全文获取类型
收费全文 | 90936篇 |
免费 | 10130篇 |
国内免费 | 5263篇 |
专业分类
电工技术 | 6899篇 |
技术理论 | 2篇 |
综合类 | 7775篇 |
化学工业 | 13338篇 |
金属工艺 | 5207篇 |
机械仪表 | 6202篇 |
建筑科学 | 7397篇 |
矿业工程 | 2913篇 |
能源动力 | 2539篇 |
轻工业 | 8367篇 |
水利工程 | 2236篇 |
石油天然气 | 3942篇 |
武器工业 | 1036篇 |
无线电 | 10432篇 |
一般工业技术 | 9604篇 |
冶金工业 | 3579篇 |
原子能技术 | 1310篇 |
自动化技术 | 13551篇 |
出版年
2024年 | 219篇 |
2023年 | 1749篇 |
2022年 | 3352篇 |
2021年 | 4689篇 |
2020年 | 3640篇 |
2019年 | 2809篇 |
2018年 | 3059篇 |
2017年 | 3369篇 |
2016年 | 2960篇 |
2015年 | 4426篇 |
2014年 | 5585篇 |
2013年 | 6432篇 |
2012年 | 7288篇 |
2011年 | 7365篇 |
2010年 | 6770篇 |
2009年 | 6278篇 |
2008年 | 6100篇 |
2007年 | 5789篇 |
2006年 | 5086篇 |
2005年 | 4154篇 |
2004年 | 2941篇 |
2003年 | 2106篇 |
2002年 | 1965篇 |
2001年 | 1555篇 |
2000年 | 1460篇 |
1999年 | 1212篇 |
1998年 | 730篇 |
1997年 | 649篇 |
1996年 | 590篇 |
1995年 | 480篇 |
1994年 | 374篇 |
1993年 | 259篇 |
1992年 | 199篇 |
1991年 | 162篇 |
1990年 | 110篇 |
1989年 | 105篇 |
1988年 | 75篇 |
1987年 | 48篇 |
1986年 | 43篇 |
1985年 | 12篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 22篇 |
1980年 | 26篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1959年 | 11篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
1.
Journal of Porous Materials - In this work, a trifluoromethanesulfonic acid (TFOH) modified clay (TFOH-Clay) was developed for the removal of trace olefins in heavy naphtha. 5%TFOH-Clay can... 相似文献
2.
Zhai Shengnan Yu Kejing Meng Chaoran Wang Hongbo Fu Jiajia 《Journal of Materials Science》2022,57(15):7491-7502
Journal of Materials Science - In this paper, an eco-friendly method of producing hybrid silica aerogels by freeze-drying method (FD) is proposed. In the freeze-drying system, deionized water was... 相似文献
3.
Bin Zhang Alexander K. Nguyen Roger J. Narayan Jie Huang 《Journal of the American Ceramic Society》2022,105(3):1821-1840
Novel inks were formulated by dissolving polycaprolactone (PCL), a hydrophobic polymer, in organic solvent systems; polyethylene oxide (PEO) was incorporated to extend the range of hydrophilicity of the system. Hydroxyapatite (HAp) with a weight ratio of 55–85% was added to the polymer-based solution to mimic the material composition of natural bone tissue. The direct ink writing (DIW) technique was applied to extrude the formulated inks to fabricate the predesigned tissue scaffold structures; the influence of HAp concentration was investigated. The results indicate that in comparison to other inks containing HAp (55%, 75%, and 85%w/w), the ink containing 65% w/w HAp had faster ink recovery behavior; the fabricated scaffold had a rougher surface as well as better mechanical properties and wettability. It is noted that the 65% w/w HAp concentration is similar to the inorganic composition of natural bone tissue. The elastic modulus values of PCL/PEO/HAp scaffolds were in the range of 4–12 MPa; the values were dependent on the HAp concentration. Furthermore, vancomycin as a model drug was successfully encapsulated in the PCL/PEO/HAp composite scaffold for drug release applications. This paper presents novel drug-loaded PCL/PEO/HAp inks for 3D scaffold fabrication using the DIW printing technique for potential bone scaffold applications. 相似文献
4.
利用水力空化过程产生局部的高温、高压、高射流以及强大的剪切力等极端化学物理条件改质处理沙特重质原油,试验结果表明:沙特重质原油经过水力空化改质后粘度由13.61降低至7.22mm2/s,残碳由7.16%降低至6.48%,实沸点蒸馏后减压渣油降低1个百分点。进一步采用APPI FT-IR MS、XRD、FT-IR、SEM和粒度分布等技术研究了水力空化改质对沙重原油分子组成,沥青质团聚体微晶结构、沥青质胶束粒径分布、沥青质官能团、沥青质形貌等方面的影响,从分子角度阐述空化改质重油的机理。研究结果表明:水力空化改质后沙重原油分子量分布、芳烃类化合物缔合作用变小;沥青质对低DBE化合物吸附性能降低;沥青质团聚体微晶结构更加松散;沥青质胶束粒度分布降低;沥青质分子相互团聚作用力减弱。进一步考察了水力空化改质前后减压渣油延迟焦化性能,改质处理后焦炭产率降低1.85个百分点,液体收率和气体产率分别增加1.52和0.33个百分点,水力空化改质对沥青质性质、结构特点的改善能够有效的提高其加工性能。 相似文献
5.
