全文获取类型
收费全文 | 54289篇 |
免费 | 5811篇 |
国内免费 | 3335篇 |
专业分类
电工技术 | 2752篇 |
技术理论 | 1篇 |
综合类 | 4937篇 |
化学工业 | 11544篇 |
金属工艺 | 3379篇 |
机械仪表 | 1953篇 |
建筑科学 | 4277篇 |
矿业工程 | 2693篇 |
能源动力 | 3038篇 |
轻工业 | 4674篇 |
水利工程 | 1358篇 |
石油天然气 | 3127篇 |
武器工业 | 599篇 |
无线电 | 4131篇 |
一般工业技术 | 5032篇 |
冶金工业 | 4419篇 |
原子能技术 | 1671篇 |
自动化技术 | 3850篇 |
出版年
2024年 | 124篇 |
2023年 | 723篇 |
2022年 | 1546篇 |
2021年 | 1843篇 |
2020年 | 1940篇 |
2019年 | 1610篇 |
2018年 | 1608篇 |
2017年 | 1958篇 |
2016年 | 2205篇 |
2015年 | 2169篇 |
2014年 | 3501篇 |
2013年 | 3838篇 |
2012年 | 4302篇 |
2011年 | 4239篇 |
2010年 | 3133篇 |
2009年 | 3122篇 |
2008年 | 2668篇 |
2007年 | 3544篇 |
2006年 | 2955篇 |
2005年 | 2532篇 |
2004年 | 2251篇 |
2003年 | 1991篇 |
2002年 | 1661篇 |
2001年 | 1431篇 |
2000年 | 1193篇 |
1999年 | 958篇 |
1998年 | 752篇 |
1997年 | 630篇 |
1996年 | 573篇 |
1995年 | 511篇 |
1994年 | 394篇 |
1993年 | 306篇 |
1992年 | 296篇 |
1991年 | 212篇 |
1990年 | 168篇 |
1989年 | 130篇 |
1988年 | 87篇 |
1987年 | 55篇 |
1986年 | 52篇 |
1985年 | 50篇 |
1984年 | 37篇 |
1983年 | 27篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1975年 | 9篇 |
1959年 | 8篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Linseed cake (LC), a byproduct of linseed oil extraction, is used as a functional filler for production of biodegradable composites. To determine the influence of residual linseed crude oil contained in lignocellulosic filler on the properties of the poly(lactic acid) (PLA)-based composites with 5–30% filler content, two types of LC were analyzed: a defatted and an unmodified one. Complex analysis of the composites' properties change was conducted in relation to their structure modification caused by the addition of a waste filler. It was found that the addition of LC resulted in simultaneous plasticization and improved crystallization of PLA. Lignocellulosic particles and crude linseed oil contained in the LC powder provided a modifying effect, influencing the level of crystallinity and mechanical and thermomechanical properties. Using LC may thus overcome one of the main drawbacks of PLA, which is brittleness and low crystallinity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47152. 相似文献
92.
Following the recent introduction of the Sustainability over Sets (SOS) concept as a sustainability analysis tool with broad flexibility in incorporating human input, in this work, the concepts of Sustainizability (SIZ) and Sustainizability over Sets (SIZOS) are introduced, as novel frameworks for sustainable system synthesis. Springing off the conceptual foundation of sustainability, SIZ (and SIZOS) refers to the existence of allowable external actions, and/or design changes that can render sustainable (sustainable over a set) an unsustainable (unsustainable over a set) system. Utilizing earlier mathematical results for SOS, rigorous necessary and sufficient conditions for SIZOS are presented. Two case studies, on a two-dimensional biological waste treatment system, and a three-dimensional food chain system, are then presented to illustrate the developed necessary and sufficient conditions for SIZOS. 相似文献
93.
94.
95.
96.
Gastón Gutiérrez-Gamboa Eva P. Pérez-Álvarez Pilar Rubio-Bretón Teresa Garde-Cerdán 《International Journal of Food Science & Technology》2019,54(4):1160-1168
Edible mushrooms production presents a potential problem for the environment, due to the large amount of waste generated. These wastes contain nitrogenous matter, which could be used as biostimulant in plants. The aim of this work was to study the effect of waste waters, from the mushroom production process, applied at veraison and 1 week later to grapevine leaves, on grape volatile compounds over two vintages. The results evidenced that mushroom water treatment decreased the grape content of certain terpenoids, C13 norisoprenoids, benzenoid compounds and esters, increasing C6 compounds content during the first season. Treated mushroom water application slightly affected grape volatile composition. This was the treatment that least affected the content of grape volatile composition. Few differences were found after the biostimulation during the second vintage. The season was the dominant factor of grape volatile content variation compared to the treatment and their interaction. 相似文献
97.
