全文获取类型
收费全文 | 54871篇 |
免费 | 5463篇 |
国内免费 | 1778篇 |
专业分类
电工技术 | 2568篇 |
技术理论 | 1篇 |
综合类 | 3113篇 |
化学工业 | 10597篇 |
金属工艺 | 2284篇 |
机械仪表 | 1692篇 |
建筑科学 | 5805篇 |
矿业工程 | 1970篇 |
能源动力 | 1609篇 |
轻工业 | 7200篇 |
水利工程 | 1666篇 |
石油天然气 | 2380篇 |
武器工业 | 310篇 |
无线电 | 4619篇 |
一般工业技术 | 6044篇 |
冶金工业 | 3308篇 |
原子能技术 | 647篇 |
自动化技术 | 6299篇 |
出版年
2024年 | 97篇 |
2023年 | 1025篇 |
2022年 | 2097篇 |
2021年 | 3430篇 |
2020年 | 1930篇 |
2019年 | 1904篇 |
2018年 | 2062篇 |
2017年 | 1682篇 |
2016年 | 2671篇 |
2015年 | 3200篇 |
2014年 | 3927篇 |
2013年 | 4119篇 |
2012年 | 3448篇 |
2011年 | 2945篇 |
2010年 | 2345篇 |
2009年 | 2272篇 |
2008年 | 2243篇 |
2007年 | 3466篇 |
2006年 | 3708篇 |
2005年 | 3158篇 |
2004年 | 2189篇 |
2003年 | 2086篇 |
2002年 | 1402篇 |
2001年 | 844篇 |
2000年 | 579篇 |
1999年 | 514篇 |
1998年 | 313篇 |
1997年 | 261篇 |
1996年 | 307篇 |
1995年 | 222篇 |
1994年 | 209篇 |
1993年 | 154篇 |
1992年 | 129篇 |
1991年 | 121篇 |
1990年 | 123篇 |
1989年 | 87篇 |
1988年 | 57篇 |
1987年 | 60篇 |
1986年 | 48篇 |
1985年 | 64篇 |
1984年 | 72篇 |
1983年 | 47篇 |
1982年 | 34篇 |
1981年 | 37篇 |
1980年 | 49篇 |
1966年 | 25篇 |
1964年 | 34篇 |
1962年 | 65篇 |
1957年 | 22篇 |
1955年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In the present work, the heating performance of a new system combined with a new modified baseboard radiator and fan coil is investigated. Using longitudinal fins with special geometry and also forced airflow at the end of the system causes that at the lower inlet water temperature compared with the conventional models, higher heat output rate be obtained. The heat output rate of the new modified system is obtained by experimental metrology based on the European Standard No. EN-442. Temperature and velocity distribution in the room space is done by simulation of the modified system in the Flovent software. Computational fluid dynamics (CFD) results are validated against experimental results and there is a good agreement between them. Also, the energy consumption of the system during the winter season is calculated in TRANSYS software. Experimental results show that the heat output rate of a new modified heating system with inlet water temperature in the range of 45–55°C is on average 4.17 times higher compared with the conventional model. CFD simulation also showed that the combined system provides good thermal comfort conditions. Energy consumption of the new system reduced about 13% compared with conventional models. 相似文献
2.
益生菌可在肠道定植从而发挥抗炎或抗氧化活性,有利于宿主肠道健康。本实验研究了从新疆传统发酵乳制品中分离得到的8?株植物乳杆菌对大肠杆菌侵袭和过氧化氢刺激肠上皮细胞HT-29的保护作用。结果表明:在8?株植物乳杆菌中,植物乳杆菌35具有最高的黏附能力。植物乳杆菌35可通过取代、竞争、排阻的方式抑制大肠杆菌对HT-29细胞的黏附,抑制率分别为42.60%、59.17%、60.19%。植物乳杆菌35及其多糖可抑制大肠杆菌刺激HT-29细胞产生白细胞介素-8;同时保护HT-29细胞免受过氧化氢的损伤,增加超氧化物歧化酶、谷胱甘肽过氧化物酶活力水平并降低丙二醛含量。结论:植物乳杆菌35及其粗胞外多糖具有抑制大肠杆菌O157诱导的炎症性肠病的潜力。 相似文献
3.
