全文获取类型
收费全文 | 17318篇 |
免费 | 1041篇 |
国内免费 | 463篇 |
专业分类
电工技术 | 478篇 |
综合类 | 938篇 |
化学工业 | 3396篇 |
金属工艺 | 1208篇 |
机械仪表 | 1470篇 |
建筑科学 | 595篇 |
矿业工程 | 305篇 |
能源动力 | 351篇 |
轻工业 | 4229篇 |
水利工程 | 76篇 |
石油天然气 | 256篇 |
武器工业 | 53篇 |
无线电 | 1063篇 |
一般工业技术 | 2124篇 |
冶金工业 | 474篇 |
原子能技术 | 254篇 |
自动化技术 | 1552篇 |
出版年
2024年 | 43篇 |
2023年 | 164篇 |
2022年 | 378篇 |
2021年 | 443篇 |
2020年 | 324篇 |
2019年 | 332篇 |
2018年 | 359篇 |
2017年 | 421篇 |
2016年 | 583篇 |
2015年 | 800篇 |
2014年 | 966篇 |
2013年 | 1065篇 |
2012年 | 1279篇 |
2011年 | 1578篇 |
2010年 | 1350篇 |
2009年 | 1211篇 |
2008年 | 1051篇 |
2007年 | 1170篇 |
2006年 | 1002篇 |
2005年 | 751篇 |
2004年 | 615篇 |
2003年 | 549篇 |
2002年 | 523篇 |
2001年 | 379篇 |
2000年 | 292篇 |
1999年 | 187篇 |
1998年 | 157篇 |
1997年 | 126篇 |
1996年 | 105篇 |
1995年 | 82篇 |
1994年 | 68篇 |
1993年 | 88篇 |
1992年 | 51篇 |
1991年 | 41篇 |
1990年 | 37篇 |
1989年 | 27篇 |
1988年 | 29篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 14篇 |
1975年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
81.
Carbon-based nanoparticles synthesized by heat treatment of nanodiamond in the temperature range of 1000–1900 °C were added to PTFE film to investigate the structural effect of the carbon particles on the tribological properties of PTFE composite film. Carbon-based nanoparticles were prepared by milling with micron sized beads in chemically treated water before their addition to PTFE film. The wear and frictional properties of PTFE nanocomposite film were measured by the ball on plate type wear test. The wear resistance of PTFE film was found to be enhanced by the addition of 2 wt% of carbon nanoparticles. The wear coefficient of PTFE film was decreased from 16.2 to 3.5 × 10−6 mm3/N m by the addition of carbon-based nanoparticles heat-treated at 1000 °C. Increasing the heating temperature of the nanodiamonds caused the extent of aggregation and particle size to increase. The wear resistance of PTFE nanocomposite film was enhanced by the addition of nanodiamonds heat-treated at 1000 °C, but decreased when the heat treatment temperature of carbon nanoparticles was further increased. Tribological behavior of PTFE nanocomposite films depending on the types of carbon nanoparticles were explained based on the structural, physical and chemical modification of carbon nanoparticles. 相似文献
82.
Paulo A. Santos Marcia A.S. Spinac Karen K.G. Fermoselli Marco-A. De Paoli 《Composites Part A》2007,38(12):2404-2411
The interest for the use of vegetal fibers as polymers reinforcement has recently increased because of their unique environmental and technological advantages. This work evaluated the use of Curauá fibers in polyamide-6 composites aiming at glass fiber replacement. Fiber content of 20, 30 or 40 wt% and fiber lengths of 0.1 or 10 mm were studied. Fibers were treated with N2 plasma or washed with NaOH solution, to improve their adhesion to PA-6. Samples with 20 wt% of short or long fibers, with or without pre-treatment, were compounded in two different co-rotating intermeshing twin-screw extruders. These samples were submitted to mechanical and thermal tests. In conclusion, non-dried raw materials improved fiber/matrix interfacial adhesion. Tensile and flexural properties of this composite are better than unfilled, but lower than glass fiber reinforced polyamide-6. However, its impact resistance and heat deflection temperature are similar to the glass fiber reinforced polyamide-6 and its lower density, enable it to replace this latter in specific non-critical applications. 相似文献
83.
84.
Hamidreza Alighourchi Mohsen Barzegar Soleiman Abbasi 《European Food Research and Technology》2008,227(3):881-887
Anthocyanins (ACs) are phenolic compounds that are distributed widely in fruits and vegetables. Apart from imparting color
to plants, ACs also have an array of health-promoting benefits. In this research, the amounts of major ACs of 15 pomegranate
(Punica granatum L.) varieties obtained from Yazd province were determined. The major ACs detected in the studied varieties were as follows:
delphinidin 3-glucoside (2.19–16.29 mg/L), delphinidin 3,5-diglucoside (2.36–63.07 mg/L), pelargonidin 3-glucoside (0.26–1.36 mg/L),
pelargonidin 3,5-diglucoside (0.01–8.11 mg/L), cyanidin 3-glucoside (5.78–30.38 mg/L), and cyanidin 3,5-diglucoside (4.39–166.32 mg/L).
