全文获取类型
收费全文 | 2587篇 |
免费 | 59篇 |
国内免费 | 73篇 |
专业分类
电工技术 | 139篇 |
综合类 | 64篇 |
化学工业 | 337篇 |
金属工艺 | 247篇 |
机械仪表 | 214篇 |
建筑科学 | 146篇 |
矿业工程 | 103篇 |
能源动力 | 118篇 |
轻工业 | 81篇 |
水利工程 | 29篇 |
石油天然气 | 102篇 |
武器工业 | 9篇 |
无线电 | 117篇 |
一般工业技术 | 280篇 |
冶金工业 | 201篇 |
原子能技术 | 79篇 |
自动化技术 | 453篇 |
出版年
2023年 | 18篇 |
2022年 | 44篇 |
2021年 | 44篇 |
2020年 | 54篇 |
2019年 | 77篇 |
2018年 | 36篇 |
2017年 | 51篇 |
2016年 | 53篇 |
2015年 | 72篇 |
2014年 | 107篇 |
2013年 | 134篇 |
2012年 | 153篇 |
2011年 | 230篇 |
2010年 | 165篇 |
2009年 | 153篇 |
2008年 | 145篇 |
2007年 | 183篇 |
2006年 | 128篇 |
2005年 | 95篇 |
2004年 | 108篇 |
2003年 | 98篇 |
2002年 | 72篇 |
2001年 | 62篇 |
2000年 | 47篇 |
1999年 | 51篇 |
1998年 | 57篇 |
1997年 | 46篇 |
1996年 | 45篇 |
1995年 | 40篇 |
1994年 | 28篇 |
1993年 | 14篇 |
1992年 | 21篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有2719条查询结果,搜索用时 15 毫秒
1.
《Soils and Foundations》2022,62(5):101215
This technical report on the compression behavior of soft soils in the Colombian capital, Bogotá, was conducted because the city’s recent construction history has led to excessive settlement of soils in the city over the last forty years. Several studies have shown the city’s soil to contain unusually high concentrations of diatoms. The stationary piston method was used to obtain samples from depths of between five and 100 m. Samples were subsequently examined in the laboratory, being subjected to triaxial and oedometer compression tests, and tested also for Atterberg limits and grain size distributions. Test results for undisturbed soil returned very high liquid limit values, compressibility indices CC, secondary compression coefficients Cα, and soil structure effects. Some samples showed particle mixtures of different sizes, mineralogy, and diatom concentrations. Although high CC and Cα indices explain the excessive settling of the city’s buildings, most construction projects do not currently take settlement caused by secondary compression into account. This report shows that secondary compression is an important parameter in the total settlement of buildings in Bogotá and that, furthermore, settlement is also affected by geological history. Finally, useful correlations such as the relationship between the liquid limit, Cα and geological history are presented. 相似文献
2.
利用低本底α、β测量仪,通过一系列比较实验和数据获得影响水中总α、总β放射性活度的实验因素。按照现行国标中的标准曲线法进行实验并分析关系曲线的拟合结果;采用^(241)Am和^(40)K标准粉末源进行串道干扰实验;最后利用热释光测量仪分析影响样品源计数值的因素。结果表明:“质量厚度净计数率”关系曲线线性拟合结果良好,可应用在实验计算中;在测量放射性活度较高的水样时,α通道对β通道产生的串道干扰需进行修正;样品源制备完毕后,不宜立刻测量,应贮存在干燥低本底的环境中,贮存后应用红外灯干燥足够长的时间并完全冷却后进行测量。 相似文献
3.
针对轻量级神经网络在移动端的安全性缺乏问题,提出模型安全的反防御和二次防御方法。通过在MobileNet v2模型上改造CW算法优化器,采用旋转、添加高斯噪声以及双边滤波器平滑的传统数据增强进行防御,进而体现出反防御效果。在MobileNet v2、ShuffleNet v2和MnasNet模型上,通过改变旋转缩放因子、采用高斯-X噪声混叠模式以及调整双边滤波像素中心点直径对模型进行二次防御。实验结果表明,ASGD优化器对CW算法的反防御能力有很好的提升,同时改进的数据增强方法可以降低对抗样本的鲁棒性,提升模型二次防御能力。 相似文献
4.
