全文获取类型
收费全文 | 67559篇 |
免费 | 7819篇 |
国内免费 | 5294篇 |
专业分类
电工技术 | 7836篇 |
综合类 | 7359篇 |
化学工业 | 10312篇 |
金属工艺 | 2849篇 |
机械仪表 | 3484篇 |
建筑科学 | 8508篇 |
矿业工程 | 3118篇 |
能源动力 | 2866篇 |
轻工业 | 5805篇 |
水利工程 | 3900篇 |
石油天然气 | 2926篇 |
武器工业 | 690篇 |
无线电 | 4073篇 |
一般工业技术 | 6303篇 |
冶金工业 | 1801篇 |
原子能技术 | 892篇 |
自动化技术 | 7950篇 |
出版年
2024年 | 172篇 |
2023年 | 1172篇 |
2022年 | 1787篇 |
2021年 | 2209篇 |
2020年 | 2473篇 |
2019年 | 2316篇 |
2018年 | 2158篇 |
2017年 | 2551篇 |
2016年 | 2655篇 |
2015年 | 2806篇 |
2014年 | 3858篇 |
2013年 | 4406篇 |
2012年 | 4772篇 |
2011年 | 5114篇 |
2010年 | 3787篇 |
2009年 | 4166篇 |
2008年 | 3835篇 |
2007年 | 4529篇 |
2006年 | 3989篇 |
2005年 | 3416篇 |
2004年 | 2895篇 |
2003年 | 2346篇 |
2002年 | 1992篇 |
2001年 | 1709篇 |
2000年 | 1553篇 |
1999年 | 1395篇 |
1998年 | 1045篇 |
1997年 | 913篇 |
1996年 | 814篇 |
1995年 | 723篇 |
1994年 | 641篇 |
1993年 | 489篇 |
1992年 | 459篇 |
1991年 | 337篇 |
1990年 | 267篇 |
1989年 | 212篇 |
1988年 | 152篇 |
1987年 | 106篇 |
1986年 | 82篇 |
1985年 | 56篇 |
1984年 | 69篇 |
1983年 | 42篇 |
1982年 | 53篇 |
1981年 | 23篇 |
1980年 | 33篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
添加剂对工业齿轮油性能影响的研究 总被引:3,自引:0,他引:3
研究了硫化烯烃、磷酸酯胺盐、硫磷酸酯极压抗磨剂,含氮杂环衍生物多功能添加剂和防锈剂等,对工业齿轮油抗乳化性能、极压抗磨性能、防锈性能的影响;以及硫化烯烃、磷酸酯盐极压抗磨剂与含氮杂环衍生物多功能添加剂之间的协和效应。试验结果表明:1.2%~1.6%复合添加剂调制的CKD220工业齿轮油中,磷酸脂盐的正确选用可以提高齿轮油的抗乳化性能、防锈性能和减少防锈剂用量。硫化烯烃与磷酸脂盐、含氮杂环衍生物多功能添加剂的合理组合,可以提高齿轮油的极压抗磨性能和防锈性能,减少添加剂总加剂量。 相似文献
92.
为了提高非稳定渗流计算的计算精度 ,通过数学分析得到了水位传导系数随时间变化时 ,一类非稳定渗流井流模型的半解析解 ,并进行了计算比较 相似文献
93.
Hiroshi Takamatsu Hikaru Yamashiro Nobuo Takata Hiroshi Honda 《International Journal of Refrigeration》2003,26(6):79
Heat and mass transfer in a falling film vertical in-tube absorber was studied experimentally with LiBr aqueous solution. The presented results include the effect of solution flow rate, solution subcooling and cooling water temperature on the absorption in a smooth copper tube 16.05 mm I.D. and 400 mm long. The experimental data in the previous report for a 1200-mm-long tube was also re-examined and compared. It was demonstrated by the observation of the flow in the tube that the break down of the liquid film into rivulets leads to deterioration of heat and mass transfer at lower film Reynolds number or in longer tubes. An attempt to evaluate physically acceptable heat and mass transfer coefficients that are defined with estimated temperature and concentration at the vapor–liquid interface was also presented. 相似文献
94.
