全文获取类型
收费全文 | 6493篇 |
免费 | 401篇 |
国内免费 | 261篇 |
专业分类
电工技术 | 250篇 |
综合类 | 344篇 |
化学工业 | 1142篇 |
金属工艺 | 931篇 |
机械仪表 | 418篇 |
建筑科学 | 266篇 |
矿业工程 | 104篇 |
能源动力 | 228篇 |
轻工业 | 300篇 |
水利工程 | 43篇 |
石油天然气 | 285篇 |
武器工业 | 37篇 |
无线电 | 691篇 |
一般工业技术 | 590篇 |
冶金工业 | 495篇 |
原子能技术 | 173篇 |
自动化技术 | 858篇 |
出版年
2024年 | 10篇 |
2023年 | 71篇 |
2022年 | 121篇 |
2021年 | 156篇 |
2020年 | 152篇 |
2019年 | 134篇 |
2018年 | 125篇 |
2017年 | 166篇 |
2016年 | 205篇 |
2015年 | 218篇 |
2014年 | 384篇 |
2013年 | 396篇 |
2012年 | 485篇 |
2011年 | 540篇 |
2010年 | 368篇 |
2009年 | 457篇 |
2008年 | 413篇 |
2007年 | 420篇 |
2006年 | 381篇 |
2005年 | 298篇 |
2004年 | 218篇 |
2003年 | 210篇 |
2002年 | 206篇 |
2001年 | 159篇 |
2000年 | 126篇 |
1999年 | 114篇 |
1998年 | 97篇 |
1997年 | 80篇 |
1996年 | 62篇 |
1995年 | 65篇 |
1994年 | 72篇 |
1993年 | 30篇 |
1992年 | 37篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1974年 | 2篇 |
1967年 | 2篇 |
1964年 | 4篇 |
排序方式: 共有7155条查询结果,搜索用时 296 毫秒
1.
Hideaki Kaneto Tomohiko Kimura Atsushi Obata Masashi Shimoda Kohei Kaku 《International journal of molecular sciences》2021,22(5)
While there are various kinds of drugs for type 2 diabetes mellitus at present, in this review article, we focus on metformin which is an insulin sensitizer and is often used as a first-choice drug worldwide. Metformin mainly activates adenosine monophosphate-activated protein kinase (AMPK) in the liver which leads to suppression of fatty acid synthesis and gluconeogenesis. Metformin activates AMPK in skeletal muscle as well, which increases translocation of glucose transporter 4 to the cell membrane and thereby increases glucose uptake. Further, metformin suppresses glucagon signaling in the liver by suppressing adenylate cyclase which leads to suppression of gluconeogenesis. In addition, metformin reduces autophagy failure observed in pancreatic β-cells under diabetic conditions. Furthermore, it is known that metformin alters the gut microbiome and facilitates the transport of glucose from the circulation into excrement. It is also known that metformin reduces food intake and lowers body weight by increasing circulating levels of the peptide hormone growth/differentiation factor 15 (GDF15). Furthermore, much attention has been drawn to the fact that the frequency of various cancers is lower in subjects taking metformin. Metformin suppresses the mechanistic target of rapamycin (mTOR) by activating AMPK in pre-neoplastic cells, which leads to suppression of cell growth and an increase in apoptosis in pre-neoplastic cells. It has been shown recently that metformin consumption potentially influences the mortality in patients with type 2 diabetes mellitus and coronavirus infectious disease (COVID-19). Taken together, metformin is an old drug, but multifaceted mechanisms of action of metformin have been unraveled one after another in its long history. 相似文献
2.
