全文获取类型
收费全文 | 25575篇 |
免费 | 2013篇 |
国内免费 | 653篇 |
专业分类
电工技术 | 2547篇 |
综合类 | 1985篇 |
化学工业 | 2984篇 |
金属工艺 | 543篇 |
机械仪表 | 1566篇 |
建筑科学 | 5209篇 |
矿业工程 | 1151篇 |
能源动力 | 2449篇 |
轻工业 | 1296篇 |
水利工程 | 432篇 |
石油天然气 | 803篇 |
武器工业 | 500篇 |
无线电 | 1206篇 |
一般工业技术 | 3249篇 |
冶金工业 | 1209篇 |
原子能技术 | 197篇 |
自动化技术 | 915篇 |
出版年
2024年 | 41篇 |
2023年 | 243篇 |
2022年 | 487篇 |
2021年 | 705篇 |
2020年 | 754篇 |
2019年 | 502篇 |
2018年 | 455篇 |
2017年 | 650篇 |
2016年 | 664篇 |
2015年 | 734篇 |
2014年 | 1620篇 |
2013年 | 1517篇 |
2012年 | 1845篇 |
2011年 | 1994篇 |
2010年 | 1452篇 |
2009年 | 1513篇 |
2008年 | 1322篇 |
2007年 | 1811篇 |
2006年 | 1702篇 |
2005年 | 1494篇 |
2004年 | 1278篇 |
2003年 | 1131篇 |
2002年 | 1004篇 |
2001年 | 713篇 |
2000年 | 584篇 |
1999年 | 435篇 |
1998年 | 334篇 |
1997年 | 269篇 |
1996年 | 196篇 |
1995年 | 186篇 |
1994年 | 135篇 |
1993年 | 100篇 |
1992年 | 80篇 |
1991年 | 70篇 |
1990年 | 42篇 |
1989年 | 38篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1959年 | 3篇 |
1956年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
In this paper, the dynamic behaviors on the basis of simulation for high-purity heat integrated air separation column (HIASC) are studied. A nonlinear generic model control (GMC) scheme is proposed based on the nonlinear behavior analyses of a HIASC process, and an adaptive generic model control (AGMC) scheme is further presented to correct the model parameters online. Related internal model control (IMC) scheme and multi-loop PID (M-PID) scheme are also developed as the comparative base. The comparative researches are carried out among these linear and nonlinear control schemes in detail. The simulation research results show that the proposed AGMC schemes present advantages in both servo control and regulatory control for the high-purity HIASC. 相似文献
73.
74.
Antoine Depoorter Carmen Kalalian Corinne Emmelin Chantal Lorentz Christian George 《Indoor air》2021,31(3):682-692
People spend approximately 80% of their time indoor, making the understanding of the indoor chemistry an important task for safety. The high surface-area-to-volume ratio characteristic of indoor environments leads the semi-volatile organic compounds (sVOCs) to deposit on the surfaces. Using a long path absorption photometer (LOPAP), this work investigates the formation of nitrous acid (HONO) through the photochemistry of adsorbed nitrate anions and its enhancement by the presence of furfural. Using a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS), this work also investigates the surface emissions of VOCs from irradiated films of furfural and a mix of furfural and nitrate anions. Among the emitted VOCs, 2(5H)-furanone/2-Butenedial was observed at high concentrations, leading to maleic anhydride formation after UV irradiation. Moreover, the addition of potassium nitrate to the film formed NOx and HONO concentrations up to 10 ppb, which scales to ca. 4 ppb for realistic indoor conditions. This work helps to understand the high levels of HONO and NOx measured indoors. 相似文献
75.
Shyfuddin Ahmed Boubakari Ibrahimou Shirmin Bintay Kader Muhammad Ashique Haider Chowdhury Habibul Ahsan Mohammad Yunus 《Indoor air》2021,31(6):2167-2175
Despite significant investment, childhood malnutrition continues to be a significant public health problem especially in least developed countries. The aim of this study was to find association between household biomass fuel (BMF) use and childhood malnutrition in Bangladesh using data from Demographic and Health Survey 2011. We included a total 6891 children under 5 years of age in the analysis. The prevalence of wasting, underweight, and stunting from BMF using household was 16.1% (n = 997; 95%CI, 15.1–17.3), 39.0% (n = 2399; 95%CI, 37.1–40.9), and 43.3% (n = 2620; 95%CI, 41.6–45.1), respectively. Underweight and stunting were significantly higher among children from households using BMF compared with the children from CF using households (underweight, biomass vs clean fuel: 39.0% vs. 23.5%, p < 0.001; stunting, biomass vs clean fuel: 43.3 vs. 31.5%, p < 0.001). The use of BMF in the household was significantly associated with underweight (OR = 1.38; 95%CI: 1.10–1.73) and stunting (OR = 1.58; 95%CI: 1.18–1.98) among children <5 years of age after adjusting possible confounders in mixed effect logistic regression analysis. This study found a significant association between chronic childhood malnutrition and household BMF use which is indicating possible alternative risk factor for malnutrition. Further prospective research is required to explore the mechanism of how BMF use results in chronic malnutrition. 相似文献
76.
77.
78.
《等离子体科学和技术》2020,22(4):45401
A low voltage circuit breaker(LVCB) is an important piece of protection equipment which will switch off the fault current in a power system. The moving contact of a low voltage circuit breaker with a higher rated current consists of two parallel contacts. Therefore, the convection effect on the air arc evolution process in a two parallel contact system is analyzed. A threedimensional(3 D) magneto–hydro–dynamic(MHD) model of arc simulation is built. In this model, the anode consists of two parallel contacts and a bonding conductor. A nonlinear voltage–current density characteristic is employed to represent the near-anode and near-cathode voltage. The current density, arc voltage and currents through every contact are obtained. The influence of convection and conduction on the arc evolution process are quantitatively calculated. The displacements of the arc roots are obtained and the asymmetry of the arc root motion is analyzed. The arc evolution process of a two parallel contact system is preliminarily revealed. 相似文献
79.
为保证经费使用效益,针对目前装备保障缺乏有效的评估方法,且制定保障方案时随意性较大的问题,提出了一种基于蒙特卡洛法的装备保障方案评估方法。根据现有装备保障的运行体制和机制,通过构建装备保障评估仿真模型,建立相对应的预防性维修过程子模型、修复性维修过程子模型和保障资源配置子模型,计算出基于现有保障方案的优化费效曲线及相关参数。通过某型飞机的保障方案实际计算,该方法能够对保障方案的备件、资源、设备利用率等方面进行评估,为任务执行前的保障方案评估提供了有效手段。提出的模型和软件能为装备保障人员提供有力的决策支持。 相似文献
80.
齐湘毅 《石油化工安全环保技术》2020,(1):47-49,I0003
介绍了某石化厂炼油中间油品罐区10台储罐的罐顶挥发性有机物治理方案,改造方案是利用炼油厂现有瓦斯管网系统将其回收利用。包括罐顶油气收集管线和增压风机,并完善储罐氮封和安全附件。该方案需根据储罐的基本情况制定合理的压力控制方案和应急安全措施。该治理方案投资小,运行费用低,不仅取消了废气排放口,而且有较高的经济效益,可作为优先选用的炼油罐顶气治理方案。 相似文献