全文获取类型
收费全文 | 275047篇 |
免费 | 25593篇 |
国内免费 | 13087篇 |
专业分类
电工技术 | 17513篇 |
技术理论 | 30篇 |
综合类 | 27412篇 |
化学工业 | 34189篇 |
金属工艺 | 12240篇 |
机械仪表 | 16249篇 |
建筑科学 | 36788篇 |
矿业工程 | 16979篇 |
能源动力 | 11259篇 |
轻工业 | 20054篇 |
水利工程 | 13120篇 |
石油天然气 | 18932篇 |
武器工业 | 3841篇 |
无线电 | 16946篇 |
一般工业技术 | 21288篇 |
冶金工业 | 13775篇 |
原子能技术 | 2540篇 |
自动化技术 | 30572篇 |
出版年
2024年 | 1230篇 |
2023年 | 3567篇 |
2022年 | 6957篇 |
2021年 | 8994篇 |
2020年 | 8980篇 |
2019年 | 6859篇 |
2018年 | 6488篇 |
2017年 | 8039篇 |
2016年 | 9635篇 |
2015年 | 10359篇 |
2014年 | 18597篇 |
2013年 | 16799篇 |
2012年 | 20221篇 |
2011年 | 21963篇 |
2010年 | 16089篇 |
2009年 | 16274篇 |
2008年 | 14727篇 |
2007年 | 18068篇 |
2006年 | 16640篇 |
2005年 | 14434篇 |
2004年 | 12184篇 |
2003年 | 10417篇 |
2002年 | 8658篇 |
2001年 | 7197篇 |
2000年 | 6140篇 |
1999年 | 4842篇 |
1998年 | 3577篇 |
1997年 | 3118篇 |
1996年 | 2517篇 |
1995年 | 2140篇 |
1994年 | 1832篇 |
1993年 | 1241篇 |
1992年 | 1021篇 |
1991年 | 754篇 |
1990年 | 636篇 |
1989年 | 584篇 |
1988年 | 329篇 |
1987年 | 266篇 |
1986年 | 219篇 |
1985年 | 237篇 |
1984年 | 155篇 |
1983年 | 134篇 |
1982年 | 86篇 |
1981年 | 94篇 |
1980年 | 102篇 |
1979年 | 57篇 |
1978年 | 25篇 |
1977年 | 26篇 |
1964年 | 19篇 |
1959年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
In this paper, we report on the indoor concentrations from a suite of full-scale outdoor tracer-gas point releases conducted in the downtown area of Oklahoma City in 2003. A point release experiment consisted of releases of sulfur hexafluoride (SF6) in multiple buildings and from different outdoor locations. From the measurements, we are able to estimate the concentration variations indoors for a building operating under “typical” operating conditions. The mean indoor spatial coefficients of variation are 30% to 45% from a daytime outdoor release are around 80% during an outdoor evening release. Having estimates of the spatial coefficient of variation provides stakeholders, including first responders, with the likely range of concentrations in the building when little is known about the building characteristics and operating behavior, such as developing urban-scale hazard and consequence analyses. We show differences in indoor measurements at different distances to the release points, floors of the building, and heating, ventilation, and air conditioning system (HVAC) operation. We also show estimates at different time resolutions. The statistics show that in the studied medium to large commercial buildings, spatial differences would result in peak indoor concentrations in certain parts of the buildings that may be substantially higher than the building average. To our knowledge, very few tracer gas measurements have been conducted in buildings of this scope, particularly with measurements on multiple floors and within a floor. The resulting estimates of spatial variability provide a unique opportunity for hazard assessment, and comparison to multi-zone models. 相似文献
53.
《Geotextiles and Geomembranes》2020,48(6):897-911
Dynamic responses of the geosynthetic-encased stone column (GESC) supported embankment under traffic loads have become a hot topic. This study investigates the responses of GESC improved ground under vertical cyclic loading. A series of laboratory tests in a designed model test tank have been carried out with different loading parameters (varied loading amplitudes and frequencies), different column dimensions (varied encasement lengths and column diameters). In the tests, the soil-column stress distribution, accumulated settlement of loading plate, excess pore water pressure in the surrounding soil and lateral bulging of the stone column are monitored. Experimental results indicate that the vertical stress on the stone column increases with the increment of encasement length, and decreases with the increment of column diameter, loading amplitude and loading frequency. The increasing stress on the surrounding soil leads to a greater accumulated settlement of the loading plate and excess pore water pressure, while the increasing stress on the column leads to larger lateral bulging of the column. Excess pore water pressure dissipates effectively through vertical and horizontal drainage channels provided by the stone column and the sand bed. The geosynthetic encasement prevents the clay from obstructing the drainage channel by filtration and guarantees the drainage effect. 相似文献
54.
《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
55.
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
56.
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
57.
58.
Protective coatings from diethylphosphatoethyltriethoxysilane (DEPETS) have been deposited on different polymer substrates in a plasma discharge operated at atmospheric pressure. Plasma polymer chemistry and structure were characterized by means of Fourier transform infrared spectroscopy (FTIR), laser desorption ionization-mass spectrometry (LDI-MS), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). A chemical structure of the plasma polymer has been proposed based on the coating molecular characterization. Coatings were deposited on polycarbonate (PC) and polyamide 6 (PA6) substrates. The flame retardant properties of coated substrate samples were assessed using cone calorimetry and compared to those of bare substrates. A significant increase in the time to ignition (TTI), up to +143%, was recorded after coating deposition due to the formation of a high-performance barrier layer at the surface of both polymer substrates. 相似文献
59.
Reliability based criteria are quite popular for optimal sensor network design. We present a modified definition of system reliability for sensor network design for two applications: reliable estimation of variables in a steady state linear flow process, and reliable fault detection and diagnosis for any process. Unlike the weakest-link based definition of system reliability in the literature, the proposed definition considers the entire system and is consistent with the reliability concept used in classical reliability literature. For each application, dual approaches for defining system reliability are proposed, and their analogy with the reliability problem in the classical reliability literature is established. Using examples and stochastic simulations, the advantage of using the proposed system reliability in contrast to the existing definition is illustrated. Part II of this series of articles presents methods for efficient generation of the system reliability function and its use in optimization-based approaches for designing optimal sensor networks. 相似文献
60.
Fault detection and isolation in water distribution networks is an active topic due to the nonlinearities of flow propagation and recent increases in data availability due to sensor deployment. Here, we propose an efficient two-step data driven alternative: first, we perform sensor placement taking the network topology into account; second, we use incoming sensor data to build a network model through online dictionary learning. Online learning is fast and allows tackling large networks as it processes small batches of signals at a time. This brings the benefit of continuous integration of new data into the existing network model, either in the beginning for training or in production when new data samples are gathered. The proposed algorithms show good performance in our simulations on both small and large-scale networks. 相似文献