The carbon vacancy in high-entropy carbides (HECs) has a significant impact on their physical and chemical properties, yet relevant studies have still been relatively few. In this study, we investigate the surface energies of HECs with variable carbon vacancies through first-principles calculations. The results show that the surface energy of the (1 0 0) surface of the stoichiometric HECs is significantly lower than that of (1 1 1) surface. With the decrease in carbon stoichiometry, the surface energies of both (1 0 0) and (1 1 1) surfaces increase gradually, which is mainly due to the weakening of covalent bonding and the decrease of metal Hirshfeld-I (HI) charges. However, the surface energy of (1 0 0) surface increases more quickly than that of (1 1 1) surface and will exceed that of (1 1 1) surface when the carbon stoichiometry decreases to a certain extent, which is primarily attributed to the greater decrease rate of metal HI charges of (1 0 0) surface. 相似文献
6.
Fine-grained few-shot learning is a difficult task in image classification. The reason is that the discriminative
features of fine-grained images are often located in local areas of the image, while most of the existing few-shotlearning image classification methods only use top-level features and adopt a single measure. In that way, the localfeatures of the sample cannot be learned well. In response to this problem, ensemble relation network with multi-level measure (ERN-MM) is proposed in this paper. It adds the relation modules in the shallow feature space tocompare the similarity between the samples in the local features, and finally integrates the similarity scores from thefeature spaces to assign the label of the query samples. So the proposed method ERN-MM can use local details andglobal information of different grains. Experimental results on different fine-grained datasets show that the proposedmethod achieves good classification performance and also proves its rationality. 相似文献
7.
针对配电自动化终端优化布局问题,提出了一种基于重要度排序的终端优化布局方法。首先以等年值综合费用为目标函数,供电可靠性和投入产出比为双重约束建立了配电自动化终端优化布局模型。然后通过分析配电自动化终端对供电可靠性提升的影响,给出各个节点的“二遥”及“三遥”终端安装重要度定义及计算公式。最后采用枚举法确定最优终端安装数量,基于节点终端安装重要度排序确定终端的最优安装位置。该方法考虑了已布局节点对剩余节点终端安装重要度的影响,能够在降低计算量的同时兼顾布局合理性。运用所提方法RBTS-BUS2系统及扩充模型进行终端优化布局并与智能优化算法的布局结果进行对比,验证了本文方法的有效性及优越性。 相似文献
8.
9.
Xuejie Li Yaqing Wen Jian Zhang Dongyun Ma Jie Zhang Yanxia An Xiaoyan Song Xiujuan Ren Weifeng Zhang 《International Journal of Food Science & Technology》2022,57(3):1544-1553
The effects of non-thermal plasma (NTP) on the physicochemical properties of wheat flour and the quality of fresh wet noodles ( FWN) were investigated. The results showed that NTP effectively decreased the total plate count (TPC), yeast and mould count (YMC) and Bacillus spp. in wheat flour. Wet gluten contents and the stability time reached the maximum when treated for 20 s. The viscosity of starch increased significantly after treatment due to the increased of damaged starch. The contents of secondary structure were altered to some extent, which was because that the ordered network structure of gluten protein broken. Furthermore, compared with the control, texture properties of FWN were enhanced significantly at 20 s, and the darkening rate of FWN was greatly inhibited due to the low polyphenol oxidase (PPO) activity. Consequently, the most suitable treatment was 500 W for 20 s, providing a basis for the application of NTP in flour products. 相似文献
10.
Xiuyun Guo Junjun Wu Xiangren Meng Yawei Zhang Zengqi Peng 《International Journal of Food Science & Technology》2022,57(4):2556-2567
This study investigated the effects of l -lysine (Lys) and l -histidine (His) on the oxidative characteristics and gel properties of porcine myofibrillar proteins (MP). Results showed that Lys and His had a strong ferrous ion-chelating ability and hydroxyl radical-scavenging activity. Moreover, Lys and His inhibited the protein carbonyl formation and MP aggregation at 0.2 M and 0.6 M NaCl, respectively, in a dose-dependent manner. Furthermore, 2 and 4 mg mL−1 Lys and His decreased the oxidation-induced loss of the tertiary structure of MP accompanied by the lower surface hydrophobicity. The water-holding capacity and gel strength of MP gels increased with increasing Lys and His concentrations due to more regular and lamellar structures with smaller and homogeneous pores at 0.6 M NaCl and more orderly crosslinking via fibrous filament at 0.2 M NaCl. In summary, Lys and His chelated the ferrous ions and scavenged hydroxyl radicals, decreased the oxidation-induced physicochemical changes, thus preventing oxidative damage during the formation of a three-dimensional gel network, which resulted in better gel quality. 相似文献