全文获取类型
收费全文 | 27197篇 |
免费 | 4708篇 |
国内免费 | 3573篇 |
专业分类
电工技术 | 2288篇 |
技术理论 | 3篇 |
综合类 | 3776篇 |
化学工业 | 3108篇 |
金属工艺 | 679篇 |
机械仪表 | 1377篇 |
建筑科学 | 1481篇 |
矿业工程 | 933篇 |
能源动力 | 670篇 |
轻工业 | 2054篇 |
水利工程 | 816篇 |
石油天然气 | 1013篇 |
武器工业 | 370篇 |
无线电 | 2567篇 |
一般工业技术 | 1791篇 |
冶金工业 | 666篇 |
原子能技术 | 124篇 |
自动化技术 | 11762篇 |
出版年
2024年 | 208篇 |
2023年 | 543篇 |
2022年 | 1003篇 |
2021年 | 1101篇 |
2020年 | 1239篇 |
2019年 | 1065篇 |
2018年 | 1073篇 |
2017年 | 1197篇 |
2016年 | 1365篇 |
2015年 | 1404篇 |
2014年 | 1924篇 |
2013年 | 1899篇 |
2012年 | 2476篇 |
2011年 | 2390篇 |
2010年 | 1879篇 |
2009年 | 1831篇 |
2008年 | 1824篇 |
2007年 | 2134篇 |
2006年 | 1591篇 |
2005年 | 1260篇 |
2004年 | 1021篇 |
2003年 | 867篇 |
2002年 | 673篇 |
2001年 | 628篇 |
2000年 | 448篇 |
1999年 | 456篇 |
1998年 | 340篇 |
1997年 | 250篇 |
1996年 | 238篇 |
1995年 | 208篇 |
1994年 | 191篇 |
1993年 | 146篇 |
1992年 | 101篇 |
1991年 | 114篇 |
1990年 | 85篇 |
1989年 | 61篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 31篇 |
1983年 | 20篇 |
1982年 | 24篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1964年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
It seems clear that, for whatever reasons, the dementia of the Alzheimer type patient group (as well as other patient groups) exhibits behavior that is different from the normal control group. G. Storms, T. Dirikx, J. Saerens, S. Verstraeten, and P. P. De Deyn (2003) rightfully argue that the observed behavior (similarity judgments) does not tell us the source (cause) of the differences between the 2 groups. Rather, the focus of the study should be placed more on finding the ways the 2 groups are different. They also point out various methodological problems in some of the previous attempts to characterize the nature of the differences. Further methodological issues in G. Storms et al.'s study are examined. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
32.
33.
The physical preconditions are considered for the temperature of a body to influence the force of gravity experienced by it. The results are given of experiments on weighing metal rods heated by ultrasound which confirm a dependence of the weight of the rods on their temperature. 相似文献
34.
A generalized equation was derived to calculate the melting temperatures of homopolymers and copolymers. The Gibbs‐Thomson equation for homopolymers and a modified application to copolymers were derived using the proposed equation. The melting temperature Tm0 in the Flory equation corresponds to the melting temperature TmC,∞ of copolymer crystals with stems of infinite length. Also, TmC,n*, the melting temperature for copolymer crystals with stems containing the maximum possible number of structural units, n*, should be used instead of Tm0 as the basis of supercooling in crystallization. The proposed equation shows good agreement with experimental data for α‐alkene‐ethylene homogeneous copolymers. 相似文献
35.
This paper deals with the non-steady-state kinetics of direct thermal initiated polymerization. The initiation is assumed to be a bimolecular reaction of the monomer. The relationship between the radical concentration and the monomer conversion is rigorously derived. In further treatment a few very close approximations are introduced based on the fact that the number of monomer molecules reacting in the initiation step is much less than that consumed in the propagation step for a process producing high polymer, and the value of the rate constant for propagation or chain transfer is much lower than that for chain termination. Expressions for various molecular parameters, such as molecular weight distribution, number-average and weight-average degrees of polymerization, and dispersity, are given. Several numerical examples are provided. 相似文献
36.
37.
模糊聚类在三维地震参数处理中的应用 总被引:1,自引:1,他引:0
三维地震参数是一个庞大的三维数据体,能从不同侧面反映储集层的特征。通过对三维地震参数的分析,可以评估油藏表征的参数(沉积相、构造、生长历史、流体饱和度等)。针对传统的聚类方法不能很好地综合考虑各个参数之间的相似程度,提出了用模糊C-均值聚类(fuzzy c-means clustering,简称FCM)对三维地震参数进行处理。从三维地震参数和油藏表征参数之间的关系出发,采用模糊C-均值聚类方法对三维地震参数进行处理,依此评估油藏表征的参数。测试结果表明,模糊C-均值聚类方法能够对三维地震参数进行较为准确的分类,并为储集层的研究提供了很好的依据。 相似文献
38.
Polyurethanes were prepared from pure 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) or 1,2-ethane diol (EDO) and α,ω-hydroxyl poly(propylene oxide) (PPO) by reaction injection moulding (RIM). Hard segment (MDI + BDO or EDO) level was 45–50 wt%. The PPO had about 20% ethylene oxide copolymerized in at the chain ends to provide 80% primary OH end groups. Mn was varied from 2000 to 4000. Dibutyl tin dilaurate catalyst and mould temperature were varied. Dynamic mechanical, wide-angle X-ray, differential scanning calorimeter, molecular weight and tensile elongation measurements were made on the RIM polyurethanes. At low reaction rates (low catalyst or temperature) highly crystalline, well phase separated but low molecular weight polymers were produced. At high catalyst or temperature levels more poorly phase separated but high molecular weight, tough polymers resulted. Higher Mn PPO gave better phase separation and EDO gave higher melting temperatures. Preventing hard segment crystallinity by substituting asymmetric MDI or glycols resulted in phase compatibility. 相似文献
39.
超高分子量聚乙烯衬板在煤仓中的应用 总被引:2,自引:0,他引:2
介绍了井底煤仓溜煤斜面采用超高分子量聚乙烯衬板安装及应用情况 ,对井底煤仓棚煤原因及解决办法进行了探讨 相似文献
40.
热带城市垃圾典型组分的热解特性研究 总被引:7,自引:0,他引:7
对热带城市垃圾的几种典型组分进行了热解实验,得到了它们的失重曲线,通过对失重曲线进行分析,得到了这几种典型组分的热解规律,并通过建立热解动力学模型,求出了其中两种组分的活化能E和频率因子A。 相似文献