Ph. D. Candidate:Chen Xue-fengState Key Laboratory of Offshore Coastal Engineering Dalian University of Technology Dalian China e-mail: cxfeng @ student dlut. edu.cn 《水动力学研究与进展(B辑)》2003,15(6)
The reflection coefficient of perforated caissons and the total horizontal forces acting on them were experimentally and numerically analyzed and discussed when wave propagates normally. To consider the viscosity effect of fluid and nonlinear action of waves on structures, the VOF (Volume Of Fluid) method combined with the k-ε turbulence model was used to simulate the interaction between waves and structures. Governing equations were solved with the finite difference method. Through 2D experimental study in the wave flume, the empirical relationship between the reflection coefficient of perforated caissons and the main affecting factors were obtained from the experimental data using the least square method. Also the correlation between the ratio of the total horizontal force acting on perforated caisson and the force acting on solid caisson and the main affecting factors were regressed from the experimental data. 相似文献
95.
96.
讨论了不同分布两两NQD列的Jamison型加权乘积和的强稳定性。推广了不同分布独立列部分和和同分布NQD列部分和情形相类似的结论,得到了一些新的结果。 相似文献
97.
Lebedev A. A. Makovetskii I. V. Lamashevskii V. P. Volchek N. L. 《Strength of Materials》2003,35(6):568-573
The authors discuss the results of experimental investigation of structural degradation of gray cast iron at various stages of static tensile deformation. Analysis of the deformation process has revealed that damageability of a material under loading can be assessed by both a special strain parameter and scatter of hardness characteristics or a ratio of the modulus deviation to the current value of the elastic modulus. A correlation between these parameters has been established. 相似文献
98.
运用非恒定的动量方程和时均值计算方法,对脉冲液体射流泵时均值基本方程中的流速系数进行了理论研究,推导出了喉管和喉管进口段流速系数φ2和φ5的计算式。通过与恒定射流的流速系数计算式对比,阐明了脉冲频率是影响φ2和φ5的主要因素,沟通了脉冲射流与恒定射流流速系数之间的关系。 相似文献
99.
The planimetric shifts in channel location of large alluvial rivers are a critical component in the creation of diverse structures and functions in riverine habitats. Engineered management schemes must also compensate for this type of channel change to protect resources and maintain navigation channels. The stability of the Lower Mississippi River channel was assessed through an analysis of historical records of channel position produced and archived by the United States Army Corps of Engineers. Channel location was recorded for the years 1765, 1820, 1881, 1915, 1930, 1937, 1960 and 1970. Channel stability was measured by two introduced metrics on a cell‐by‐cell basis: (1) the standard deviation of Euclidean distance to a channel cell for the entire period of record, and (2) the rate of Euclidean distance change between years in the period of record. At a coarse spatial scale, channel instability increased in the downstream direction. The variability of channel stability also increased in the downstream direction. Analysis of this variability identified alternating areas of high and low stability occurring with greater frequency as distance downstream increased. These findings are validated by past studies of channel stability along the Lower Mississippi River. As a result, the proposed metrics provide a consistent, quantitative, efficient and cost‐effective means of identifying areas of channel instability at several spatial scales. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
100.
为了研究油井各参数对超声波透射系数的影响,根据超声波在媒质中的波函数和边界条件,求出了油井中超声波的透射系数。当井液和水泥层的声速和密度增大时,超声波的透射系数也随之增大,但变化幅度不大,特别是水泥层密度对超声波的透射系数影响很小;当岩层的声速增大时,超声波的透射系数会出现一个极大值;岩层密度对超声波的透射系数影响较大,且随岩层密度的增大超声波的透射系数随之降低。 相似文献