全文获取类型
收费全文 | 34852篇 |
免费 | 4358篇 |
国内免费 | 2576篇 |
专业分类
电工技术 | 3592篇 |
综合类 | 4274篇 |
化学工业 | 4733篇 |
金属工艺 | 1998篇 |
机械仪表 | 2453篇 |
建筑科学 | 4792篇 |
矿业工程 | 1264篇 |
能源动力 | 2122篇 |
轻工业 | 1164篇 |
水利工程 | 1845篇 |
石油天然气 | 1562篇 |
武器工业 | 449篇 |
无线电 | 3076篇 |
一般工业技术 | 3880篇 |
冶金工业 | 1338篇 |
原子能技术 | 832篇 |
自动化技术 | 2412篇 |
出版年
2024年 | 158篇 |
2023年 | 493篇 |
2022年 | 961篇 |
2021年 | 1066篇 |
2020年 | 1234篇 |
2019年 | 1041篇 |
2018年 | 1044篇 |
2017年 | 1397篇 |
2016年 | 1460篇 |
2015年 | 1510篇 |
2014年 | 1960篇 |
2013年 | 2276篇 |
2012年 | 2643篇 |
2011年 | 2664篇 |
2010年 | 1994篇 |
2009年 | 2035篇 |
2008年 | 1999篇 |
2007年 | 2304篇 |
2006年 | 2045篇 |
2005年 | 1750篇 |
2004年 | 1464篇 |
2003年 | 1219篇 |
2002年 | 1037篇 |
2001年 | 902篇 |
2000年 | 814篇 |
1999年 | 695篇 |
1998年 | 548篇 |
1997年 | 507篇 |
1996年 | 462篇 |
1995年 | 388篇 |
1994年 | 352篇 |
1993年 | 235篇 |
1992年 | 235篇 |
1991年 | 183篇 |
1990年 | 181篇 |
1989年 | 137篇 |
1988年 | 102篇 |
1987年 | 67篇 |
1986年 | 56篇 |
1985年 | 47篇 |
1984年 | 29篇 |
1983年 | 11篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1976年 | 3篇 |
1965年 | 2篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
本文用不同的测试技术和方法测定了锗酸铋(BGO)单晶的比热(300~800K)热膨胀系数(100~1100K)和导温系数(140~700K),进而导出了 BGO 单晶不同温度下的导热系数、定容比热、德拜温度和格虑内森数。本文还对 BGO 单晶热物理性质的变化规律作了理论解释。 相似文献
43.
引入自然对流换热系数 ,将固液蓄能数学模型简化为仅用能量方程加以描述。并通过实验测得相变过程的实际温度场 ,证明了自然对流固液相变换热的影响不可忽略 ,验证了固液相变界面移动速率随自然对流换热系数的增大而增大的定性关系 相似文献
44.
MODELING LIQUID MASS TRANSFER IN HIGEE SEPARATION PROCESS 总被引:1,自引:0,他引:1
Correspondence concerning this paper should be addressed to Professor Richard S.H. Mah. Hsien-Hsin Tung is now affiliated with Department of Chemical Engineering, California Institute of Technology
Penetration theory is used to describe the liquid mass transfer in Higee separation process. Within a possible range of effective areas, it is shown that the predicted mass transfer coefficients are in reasonable agreement with the estimated mass transfer coefficients. The estimated coefficients were calculated from the experimental data and the possible effective areas. Hence it is concluded the penetration theory is generally applicable to describe liquid mass transfer in Higee separation process. The comparison also suggests that liquid mixing at the junctions of packing materials may be more complete in Higee process than in traditional process. 相似文献
Penetration theory is used to describe the liquid mass transfer in Higee separation process. Within a possible range of effective areas, it is shown that the predicted mass transfer coefficients are in reasonable agreement with the estimated mass transfer coefficients. The estimated coefficients were calculated from the experimental data and the possible effective areas. Hence it is concluded the penetration theory is generally applicable to describe liquid mass transfer in Higee separation process. The comparison also suggests that liquid mixing at the junctions of packing materials may be more complete in Higee process than in traditional process. 相似文献
45.
Thermodynamic parameters have been determined for the interaction of methyl orange and poly(vinylpyrrolidone) in aqueous solutions containing tris, tris and hydrochloric acid, or water only. Enthalpy changes were determined by use of a flow microcalorimeter. Free energy changes were calculated from the results of equilbrium dialysis studies. The results are interpreted in terms of the behaviour of poly(vinylpyrrolidone) in these systems. Analysis of data shows that the hydrophobic interactions in the systems are in the order: tris > wateronly > tris-HC1. 相似文献
46.
ˮ�ཬ������������Ƽ�����Ľ�������о� 总被引:2,自引:1,他引:1
解决注水泥作业的防气窜问题,是提高固井质量,保护油气层的关键技术。现有预测和防止水泥浆气管理的方法虽然较多,但应用于现场却有一定困难,主要表现在所考虑的因素比较单一,有些高温、高压下的水泥浆性能参数难以测定。文章在分析国内外预测和防止气窜方法的基础上,应用水泥浆浆体在环空的组成,GFP系数、水泥浆稠度阻力系数(A)及多凝水泥和环空加压等措施,拟定出一套提高水泥浆顶替效率,保证水泥浆动态和静态过程压力平衡关系的具体设计方法。 相似文献
47.
48.
热释电系数的测量方法 总被引:2,自引:0,他引:2
描述热释电系数的两种测量方法。其一为电荷积分法,测试系统简单,测量数据准确,且能满足零电场条件下的测量。其二为动态电流法,采用调制热源技术,研究在特定温度条件下热释电材料的动态热释电响应。 相似文献
49.
50.
Because of its high–temperature chemical stability, SiC ceramic is a promising material for high-temperature device applications such as thermoelectric energy converters. However, the electrical conductivity of SiC ceramic is too low for it to be used as a thermoelectric energy converter at the cold junction. Therefore, we propose a SiC-Si functionally gradient material (FGM) in order to improve the electrical conductivity of the SiC ceramic at the cold junction. An SiC rod was fired in a temperature gradient furnace. One end of the SiC rod was maintained at 2473 K and the other end was maintained at 1973 K for 30 min. After firing, the porous SiC edge fired at 1973 K was dipped into molten Si in order to infiltrate molten Si into the porous SiC. The microstructure of the FGM is classified into three regions: the SiC-Si composite material; the porous SiC ceramic; and the densified SiC ceramic. The electrical conductivity, the Seebeck coefficient and the thermal conductivity for each region of SiC-Si FGM was measured at 300 K; a figure of merit was calculated. The figure of merit of the SiC-Si FGM at the cold junction, at room temperature, was 108 times higher than that of a nongradient SiC ceramic. 相似文献