1995,50(4):243
Presents the citation, biography, and selected bibliography for Robert B. McCall, one of the 1994 recipients of the American Psychological Association's Award for Distinguished Professional Contributions--Distinguished Professional Contributions to Public Service. From McCall's citation: "Building on a prolific research career in child development, Robert B. McCall communicated the scientific findings of his colleagues to the public through the mass media, winning four national awards and demonstrating to a sometimes skeptical profession that such articles and TV programs could be both accurate and interesting. Subsequently, he became the inaugural director for the University of Pittsburgh Office of Child Development, a unique interdisciplinary, university-community facilitative unit that has broadened the definition of university public service to embrace partnerships among faculty and community service professionals, funders, and policymakers that have created innovative interdisciplinary training and research programs, human service demonstration and evaluation projects, and policy studies." (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
79.
多变量系统故障诊断和容错控制新方法及其在精馏过程中的应用 总被引:1,自引:0,他引:1
本文提出一种多变量系统的故障诊断和容错控制新方法,整个系统由四个神经元组成。将本文方法用于二元精馏塔顶和塔底组分的容错控制,仿真结果证实了本文方法的有效性。该方法可望在难以建模的复杂化工过程中得到应用。 相似文献
80.
Shane Y. Hong 《Journal of Intelligent Manufacturing》1993,4(3):233-241
One major bottleneck in the automation of the drilling process by robots in the aerospace industry is drill condition monitoring. This paper describes a system approach to solve this problem through the advancement of new machine design, sensor instrumentation, metal-cutting research, and intelligent software development. All drill failures can be detected and distinguished: chisel edge wear, flank wear, crater wear, margin wear, corner wear, breakage, asymmetry, lip height difference, and chipping at lips. However, in the real manufacturing environment, different workpiece materials, drill size, drill geometry, drill material, cutting speed, feed rate, etc. will change the criteria for judging the drill condition. The knowledge base used for diagnosing the drill failures requires a huge data bank and prior exhaustive testing. A self-learning scheme is therefore introduced to the machine in order to acquire the threshold history needed for automatic diagnosis by using the same new tool under the same drilling conditions. 相似文献