全文获取类型
收费全文 | 79904篇 |
免费 | 7313篇 |
国内免费 | 4428篇 |
专业分类
电工技术 | 5696篇 |
技术理论 | 2篇 |
综合类 | 6156篇 |
化学工业 | 14294篇 |
金属工艺 | 8312篇 |
机械仪表 | 4418篇 |
建筑科学 | 6648篇 |
矿业工程 | 1915篇 |
能源动力 | 4671篇 |
轻工业 | 5205篇 |
水利工程 | 1842篇 |
石油天然气 | 3788篇 |
武器工业 | 711篇 |
无线电 | 6926篇 |
一般工业技术 | 9782篇 |
冶金工业 | 5358篇 |
原子能技术 | 1451篇 |
自动化技术 | 4470篇 |
出版年
2024年 | 351篇 |
2023年 | 1262篇 |
2022年 | 2214篇 |
2021年 | 2741篇 |
2020年 | 2810篇 |
2019年 | 2375篇 |
2018年 | 2222篇 |
2017年 | 2846篇 |
2016年 | 2953篇 |
2015年 | 3014篇 |
2014年 | 4618篇 |
2013年 | 4949篇 |
2012年 | 5607篇 |
2011年 | 6134篇 |
2010年 | 4293篇 |
2009年 | 4523篇 |
2008年 | 4024篇 |
2007年 | 5119篇 |
2006年 | 4679篇 |
2005年 | 3846篇 |
2004年 | 3431篇 |
2003年 | 2968篇 |
2002年 | 2456篇 |
2001年 | 2142篇 |
2000年 | 1808篇 |
1999年 | 1451篇 |
1998年 | 1149篇 |
1997年 | 1024篇 |
1996年 | 899篇 |
1995年 | 698篇 |
1994年 | 610篇 |
1993年 | 446篇 |
1992年 | 414篇 |
1991年 | 356篇 |
1990年 | 278篇 |
1989年 | 190篇 |
1988年 | 155篇 |
1987年 | 95篇 |
1986年 | 91篇 |
1985年 | 89篇 |
1984年 | 75篇 |
1983年 | 65篇 |
1982年 | 49篇 |
1981年 | 23篇 |
1980年 | 29篇 |
1979年 | 19篇 |
1977年 | 9篇 |
1975年 | 6篇 |
1959年 | 15篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The isothermal strain‐life approach is the most commonly used approach for determining fatigue damage, particularly when yielding occurs. Computationally it is extremely fast and generally requires elastic finite element analyses only. Therefore, it has been adapted for variable temperatures. Local temperature—stress–strain behaviour is modelled with an operator of the Prandtl type. The hysteresis loops are supposed to be stabilized and no creep is considered. The consequences of reversal point filtering are analysed. The approach is finally compared to several thermo‐mechanical fatigue tests and the Skelton model. 相似文献
92.
93.
Low carbon steel was oxidized over the temperature range 1000‐1250°C in O2‐CO2‐H2O‐N2, O2‐H2O‐N2, and O2‐CO2‐N2 gas mixtures. Oxidation times were 12‐120 min. and the scales were 50‐2000 μm thick. The variations of these parameters were chosen to elucidate the phase composition of oxide scales under conditions similar to those of reheating furnaces in hot strip mills, using either thin slab casting or conventional casting and rolling technology. Two types of scales have been observed which are influenced by the furnace atmosphere, oxidation time, and temperature. The first type is a crystalline scale with an irregular outer surface, composed mostly of wustite (FeO), and a negligible amount of magnetite (Fe3O4). The second type is the classical three‐layer scale, composed of wustite (FeO), magnetite (Fe3O4), and hematite (Fe2O3). In general, the experiments showed that an increase in oxidation time decreased the percentage of wustite while the percentages of magnetite and hematite increased. A rise in oxygen concentration in the gas mixture increased the percentages of magnetite and hematite, confirming earlier experimental findings. In water vapour‐free atmospheres O2‐CO2‐N2, the oxide scales had a low percentage of wustite, and high percentage of magnetite and hematite. Carbon dioxide showed a small influence at 1100°C, and a negligible one at 1250°C. 相似文献
94.