Yuhang Xing Ruyi Li Lu Xue Mianhong Chen Xuli Lu Zhihao Duan Wei Zhou Jihua Li 《International Journal of Food Science & Technology》2022,57(8):5268-5279
Mangiferin (MGF) is a phenolic compound isolated from mango, but its poor solubility significantly limits its use. In this study, MGF was embedded into the inner aqueous phase of W1/O/W2 emulsions. Firstly, the dissolution method of MGF was determined. MGF remained stable in solution with pH 13 at 30 min, and its solubility reached 10 mg mL−1. When the pH of MGF solutions was adjusted from pH 13 to pH 6, MGF did not immediately crystallise, providing sufficient time to construct the MGF-loaded W1/O/W2 emulsions. Subsequently, the MGF-loaded W1/O/W2 emulsions were constructed using polyglycerol polyricinoleate (PGPR) and calcium caseinate (CAS). The formation and stability of the W1/O/W2 emulsions were investigated. The MGF-loaded W1/O/W2 emulsions stabilised with 1% PGPR and 1% – 3% CAS exhibited a low viscosity, limited loading capacity, and poor stability. Conversely, the MGF-loaded W1/O/W2 emulsions stabilised by 3%PGPR–3%CAS exhibited optimal loading capacity (encapsulation efficiency = 95.31% and loading efficiency = 0.91%) and stability, which was attributed to the fact that high viscosity and gel state retarded the migration of inner aqueous phase. These results indicated that the W1/O/W2 emulsions stabilised by PGPR and CAS may be a potential alternative for encapsulating mangiferin. 相似文献
3.
4.
5.
《中国有色金属学会会刊》2021,31(9):2773-2786
W45Cu55, Cr65Cu35, and Cr32W14Cu54 alloys were obtained in order to study the mechanism of “smart response” of the structure of these alloys when using them as arc-resistant circuit-breakers. These alloys differ from industrial ones with frameless packing of Cr and W phases in the copper matrix. The alloy production method is based on the infiltration of copper melt into a mixture of non-compacted Cr and W powders under vibration exposure (80 Hz). The research results show an increase in the arc resistance of contacts when changing from “frame” packing of W to “frameless,” as well as the decisive role of Cr in the processes of self-dispersion of arc-resistant phases and passivation of W and Cu. Based on the obtained results, conclusions are drawn about the advantage of frameless packing of arc-resistant phases in copper and the reasons for the “smart behavior” of the structure of Cr-containing contacts in response to functional loads in the presence of oxygen and an inert atmosphere. 相似文献
6.
《International Journal of Hydrogen Energy》2019,44(37):20839-20850
A highly active and stable boron-promoted catalyst was successfully prepared by using the sequential incipient wetness impregnation technique and examined for methane bi-reforming reaction. The initial investigation found that the NiO and B2O3 particles were dispersed on the outer surface of the high surface area SBA-15 support. In addition, the catalytic activity was increased linearly with the tested reaction temperature due to the endothermic nature of the reaction. In fact, the catalyst achieved the CH4 conversion and H2/CO molar ratio of approximately 67.3% and 2.7, respectively at 1073 K. The resulting product ratio is highly suitable for downstream Fischer-Tropsch (FT) synthesis. The B-promoted catalyst showed the lowest degree of catalyst deactivation (4%) at 1023 K. Additionally, the XPS measurements unveiled that the boron facilitates the adsorption of CO2 by donating electrons to the neighbouring Ni cluster and thus improved its catalytic performance. Furthermore, Raman and XRD analysis revealed that the boron promotion on 10%Ni/SBA-15 could prevent the reoxidation and deposition of carbonaceous species. 相似文献
7.
吐哈盆地葡北地区“两宽一高”地震勘探技术及应用效果 总被引:1,自引:0,他引:1
吐哈盆地台北凹陷圈闭落实的准确度和储层分布预测的精度一直是制约该区油气发现的关键因素。通过可控震源“两宽一高”地震采集、OVT域时间偏移、地质导向深度偏移初始模型建立及各向异性深度偏移迭代处理,在地震资料的信噪比、频带宽度和分辨率等方面明显提高的基础上,以高精度层序地层学为指导,基于高分辨率地震资料与钻井、测井资料的综合分析,识别出侏罗系6个三级层序,在三级层序格架内将研究区七克台组底部和三间房组顶部砂体识别为两个连续上升半旋回四级层序;通过构造几何属性分析及精细构造分析,揭示了本区“四带、两凹”的构造格局及形成机制;以宽频带多种反演技术为手段,对含油气层段的七克台组和三间房组砂体分布进行了预测;在综合构造分析、储层分析和油藏成藏规律分析的基础上,提出本区油气沿构造带脊线聚集,断裂系统是油气运移的优势路径,七克台组、三间房组储层在葡北构造带发育,向玉果构造带和胜北次凹减薄尖灭,葡北构造带与玉果构造带结合部位的,具有鼻状构造背景的岩性圈闭是获得油气突破的有利地区。 相似文献
8.
