全文获取类型
收费全文 | 19948篇 |
免费 | 658篇 |
国内免费 | 641篇 |
专业分类
电工技术 | 257篇 |
综合类 | 431篇 |
化学工业 | 4166篇 |
金属工艺 | 2638篇 |
机械仪表 | 526篇 |
建筑科学 | 445篇 |
矿业工程 | 244篇 |
能源动力 | 1372篇 |
轻工业 | 716篇 |
水利工程 | 47篇 |
石油天然气 | 255篇 |
武器工业 | 50篇 |
无线电 | 1834篇 |
一般工业技术 | 4543篇 |
冶金工业 | 1237篇 |
原子能技术 | 310篇 |
自动化技术 | 2176篇 |
出版年
2024年 | 123篇 |
2023年 | 1220篇 |
2022年 | 677篇 |
2021年 | 1070篇 |
2020年 | 1141篇 |
2019年 | 1049篇 |
2018年 | 999篇 |
2017年 | 1024篇 |
2016年 | 1181篇 |
2015年 | 1182篇 |
2014年 | 1543篇 |
2013年 | 2991篇 |
2012年 | 923篇 |
2011年 | 760篇 |
2010年 | 637篇 |
2009年 | 675篇 |
2008年 | 441篇 |
2007年 | 540篇 |
2006年 | 426篇 |
2005年 | 359篇 |
2004年 | 292篇 |
2003年 | 324篇 |
2002年 | 285篇 |
2001年 | 287篇 |
2000年 | 220篇 |
1999年 | 160篇 |
1998年 | 128篇 |
1997年 | 128篇 |
1996年 | 84篇 |
1995年 | 68篇 |
1994年 | 78篇 |
1993年 | 34篇 |
1992年 | 40篇 |
1991年 | 30篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
131.
G. N. Lilis A. Halder S. Telukunta S. Servetto 《International journal for numerical methods in engineering》2007,71(3):277-312
Many problems in geophysics, acoustics, elasticity theory, cancer treatment, food process control and electrodynamics involve study of wave field synthesis (WFS) in some form or another. In the present work, modelling of wave propagation phenomena is studied as a static problem, using finite element method and treating time as an additional spatial dimension. In particular, WFS problems are analysed using discrete methods. It is shown that a fully finite element-based scheme is very natural and effective method for the solution of such problems. Distributed WFS in the context of two-dimensional problems is outlined and incorporation of any geometric or material non-linearities is shown to be straightforward. This has significant implications for problems in geophysics or biological media, where material inhomogeneities are quite prevalent. Numerical results are presented for several problems referring to media with material inhomogeneities and predefined absorption profiles. The method can be extended to three-dimensional problems involving anisotropic media properties in a relatively straightforward manner. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
132.
金属迁移能导致混合微电路发生灾难性失效。本文介绍一种简单易行的测试方法-水滴试验法,来测量厚膜电路的实际金属迁移率。用引方法测量时,发现Pd-Ag导体的迁移率最大,Pt-Au导体的金属迁移率最小。 相似文献
133.
研究了添加微量锡对铜基摩擦的摩擦性能的影响。结果表明,微量锡对摩擦系数无显著影响,但对磨损有显著影响,当锡含量为0.50%时,摩擦材料及对偶材料的磨损都较小。 相似文献
134.
Chaosuan Kanchanomai Yukio Miyashita Yoshiharu Mutoh 《Journal of Electronic Materials》2002,31(5):456-465
Low-cycle fatigue (LCF) tests on as-cast Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi, and Sn-3Ag-0.5Cu-3Bi solders was carried
out using a noncontact strain-controlled system at 20°C with a constant frequency of 0.1 Hz. The addition of Cu does not significantly
affect the fatigue life of eutectic Sn-Ag solder. However, the fatigue life was significantly reduced with the addition of
Bi. The LCF behavior of all solders followed the Coffin-Manson relationship. The fatigue life of the present solders is dominated
by the fracture ductility and can be described by the ductility-modified Coffin-Manson’s relationship. Steps at the boundaries
of dendrite phases were the initiation sites for microcracks for Sn-3.5Ag, Sn-3Ag-0.5Cu, and Sn-3Ag-0.5Cu-1Bi solders, while
for Sn-3Ag-0.5Cu-3Bi solder, cracks initiated along both the dendrite boundaries and subgrain boundaries in the dendrite phases.
