全文获取类型
收费全文 | 57015篇 |
免费 | 5031篇 |
国内免费 | 1829篇 |
专业分类
电工技术 | 3770篇 |
技术理论 | 9篇 |
综合类 | 4125篇 |
化学工业 | 8945篇 |
金属工艺 | 3011篇 |
机械仪表 | 3522篇 |
建筑科学 | 4563篇 |
矿业工程 | 1663篇 |
能源动力 | 1920篇 |
轻工业 | 4280篇 |
水利工程 | 1121篇 |
石油天然气 | 2585篇 |
武器工业 | 548篇 |
无线电 | 6707篇 |
一般工业技术 | 6496篇 |
冶金工业 | 2261篇 |
原子能技术 | 748篇 |
自动化技术 | 7601篇 |
出版年
2025年 | 290篇 |
2024年 | 1434篇 |
2023年 | 1369篇 |
2022年 | 2051篇 |
2021年 | 2679篇 |
2020年 | 2173篇 |
2019年 | 1841篇 |
2018年 | 1804篇 |
2017年 | 1920篇 |
2016年 | 1786篇 |
2015年 | 2386篇 |
2014年 | 2837篇 |
2013年 | 3317篇 |
2012年 | 3652篇 |
2011年 | 3697篇 |
2010年 | 3523篇 |
2009年 | 3348篇 |
2008年 | 3217篇 |
2007年 | 2823篇 |
2006年 | 2827篇 |
2005年 | 2237篇 |
2004年 | 1614篇 |
2003年 | 1348篇 |
2002年 | 1451篇 |
2001年 | 1264篇 |
2000年 | 1123篇 |
1999年 | 1165篇 |
1998年 | 849篇 |
1997年 | 724篇 |
1996年 | 677篇 |
1995年 | 521篇 |
1994年 | 468篇 |
1993年 | 321篇 |
1992年 | 288篇 |
1991年 | 205篇 |
1990年 | 152篇 |
1989年 | 135篇 |
1988年 | 91篇 |
1987年 | 62篇 |
1986年 | 45篇 |
1985年 | 33篇 |
1984年 | 30篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 18篇 |
1979年 | 7篇 |
1959年 | 3篇 |
1953年 | 4篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Natural weather changes due to diurnal and seasonal temperature and relative humidity cycles affect micro-environment of concrete; temperature and moisture content in the concrete fluctuates correspondingly with variations in the weather. This paper mainly discusses the temperature response in concrete. The temperature response of the concrete shows obvious hysteresis characteristics compared with the climate temperature variations due to the thermal properties of the concrete. The temperature in concrete is a main factor influencing concrete carbonization, chloride diffusion and the corrosion rate of steel bars in the concrete. To predict the temperature response in concrete in a natural climate environment, a model based on the behavior of the concrete’s thermal conduction was presented. A method for processing the climate temperature data was devised using the mathematical principle of extreme difference dissection; in this way, a temperature action spectrum can be formed. In view of the above mentioned studies, the corresponding temperature response in the concrete could be predicted. Comparisons between the prediction and the measurement of the temperature responses were carried out. 相似文献
83.
84.
毛泽东文艺思想的权威阐释者作为对周扬的定评,文艺理论家的周扬却被遮蔽,这是欠公允的.1941年前周扬在文学与生活关系上的认识是较为客观的,表现出他作为理论家的时代超前意义.他谈到毛泽东1942年所谈论的问题,包含着他作为文艺理论家独特的理论感受.这里立足<文学与生活漫谈>一文,对1942年以前周扬在文学理论上的贡献作论述. 相似文献
85.
86.