流量替代渗透率评价破碎性储层工作流体伤害程度 总被引:2,自引:0,他引:2
若地层岩石整体强度偏低,在力学环境改变后岩石易破碎成不规则破裂体,则储存油气资源的此类破碎地层被称为破碎性储层。由于破碎性储层在纵向上存在着较强的非均质性,通过测试单个柱塞岩样在工作流体伤害前后的渗透率变化难以体现工作流体对储层的整体伤害程度。为此,利用达西定律先从理论上探讨用流量替代渗透率定量表征储层伤害程度的可行性,再开展单层开采、双层及三层并采的流量测试实验,评价工作流体对单层、多层储层的整体伤害程度,并将流量损害率与渗透率损害率进行对比以求证流量替代渗透率的可行性。研究结果表明:①单层开采时,流量损害率与渗透率损害率基本一致,渗透率损害率是流量损害率的一种特殊形式;②双层及三层并采时,单层各自稳定流量损害率与渗透率损害率接近,且流量损害率可以定量表征并采储层的整体伤害程度,而渗透率损害率则无法定量表证;③稳定流量损害率较累积流量损害率更接近渗透率损害率。结论认为,测定稳定流量可以替代测定渗透率评价工作流体对破碎性储层的伤害程度,从而为优选工程技术与评价工作流体的适应性提供了方法依据。 相似文献
98.
《International Journal of Hydrogen Energy》2019,44(1):164-173
Biogas utilization in fuel cell technology and hydrogen generation is a modern and economically viable approach. A pretreatment step prior to anaerobic digestion (AD) is obligatory to increase the hydrolysis, solubilize the complex matter present in organic fraction of municipal solid waste (OFMSW) and to achieve higher yield of biogas. This study was intended to find out the effects of thermal, chemical and thermochemical pretreatments on the properties and structure of OFMSW and also on biogas production. There was an increase in chemical oxygen demand of 6.87, 1.61 and 11.60% for thermal, chemical and thermochemical pretreatments, respectively. Also, the content of volatile solids was reduced by 2.36% by thermochemical pretreatment. FTIR, XRD and SEM analysis revealed that these pretreatments also caused chemical and morphological changes on the substrate, as a result reduced its crystallinity and enhanced the rate of hydrolysis. A significant increase of 54% in biogas yield was achieved after thermochemical pretreatment in comparison to untreated OFMSW sample. 相似文献
99.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
100.
摘要:为了深入了解铁素体基Ti-Mo高强钢在连续冷却相变过程中组织及硬度的变化及其原因,通过热膨胀法、金相及硬度等实验研究了Ti-Mo微合金钢在连续冷却条件下组织及性能的变化,探讨了冷却速率对组织、硬度及相变行为的影响机理,揭示了(Ti,Mo)C在奥氏体和铁素体中Ti/Mo原子比变化的原因。结果表明,随着冷却速率由0.06℃/s增加至17.9℃/s,组织依次为多边形铁素体+珠光体→多边形铁素体+粒状贝氏体→粒状贝氏体,硬度由144HV逐渐增大至228HV。当冷速由0.14℃/s增大至0.90℃/s时,组织中多边形铁素体比例不断增大,珠光体比例不断降低,硬度的提高主要来自于铁素体晶粒尺寸的细化及纳米级(Ti,Mo)C粒子的增多;当冷速由1.79℃/s增大至17.9℃/s时,组织中多边形铁素体比例不断降低,贝氏体比例不断提高,硬度的提高主要是由于贝氏体组织的细化及其比例的增加。(Ti,Mo)C粒子主要有2类:一类是奥氏体中析出的10~20nm的粒子,Ti原子数分数约为88%,另一类是铁素体中析出的小于10nm的粒子,Ti原子数分数约为68%,EDS测量结果与计算结果大致相当。 相似文献