目的:探讨姜黄素的主要肠道代谢物四氢姜黄素(tetrahydrocurcumin,THC)对血小板活化和聚集的影响及其可能的分子机制。方法:在体外实验中,用不同浓度的THC(0、0.5、1、10 μmol/L)提前与健康人纯化血小板共同孵育40 min,然后加入凝血酶激活血小板2 min,用流式细胞术测定血小板表面CD62P和CD63的表达量,用酶联免疫吸附法测定血小板释放血小板因子-4(platelet factor-4,PF4)和趋化因子配体-5(chemokine ligand 5,CCL5)水平,用血小板聚集仪检测血小板释放ATP水平和血小板最大聚集率,用Western blot蛋白免疫印迹法检测血小板磷酸肌醇-3-激酶(phosphoinositide 3-kinase,PI3K)和Akt蛋白的磷酸化水平。结果:与模型组(血小板悬液中加入0.05%二甲基亚砜)相比,THC能抑制凝血酶诱导的血小板表面CD62P和CD63的表达,抑制PF4、CCL5和ATP的释放,降低血小板最大聚集率,下调PI3K和Akt蛋白的磷酸化水平,且呈浓度依赖效应,其中10 μmol/L的浓度下作用效果显著(P<0.01、P<0.001)。PI3K的特异性激动剂740 Y-P可部分逆转THC对PF4和CCL5释放和血小板聚集的抑制作用(P<0.05、P<0.01)。结论:THC具有显著抑制血小板活化和聚集的作用,其机制可能是THC可下调PI3K/Akt介导的信号通路。 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(57):24107-24118
Vehicle fires in the tunnel are a great threat to the safe operation of the tunnel. Due to the rapid development of the hydrogen economy, the fire due to the hydrogen leakage could not be avoided and may bring great damage to the passengers and infrastructure. Due to the large difference between pool fires of traditional fossil-fueled and jet fires of hydrogen-powered vehicles, it is in doubt whether the existing longitudinal ventilation design could still be effective for the safety issue of hydrogen powered vehicles. To solve this problem, it is necessary to compare temperature characteristics of hydrogen-powered and traditional vehicle fires with and without longitudinal ventilations. In present work, we conducted a numerical investigation to discuss the different temperature distributions of traditional and hydrogen-fueled vehicle fires. Results indicate that the high temperature zone of the pool fire only exists above the ceiling of the vehicle. For hydrogen-powered vehicle fire, the high-speed hydrogen jet with the strong inertial force could push the hot smoke flows back to the ground. The ceiling temperature of hydrogen-powered vehicle fire is larger since hydrogen-powered vehicle has a larger heat release rate and the fire hazard of jet fires bring more danger compared with the pool fire. Although the temperature stratification is also obvious for the hydrogen-powered vehicle fire, the air temperature in the lower region could be heated and still high enough to bring a great damage to the passengers’ lives. This is quite different with the traditional pool fire. In addition, the critical ventilation velocity is also discussed. The theoretical equation could well predicted the critical ventilation velocity of traditional vehicle fires. For hydrogen-powered vehicle fires, the critical ventilation velocity could reach up to 6 m/s. The theoretical equation could not well predict the critical ventilation velocity of hydrogen-powered vehicle fires due to exist of hydrogen jet fires. 相似文献
5.
