全文获取类型
收费全文 | 293861篇 |
免费 | 25707篇 |
国内免费 | 12739篇 |
专业分类
电工技术 | 16596篇 |
技术理论 | 34篇 |
综合类 | 27523篇 |
化学工业 | 46580篇 |
金属工艺 | 16339篇 |
机械仪表 | 16296篇 |
建筑科学 | 34644篇 |
矿业工程 | 15066篇 |
能源动力 | 11352篇 |
轻工业 | 22137篇 |
水利工程 | 11654篇 |
石油天然气 | 15532篇 |
武器工业 | 3740篇 |
无线电 | 17547篇 |
一般工业技术 | 24015篇 |
冶金工业 | 16736篇 |
原子能技术 | 2137篇 |
自动化技术 | 34379篇 |
出版年
2024年 | 630篇 |
2023年 | 3541篇 |
2022年 | 6669篇 |
2021年 | 9267篇 |
2020年 | 9102篇 |
2019年 | 6951篇 |
2018年 | 6482篇 |
2017年 | 8120篇 |
2016年 | 10022篇 |
2015年 | 10929篇 |
2014年 | 19629篇 |
2013年 | 18143篇 |
2012年 | 21174篇 |
2011年 | 23373篇 |
2010年 | 17203篇 |
2009年 | 17475篇 |
2008年 | 15825篇 |
2007年 | 19451篇 |
2006年 | 17906篇 |
2005年 | 15528篇 |
2004年 | 13132篇 |
2003年 | 11459篇 |
2002年 | 9507篇 |
2001年 | 7860篇 |
2000年 | 6676篇 |
1999年 | 5318篇 |
1998年 | 3893篇 |
1997年 | 3305篇 |
1996年 | 2743篇 |
1995年 | 2298篇 |
1994年 | 1974篇 |
1993年 | 1351篇 |
1992年 | 1122篇 |
1991年 | 814篇 |
1990年 | 664篇 |
1989年 | 589篇 |
1988年 | 374篇 |
1987年 | 261篇 |
1986年 | 223篇 |
1985年 | 259篇 |
1984年 | 207篇 |
1983年 | 176篇 |
1982年 | 106篇 |
1981年 | 90篇 |
1980年 | 108篇 |
1979年 | 50篇 |
1978年 | 25篇 |
1977年 | 36篇 |
1959年 | 33篇 |
1951年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 124 毫秒
81.
This study proposes that a novel integrated circuit (IC) and system design for renewable energy inverters can harvest renewable energy to power direct current (DC) and alternating current (AC) loads. In addition, an intelligent synthesis and management tool is developed to design the proposed system and to judge the system’s operational maintenance decisions. Finally, a renewable energy inverter’s information is posted to an online system. Users can obtain the proposed system’s information at any time and place. The accurate and superior performance of the proposed IC and system is confirmed by computer simulations and experimental results. 相似文献
82.
83.
为实现对干湿联合冷却塔冷却特性、节水特性的综合分析,编制干湿联合冷却塔校核计算流程,基于Visual Studio开发平台,本文开发了干湿联合冷却塔冷却节水特性分析优化软件。通过对某在运干湿联合冷却塔进行冷却节水特性计算,验证了所开发软件计算结果的准确性;在消雾节水计算结果基础上,对标干湿联合消雾冷却塔验收测试规程,生成其成雾频率曲线、耗水量曲线、塔雾指数、冷却特性曲线,综合分析其消雾特性、节水特性及冷却特性,从而确定了干湿联合冷却塔的最佳运行工况。同时运用所开发软件对比分析了某冷却塔设计干段散热面积对其消雾特性、节水特性及冷却特性的耦合影响,并分析了百叶窗开度对干湿联合冷却塔性能的影响,为干湿联合冷却塔的运行优化和设计优化提供了工具性软件支持。 相似文献
84.
85.
Through improved synthesis process, resistance reduction effect of (K0.5Bi0.5)TiO3 (KBT) doping in Y–Mn co-doped BaTiO3 (BT) lead free ceramics was investigated. By different doping methods (doping K2O, Bi2O3 and TiO2 or synthesized KBT), medium Curie temperature (around 130 °C) lead free BT ceramics were obtained with ultra-low resistivity (13.84 Ωcm) with a temperature maintaining process at 700 °C. In this contribution, effect of sintering process and doping methods is discussed in detail. 相似文献
86.
