全文获取类型
收费全文 | 2562篇 |
免费 | 531篇 |
国内免费 | 237篇 |
专业分类
电工技术 | 267篇 |
综合类 | 329篇 |
化学工业 | 180篇 |
金属工艺 | 49篇 |
机械仪表 | 220篇 |
建筑科学 | 168篇 |
矿业工程 | 63篇 |
能源动力 | 176篇 |
轻工业 | 147篇 |
水利工程 | 770篇 |
石油天然气 | 117篇 |
武器工业 | 18篇 |
无线电 | 98篇 |
一般工业技术 | 150篇 |
冶金工业 | 64篇 |
原子能技术 | 9篇 |
自动化技术 | 505篇 |
出版年
2024年 | 24篇 |
2023年 | 103篇 |
2022年 | 202篇 |
2021年 | 247篇 |
2020年 | 207篇 |
2019年 | 174篇 |
2018年 | 163篇 |
2017年 | 154篇 |
2016年 | 179篇 |
2015年 | 152篇 |
2014年 | 182篇 |
2013年 | 147篇 |
2012年 | 174篇 |
2011年 | 164篇 |
2010年 | 104篇 |
2009年 | 102篇 |
2008年 | 91篇 |
2007年 | 94篇 |
2006年 | 119篇 |
2005年 | 106篇 |
2004年 | 66篇 |
2003年 | 60篇 |
2002年 | 50篇 |
2001年 | 40篇 |
2000年 | 34篇 |
1999年 | 34篇 |
1998年 | 26篇 |
1997年 | 34篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 19篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1957年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有3330条查询结果,搜索用时 15 毫秒
1.
边坡位移的时间序列曲线存在复杂的非线性特性,传统的预测模型精度不足以满足预测要求。为此提出了基于变分模态分解的鸟群优化-核极限学习机的预测模型,并用于河北省某水泥厂的边坡位移预测。该方法首先采用VMD把边坡位移序列分解为一系列的有限带宽的子序列,再对各子序列分别采用相空间重构并用核极限学习机预测,采用鸟群算法优化相空间重构的嵌入维度和KELM中惩罚系数和核参数三个数值,以取得最优预测模型。最后将各个子序列预测值叠加,得到边坡位移的最终预测值。结果表明:和KELM、BSA-KELM、EEMD-BSA-KELM模型相比,基于VMD的BSA-KELM预测精度更高,为边坡位移的预测提供一种有效的方法。 相似文献
2.
3.
4.
Li Yu-cheng He Ming Dept.of Civil Engineering Dalian Univ.of Technology Dalian P.R.China 《水动力学研究与进展(B辑)》1993,(4)
Based on model test,the statistical distribution of extreme values of wave-current in-line forces acting on vertical circular cylinder is analyzed in this paper.It is shownthat the results calculated by the simplified method,proposed by authors,agree well with the testdata;Weibull distribution is also adoptable in the region of high KC number, and the shapeparameter a and scale parameter β are related well with KC number respectively. 相似文献
5.
6.
7.
金属清净剂的性能研究 总被引:2,自引:0,他引:2
为了改进金属清净剂的抗氧性和极压抗磨性能,用一种含硫磷的羧酸衍生物部分中和清净剂中过碱性组分,得到两种改进的金属清净剂,并用四球机和热重分析仪评价其极压抗磨和抗氧化性能。结果表明功能化处理提高了金属清净剂抗氧化和极压性能,但未对分散和抗磨性能产生显著影响。 相似文献
8.
Preacher Kristopher J.; Rucker Derek D.; MacCallum Robert C.; Nicewander W. Alan 《Canadian Metallurgical Quarterly》2005,10(2):178
Analysis of continuous variables sometimes proceeds by selecting individuals on the basis of extreme scores of a sample distribution and submitting only those extreme scores to further analysis. This sampling method is known as the extreme groups approach (EGA). EGA is often used to achieve greater statistical power in subsequent hypothesis tests. However, there are several largely unrecognized costs associated with EGA that must be considered. The authors illustrate the effects EGA can have on power, standardized effect size, reliability, model specification, and the interpretability of results. Finally, the authors discuss alternative procedures, as well as possible legitimate uses of EGA. The authors urge researchers, editors, reviewers, and consumers to carefully assess the extent to which EGA is an appropriate tool in their own research and in that of others. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
9.
To find the exact probability distribution of the global maximum or minimum of a random field within a bounded domain is a pending problem even for Gaussian fields. Except for very special examples of fields, recourse must be taken to approximate reasoning or asymptotic considerations to be judged with respect to accuracy by simulations. In this paper, the problem is addressed through a functional equation that leads to the definition of a class of distribution functions that depend solely on process or field characteristics and domain quantities that can be calculated explicitly. This distribution function class is studied for Gaussian processes in earlier works by the author and it has been obtained explicitly for Gaussian fields on rectangular domains in the plane. Simulation studies show that rather good predictions are obtained for sufficiently smooth wide band Gaussian processes and fields. In this paper, the distribution function is obtained in general for Gaussian fields over arbitrary bounded domains with piecewise continuous and differentiable boundaries, and as in earlier works the distribution function is tested against empirical distribution functions obtained by simulation of sample functions of a smooth approximately Gaussian field, herein called a broken line Hino field. For completeness this particular field type is defined in appendix a and appendix b. The paper concludes with a statistical application on data for plain concrete tensile strength. 相似文献
10.