全文获取类型
收费全文 | 72853篇 |
免费 | 741篇 |
国内免费 | 2021篇 |
专业分类
电工技术 | 1234篇 |
技术理论 | 1篇 |
综合类 | 864篇 |
化学工业 | 7443篇 |
金属工艺 | 2221篇 |
机械仪表 | 3963篇 |
建筑科学 | 4385篇 |
矿业工程 | 1893篇 |
能源动力 | 521篇 |
轻工业 | 15179篇 |
水利工程 | 1454篇 |
石油天然气 | 1448篇 |
武器工业 | 297篇 |
无线电 | 4370篇 |
一般工业技术 | 23928篇 |
冶金工业 | 1512篇 |
原子能技术 | 902篇 |
自动化技术 | 4000篇 |
出版年
2023年 | 275篇 |
2022年 | 280篇 |
2021年 | 353篇 |
2020年 | 257篇 |
2019年 | 301篇 |
2018年 | 277篇 |
2017年 | 156篇 |
2016年 | 224篇 |
2015年 | 316篇 |
2014年 | 580篇 |
2013年 | 612篇 |
2012年 | 7102篇 |
2011年 | 8949篇 |
2010年 | 1964篇 |
2009年 | 1038篇 |
2008年 | 6206篇 |
2007年 | 5855篇 |
2006年 | 5191篇 |
2005年 | 4562篇 |
2004年 | 3788篇 |
2003年 | 3199篇 |
2002年 | 2964篇 |
2001年 | 2444篇 |
2000年 | 2425篇 |
1999年 | 1577篇 |
1998年 | 942篇 |
1997年 | 917篇 |
1996年 | 843篇 |
1995年 | 778篇 |
1994年 | 758篇 |
1993年 | 584篇 |
1992年 | 763篇 |
1991年 | 709篇 |
1990年 | 770篇 |
1989年 | 744篇 |
1988年 | 551篇 |
1987年 | 654篇 |
1986年 | 610篇 |
1985年 | 664篇 |
1984年 | 623篇 |
1983年 | 563篇 |
1982年 | 554篇 |
1981年 | 476篇 |
1980年 | 391篇 |
1979年 | 279篇 |
1978年 | 206篇 |
1976年 | 100篇 |
1975年 | 102篇 |
1974年 | 104篇 |
1964年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
石油是国家的重要能源,其安全稳定供应与国家安全、公共安全和人民群众的生活息息相关。长输管道是我国陆上石油的主要运输通道,长输管道的安全稳定运行直接关乎着石油的安全稳定供应。但在实际的建设过程中,由于路线较长、工程浩大,其质量要求也极高。必须采用科学的手段进行施工,并进行严格的监控控制。一旦施工中存在要求控制不严格问题便很容易导致工程拖期、质量下降,不但导致资金浪费,还会造成严重的安全事故,因此,对于类似问题必须予以重视。 相似文献
2.
立面和立面设计是建筑的基本要素,媒体立面是立面设计相对较新的分支领域。文章概述了媒体立面的设计与研究过程,并以六个项目为例介绍立面设计涉及的元素与子元素如何与通信技术相互结合。 相似文献
4.
针对软件缺陷预测时缺陷数据集中存在的类别分布不平衡问题,结合上采样算法SMOTE与Edited Nearest Neighbor (ENN) 数据清洗策略,提出了一种基于启发式BP神经网络算法的软件缺陷预测模型。模型中采用上采样算法SMOTE增加少数类样本以改善项目中的数据不平衡状况,并针对采样后数据噪声问题进行ENN数据清洗,结合基于启发式学习的模拟退火算法改进四层BP神经网络后建立分类预测模型,在AEEEM数据库上使用交叉验证对提出的方案进行性能评估,结果表明所提出的算法能够有效提高模型在预测类不平衡数据时的分类准确度。 相似文献
6.
Mohamed A.El-Nemr Ibrahim M.A.Ismail Nabil M.Abdelmonem Ahmed El Nemr Safaa Ragab 《中国化学工程学报》2021,36(8):199-222
Watermelon peel residues were used to produce a new biochar by dehydration method. The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI) ions from aqueous solution has been investigated. Three biochars, Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, were made from watermelon peel via dehydration with 50% sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH_2 or Triethylenetetramine(TETA) to give Melon-BO-TETA. The prepared biochars were characterized by BET, BJH,SEM, FT-IR, TGA, DSC and EDAX analyses. The highest removal percentage of Cr(VI) ions was 69% for Melon-B,98% for Melon-BO-NH_2 and 99% for Melon-BO-TETA biochars of 100 mg·L~(-1) Cr(VI) ions initial concentration and 1.0 g·L~(-1) adsorbents dose. The unmodified biochar(Melon-B) and modified biochars(Melon-BO-NH_2 and Melon-BO-TETA) had maximum adsorption capacities(Qm) of 72.46, 123.46, and 333.33 mg·g~(-1), respectively.The amination of biochar reduced the pore size of modified biochar, whereas the surface area was enhanced.The obtained data of isotherm models were tested using different error function equations. The Freundlich,Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B, Melon-BO-NH_2 and Melon-BO-TETA, respectively. The adsorption rate was primarily controlled by pseudo-second–order rate model. Conclusively, the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process. The adsorption for the Melon-B, Melon-BO-NH_2 and Melon-BO-TETA could be explained for acid–base interaction and hydrogen bonding interaction. 相似文献
7.
Pablo Salcedo-Abraira Sergio M.F.Vilela Artem A.Babaryk Maria Cabrero-Antonino Pedro Gregorio Fabrice Salles Sergio Navalon Hermenegildo Garcia Patricia Horcajada 《Nano Research》2021,14(2):450-457
A novel microporous two-dimensional(2D)Ni-based phosphonate metal-organic framework(MOF;denoted as IEF-13)has been successfully synthesized by a simple and green hydrothermal method and fully characterized using a combination of experimental and computational techniques.Structure resolution by single-crystal X-ray diffraction reveals that IEF-13 crystallizes in the triclinic space group Pi having bi-octahedra nickel nodes and a photo/electroactive tritopic phosphonate ligand.Remarkably,this material exhibits coordinatively unsaturated nickel(II)sites,free-P03H2and-P03H acidic groups,a C02accessible microporosity,and an exceptional thermal and chemical stability.Further,its in-deep optoelectronic characterization evidences a photoresponse suitable for photocatalysis.In this sense,the photocatalytic activity for challenging H2generation and overall water splitting in absence of any co-catalyst using UV-Vis irradiation and simulated sunlight has been evaluated,constituting the first report for a phosphonate-MOF photocatalyst.IEF-13 is able to produce up to 2,200 fimol of H2per gram using methanol as sacrificial agent,exhibiting stability,maintaining its crystal structure and allowing its recycling.Even more,170μmol of H2per gram were produced using IEF-13 as photocatalyst in the absence of any co-catalyst for the overall water splitting,being this reaction limited by the 02reduction.The present work opens new avenues for further optimization of the photocatalytic activity in this type of multifunctional materials. 相似文献
8.
This paper reviews the fire problem in critical transportation infrastructures such as bridges and tunnels. The magnitude of the fire problem is illustrated, and the recent increase in fire problems in bridges and tunnels is highlighted. Recent research undertaken to address fire problems in transportation structures is reviewed, as well as critical factors governing the performance of those structures. Furthermore, key strategies recommended for mitigating fire hazards in bridges and tunnels are presented, and their applicability to practical situations is demonstrated through a practical case study. Furthermore, research needs and emerging trends for enhancing the “state-of-the-art” in this area are discussed. 相似文献
9.
The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions. 相似文献
10.