Sihan Chen Tian Liang Guangcai Ma Chengwu Zheng Deli Chen Yingche Ma Kui Liu 《金属学报(英文版)》2022,35(9):1519
An austenitic stainless steel with 6 wt% Si and multiple secondary phases was produced with the aim to achieve enhanced plasticity during hot deformation. The microstructure of the steel after fracture was characterized via electron back-scattered diffraction, transmission Kikuchi diffraction and scanning transmission electron microscopy. From the tail of the gage to the necking region, the microstructure of the material evolved from low-angle grain boundaries (LAGBs) to mixtures of LAGBs and high-angle grain boundaries (HAGBs), and fine equiaxed recrystallized grains. The elongation to failure in the tensile test exceeds 167%. During the hot deformation, continuous dynamic recrystallization of the austenitic matrix was promoted by the multiple secondary phases. The dislocations introduced by the secondary phases were rearranged and continuously transformed into HAGBs. The initially coarse grains (30.5 μm) were refined into ultra-fine equiaxed grains (1 μm), which contributed significantly the enhanced plasticity during hot deformation of the steel. In the necking area of the sample, twins were nucleated in the stress concentration regions and accommodated the local strain by discontinuous dynamic recrystallization, which was also beneficial to improving the plasticity. 相似文献
5.
6.
《International Journal of Hydrogen Energy》2022,47(72):30830-30842
Carbon dioxide (CO2) and methane (CH4) are the primary greenhouse gases (GHGs) that drive global climate change. CO2 reforming of CH4 or dry reforming of CH4 (DRM) is used for the simultaneous conversion of CO2 and CH4 into syngas and higher hydrocarbons. In this study, DRM was investigated using Ag–Ni/Al2O3 packing and Sn–Ni/Al2O3 packing in a parallel plate dielectric barrier discharge (DBD) reactor. The performance of the DBD reactor was significantly enhanced when applying Ag–Ni/Al2O3 and Sn–Ni/Al2O3 due to the relatively high electrical conductivity of Ag and Sn as well as their anti-coke performances. Using Ag–Ni/Al2O3 consisting of 1.5 wt% Ag and 5 wt% Ni/Al2O3 as the catalyst in the DBD reactor, 19% CH4 conversion, 21% CO2 conversion, 60% H2 selectivity, 81% CO selectivity, energy efficiency of 7.9% and 0.74% (by mole) coke formation were achieved. In addition, using Sn–Ni/Al2O3, consisting of 0.5 wt% Sn and 5 wt% Ni/Al2O3, 15% CH4 conversion, 19% CO2 conversion, 64% H2 selectivity, 70% CO selectivity, energy efficiency of 6.0%, and 2.1% (by mole) coke formation were achieved. Sn enhanced the reactant conversions and energy efficiency, and resulted in a reduction in coke formation; these results are comparable to that achieved when using the noble metal Ag. The decrease in the formation of coke could be correlated to the increase in the CO selectivity of the catalyst. Good dispersion of the secondary metals on Ni was found to be an important factor for the observed increases in the catalyst surface area and catalytic activities. Furthermore, the stability of the catalytic reactions was investigated for 1800 min over the 0.5 wt% Ag-5 wt% Ni/Al2O3 and 0.5 wt% Sn-5 wt% Ni/Al2O3 catalysts. The results showed an increase in the reactant conversions with an increase in the reaction time. 相似文献
7.
山西沁水盆地柿庄南区块煤层气井初次压裂生产多年后整体产气量下降,迫切需要进行二次压裂以提高产能,而目标井段的选取对二次压裂的设计施工及增产效果具有极为重要的影响。针对区块二次压裂试验井数少、样本数量有限的问题,提出基于聚类分析的煤层气二次压裂选井选层方法。综合考虑地质储量、可压性和工程三方面因素建立二次压裂选井的层次聚类模型;再根据施工曲线特征设置压裂风险短路条件,排除复压风险高的井,并结合聚类集成算法,最终确定每口井的复压潜力大小。以本区块15口井为例开展了各井二次压裂改造潜力评价,优选B01井为目标井,二次压裂后取得了较好的增产效果。该研究可为井数有限条件下的二次压裂选井选层提供一种有效方法,为后续压裂生产提供依据和借鉴。 相似文献
8.
9.
利用低本底α、β测量仪研究影响水中总α、β放射性活度浓度测量的实验因素。通过一系列对比实验,获得样品放置时间、水样的贮存时间和贮存温度、样品制备方式等条件对实验结果的影响。结果表明:井水、自来水、地下水等水体内溶解的氡和红外线加热可能对水样残渣的计数产生干扰,样品制备完毕后,宜在室温且干燥环境下静置至少3小时后再进行上机测量;水样在密封贮存的情况下,贮存温度和时间对水样的总α、总β放射性活度无显著影响;采用现行国标推荐的硫酸酸化水样的方法可以有效避免样品可能存在的吸潮现象,减少实验误差。 相似文献
10.