The effect of storage time of unprocessed and pasteurized juices on ACs content of four selected varieties was also studied.
Average degradation percentage of each AC was between 23.0 and 83.0% during 10 days at 4 °C. Moreover, in pasteurized juices
average degradation of ACs was 42.8 ± 0.5% after 10 weeks storage at 4 °C. 相似文献
85.
基于M68HC908Q系列单片机掉电保护系统的设计与实现 总被引:1,自引:0,他引:1
介绍一种由电源监控芯片MAX708和串行E~2PROM AT24C02构成的低成本、高可靠性的掉电检测和保护电路。在软件上,通过对现场数据的保护实现了上电后现场数据的恢复。同时对E~2PROM存储区的循环写入增加了可擦写次数,特别适用于数据更新频繁的智能仪表的数据掉电保护。 相似文献
86.
Development of adolescent reading comprehension in language 1 and language 2: A longitudinal analysis of constituent components. 总被引:1,自引:0,他引:1
van Gelderen Amos; Schoonen Rob; Stoel Reinoud D.; de Glopper Kees; Hulstijn Jan 《Canadian Metallurgical Quarterly》2007,99(3):477
This study investigated the relationship between reading comprehension development of 389 adolescents in their dominant language (Language 1 [L1], Dutch) and a foreign language (Language 2 [L2], English). In each consecutive year from Grades 8 through 10, a number of measurements were taken. Students' reading comprehension, their linguistic knowledge (vocabulary and grammar knowledge) and processing efficiency (speed of word recognition and sentence comprehension) in both languages, and their metacognitive knowledge about reading were assessed. The relative strengths of the effects of these components of reading were analyzed to distinguish among 3 hypotheses about the relationship between L1 and L2 reading comprehension: the transfer hypothesis, the threshold hypothesis, and the processing efficiency hypothesis. The transfer hypothesis predicts a strong relationship between L1 and L2 reading comprehension and a strong effect of metacognitive knowledge on L2 reading comprehension, whereas the threshold and processing efficiency hypotheses predict a more important role of language-specific knowledge and processing skills. Results support the transfer hypothesis, although language-specific knowledge and fluency also contribute to L2 reading performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
87.
L2-P5三靶点绕障拱型水平井钻井技术 总被引:1,自引:1,他引:0
介绍了胜利油田L2—P5三靶点绕障拱型水平井的设计和施工情况,重点分析了该井直井段和水平段井眼轨迹控制技术,对施工中出现的问题进行了分析并给出了相应的对策,为该区类似井钻井提供了有益的借鉴。 相似文献
88.
89.
用WAXD和FT-IR对高温超高压处理前后的HDPE进行了研究。发现经5.0GPa的高压处理或200℃下4.0GPa的高压同时处理后的HDPE分子链的化学结构未发生变化。HDPE晶体中(200)面与(110)面衍射峰的峰高比(γ)随着压力的升高而增大,表明HDPE分子链在超高压作用下发生了取向排列,且升高温度更有利于这种取向排列,但当压力增大至5.0GPa及温度升高至200℃时,γ反而大幅度下降。 相似文献
90.
Sandra L. McLellan Erika J. HollisMorgan M. Depas Meredith Van DykeJosh Harris Caitlin O. Scopel 《Journal of Great Lakes research》2007,33(3):566-580
Escherichia coli distribution and persistence in nearshore Lake Michigan were assessed following heavy rains and sanitary sewer overflow (SSO) and combined sewer overflow (CSO) events over a 5-year period, including an 18-day period following 25.4 cm of rainfall in which intensive studies were conducted following multiple CSO and SSO events. E. coli levels in the Milwaukee estuary and harbor following SSO and CSO events ranged from 104 to nearly 105 CFU/100 mL, which were significantly higher (p ≤ 0.05) than levels following rainfall alone. Sites outside of the breakwall but within the contamination plume (e.g., within 2 km of the harbor) were an order of magnitude lower. Locations 2–5 km from the harbor ranged from below detection limits, of < 1 to 5 CFU/100 mL. E. coli levels corrected for dilution based on specific conductivity measurements were lower than what would be expected for loss due to dilution alone, suggesting a combination of die-off and dilution, were responsible for the rapid disappearance of these organisms outside of the harbor. E. coli and fecal coliforms measured concurrently demonstrated that fecal coliforms could be recovered longer than E. coli in the open waters of the lake. E. coli isolated directly from sewage treatment plant influent were found to have a marked increase in antibiotic resistance traits for ten antibiotics commonly used in the human population compared with isolates from two animal sources of fecal pollution. However, E. coli obtained from sewage impacted water (n = 2,513) and from stormwater impacted water (n = 1,465) collected the previous year when there were no sewage overflows, were found to have no significant difference (p < 0.05) in the frequency of resistance when comparing the two conditions. E. coli survival characteristics and population dynamics are most likely influenced by multiple factors in complex systems such as the watershed/estuarine/lake environments of the Great Lakes. 相似文献