The linking of these cracks and the propagation of cracks inside the specimen occurred both transgranularly through eutectic
phases and intergranularly along dendrite boundaries or subgrain boundaries. 相似文献
135.
通过对AlSn20Cu/Steel双金属板(带)复合轧制过程变形区变形规律的分析,确定了轧制过程的总变形率与各分层变形率的关系,解决了实际生产中各分层原料的厚度匹配问题。 相似文献
136.
采用真空蒸发的方法交替沉积Ag和TCNQ分子制备了Ag TCNQ金属 有机络合物薄膜 ,并研究了多种外加电压激发下膜的电阻转变特性。发现在转变过程中存在着一种能量效应 ,即当外电压超过某一阈值后 ,完成转变的能量不变。对此现象的可能解释是薄膜内分子在一定的外部电场能量诱导下发生重排 ,致使电导率发生跃变 相似文献
137.
在30CrMnSiA钢中加入不同量的As,Sb,Sn元素,研究了这些元素单独存在及复合存在时对钢的强度,塑性,冲击韧度及韧脆转变温度的影响规律,并用扫描电镜及俄歇能谱分析了As,Sb,Sn导致晶界脆化的机理。 相似文献
138.
The paper suggests a new methodology for secure cyber–physical systems design. The proposed methodology consists of two main cycles. The main goal of the first cycle is in design of the system model, while the second one is about development of the system prototype. The key idea of the methodology is in providing of the most rational solutions that are improving the security of cyber–physical systems. Such solutions are called alternatives and built according to functional requirements and non-functional limitations to the system. Each cycle of the methodology consists of the verification process and seven stages that are associated with the used cyber–physical system model. The objective of the verification process is in checking of constructed models and prototypes in terms of their correctness and compatibility. The model represents cyber–physical systems as sets of building blocks with network between them, takes elements internal structure into account and allows direct and reverse transformations. The novelty of the suggested methodology is in the combination of design, development and verification techniques within a single approach. To provide an example of the design methodology application, in this paper it is used to improve the semi-natural model of the railway infrastructure. 相似文献
139.
Cyber–physical systems are becoming increasingly complex. In these advanced systems, the different engineering domains involved in the design process become more and more intertwined. Therefore, a traditional (sequential) design process becomes inefficient in finding good design options. Instead, an integrated approach is needed where parameters in multiple different engineering domains can be chosen, evaluated, and optimized to achieve a good overall solution. However, in such an approach, the combined design space becomes vast. As such, methods are needed to mitigate this problem.In this paper, we show a method for systematically capturing and updating domain knowledge in the context of a co-design process involving different engineering domains, i.e. control and embedded. We rely on ontologies to reason about the relationships between parameters in the different domains. This allows us to derive a stepwise design space exploration workflow where this domain knowledge is used to quickly reduce the design space to a subset of likely good candidates. We illustrate our approach by applying it to the design space exploration process for an advanced electric motor control system and its deployment on embedded hardware. 相似文献
140.
《Calphad》2021
The isothermal sections of the Mg–Sn–Sr ternary system in the Mg-rich region at 415 and 350 °C have been determined using the scanning electron microscopy (SEM) equipped with energy dispersive X-Ray spectrometry (EDS). The existence of the MgSnSr ternary compound was confirmed in these two isothermal sections. Two new compounds, named Mg5Sn3Sr and Mg25Sn24Sr14, were found in the present work based on the SEM/EDS results. Thermodynamic optimization of the Sn–Sr binary and Mg–Sn–Sr ternary systems were carried out using the CALPHAD (CALculation of PHAse Diagrams) technique. The Modified quasi-chemical model (MQM) was used for the liquid solution which exhibits a high degree of short-range ordering behavior. The solid phases were described with the Compound energy formalism (CEF). Finally, a self-consistent thermodynamic databases for the Mg–Sn–Sr ternary system has been constructed in the present work, which can be an efficient and convenient guidance to investigate and develop the Mg-based alloys. 相似文献