全文获取类型
收费全文 | 2437篇 |
免费 | 255篇 |
国内免费 | 243篇 |
专业分类
电工技术 | 54篇 |
综合类 | 244篇 |
化学工业 | 310篇 |
金属工艺 | 431篇 |
机械仪表 | 167篇 |
建筑科学 | 408篇 |
矿业工程 | 110篇 |
能源动力 | 27篇 |
轻工业 | 221篇 |
水利工程 | 81篇 |
石油天然气 | 100篇 |
武器工业 | 31篇 |
无线电 | 24篇 |
一般工业技术 | 485篇 |
冶金工业 | 212篇 |
原子能技术 | 17篇 |
自动化技术 | 13篇 |
出版年
2024年 | 8篇 |
2023年 | 28篇 |
2022年 | 71篇 |
2021年 | 66篇 |
2020年 | 88篇 |
2019年 | 59篇 |
2018年 | 77篇 |
2017年 | 99篇 |
2016年 | 87篇 |
2015年 | 110篇 |
2014年 | 119篇 |
2013年 | 137篇 |
2012年 | 191篇 |
2011年 | 192篇 |
2010年 | 116篇 |
2009年 | 131篇 |
2008年 | 103篇 |
2007年 | 146篇 |
2006年 | 136篇 |
2005年 | 130篇 |
2004年 | 146篇 |
2003年 | 97篇 |
2002年 | 70篇 |
2001年 | 92篇 |
2000年 | 67篇 |
1999年 | 58篇 |
1998年 | 57篇 |
1997年 | 45篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 20篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1979年 | 1篇 |
排序方式: 共有2935条查询结果,搜索用时 46 毫秒
1.
Shuncheng Liu Kejian Wang Zhongfeng Zhang Yueqing Ren Lanlan Chen Xiaojie Sun Wenbin Liang 《Polymer Engineering and Science》2020,60(10):2640-2652
Three kinds of ethylene-octene copolymers (POE) were melt-blended with high-density polyethylene (PE-HD) in different proportions. Detailed characterizations were conducted to analyze their structural differences of POE and its effects in toughening PE-HD. The higher molecular weight POE can improve the toughness of PE-HD. 60:40 PE-HD/POE is elongated to break up to 700% while impact strength is 84.7 kJ/m2 at −30°C, which is 21-fold of PE-HD. In the brittle to ductile transition (BDT) during impact, the fracture mechanism changes from the crazing mode to the shear yield-plastic deformation mode. The BDT temperature decreases as the POE molecular weight and its content increase. The interface strength in tension is estimated to access their effects. The Boltzmann-type models were successfully extended to describe the typical S-shaped curves in BDT of notched impact strength vs POE content or temperature. The supplementary decay model is suggested for the attenuation in toughening. Transition map in impact is proposed to select the use range of composition (c ) and temperature (T ) for high toughness. The curves are converted into 3D graph of T -c -impact strength for illustrating their coupling-separate effects, and further into the contour map of impact strength in T -c space for finding their partial equivalence. 相似文献
2.
The analysis of 124 curves obtained in short-term tensile tests demonstrate that they can be described by varying strain hardening and softening characteristics. Different stress–strain curves can be produced at invariable yield strength and ultimate strength and interrelated proportional variations of the above characteristics. To determine some specific stress–strain curve, it is necessary to take account of yield strength and ultimate strength as well as strain corresponding to the latter. The relations between yield strength, ultimate strength and hardening and their practically complete absence between these parameters and softening were statistically established. 相似文献
3.
Jonathan P. Belnoue Giang D. Nguyen Alexander M. Korsunsky 《International Journal of Fracture》2007,144(1):53-60
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic
framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach.
A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple
model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing
both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness
and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving
some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the
model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that
is needed to cause tensile failure of a specimen. 相似文献
4.
In this paper, two brittle fracture problems are numerically simulated: the failure of a ceramic ring under centrifugal loading and crack branching in a PMMA strip. A three‐dimensional finite element package in which cohesive elements are dynamically inserted has been developed. The cohesive elements' strength is chosen to follow a modified weakest link Weibull distribution. The probability of introducing a weak cohesive element is set to increase with the cohesive element size. This reflects the physically based effect according to which larger elements are more likely to contain defects. The calculations illustrate how the area dependence of the Weibull model can be used to effectively address mesh dependency. On the other hand, regular Weibull distributions have failed to reduce mesh dependency for the examples shown in this paper. The ceramic ring calculations revealed that two distinct phenomena appear depending on the magnitude of the Weibull modulus. For low Weibull modulus, the fragmentation of the ring is dominated by heterogeneities. Whereas many cracks were generated, few of them could propagate to the outer surface. Monte Carlo simulations revealed that for highly heterogeneous rings, the number of small fragments was large and that few large fragments were generated. For high Weibull modulus, signifying that the ring is close to being homogeneous, the fragmentation process was very different. Monte Carlo simulations highlighted that a larger number of large fragments are generated due to crack branching. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
6.
The mechanism of “475°C embrittlement” of a duplex stainless steel was investigated using finite element modelling of the stress distribution at brittle fracture initiation. Brittle fracture initiated at a critical shear stress, which increased with ferrite hardness. The fracture stress was affected by the duplex microstructure. Fracture was nucleated by deformation twins, which were identified using electron back-scatter diffraction. The ductile-to-brittle fracture transition was sensitive to age-hardening and could be described simply by the effect of age-hardening and test temperature on the yield stress. 相似文献
7.
8.
《Petroleum Science and Technology》2007,25(7):915-923
Polymer modified bitumen (PMB) is used in various construction applications, especially in motorways. The aim of this study is to improve features of 60/70 penetration grade, modified bitumen used on highways. Increasing the sensitivity to temperature and oxidation resistance are very important points for the modified bitumen. This condition was provided by reacting the carboxylic acid groups in asphaltene with the reactive ethylene terpolymer to form ester. Reactive ethylene terpolymer (RETP) and ethylene terpolymer (ETP) manufactured by DuPont USA were used as additives in this study. Infrared Spectrophotometer (IR) graphics and optical pictures of the modified bitumen have been examined. It has been observed that the softening point has increased on the other hand, the penetration and ductility values have decreased according to the test results. 相似文献
9.
10.