全文获取类型
收费全文 | 21448篇 |
免费 | 1808篇 |
国内免费 | 830篇 |
专业分类
电工技术 | 677篇 |
综合类 | 1534篇 |
化学工业 | 4371篇 |
金属工艺 | 1433篇 |
机械仪表 | 456篇 |
建筑科学 | 1730篇 |
矿业工程 | 970篇 |
能源动力 | 570篇 |
轻工业 | 3796篇 |
水利工程 | 566篇 |
石油天然气 | 1373篇 |
武器工业 | 72篇 |
无线电 | 986篇 |
一般工业技术 | 1417篇 |
冶金工业 | 1726篇 |
原子能技术 | 228篇 |
自动化技术 | 2181篇 |
出版年
2024年 | 46篇 |
2023年 | 257篇 |
2022年 | 536篇 |
2021年 | 639篇 |
2020年 | 659篇 |
2019年 | 618篇 |
2018年 | 601篇 |
2017年 | 708篇 |
2016年 | 782篇 |
2015年 | 794篇 |
2014年 | 1358篇 |
2013年 | 1440篇 |
2012年 | 1620篇 |
2011年 | 1663篇 |
2010年 | 1207篇 |
2009年 | 1168篇 |
2008年 | 992篇 |
2007年 | 1286篇 |
2006年 | 1149篇 |
2005年 | 1016篇 |
2004年 | 942篇 |
2003年 | 810篇 |
2002年 | 643篇 |
2001年 | 520篇 |
2000年 | 453篇 |
1999年 | 361篇 |
1998年 | 295篇 |
1997年 | 244篇 |
1996年 | 211篇 |
1995年 | 200篇 |
1994年 | 186篇 |
1993年 | 120篇 |
1992年 | 100篇 |
1991年 | 79篇 |
1990年 | 57篇 |
1989年 | 45篇 |
1988年 | 44篇 |
1987年 | 28篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1964年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This paper presents a novel No-Reference Video Quality Assessment (NR-VQA) model that utilizes proposed 3D steerable wavelet transform-based Natural Video Statistics (NVS) features as well as human perceptual features. Additionally, we proposed a novel two-stage regression scheme that significantly improves the overall performance of quality estimation. In the first stage, transform-based NVS and human perceptual features are separately passed through the proposed hybrid regression scheme: Support Vector Regression (SVR) followed by Polynomial curve fitting. The two visual quality scores predicted from the first stage are then used as features for the similar second stage. This predicts the final quality scores of distorted videos by achieving score level fusion. Extensive experiments were conducted using five authentic and four synthetic distortion databases. Experimental results demonstrate that the proposed method outperforms other published state-of-the-art benchmark methods on synthetic distortion databases and is among the top performers on authentic distortion databases. The source code is available at https://github.com/anishVNIT/two-stage-vqa. 相似文献
2.
3.
通过共沉淀法制备了锌铝水滑石(ZnAl-LDH),采用XRD、FTIR、SEM对其结构进行了表征.将其配合用量为皮质量2%的铬粉(记为2%铬粉)应用于制革鞣制工艺中.考察了ZnAl-LDH制备时的金属源物质的量比、陈化时间对鞣制坯革收缩温度、鞣后废液中的Cr2O3质量浓度的影响.结果表明,ZnAl-LDH是尺寸在100~400 nm之间的片状材料.当n〔(Zn(NO3)2?6H2O)〕:n〔Al(NO3)3?9H2O〕=2.0:1.0,陈化时间为6 h时,制备的ZnAl-LDH-4具有优异的性能.与单独使用2%铬粉鞣制坯革相比,ZnAl-LDH-4(用量为皮质量的4%)配合2%铬粉鞣制坯革收缩温度由75℃提高到94℃,废液中的Cr2O3质量浓度由99.58 mg/L降低至46.98 mg/L,且加入ZnAl-LDH-4鞣制后,鞣后废液化学需氧量和生物需氧量均降低. 相似文献
4.
介绍了采用变温吸附技术对氯乙烯进行干燥脱水的工艺流程及运行效果,阐述了变温吸附装置运行过程中出现的问题及相应的解决方法。 相似文献
5.
