全文获取类型
收费全文 | 153567篇 |
免费 | 13678篇 |
国内免费 | 6500篇 |
专业分类
电工技术 | 5635篇 |
技术理论 | 7篇 |
综合类 | 13951篇 |
化学工业 | 16546篇 |
金属工艺 | 19877篇 |
机械仪表 | 5831篇 |
建筑科学 | 40703篇 |
矿业工程 | 2426篇 |
能源动力 | 2661篇 |
轻工业 | 8619篇 |
水利工程 | 5877篇 |
石油天然气 | 2729篇 |
武器工业 | 851篇 |
无线电 | 10019篇 |
一般工业技术 | 16453篇 |
冶金工业 | 16022篇 |
原子能技术 | 742篇 |
自动化技术 | 4796篇 |
出版年
2024年 | 501篇 |
2023年 | 1749篇 |
2022年 | 3658篇 |
2021年 | 4209篇 |
2020年 | 4536篇 |
2019年 | 3539篇 |
2018年 | 3318篇 |
2017年 | 4754篇 |
2016年 | 4900篇 |
2015年 | 5664篇 |
2014年 | 9527篇 |
2013年 | 8300篇 |
2012年 | 10868篇 |
2011年 | 11967篇 |
2010年 | 9304篇 |
2009年 | 10042篇 |
2008年 | 8819篇 |
2007年 | 11187篇 |
2006年 | 9999篇 |
2005年 | 8530篇 |
2004年 | 6830篇 |
2003年 | 5792篇 |
2002年 | 5045篇 |
2001年 | 4094篇 |
2000年 | 3413篇 |
1999年 | 2747篇 |
1998年 | 2006篇 |
1997年 | 1798篇 |
1996年 | 1476篇 |
1995年 | 1150篇 |
1994年 | 1041篇 |
1993年 | 751篇 |
1992年 | 618篇 |
1991年 | 452篇 |
1990年 | 322篇 |
1989年 | 265篇 |
1988年 | 160篇 |
1987年 | 95篇 |
1986年 | 50篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 33篇 |
1982年 | 38篇 |
1981年 | 18篇 |
1980年 | 66篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1975年 | 5篇 |
1964年 | 4篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Chen Tang Tiehu Li Yuhang Bai Junjie Gao Wenbo Yang Shasha Jiao Tingkai Zhao 《Ceramics International》2018,44(10):11812-11819
Recently, ceramic matrix composites reinforced by short carbon fibers (CFs) attracted increasing attentions. To further improve mechanical properties and oxidation resistances, CFs were subjected to oxidation and acidification followed by sol-gel dip-coating to deposit ZrO2 on their surfaces. ZrO2-Cf/SiC composites were fabricated by joint hot compression molding and sintering, compared to Cf/SiC and SiC prepared by the same method. Microstructural analyses indicated that ZrO2 coatings were successfully deposited on CF surfaces, formed strong bonding and interfaces between CF and the matrix. Meanwhile, CFs were found uniformly distributed in SiC matrix with random orientations. Flexural curves of ZrO2-Cf/SiC and Cf/SiC revealed the presence of “false plasticity” regions after sharp drops, which were quite different from brittle flexural behavior of SiC ceramic. Compression strength of the three samples showed step-up growth. ZrO2-Cf/SiC exhibited the highest value, indicating the introduction of CFs and ZrO2 coatings do have great influence on mechanical performances. After heat treatment, ZrO2-Cf/SiC exhibited better oxidation resistance than Cf/SiC, with weight loss ratios estimated to ??3.76% and ??6.43%, respectively. These improved properties indicated that ZrO2-Cf/SiC would be excellent alternatives to other existence materials under ultra-high temperature environments. 相似文献
52.
This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity. 相似文献
53.
Pietro Galizia Simone Failla Luca Zoli Diletta Sciti 《Journal of the European Ceramic Society》2018,38(2):403-409
One of the biggest challenges of the materials science is the mutual exclusion of strength and toughness. This issue was minimized by mimicking the natural structural materials. To date, few efforts were done regarding materials that should be used in harsh environments. In this work we present novel continuous carbon fiber reinforced ultra-high-temperature ceramic matrix composites (UHTCMCs) for aerospace featuring optimized fiber/matrix interfaces and fibers distribution. The microstructures – produced by electrophoretic deposition of ZrB2 on unidirectional carbon fibers followed by ZrB2 infiltration and hot pressing – show a maximum flexural strength and fracture toughness of 330 MPa and 14 MPa m1/2, respectively. Fracture surfaces are investigated to understand the mechanisms that affect strength and toughness. The EPD technique allows the achievement of a peculiar salami-inspired architecture alternating strong and weak interfaces. 相似文献
54.
55.
56.
57.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
58.
热轧态中锰TRIP钢首先经650 ℃退火2 h,随后在550 ℃进行等温时效热处理,采用场发射扫描电镜(FE-SEM)研究该钢中P的偏聚和时效析出行为的变化情况。结果表明,中锰TRIP钢中P在晶界的偏聚是一种非平衡偏聚现象,临界时间约为50 h,与理论计算结果48 h较为吻合。在局部偏聚区域内,C与P存在共偏聚的关系,即P偏聚量高的地方,C含量也高。而合金元素Nb具有抑制P偏聚的效果,在20~70 h时效时间内,可以相对降低6.57%~19.5%的最大P偏聚量。根据电子背散射衍射(EBSD)菊池线分析,P偏聚量低于2.28at%时,P为固溶状态,高于2.28at.%时,P为析出状态。 相似文献
59.
3D laser ultramicroscopy (3D LUM) is intended specially for determining the concentration and size distribution of submicron inclusions in the bulk samples of high-purity materials for visible and IR fiber optics. In this work the 3D LUM technique is shown to be able to identify the nature of individual inclusions detected. The measurement of the light scattered by an inclusion at a varied probe beam wavelength and polarization and at a varied scattered light collection angle makes it possible to determine the inclusion refractive index. The 3D LUM possibilities are illustrated by the example of studying the inclusion nature in the As2S3 glass samples prepared by the direct synthesis from elements in a quartz container at elevated temperatures. 相似文献
60.
Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C?s??1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050?mm. 相似文献