全文获取类型
收费全文 | 63367篇 |
免费 | 7518篇 |
国内免费 | 3148篇 |
专业分类
电工技术 | 1364篇 |
技术理论 | 6篇 |
综合类 | 4411篇 |
化学工业 | 22464篇 |
金属工艺 | 9587篇 |
机械仪表 | 3959篇 |
建筑科学 | 3798篇 |
矿业工程 | 1832篇 |
能源动力 | 1409篇 |
轻工业 | 4902篇 |
水利工程 | 807篇 |
石油天然气 | 1988篇 |
武器工业 | 792篇 |
无线电 | 2423篇 |
一般工业技术 | 8987篇 |
冶金工业 | 3626篇 |
原子能技术 | 434篇 |
自动化技术 | 1244篇 |
出版年
2024年 | 439篇 |
2023年 | 1352篇 |
2022年 | 2050篇 |
2021年 | 2796篇 |
2020年 | 2675篇 |
2019年 | 2171篇 |
2018年 | 2181篇 |
2017年 | 2527篇 |
2016年 | 2622篇 |
2015年 | 2702篇 |
2014年 | 3726篇 |
2013年 | 3837篇 |
2012年 | 4625篇 |
2011年 | 4448篇 |
2010年 | 3276篇 |
2009年 | 3429篇 |
2008年 | 2807篇 |
2007年 | 3822篇 |
2006年 | 3597篇 |
2005年 | 2927篇 |
2004年 | 2588篇 |
2003年 | 2186篇 |
2002年 | 1817篇 |
2001年 | 1615篇 |
2000年 | 1425篇 |
1999年 | 1069篇 |
1998年 | 928篇 |
1997年 | 791篇 |
1996年 | 689篇 |
1995年 | 545篇 |
1994年 | 458篇 |
1993年 | 335篇 |
1992年 | 321篇 |
1991年 | 220篇 |
1990年 | 212篇 |
1989年 | 218篇 |
1988年 | 72篇 |
1987年 | 88篇 |
1986年 | 64篇 |
1985年 | 74篇 |
1984年 | 66篇 |
1983年 | 51篇 |
1982年 | 83篇 |
1981年 | 15篇 |
1980年 | 24篇 |
1979年 | 11篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%. 相似文献
2.
The mechanical properties of a medium molecular weight polyethylene (MMW‐PE) and an ultrahigh molecular weight PE (UHMW‐PE) binary mixture with different weight fractions crystallized from the melt at 0.1 and 450 MPa were studied. The tensile modulus, yield stress, and strain were obtained as a function of the weight fractions in the PE mixtures at 25 and 85°C. The tensile modulus in the sample crystallized at 0.1 MPa decreased from 1.5 GPa of pure MMW‐PE to about 0.4 GPa of pure UHMW‐PE with the UHMW‐PE content but it did not decrease with the UHMW‐PE in the sample crystallized at 450 MPa in testing at 25°C. A decreasing rate of the storage modulus E′ of UHMW‐PE in a dynamic measurement for the sample crystallized at 0.1 MPa with the temperature is larger than that of the sample crystallized at 450 MPa. These experimental facts are interpreted in relation to the molecular motion and crystallinity of the sample. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1962–1968, 2003 相似文献
3.
机械合金化Fe-Ni粉末的相结构 总被引:1,自引:0,他引:1
使用XRD和Moessbauer等方法,研究了在Ar气氛下机械合金化Fe—Ni粉末相结构的变化.结果表明,在机械合金化Fe64-Ni36粉末过程中,fcc相的数量随着球磨时间的增加先增加然后减少,与加乙醇球磨Fe64-Ni36的情形相同.当Ni的含量(原子分数)大于50%时,有fcc相、顺磁相和FeNi3形成,当Ni的含量低于50%时,bcc相的数量随着Ni含量减少而增加.Moessbauer谱的结果表明,因球磨时间或Fe、Ni比例的不同,Fe—Ni球磨粉末固溶体具有不同结构的原子配比。 相似文献
4.
Preparation and properties of nano-sized SnO2 powder 总被引:2,自引:0,他引:2
1 INTRODUCTIONSnO2isoneofthemainmaterialsusedingassensor.Becauseofthehumidityandgassensingfunction,itattractsmoreandmoreattentions.Butthepresentproblemishowtoimprovethestabilityandsensibilityofgassensor.Researchershavetakenmanymeasurestoresolvethisproble… 相似文献
5.
超细Fe3O4粒子表面包覆酞菁钴性质研究 总被引:3,自引:1,他引:2
本文研究了合成载氧体的金属有机化学液相淀积法制造工艺,所得产物经TEM、XPS、Moss-bauer谱和B-H仪等手段,研究了它的结构和磁性能。实验表明,酞青钴以薄层形式包覆在Fe_3O_4的表面,封闭了Fe_3O_4的表面孔洞,稳定了Fe_3O_4的物相,增强了磁性能。 相似文献
6.
7.
The mechanical fracture strength and toughness of short-fibre composites, injection moulded from compounds of poly(ethylene terephthalate) (PET) containing 10 and 30% (by weight) (w/o) glass, have been investigated and the dependence upon matrix hydrolytic stability determined. Mouldings have been characterised by several physical techniques to evaluate molecular weight, degradation rates, crystallinity and morphology, whilst time-dependent gravimetric data were derived to quantify sorption kinetics and allow comparisons with theoretical reaction rates to be made. During melt processing, PET is hydrolysed extremely rapidly by traces of moisture (<0.02w/o). yet the inherent strength of moulded composites declines significantly only below an apparently critical molecular weight. However, on long-term humid ageing in hot water, impact behaviour especially is rendered more complex by simultaneous crystallisation, molecular reorder and losses of interfacial bond strength. 相似文献
8.
9.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献
10.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献