全文获取类型
收费全文 | 13779篇 |
免费 | 1431篇 |
国内免费 | 822篇 |
专业分类
电工技术 | 801篇 |
综合类 | 1697篇 |
化学工业 | 956篇 |
金属工艺 | 815篇 |
机械仪表 | 667篇 |
建筑科学 | 3167篇 |
矿业工程 | 932篇 |
能源动力 | 333篇 |
轻工业 | 524篇 |
水利工程 | 920篇 |
石油天然气 | 1069篇 |
武器工业 | 133篇 |
无线电 | 1139篇 |
一般工业技术 | 1049篇 |
冶金工业 | 566篇 |
原子能技术 | 512篇 |
自动化技术 | 752篇 |
出版年
2024年 | 23篇 |
2023年 | 119篇 |
2022年 | 310篇 |
2021年 | 346篇 |
2020年 | 406篇 |
2019年 | 330篇 |
2018年 | 272篇 |
2017年 | 380篇 |
2016年 | 452篇 |
2015年 | 502篇 |
2014年 | 880篇 |
2013年 | 851篇 |
2012年 | 1068篇 |
2011年 | 1096篇 |
2010年 | 828篇 |
2009年 | 878篇 |
2008年 | 731篇 |
2007年 | 944篇 |
2006年 | 854篇 |
2005年 | 678篇 |
2004年 | 609篇 |
2003年 | 539篇 |
2002年 | 520篇 |
2001年 | 458篇 |
2000年 | 412篇 |
1999年 | 292篇 |
1998年 | 203篇 |
1997年 | 191篇 |
1996年 | 149篇 |
1995年 | 179篇 |
1994年 | 121篇 |
1993年 | 75篇 |
1992年 | 81篇 |
1991年 | 49篇 |
1990年 | 37篇 |
1989年 | 59篇 |
1988年 | 32篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1976年 | 2篇 |
1964年 | 1篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
针对二连盆地乌兰花凹陷安山岩储层的特性认识不清、有效储层划分不准确的问题,利用岩心薄片、黏土矿物分析、物性测试以及核磁共振实验等手段开展了岩石储集空间特征、岩石蚀变程度、测井响应特征分析。在此基础上,重点开展了基于核磁共振实验的安山岩储层有效孔隙度计算模型研究,开发了相适应的测井解释评价模块,并结合常规测井和试油结果建立了安山岩储层的分类标准。结果表明:安山岩储集空间具有发育"微孔"、"杏仁孔"双孔隙的特征,且以微孔为主;根据不同蚀变程度所建立的安山岩有效孔隙度计算模型具有很高的精度,平均绝对误差为0.16%,平均相对误差为19.40%;新测井解释储层分类标准在实际应用中与试油结论具有很好的一致性,有利于乌兰花凹陷安山岩有效储层的精确划分,并为该地区开发方案的设计及可采储量评价提供技术支持。 相似文献
5.
The flow characteristics of the hydraulic jump due to parallel jets are different from the classical jump emerging from a single gate. Due to the highly complex flow field at the downstream pool, deciding about the tailwater measuring location is a challenging issue affecting the flow measuring accuracy. Experiments are conducted herein, on different parallel jets’ configurations for both free and submerged flow conditions. To quantify the flow uniformity, for any downstream cross section, the associated momentum correction factors, β2, were estimated for the free-flow condition. It is found that β2-values depend significantly on the measuring location, and consequently the available conjugated depths relationship results in poor estimation when measuring location moves downstream. Employing Buckingham analysis, a general formula is proposed to calculate the momentum correction factors associated with the free hydraulic jump at different downstream measuring locations. The experimental results of this study indicated that such a formula enhances distinguishing between free and submerged flow conditions of the gates installed in parallel. Finally, a dimensionless stage-discharge formula is presented to predict the submerged flow rate through parallel gates of different gate openings and widths. 相似文献
6.
针对含噪信号的有效奇异值个数难以确定的问题,提出了一种改进的奇异值分解降噪方法--奇异值累积法。该方法通过计算奇异值的实际下降值与奇异值平均下降速度累积量的差值,并取该差值最大值点的位置作为有效奇异值的分界点来确定有效奇异值的个数。在此基础上,提出了一种基于奇异值累积法与快速谱峭度的滚动轴承故障诊断方法。采用奇异值累积法对原信号进行降噪处理,然后利用快速谱峭度确定滤波器中心频率及带宽,通过分析频段包络谱中明显的频率成分来诊断故障。该方法可以有效去除信号中的噪声,使得到的峭度值所反映的故障冲击更接近实际情况。对含内圈、外圈故障的滚动轴承实验数据进行分析,实验结果表明,相比快速谱峭度的故障诊断方法,该方法具有更好的故障识别效果。 相似文献
7.
通过对梳棉机活动盖板结构和在梳理区运转时的运行状态分析,阐述了活动盖板踵趾面磨损原因,提出了踵趾面的测试方法;并针对目前使用的铸铁盖板和铝合金盖板进行对比试验。结果表明:铝合金盖板具有成纱质量较好、耐磨性好和重量轻等优点,能降低梳棉机的消耗,延长活动盖板使用周期。 相似文献
8.
随着互联网的高速发展,引发了网络流量、电信骨干网流量急速增长,使得网络容量的提升迫在眉睫。目前,100G 系统已经商用,超100G系统能够更有效地解决流量和网络带宽持续增长带来的压力,本文主要介绍新型单模光纤的特性以及探讨基于新型单模光纤的传输技术。 相似文献
9.
10.
Red dairy breeds are a valuable cultural and historical asset, and often a source of unique genetic diversity. However, they have difficulties competing with other, more productive, dairy breeds. Improving competitiveness of Red dairy breeds, by accelerating their genetic improvement using genomic selection, may be a promising strategy to secure their long-term future. For many Red dairy breeds, establishing a sufficiently large breed-specific reference population for genomic prediction is often not possible, but may be overcome by adding individuals from another breed. Relatedness between breeds strongly decides the benefit of adding another breed to the reference population. To prioritize among available breeds, the effective number of chromosome segments (Me) can be used as an indicator of relatedness between individuals from different breeds. The Me is also an important parameter in determining the accuracy of genomic prediction. The Me can be estimated both within a population and between 2 populations or breeds, as the reciprocal of the variance of genomic relationships. We investigated relatedness between 6 Dutch Red cattle breeds, Groningen White Headed (GWH), Dutch Friesian (DF), Meuse-Rhine-Yssel (MRY), Dutch Belted (DB), Deep Red (DR), and Improved Red (IR), focusing primarily on the Me, to predict which of those breeds may benefit from including reference animals of the other breeds. All of these breeds, except MRY, are under high risk of extinction. Our results indicated high variability of Me, especially between Me ranging from ~3,500 to ~17,400, indicating different levels of relatedness between the breeds. Two clusters are especially important, one formed by MRY, DR, and IR, and the other comprising DF and DB. Although relatedness between breeds within each of these 2 clusters is high, across-breed genomic prediction is still limited by the current number of genotyped individuals, which for many breeds is low. However, adding MRY individuals would increase the reference population of DR substantially. We estimated that between 11 and 133 individuals from other breeds are needed to achieve accuracy of genomic prediction equivalent to using one additional individual from the same breed. Given the variation in size of the breeds in this study, the benefit of a multibreed reference population is expected to be lower for larger breeds than for the smaller ones. 相似文献