全文获取类型
收费全文 | 230899篇 |
免费 | 27529篇 |
国内免费 | 26737篇 |
专业分类
电工技术 | 21583篇 |
技术理论 | 11篇 |
综合类 | 17188篇 |
化学工业 | 45468篇 |
金属工艺 | 10146篇 |
机械仪表 | 13468篇 |
建筑科学 | 12460篇 |
矿业工程 | 3369篇 |
能源动力 | 7364篇 |
轻工业 | 17986篇 |
水利工程 | 3629篇 |
石油天然气 | 6774篇 |
武器工业 | 2226篇 |
无线电 | 33755篇 |
一般工业技术 | 27556篇 |
冶金工业 | 6048篇 |
原子能技术 | 3948篇 |
自动化技术 | 52186篇 |
出版年
2024年 | 1196篇 |
2023年 | 4099篇 |
2022年 | 7609篇 |
2021年 | 8762篇 |
2020年 | 8246篇 |
2019年 | 7426篇 |
2018年 | 6942篇 |
2017年 | 9280篇 |
2016年 | 10082篇 |
2015年 | 11273篇 |
2014年 | 11652篇 |
2013年 | 15170篇 |
2012年 | 16875篇 |
2011年 | 19211篇 |
2010年 | 13924篇 |
2009年 | 13858篇 |
2008年 | 14943篇 |
2007年 | 16636篇 |
2006年 | 15666篇 |
2005年 | 13455篇 |
2004年 | 11387篇 |
2003年 | 9020篇 |
2002年 | 7087篇 |
2001年 | 5433篇 |
2000年 | 4563篇 |
1999年 | 3782篇 |
1998年 | 3186篇 |
1997年 | 2572篇 |
1996年 | 2083篇 |
1995年 | 1724篇 |
1994年 | 1516篇 |
1993年 | 1131篇 |
1992年 | 960篇 |
1991年 | 783篇 |
1990年 | 698篇 |
1989年 | 507篇 |
1988年 | 420篇 |
1987年 | 246篇 |
1986年 | 227篇 |
1985年 | 289篇 |
1984年 | 273篇 |
1983年 | 175篇 |
1982年 | 229篇 |
1981年 | 125篇 |
1980年 | 115篇 |
1979年 | 35篇 |
1978年 | 22篇 |
1977年 | 41篇 |
1976年 | 22篇 |
1959年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
含氯取代基的聚间苯二甲酰间苯二胺的合成与表征 总被引:7,自引:0,他引:7
以 2 ,5 -二氯对苯二甲酰氯作为第三单体 ,将其与间苯二甲酰氯、间苯二胺在N ,N -二甲基乙酰胺中进行低温溶液共缩聚反应 ,合成了含氯取代基的聚间苯二甲酰间苯二胺。研究了单体摩尔浓度、反应初始温度、叔胺添加剂种类、第三单体用量等对共聚物相对分子质量的影响 ,并用红外光谱、热重分析等方法对共聚物进行了表征。 相似文献
62.
63.
医用聚氯乙烯材料的表面光接枝改性 总被引:6,自引:0,他引:6
研究了在不排氧氛围下 ,紫外光照射 ,以二苯甲酮 (BP)为光引发剂 ,甲基丙烯酸缩水甘油酯(GMA)在医用聚氯乙烯 (PVC)薄膜表面的气相接枝聚合。探讨了反应条件对接枝结果的影响 ,并用正交法指出了影响因素的显著性。用傅立叶红外 (FT- IR)、水接触角作为接枝改性结果的表征。FT- IR谱图表明 GMA已接枝到 PVC膜表面。水接触角由接枝前的 78°下降到 5 4° 相似文献
64.
65.
Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (Tg). melting points (Tm) and crystallisation temperatures (Tc) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in Tg, Tm and Tc. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation. 相似文献
66.
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
67.
介绍了单端正向变换器基本电路,重点叙述带三路调节DC电压的100KHZ180W离线电源。它采用具有低导电阻RDS和低栅极电荷Qg的新型场效应管(QFET)作为变换电路的主开关器件,降低了电源开关损耗并提高了效率3%-5%。 相似文献
68.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
69.
70.
On the basis of the experimental data, we show that the difference between the macroscopic and microscopic fatigue crack growth rates in the second section of the kinetic diagram of fatigue fracture is caused by the effect of crack closure within the limits of its existence. We establish the relationships between the macroscopic and microscopic fatigue crack growth rates and the structure of the material in the second section of the diagram for various values of the load ratio with regard for the effect of crack closure and propose a procedure of examination of the fracture processes in structural materials based on the analysis of microscopic and macroscopic fatigue crack growth rates. 相似文献