全文获取类型
收费全文 | 76070篇 |
免费 | 10278篇 |
国内免费 | 3990篇 |
专业分类
电工技术 | 3522篇 |
技术理论 | 2篇 |
综合类 | 4795篇 |
化学工业 | 14293篇 |
金属工艺 | 3016篇 |
机械仪表 | 2739篇 |
建筑科学 | 6632篇 |
矿业工程 | 2134篇 |
能源动力 | 1496篇 |
轻工业 | 7051篇 |
水利工程 | 1306篇 |
石油天然气 | 1779篇 |
武器工业 | 461篇 |
无线电 | 12919篇 |
一般工业技术 | 7598篇 |
冶金工业 | 2993篇 |
原子能技术 | 662篇 |
自动化技术 | 16940篇 |
出版年
2024年 | 223篇 |
2023年 | 1187篇 |
2022年 | 2776篇 |
2021年 | 4357篇 |
2020年 | 2360篇 |
2019年 | 2243篇 |
2018年 | 2463篇 |
2017年 | 3114篇 |
2016年 | 4314篇 |
2015年 | 4969篇 |
2014年 | 5779篇 |
2013年 | 5582篇 |
2012年 | 4894篇 |
2011年 | 4398篇 |
2010年 | 3609篇 |
2009年 | 3678篇 |
2008年 | 3882篇 |
2007年 | 5156篇 |
2006年 | 5083篇 |
2005年 | 4532篇 |
2004年 | 3231篇 |
2003年 | 2979篇 |
2002年 | 2258篇 |
2001年 | 1619篇 |
2000年 | 1355篇 |
1999年 | 830篇 |
1998年 | 543篇 |
1997年 | 466篇 |
1996年 | 376篇 |
1995年 | 282篇 |
1994年 | 245篇 |
1993年 | 163篇 |
1992年 | 141篇 |
1991年 | 135篇 |
1990年 | 142篇 |
1989年 | 115篇 |
1988年 | 69篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 65篇 |
1984年 | 70篇 |
1983年 | 48篇 |
1982年 | 41篇 |
1981年 | 37篇 |
1980年 | 52篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 64篇 |
1959年 | 22篇 |
1955年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(45):19718-19731
Metals and alloys forming reversible hydrides with hydrogen gas are potential building blocks for compact, solid state hydrogen storage systems. Based on the materials’ thermodynamic characteristics, their use as temperature-swing gas compression and delivery systems in the hydrogen economy is also possible. Given the wide variety of materials developed and tested at laboratory and pilot scales, a harmonized method of selecting the feasible material(s) for a particular real-life application is required. This study proposes a system selection framework based on a normalized, multi-criteria metric. Using calculated values of multi-criteria metric, multi-criteria screening and ranking of potential materials has been demonstrated for a particular use case. It is found that the alloy TiMn1.52 having value of additive metric between 0.25 and 0.35 represents the best material for a single stage system. The alloy pair CaNi5–Ti1.5CrMn represents the best alternative for a two-stage system with additive metric values between 0.63 and 0.82. Energy and economic characteristics of the metal hydride gas compression and delivery systems are evaluated and compared with an equivalent mechanical compression system producing the same final effect (i.e., delivery of a given quantity of gas at a defined pressure). 相似文献
2.
Ji Hye Yang Sae Kwang Ku IL Je Cho Je Hyeon Lee Chang-Su Na Sung Hwan Ki 《International journal of molecular sciences》2021,22(4)
Hepatic fibrosis occurs when liver tissue becomes scarred from repetitive liver injury and inflammatory responses; it can progress to cirrhosis and eventually to hepatocellular carcinoma. Previously, we reported that neoagarooligosaccharides (NAOs), produced by the hydrolysis of agar by β-agarases, have hepatoprotective effects against acetaminophen overdose-induced acute liver injury. However, the effect of NAOs on chronic liver injury, including hepatic fibrosis, has not yet been elucidated. Therefore, we examined whether NAOs protect against fibrogenesis in vitro and in vivo. NAOs ameliorated PAI-1, α-SMA, CTGF and fibronectin protein expression and decreased mRNA levels of fibrogenic genes in TGF-β-treated LX-2 cells. Furthermore, downstream of TGF-β, the Smad signaling pathway was inhibited by NAOs in LX-2 cells. Treatment with NAOs diminished the severity of hepatic injury, as evidenced by reduction in serum alanine aminotransferase and aspartate aminotransferase levels, in carbon tetrachloride (CCl4)-induced liver fibrosis mouse models. Moreover, NAOs markedly blocked histopathological changes and collagen accumulation, as shown by H&E and Sirius red staining, respectively. Finally, NAOs antagonized the CCl4-induced upregulation of the protein and mRNA levels of fibrogenic genes in the liver. In conclusion, our findings suggest that NAOs may be a promising candidate for the prevention and treatment of chronic liver injury via inhibition of the TGF-β/Smad signaling pathway. 相似文献
3.
为研究低压静电场辅助冷冻对竹笋冻结特性的影响,以冻结曲线、硬度、水分损失率、水分迁移、冰晶形态和组织微观结构为指标,探究低压静电场辅助冷冻(-35 ℃)和普通冷冻(-35 ℃)条件下竹笋品质的变化规律。结果表明:低压静电场辅助冷冻提高了冻结效率,改变了冰晶形态及分布,减轻了组织微观结构破损程度,改善了解冻汁液流失情况。与静电板间距10、20、30、40 cm处的冷冻竹笋解冻后水分损失率分别为14.16%、12.58%、9.73%、10.44%,显著低于对照组(21.01%)(P<0.05),硬度分别为461.19、507.48、496.65 g和455.31 g,显著高于对照组(350.70 g)(P<0.05)。低场核磁共振分析结果表明,在低压静电场辅助冷冻下竹笋解冻后汁液流失减少,扫描电子显微镜观察结果显示,竹笋纤维排列整齐,组织微观结构保持较好。低压静电场辅助冷冻可有效改善竹笋品质,可为利用低压静电场进行果蔬的冷冻贮藏和冷链运输提供参考。 相似文献
4.
5.
6.
7.
Anna Stasiowicz Natalia Rosiak Ewa Tykarska Maciej Kozak Jacek Jenczyk Piotr Szulc Joanna Kobus-Cisowska Kornelia Lewandowska Anita Paziska Wojciech Paziski Judyta Cielecka-Piontek 《International journal of molecular sciences》2021,22(8)
Piperine is an alkaloid that has extensive pharmacological activity and impacts other active substances bioavailability due to inhibition of CYP450 enzymes, stimulation of amino acid transporters and P-glycoprotein inhibition. Low solubility and the associated low bioavailability of piperine limit its potential. The combination of piperine with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) causes a significant increase in its solubility and, consequently, an increase in permeability through gastrointestinal tract membranes and the blood–brain barrier. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) were used to characterize interactions between piperine and HP-β-CD. The observed physicochemical changes should be combined with the process of piperine and CD system formation. Importantly, with an increase in solubility and permeability of piperine as a result of interaction with CD, it was proven to maintain its biological activity concerning the antioxidant potential (2,2-diphenyl-1-picryl-hydrazyl-hydrate assay), inhibition of enzymes essential for the inflammatory process and for neurodegenerative changes (hyaluronidase, acetylcholinesterase, butyrylcholinesterase). 相似文献
8.
9.
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
10.