This paper presents a stochastic performance modelling approach that can be used to optimise design and operational reliability of complex chemical engineering processes. The framework can be applied to processes comprising multiple units, including the cases where closed form process performance functions are unavailable or difficult to derive from first principles, which is often the case in practice. An interface that facilitates automated two-way communication between Matlab® and process simulation environment is used to generate large process responses. The resulting constrained optimisation problem is solved using both Monte Carlo Simulation (MCS) and First Order Reliability Method (FORM); providing a wide range of stochastic process performance measures. Adding such capabilities to traditional deterministic process simulators provides a more informed basis for selecting optimum design factors; giving a simple way of enhancing overall process reliability and cost-efficiency. Two case study systems are considered to highlight the applicability and benefits of the approach. 相似文献
87.
Characteristics and formation mechanism of porosities in CFRP during laser joining of CFRP and steel
An experimental investigation on the mechanism of porosity formation during the laser joining of carbon fiber reinforced polymer (CFRP) and steel is presented. The porosity morphology and distribution were characterized by optical and scanning electron microscopy, and the thermal pyrolysis behaviors were investigated by thermal analysis and designed back-side cooling experiments. The results show that there are two types of porosities in CFRP. Porosity I only appears when the heat input is more than 77.8 J/mm. It has a smooth inner wall and distributes near the bonding interface between CFRP and steel at the central area of melted zone, which is caused by gaseous products such as CO2, NH3, H2O, and hydrocarbons produced by the pyrolysis of CFRP. Porosity II can be seen under all joining conditions. It has a rough inner wall and distributes far away from the bonding interface, concentrating at the final solidification locations. Porosity II is caused by the shrinkage of melted CFRP during solidification stage. 相似文献
88.
《Food Control》2015
The aim of the study was to investigate annual and regional differences in the level of aflatoxin B1 (AFB1) in grains and dairy cattle feed. Maize (n = 972), wheat (n = 201), barley (n = 147), oat (n = 136), grain mixtures (n = 168), and dairy cattle feed (n = 325) were sampled from 2009 to 2013 on different farms and in different farm factories situated in four Croatian regions. The samples were analysed for AFB1 using the validated ELISA immunoassay. AFB1 was determined in 16.4% of all investigated samples, among which maize was proven to be the most contaminated, with 21.7% of the samples recovered during 2013 harbouring AFB1 in concentrations over the permissible ones. Levels higher than permitted were observed in 17.9% and 12.3% of grain mixtures and dairy cattle feed, respectively, whereas concentrations of AFB1 determined in other crops throughout the investigated period met the stipulated requirements. The results revealed the AFB1 occurrence to be significantly (p < 0.05) dependent on the cultivation region, with the highest levels generally found in maize harvested in 2013 and consequently in grain mixtures and cattle feed that can most likely be associated with climatic conditions as the most critical factor for mould formation, and thus also AFB1 production. 相似文献
89.
为检查工程质量,查找输水系统可能存在的问题并消除隐患,保障电站安全运行,福建仙游抽水蓄能电站在投产发电前,要对输水发电系统进行充水试验与放空排水试验,在试验过程中监测输水系统的应力、应变与渗漏水情况。本文以尾水系统为例,介绍了试验所应具备的工程条件、工作程序及技术要求、试验成果分析和存在问题处理等。试验表明,仙游抽水蓄能电站尾水系统设计合理,施工质量优良,结构可靠,可供同类工程参考与借鉴。 相似文献
90.
氢工质在新能源与动力、航天推进、化工材料等领域有着广泛应用。通过开展高温氢工质热力学与输运性质研究,建立了原子态氢、分子态氢、热解平衡态氢的热物理性质计算模型,开发了热物性计算程序Prop_H_H2,适用范围为温度100~3 500 K、压力104~5×107 Pa 。验证表明,Prop_H_H2在适用范围内计算氢工质的物性参数合理可靠,在温度200~3 000 K、压力104~107 Pa范围内,程序预测值更加准确,相对偏差在±5%左右。本研究可为氢工质相关的航天推进、应用物理学、能源动力等行业的科研和应用提供支持借鉴。 相似文献