全文获取类型
收费全文 | 24164篇 |
免费 | 2300篇 |
国内免费 | 870篇 |
专业分类
电工技术 | 491篇 |
综合类 | 1860篇 |
化学工业 | 8412篇 |
金属工艺 | 917篇 |
机械仪表 | 742篇 |
建筑科学 | 2284篇 |
矿业工程 | 906篇 |
能源动力 | 674篇 |
轻工业 | 3191篇 |
水利工程 | 877篇 |
石油天然气 | 1515篇 |
武器工业 | 71篇 |
无线电 | 779篇 |
一般工业技术 | 1718篇 |
冶金工业 | 1616篇 |
原子能技术 | 382篇 |
自动化技术 | 899篇 |
出版年
2024年 | 68篇 |
2023年 | 340篇 |
2022年 | 662篇 |
2021年 | 860篇 |
2020年 | 938篇 |
2019年 | 771篇 |
2018年 | 666篇 |
2017年 | 789篇 |
2016年 | 854篇 |
2015年 | 915篇 |
2014年 | 1353篇 |
2013年 | 1515篇 |
2012年 | 1863篇 |
2011年 | 1742篇 |
2010年 | 1351篇 |
2009年 | 1434篇 |
2008年 | 1208篇 |
2007年 | 1531篇 |
2006年 | 1433篇 |
2005年 | 1138篇 |
2004年 | 954篇 |
2003年 | 843篇 |
2002年 | 693篇 |
2001年 | 525篇 |
2000年 | 453篇 |
1999年 | 386篇 |
1998年 | 297篇 |
1997年 | 257篇 |
1996年 | 211篇 |
1995年 | 181篇 |
1994年 | 149篇 |
1993年 | 113篇 |
1992年 | 114篇 |
1991年 | 103篇 |
1990年 | 94篇 |
1989年 | 68篇 |
1988年 | 60篇 |
1987年 | 68篇 |
1986年 | 66篇 |
1985年 | 71篇 |
1984年 | 64篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1957年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
61.
安徽省境内765km的长江干堤,由于均是在原来旧堤的基础上经逐年加高培厚的,修筑时均未按设计要求施工,致使堤身密实度不够,新老堤土之间结合不牢,在汛期高水位时易产生渗漏。20世纪70年代以来,安徽省高度重视对长江干堤渗漏隐患的处理,经过长期的实践,逐渐摸索出一套行之有效的除险加固方法,如锥探灌浆、灭杀白蚁、冲抓套吉、垂直铺塑防渗、粘土铺盖及压渗盖重等处理措施。使长江干堤的渗漏隐患得以基本消除,其具体作法可供类似工程借鉴。 相似文献
62.
本文主要从土壤 pH ,重碳酸盐 ,和氮素形态等几方面综述了各种土壤因子对土壤缺铁失绿的影响 ,并提出了进一步加强研究的方向 相似文献
63.
64.
DO浓度对SUFR系统同步硝化反硝化的影响 总被引:1,自引:1,他引:0
采用螺旋升流式反应器(SUFR)处理生活污水,考察了好氧反应池中DO浓度对其同步硝化反硝化的影响。结果表明,在好氧反应池上部溶解氧浓度为3.0~3.5mg/L时,发生了明显的同步硝化反硝化现象,其对TN的去除量占SUFR系统对TN去除总量的16%左右;好氧反应池中的同步硝化反硝化反应只发生在池的下部,其中、上部只进行了好氧硝化反应;SUFR系统中好氧反应池上部的最佳溶解氧浓度范围为3.0~3.5mg/L,此时系统的硝化和反硝化效果最佳,好氧反应池中的脱氮效果也较好,系统对TN的去除率〉84%。 相似文献
65.
The causes of degradation of aquatic systems are often complex and stem from a variety of human influences. Comprehensive, multimetric biological indices have been developed to quantify this degradation and its effect on aquatic communities, and measure subsequent recovery from anthropogenic stressors. Traditionally, such indices have concentrated on small‐to medium‐sized streams. Recently, however, the Ohio River Fish Index (ORFIn) was created to assess biotic integrity in the Ohio River. The goal of the present project was to begin developing a companion Ohio River multimetric index using benthic macroinvertebrates. Hester–Dendy multiplate samplers were used to evaluate benthic macroinvertebrate assemblages in relation to a gradient of water quality disturbance, represented by varying distances downstream of industrial and municipal wastewater outfalls in the Ohio River. In August 1999 and 2000, samplers were set every 100 m downstream of outfalls (12 outfalls in 1999, 22 in 2000) for 300–1000 m, as well as at upstream reference sites. Candidate metrics (n = 55) were examined to determine which have potential to detect changes in water quality downstream of outfalls. These individual measures of community structure were plotted against distance downstream of each outfall to determine their response to water quality disturbance. Values at reference and outfall sites were also compared. Metrics that are ecologically relevant and showed a response to outfall disturbance were identified as potentially valuable in a multimetric index. Multiple box plots of index scores indicated greater response to outfall disturbance during periods of low‐flow, and longitudinal river‐wide trends. Evaluation of other types of anthropogenic disturbance, as well as continued analysis of the effects of chemical water quality on macroinvertebrate communities in future years will facilitate further development of a multimetric benthic macroinvertebrate index to evaluate biotic integrity in the Ohio River. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
66.
1 故障现象一次 ,我们用KL -1 5型制氧制氮车开机制氮 ,给一只容积为 40升、最高工作压力为1 4 7MPa的气瓶灌充氮气 ,当气瓶充气压力升高到一定值时不再上升。反复开泵 ,压力基本不变。液氧泵停止时 ,出口压力无明显下降。经分析判断导致气瓶压力升高到一定值时不再上升的原因是由于液氧泵被冻结所致。2 排除方法首先关闭液氧泵。拧开制冷机氢气放气阀 ,使压力下降到 1 0MPa。开大放气阀 ,使二级压力保持在 0 3 5MPa左右。调整正流空气调节阀 ,调节好中部温度。关闭液氮进液氧泵阀和气氮出液氧泵阀。戴棉布手套 ,拆开液氮进口接头、… 相似文献
67.
Johann Vollmann Heinrich Grausgruber Helmut Wagentristl Heinrich Wohleser Pavel Michele 《Journal of the science of food and agriculture》2003,83(15):1581-1586
The presence of protease inhibitors in soybean prohibits the utilisation of the raw beans for food and feed. However, little information is available about environmental influences and the effects of nitrogen and sulphur supply on the antinutritional constituents of soybean. As these factors may influence protease inhibitors, soybean genotypes segregated according to the presence or absence of the Kunitz trypsin inhibitor have been evaluated for trypsin inhibitor activity (TIA) in field trials. TIA was affected significantly by environment (geographical location), fertilisation treatment and genotype. Environmental means of TIA were between 69.5 and 104.8 mg g?1. Nitrogen application, which caused an increase in seed protein content, resulted in a reduction in TIA by about 15% as compared with the control. Remarkably, simultaneous application of nitrogen and sulphur in the form of ammonium sulphate had a similar reductive effect on TIA to that of nitrogen application alone, although soybean protease inhibitors are rich in sulphur amino acids. Significant genetic variation in TIA was found both within the genotype class with the Kunitz inhibitor present as well as within the class lacking this inhibitor. The results suggest that TIA of soybean may be modified considerably by genetic improvement and appropriate agronomic management. Copyright © 2003 Society of Chemical Industry 相似文献
68.
69.
70.