Software is a central component in the modern world and vastly affects the environment’s sustainability. The demand for energy and resource requirements is rising when producing hardware and software units. Literature study reveals that many studies focused on green hardware; however, limited efforts were made in the greenness of software products. Green software products are necessary to solve the issues and problems related to the long-term use of software, especially from a sustainability perspective. Without a proper mechanism for measuring the greenness of a particular software product executed in a specific environment, the mentioned benefits will not be attained. Currently, there are not enough works to address this problem, and the green status of software products is uncertain and unsure. This paper aims to identify the green measurements based on sustainable dimensions in a software product. The second objective is to reveal the relationships between the elements and measurements through empirical study. The study is conducted in two phases. The first phase is the theoretical phase, where the main components, measurements and practices that influence the sustainability of a software product are identified. The second phase is the empirical study that involved 103 respondents in Malaysia investigating current practices of green software in the industrial environment and further identifying the main sustainability dimensions and measurements and their impact on achieving green software products. This study has revealed seven green measurements of software product: Productivity, Usability, Cost Reduction, Employee Support, Energy Efficiency, Resource Efficiency and Tool Support. The relationships are statistically significant, with a significance level of less than 0.01 (p = 0.000). Thus, the hypothesised relationships were all accepted. The contributions of this study revolve around the research perspectives of the measurements to attain a green software product. 相似文献
6.
Cho-Yi Chen Masaoki Kawasumi Tien-Yun Lan Chi-Lam Poon Yi-Sian Lin Pin-Jou Wu Yao-Chung Chen Bing-Hong Chen Cheng-Hsien Wu Jeng-Fan Lo Rueyhung Roc Weng Yi-Chen Sun Kai-Feng Hung 《International journal of molecular sciences》2021,22(1)
Endoplasmic reticulum (ER) stress response is an adaptive program to cope with cellular stress that disturbs the function and homeostasis of ER, which commonly occurs during cancer progression to late stage. Late-stage cancers, mostly requiring chemotherapy, often develop treatment resistance. Chemoresistance has been linked to ER stress response; however, most of the evidence has come from studies that correlate the expression of stress markers with poor prognosis or demonstrate proapoptosis by the knockdown of stress-responsive genes. Since ER stress in cancers usually persists and is essentially not induced by genetic manipulations, we used low doses of ER stress inducers at levels that allowed cell adaptation to occur in order to investigate the effect of stress response on chemoresistance. We found that prolonged tolerable ER stress promotes mesenchymal–epithelial transition, slows cell-cycle progression, and delays the S-phase exit. Consequently, cisplatin-induced apoptosis was significantly decreased in stress-adapted cells, implying their acquisition of cisplatin resistance. Molecularly, we found that proliferating cell nuclear antigen (PCNA) ubiquitination and the expression of polymerase η, the main polymerase responsible for translesion synthesis across cisplatin-DNA damage, were up-regulated in ER stress-adaptive cells, and their enhanced cisplatin resistance was abrogated by the knockout of polymerase η. We also found that a fraction of p53 in stress-adapted cells was translocated to the nucleus, and that these cells exhibited a significant decline in the level of cisplatin-DNA damage. Consistently, we showed that the nuclear p53 coincided with strong positivity of glucose-related protein 78 (GRP78) on immunostaining of clinical biopsies, and the cisplatin-based chemotherapy was less effective for patients with high levels of ER stress. Taken together, this study uncovers that adaptation to ER stress enhances DNA repair and damage tolerance, with which stressed cells gain resistance to chemotherapeutics. 相似文献
7.
Tomasz Pdzinski Katarzyna Grzyb Konrad Skotnicki Piotr Filipiak Krzysztof Bobrowski Chryssostomos Chatgilialoglu Bronislaw Marciniak 《International journal of molecular sciences》2021,22(9)
Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO•) play an important role, being the most aggressive towards biomolecules. The reactions of HO• with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO• generated by ionizing radiation in aqueous solutions under anoxic conditions. We performed the identification and quantification of transient species by pulse radiolysis and of final products by LC-MS and high-resolution MS/MS after γ-radiolysis. By parallel photochemical experiments, using 3-carboxybenzophenone (CB) triplet with the model peptide, we compared the outcomes in terms of short-lived intermediates and stable product identification. The result is a detailed mechanistic scheme of Met oxidation by HO•, and by CB triplets allowed for assigning transient species to the pathways of products formation. 相似文献
8.
9.
10.