Covalent triazine frameworks (CTFs) have been recently employed for visible light-driven photocatalysis due to their unique optical and electronic properties. However, the usually highly hydrophobic nature of CTFs, which originates from their overall aromatic backbone, leads to limitations of CTFs for applications in aqueous media. In this study, we aim to extend the range of the application media of CTFs and design hybrid material of a CTF and mesoporous silica (SBA-15) for efficient photocatalysis in aqueous medium. A thiophene-containing CTF was directly synthesized in mesopores of SBA-15. Due to the high surface area and the added hydrophilic properties by silica, the hybrid material demonstrated excellent adsorption of organic molecules in water. This leads not only to high photocatalytic performance of the hybrid material for the degradation of organic dyes in water, but also for efficient photocatalysis in solvent-free and solid state. Furthermore, the reusability, stability and easy recovery of the hybrid material offers promising metal-free heterogeneous photocatalyst for broader applications in different reaction media. 相似文献
9.
Lili Zheng Qingsong Hua Xichao Li Meishuan Li Yuhai Qian Jingjun Xu Zuoqiang Dai Hongxin Zhang Tiezhu Zhang Junwei Wu 《International Journal of Hydrogen Energy》2018,43(15):7483-7491
A solid solution (Ti,W)3SiC2 possessing good oxidation resistance and low area-specific resistance (ASR) after oxidation has been synthesized by an in-situ hot pressing process. The oxidation rate constant at 800 °C in air is 6.29 × 10?14 g2 cm?4 s?1 for (Ti,W)3SiC2. The formed single-layer oxide is composed of W doped rutile TiO2 and amorphous SiO2. SiO2 is evenly inlaid in the communicative body frame of TiO2. W doped in TiO2 mainly exists as W6+. W doping not only hinders the outward diffusion of Ti by decreasing the concentration of native Ti interstitials in TiO2, but also restrains the inward diffusion of oxygen by decreasing the concentration of O vacancies. Furthermore, W dopant in TiO2 enhances the electrical conductivity of TiO2 by increasing the concentration of semi-free electron. Therefore, the low ASR of (Ti,W)3SiC2 after oxidation owes to high electrical conductivity of TiO2 as well as the reduced thickness of oxide scale. All the results render (Ti1-xWx)3SiC2 promising as interconnects for the intermediate temperature solid oxide fuel cell. 相似文献
10.
Yan-chun ZHU Qing-xue HUANG Xiao-hui SHI Mei-rong SHUAI Wei-dong ZENG Yong-qing ZHAO Zhi-quan HUANG Li-feng MA 《中国有色金属学会会刊》2018,28(8):1521-1529
The microstructural evolution and precipitation location of the secondary phase of an as-cast Ti-25V-15Cr-0.3Si titanium alloy were investigated via isothermal compression experiments and heat treatment. The average aspect (length-to-width) ratio, average area and size of the grains at different heat treatment temperatures and holding time were analyzed and the effects of deformation and annealing time on the grain area and size were considered. It was found that the grain size was strongly influenced by the height reduction and holding time. Grain growth was significant when annealing time increased from 10 min to 2 h at 950 °C and height reduction of 30%; however, grain growth was minimal at annealing time between 2 and 4 h. Many dispersion particles were observed to form in continuous chains; the precipitation location was confirmed to be along initial grain boundaries, and the dispersion particles were identified to be Ti5Si3 phase by TEM. 相似文献