《Ceramics International》2021,47(23):33353-33362
High thermal conductivity Si3N4 ceramics were fabricated using a one-step method consisting of reaction-bonded Si3N4 (RBSN) and post-sintering. The influence of Si content on nitridation rate, β/(α+β) phase rate, thermal conductivity and mechanical properties was investigated in this work. It is of special interest to note that the thermal conductivity showed a tendency to increase first and then decrease with increasing Si content. This experimental result shows that the optimal thermal conductivity and fracture toughness were obtained to be 66 W (m K)-1 and 12.0 MPa m1/2, respectively. As a comparison, the nitridation rate and β/(α+β) phase rate in a static pressure nitriding system, i.e., 97% (MS10), 97% (MS15), 97% (MS20) and 8.3% (MS10), 8.3% (MS15), 8.9% (MS20), respectively, have obvious advantages over those in a flowing nitriding system, i.e., 91% (MS10), 91% (MS15), 93% (MS20) and 3.1% (MS10), 3.3% (MS15), 3.3% (MS20), respectively. Moreover, high lattice integrity of the β-Si3N4 phase was observed, which can effectively confine O atoms into the β-Si3N4 lattice using MgO as a sintering additive. This result indicates that one-step sintering can provide a new route to prepare Si3N4 ceramics with a good combination of thermal conductivity and mechanical properties. 相似文献
6.
《Ceramics International》2022,48(22):33092-33100
CeNbO4+δ ceramics have attracted extensive research interest because of their unique mixed ion-electron transport characteristics and interesting structure-functional characteristics caused by the difference in oxygen ion content. Although the change of oxygen ion content brings rich redox properties, it also causes serious crystal transformation and abnormal electrical transport properties. In order to obtain stable structure and excellent electrical transport properties, the directional regulation of the oxygen ion content has been realized through introducing Al2O3 and high temperature aging. After 600 h of aging at 1073 K, the prepared composite ceramics not only obtain a stable structure without crystal transformation, but also show good negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K–1273 K, in which the linear fitting maximum Pearson's r of the relationship between lnρ and 1000/T can reach 99.97%. The proposed method provides a new thought for the design and application of high-temperature electronic ceramics. 相似文献
7.
8.
通过显微组织观察与力学性能测试研究了氮含量(0.08%~0.22%,质量分数)对HPD-1双相不锈钢硬度、拉伸性能、低温冲击性能及疲劳性能的影响。结果表明,氮含量变化可显著影响试验钢γ/α相比例,当氮含量由0.08%升高到0.22%,γ相含量由38.1%提高至56.5%。α相的硬度由273 HV10提高到343 HV10,γ相的硬度由238 HV10提高到299 HV10,试验钢强度明显提升。氮元素对两相比例和奥氏体相韧性的双重影响导致试验钢低温冲击性能呈先上升后下降的趋势;更高的氮含量抑制疲劳裂纹萌生与拓展,是影响HPD-1双相不锈钢室温疲劳性能的主要因素。撕裂棱是疲劳断口的显著特征。 相似文献
9.
针对高含盐氨氮废水,选择具有不同功能基团的树脂为载体,进行负载Cu2+改性制得载铜树脂并对其处理高含盐氨氮废水的性能进行研究。在筛选出最佳载铜树脂的基础上,研究pH及Na+浓度、树脂投加量、反应时间对载铜树脂处理高含盐氨氮废水效果的影响,通过对吸附氨氮前后的载铜树脂进行SEM和EDS表征分析并构建吸附动力学模型以进一步探究配位吸附的过程。结果表明,Cu2+可与螯合树脂D751稳定结合且在宽pH值下均表现出耐盐性和良好的氨氮吸附效果;在室温(25℃)、pH=11及Na+浓度4 g/L、树脂投加量8 g/L、反应时间60 min的条件下,D751载铜树脂对氨氮的去除率为34.8%。D751载铜树脂吸附氨氮后其表面出现明显的晶状结构物质,该物质可能为铜氨络合物。D751载铜树脂对高含盐氨氮的吸附符合准二级动力学模型。 相似文献
10.