通常的数据采集与记录装置不易实现多量程测量。通过对标度方程进行分析得知,要改变量程只须改变两个参数——标度因子和量程下限。我们设计了一个使用单片机的多量程数据采集和记录装置,能处理多达256种量程。本文叙述了算法分析、硬件和软件的设计以及该装置的性能指标。 相似文献
95.
The role of gas phase CH3 radicals in the oxidative coupling of CH4 over 1 wt% Sr/La2O3 is supported by the observations that (i) this is a very effective catalyst for the generation of CH3 · radicals and (ii) the concentration of CH3 · radicals increases with temperature over the range of 450 °C–800 °C. 相似文献
96.
中原高温高盐油藏疏水缔合聚合物凝胶调剖剂研究 总被引:3,自引:1,他引:2
针对中原油田高温(>80℃)、高盐度(>50 g/L)、高硬度(>1 g/L)砂岩油藏,研制了地下成胶的高热稳定性聚合物凝胶调剖剂。所用聚合物为疏水缔合聚合物AP-P4,M=9.0×106,HD=27%,疏水基摩尔分数0.2%;交联剂为可生成酚醛树脂的3种化合物;调剖剂胶液用矿化度160 g/L的马寨油田污水配制;实验温度95℃。根据形成的凝胶黏度(95℃,1.1 s-1)确定交联剂各组分用量为:MZ-YL 0.429%,MZ-BE 0.060%,MZ-XS 0.012%;酸度调整剂用量0.12%;成胶时间10~15小时。2.5、3.0、3.5 g/L AP-P4的凝胶在95℃老化100天后黏度保持在~40 Pa.s及以上。初配制胶液在3000 r/min下剪切15分钟后黏度降低87.5%~89.0%,但成胶后和老化过程中凝胶黏度只比未剪切样降低17.1%~6.6%。3.5 g/L AP-P4的调剖剂对~1μm2的6支储层岩心的堵塞率在88.1%~95.8%范围,平均93.3%,造成的残余阻力系数在15.2~28.6范围,平均19.8,使渗透率级差2.3~8.0的4组双人造岩心的注水流量比发生不同程度的反转。认为该凝胶调剖剂高温下稳定性好的原因,是强化学交联密度低,因而凝胶脱水收缩作用弱。图2表5参5。 相似文献
97.
针对显色剂-过渡金属元素-过氧化氢体系,用分光光度法间接测定羟自由基。通过大量试验,确定了三苯甲烷类酸性酚醌吡喃类为有效显色剂,并确定了溴邻苯三酚红-亚铁离子-过氧化氢体系测定羟自由基的最佳条件,首次推测出其最可能的反应机理为:亚铁离子催化过氧化氢产生羟自由基,羟自由基氧化溴邻苯三酚红上的羰基碳氧双键,破坏其显色的共轭结构,使其褪色,此法可作为筛选羟自由基清除剂的有效方法。 相似文献
98.
99.
Baudilio Coto Carmen Martos Jos L. Pea Juan J. Espada María D. Robustillo 《Fuel》2008,87(10-11):2090-2094
Wax precipitation is one of the most important flow assurance problems. Unfortunately, experimental data are very scarce to confirm existing models for prediction of such precipitation problem. This work reports a new experimental method. Multistage fractional wax precipitation was carried out by decreasing the temperature of crude oil. No solvent dilution was used, so the effect of solvent on temperature wax precipitation was avoided. The reproducibility of the method was tested with comparable results. The precipitation curve and the wax appearance temperature were obtained for two crude oils with different chemical nature using the reported method. 相似文献
100.
Degumming of hemp fiber by high temperature alkali cooking was investigated, and the effect of temperature and dosage of alkali on the constituents, structure, and thermal degradation of hemp fiber was also discussed in this work. The morphology, structure, and thermal degradation of hemp fiber after high temperature cooking were investigated through SEM, FTIR, WAXD, and TG analysis. The results indicated that the high temperature cooking process was effective for removing hemicelluloses and lignin and could also improve the thermal stability of cellulose. Crystallinity index of the treated hemp fiber was increased, which was related to the cooking temperature and NaOH dosage. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献