全文获取类型
收费全文 | 45817篇 |
免费 | 4593篇 |
国内免费 | 2226篇 |
专业分类
电工技术 | 3134篇 |
技术理论 | 5篇 |
综合类 | 3363篇 |
化学工业 | 7440篇 |
金属工艺 | 2408篇 |
机械仪表 | 3103篇 |
建筑科学 | 3741篇 |
矿业工程 | 1373篇 |
能源动力 | 1489篇 |
轻工业 | 3382篇 |
水利工程 | 982篇 |
石油天然气 | 2069篇 |
武器工业 | 411篇 |
无线电 | 5212篇 |
一般工业技术 | 5773篇 |
冶金工业 | 1982篇 |
原子能技术 | 506篇 |
自动化技术 | 6263篇 |
出版年
2024年 | 149篇 |
2023年 | 715篇 |
2022年 | 1364篇 |
2021年 | 1880篇 |
2020年 | 1439篇 |
2019年 | 1227篇 |
2018年 | 1322篇 |
2017年 | 1500篇 |
2016年 | 1325篇 |
2015年 | 1911篇 |
2014年 | 2258篇 |
2013年 | 2790篇 |
2012年 | 3161篇 |
2011年 | 3163篇 |
2010年 | 2806篇 |
2009年 | 2625篇 |
2008年 | 2702篇 |
2007年 | 2525篇 |
2006年 | 2457篇 |
2005年 | 2167篇 |
2004年 | 1550篇 |
2003年 | 1539篇 |
2002年 | 1643篇 |
2001年 | 1486篇 |
2000年 | 1219篇 |
1999年 | 1106篇 |
1998年 | 808篇 |
1997年 | 711篇 |
1996年 | 641篇 |
1995年 | 550篇 |
1994年 | 407篇 |
1993年 | 330篇 |
1992年 | 263篇 |
1991年 | 209篇 |
1990年 | 162篇 |
1989年 | 136篇 |
1988年 | 110篇 |
1987年 | 51篇 |
1986年 | 59篇 |
1985年 | 50篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1970年 | 3篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 99 毫秒
101.
喷射沉积SiCP/Al复合材料及6066铝合金热挤压工艺的研究 总被引:4,自引:0,他引:4
作者应用喷射共沉积工艺制备 6 0 6 6 / Si Cp复合材料和 6 0 6 6铝合金锭坯 ,在不同的挤压比、挤压温度下挤压成 型 ,用金相显微镜观察材料的显微组织 ,并测试了材料的力学性能。结果表明 :Si C/ Al复合材料喷射沉积状态的组织很疏松 ,存在许多的间隙 ,其密度约为理论密度的 86 % ,Si C颗粒在复合材料中分布不均匀 ,喷射沉积铝合金基体的致密度可达 90 % ;挤压过程使 Al/ Si Cp复合材料的大多数空隙消失 ,致密程度随挤压比的增大而增大 ,挤压比超过 14 .7后不会明显变化 ,而铝合金基体的致密程度与挤压比的变化关系不明显 ;挤压温度对材料的致密程度影响不大 ;Al/ Si Cp复合材料性能在挤压比超过 14 .7后变化不大 ;铝合金的性能不受挤压比变化的影响 ;而挤压温度过高使材料性能下降 相似文献
102.
The combination of the chemical aggressivity of water and lead piping, as is well known, can cause severe cases of lead poisoning in those who consume such water. After a great number of observations and epidemiological studies which have strongly incriminated this metal in a wide range of pathologic conditions, other materials have been gradually substituted for lead; however, the problem remains.In compliance with a European Directive to survey the risk of lead poisoning (Council Directive, 1977), a random sample of 321 residents was selected from the Vosgian Mountains of France. This region is noted for its high incidence of cases of lead poisoning: 150 reported during 8 months in 1983 (Barbier et al., 1983).During the course of a health evaluation, a blood sample was taken from each subject for lead analysis. At the same time, a sample of tap-water (after running for 5 s) was taken from each subject home. Both lead analyses (blood and water) were performed by electrothermal atomization-atomic absorption spectrophotometry. Because of the log-normality of the distributions of the blood lead levels and the concentrations of lead in the drinking water, a logarithmic transformation was performed so that the results are expressed as the geometric mean, which for the amount of lead in the drinking water of our sample was found to be 0.16 mg l?1.Among the subjects of this study, 28% are served by water containing more than 0.10 mg l?1 of lead (the standard for France) and 48% by water containing more than 0.05 mg l?1 (the European and WHO standard). In concurrence with numerous authors, our study indicates that, among our subjects, the blood lead level is much higher in men than in women (geometric means 22.9 and 15.0 μg dl?1 respectively); this difference is highly significant (t-test:P < 0.001). Table 1 summarizes the results, by sex, obtained in this region compared with those from a study (Huel, 1982) concerning an urban French population whose geometric mean blood lead levels were 15.9 μg dl?1 for men and 11.4 μg dl?1 for women. The irrespective of sex, is highly significant (P < 0.001). Table 2 shows the significance of the relation between these subjects, high blood lead levels and the concentration of lead in their drinking water, while Fig. 1 shows that for contamination levels up to 0.02 mg l?1 of lead in water, the blood lead level remains relatively stable, while above this apparent “threshold” value, the blood lead level begins to increase finally reaching quite high values in response to high contamination levels, suggesting a direct translation of increases in the water above the 0.02 mg l?1 level to increases in the blood. 相似文献
103.
Xinying. Lu Kaiming. Liang Shouren. Gu Yankang. Zheng Hongsheng. Fang 《Journal of Materials Science》1997,32(24):6653-6656
The effect of oxygen vacancy on the stability of phase structures and phase transformation of zirconia at low temperatures
was studied using an electrochemical technique. It is suggested that the decrease of oxygen vacancies decreases the stability
of metastable tetragonal zirconia and promotes its transformation to the monoclinic phase.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
104.
105.
106.
107.
研究了电子束、离子束作用于Al2O3表面时成分的变化,表明无论电子束或离子束都能使Al2O3发生分解,产生导电的元素Al。实验在PHI610·SAM上进行,电子束轰击下(3keV,O.5μA,入射角60°)10s就有元素Al分解出来,2min以后就达到饱和,分解析出量随时间成a(1-e-bt)的关系。离子束轰击下同样发生元素Al的分解,但当Ei>3keV时,由于剥离速率加大,溅射5min时表面Al峰反而比1min时要弱。这时表面Al含量处于分解析出与溅射剥离的动态平衡中。实验还发现了Al2O3的解析与表面成分有关(如碳的含量)。最后讨论电子束与离子束的解析机理。 相似文献
108.
Myostatin (GDF-8) is a member of the transforming growth factor-beta superfamily and plays a role in muscle growth and development. Mice having targeted disruption of this gene display marked increases in muscle mass, a phenotype similar to the muscular hypertrophy (mh) in several cattle breeds. Physical mapping data developed from YAC clones indicate the bovine myostatin gene lies close to the centromere of bovine Chromosome (Chr) 2 (BTA2) at 2q11, indistinguishable from the cytogenetic location of the mh locus. In addition, a polymorphism in the second intron of the gene was used to show that myostatin maps within the interval previously shown to contain mh. These data suggest myostatin may be the gene causing muscular hypertrophy in cattle. 相似文献
109.
110.
介绍了替代进口梳棉机测厚传感器集成电路分立元件的电路图,工作原理及特点。一年多的实际运行证明,电路参数达到了设计要求。 相似文献