全文获取类型
收费全文 | 5371篇 |
免费 | 342篇 |
国内免费 | 134篇 |
专业分类
电工技术 | 155篇 |
综合类 | 667篇 |
化学工业 | 1162篇 |
金属工艺 | 45篇 |
机械仪表 | 137篇 |
建筑科学 | 1355篇 |
矿业工程 | 123篇 |
能源动力 | 200篇 |
轻工业 | 123篇 |
水利工程 | 736篇 |
石油天然气 | 312篇 |
武器工业 | 54篇 |
无线电 | 195篇 |
一般工业技术 | 101篇 |
冶金工业 | 172篇 |
原子能技术 | 6篇 |
自动化技术 | 304篇 |
出版年
2024年 | 9篇 |
2023年 | 30篇 |
2022年 | 85篇 |
2021年 | 135篇 |
2020年 | 140篇 |
2019年 | 66篇 |
2018年 | 83篇 |
2017年 | 133篇 |
2016年 | 146篇 |
2015年 | 176篇 |
2014年 | 376篇 |
2013年 | 312篇 |
2012年 | 499篇 |
2011年 | 417篇 |
2010年 | 346篇 |
2009年 | 336篇 |
2008年 | 316篇 |
2007年 | 385篇 |
2006年 | 367篇 |
2005年 | 237篇 |
2004年 | 244篇 |
2003年 | 212篇 |
2002年 | 141篇 |
2001年 | 150篇 |
2000年 | 91篇 |
1999年 | 62篇 |
1998年 | 52篇 |
1997年 | 44篇 |
1996年 | 41篇 |
1995年 | 44篇 |
1994年 | 32篇 |
1993年 | 28篇 |
1992年 | 15篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1979年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有5847条查询结果,搜索用时 15 毫秒
31.
现浇混凝土防渗渠道普遍采用设置伸缩缝的方法防止混凝土产生裂缝,而伸缩缝的止水易因老化和长草等遭受破坏,导致渠道渗漏。针对上述弊端提出了无伸缩缝混凝土防渗衬砌渠道的隔板跳仓浇筑施工技术。经过在多个大中型灌区节水项目中推广应用,总结出该施工技术的操作步骤和技术要点,包括基面处理措施,浇筑方法,操作要点,浇筑,振捣、抹面等的质量要求及适用范围。多年的运行实践表明,该技术可明显节约投资、缩短工期、延长使用寿命、有效改善防渗效果,且施工简便、工程质量易于保证等。 相似文献
32.
为了实现滇池流域截污效果的最大化,基于前期建立的东岸排水管网SWMM模型,结合该区域1995-2016年间降雨资料,研究环湖截污干渠的错峰调蓄技术。根据雨水干渠液位高度执行不同控制模式:当水位低于6.76 m时执行典型污染物浓度阈值控制模式;当水位高于6.76 m时执行典型污染物阈值控制的同时执行液位-污染物通量控制模式。采用SS和TN作为干渠截流的典型污染物控制指标,其控制浓度阈值分别取12和5 mg/L。模拟重现期为0.5~1 a降雨时SS、TN浓度-负荷通量调蓄方案下干渠负荷收集情况,结果表明两种调蓄方案均能有效提高雨水干渠的负荷收集率,提高污水干渠出口浓度,降低雨水径流对污水厂的高水量和低浓度冲击负荷。随着重现期增大,干渠对污染物的高效和最大化收集效果越明显。但是TN调控下污染负荷收集效果优于SS,因此选择TN作为干渠截流的最优典型污染物控制指标。 相似文献
33.
很多大中型灌区在输配水过程中存在水位衔接不当的问题,加之田面高程存在起伏,使得灌溉时往往存在部分田面不能上水或受淹等问题。本文提出了空间灌溉率的概念,并利用GIS的三维分析功能研究了其与渠道渠首水位之间的关系。分析表明,空间灌溉率与渠首水位之间的关系符合Logistic曲线;针对船行灌区一支渠,得到该Logistic曲线的参数,并确定了一支渠渠首和干渠渠首不同空间灌溉率所需的水位,为灌区水位实时调控提供基础数据。 相似文献
34.
35.
Extraction of Lipids from Municipal Wastewater Plant Microorganisms for Production of Biodiesel 总被引:2,自引:0,他引:2
Stephen Dufreche R. Hernandez T. French D. Sparks M. Zappi E. Alley 《Journal of the American Oil Chemists' Society》2007,84(2):181-187
Municipal wastewater treatment plants in the USA produce over 6.2 × 106 t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions
on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields
an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO2. The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield;
however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on
total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight
yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 × 106 m3/year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel
production to replace 0.5% of the national petroleum diesel demand (0.7 × 106 m3). 相似文献
36.
复合微生物处理生活污水的研究 总被引:1,自引:0,他引:1
对复合微生物进行了研究,利用4种微生物群分别与活性污泥混合使用处理城市污水,考察了这几种复合微生物群在不同水力停留时间时的污水处理效果,并且用空白活性污泥作对照,进行了出水CODcr的值及其去除率的对比、分析和研究。 相似文献
37.
The pyrolysis of sewage sludge was examined by thermogravimetric analysis using different heating rates, particle sizes and final temperatures. A semi-empirical model was developed with four global consecutive/competitive reactions to volatile and solid products including also a heat balance. This model was extrapolated to isothermal reactor conditions and compared to experimental data on fluidized bed pyrolysis. Depending on the particle size and reactor temperature, about 90% of the maximum conversion in a fluidized bed takes place under external heat transfer control, the rest under kinetic control. Incomplete conversion occurs at short particle residence times, which were calculated approximately by the model. 相似文献
38.
39.
Phosphorus (P) inputs are required for sustainable agricultural production in most acid soils of the tropics and subtropics. Phosphate rocks (PR) and organic materials have been suggested as alternative P sources in these soils. Quantitative information on the P availability from sewage sludge (SL) is scanty. Methods to improve the effectiveness of PR such as partial acidulation and compaction with water-soluble P sources have been recommended. The objective of this greenhouse study was to evaluate the relative agronomic effectiveness (RAE) of Florida PR and sewage sludges (irradiated and non-irradiated) applied alone and in mixture with a water-soluble source (triple superphosphate, TSP) at two rates (50 and 150 mg P kg–1 soil). The 32P isotope dilution technique was utilised to determine the proportion of P in the plant taken up from the P fertilizer treatments. Wheat was grown on an acid loamy sand Dystric Eutrocrepts and harvested 6 weeks after planting. Results on total P uptake and the RAE of the P fertilizer sources tested indicated that the addition of 50 mg P kg–1 soil as TSP was adequate in supplying P to the 6-week-old wheat plants as compared to PR and sewage sludge. Intermediate values were obtained for the mixtures. Similar responses were observed for the high P rate. For a given P rate, phosphorus uptake from PR and SL in presence of TSP was higher than P uptake from these sources alone, indicating an enhancement effect of TSP on the effectiveness of these non-readily available sources. With respect to P uptake from PR applied alone, the relative increases in P uptake from PR due to TSP influence were 52 and 67% for the low and high P rates, respectively. The relative increases in P uptake from SL due to TSP when compared to P uptake from SL alone were 102 and 59% for the low and high P rates of application. Application of a water-soluble P fertilizer together with a non-readily available P source shows an enhancement on the P uptake from the non-readily available P source by the wheat plants. In this experiment the estimated enhancement effects are very likely underestimated. 相似文献
40.