Wei Chen Yongqing Zeng Jingxiang Cui Qimei Chen Jinfang Du Lun Yang Yanxia Hu Yiping Song Yuan Qian 《European Food Research and Technology》2011,232(3):433-440
Antioxidant enzymes protect muscle tissues against oxidation from reactive oxygen species and increase the stability of the muscle. Phospholipid hydroperoxide glutathione peroxidase (GPx4) is an important antioxidant enzyme in muscle tissue. So the aim of this study was to identify the effects of mRNA expression level of GPx4 gene on meat quality properties in Longissimus dorsi of three pig breeds. Total 36 pigs (12 pigs for each breed) were used to measure the meat quality properties and to analyze the expression levels of GPx4 gene by quantitative real-time PCR. The results showed that meat quality, GPx4 activity, and GPx4 mRNA levels were affected by pig breeds. There were the lowest expressible moisture, drip loss, and cooking loss in Laiwu Pig among the three breeds, and also there were the highest GPx4 activity and the expression levels of GPx4 gene in Laiwu Pig compared with the other two pig breeds. Analysis of meat samples divergent for water-holding capacity identified highly negative associations between expressions levels of GPx4 gene and expressible moisture, drip loss and cooking loss. These results suggest that the higher mRNA expression level of GPx4 gene up-regulate the water-holding capacity and the activity of GPx4, and the expression of GPx4 gene plays an important role in physiological changes related to the meat quality properties and the mechanisms of the antioxidant ion of meat. 相似文献
87.
88.
Dingde Jiang Zhengzheng Xu Hongwei Xu Yang Han Zhenhua Chen Zhen YuanAuthor vitae 《Computers & Electrical Engineering》2011,37(6):1106-1121
Traffic matrix (TM) is a key input of traffic engineering and network management. However, it is significantly difficult to attain TM directly, and so TM estimation is so far an interesting topic. Though many methods of TM estimation are proposed, TM is generally unavailable in the large-scale IP backbone networks and is difficult to be estimated accurately. This paper proposes a novel method of TM estimation in large-scale IP backbone networks, which is based on the generalized regression neural network (GRNN), called GRNN TM estimation (GRNNTME) method. Firstly, building on top of GRNN, we present a multi-input and multi-output model of large-scale TM estimation. Because of the powerful capability of learning and generalizing of GRNN, the output of our model can sufficiently capture the spatio-temporal correlations of TM. This ensures that the estimation of TM can accurately be attained. And then GRNNTME uses the procedure of data posttreating further to make the output of our model closer to real value. Finally, we use the real data from the Abilene Network to validate GRNNTME. Simulation results show that GRNNTME can perform well the accurate and fast estimation of TM, track its dynamics, and holds the stronger robustness and lower estimation errors. 相似文献
89.
袁升文 《重庆科技学院学报(社会科学版)》2010,(16)
翻译人员作为不同语言人群之间沟通交流的桥梁和纽带,作用巨大.但是,文学作品中塑造的翻译人员形象常常是负面的汉奸形象,这种形象在影视片中尤为突出,其来源可以追溯到明清时期. 相似文献
90.
Der-Fong Juang Chao-Hsien Lee Chung-Shin Yuan 《The Science of the total environment》2010,408(20):4524-4531
To understand the potential threat of volatile organic compounds (VOCs) to the health of residents living close to a heavily polluted river, this study investigated the species and the concentration of VOCs evaporating from a river and surveyed the health condition of the nearby residents. Air samples were taken seasonally at the upstream, midstream, and downstream water surfaces of the river, and at different locations at certain distances from the river. These samples were analyzed qualitatively and quantitatively through gas chromatography and electron capture detector (GC/ECD) for chlorinated organic compounds, and through gas chromatography and flame ionization detector (GC/FID) for ordinary hydrocarbons. The health data obtained from valid health questionnaires of 908 residents were analyzed through Statistical Package for Social Science (SPSS) software. Twenty-six species of VOCs were identified in the environment adjacent the river, many of which are carcinogenic or believed to be carcinogenic to humans. However, results of this study shows that the VOCs evaporating from the polluted river have not been definitively identified as a major factor of cancer in the residents. However, the risk of suffering from certain chronic diseases may increase in residents living less than 225 m away from the river due to the high levels of evaporated VOCs. Residents living less than 225 m away from the river and with nearby specific industries are 3.130 times more at risk of suffering from chronic diseases than those with no nearby specific industries. 相似文献